EE-Unit-V Biofertilizers

Biofertilizers are defined as preparations containing living cells or latent cells of efficient strains of microorganisms that help crop plants’ uptake of nutrients by their interactions in the rhizosphere when applied through seed or soil.  They accelerate certain microbial processes in the soil which augment the extent of availability of nutrients in a form easily assimilated by plants.

Very often microorganisms are not as efficient in natural surroundings as one would expect them to be and therefore artificially multiplied cultures of efficient selected microorganisms play a vital role in accelerating the microbial processes in soil.

Use of biofertilizers is one of the important components of integrated nutrient management, as they are cost effective and renewable source of plant nutrients to supplement the chemical fertilizers for sustainable agriculture. Several microorganisms and their association with crop plants are being exploited in the production of biofertilizers. They can be grouped in different ways based on their nature and function.

S. No. Groups Examples
N2  fixing Biofertilizers
1. Free-living Azotobacter, Beijerinkia, Clostridium, Klebsiella, Anabaena, Nostoc, 
2. Symbiotic Rhizobium, Frankia, Anabaena azollae
3. Associative Symbiotic Azospirillum
P Solubilizing Biofertilizers
1. Bacteria Bacillus megaterium var. phosphaticum, Bacillus subtilis
Bacillus circulans, Pseudomonas striata
2. Fungi Penicillium sp, Aspergillus awamori
P Mobilizing Biofertilizers
1. Arbuscular mycorrhiza Glomus sp.,Gigaspora sp.,Acaulospora sp.,
Scutellospora sp. & Sclerocystis sp.
2. Ectomycorrhiza Laccaria sp., Pisolithus sp., Boletus sp., Amanita sp.
3. Ericoid mycorrhizae Pezizella ericae
4. Orchid mycorrhiza Rhizoctonia solani
Biofertilizers for Micro nutrients
1. Silicate and Zinc solubilizers Bacillus sp.
Plant Growth Promoting Rhizobacteria
1. Pseudomonas Pseudomonas fluorescens

2. Different types of biofertilizers

Rhizobium

Rhizobium is a soil habitat bacterium, which can able to colonize the legume roots and fixes the atmospheric nitrogen symbiotically. The morphology and physiology of Rhizobium will vary from free-living condition to the bacteroid of nodules. They are the most efficient biofertilizer as per the quantity of nitrogen fixed concerned. They have seven genera and highly specific to form nodule in legumes, referred as cross inoculation group.

Rhizobium inoculant was first made in USA and commercialized by private enterprise in 1930s and the strange situation at that time has been chronicled by Fred (1932).

Initially, due to absence of efficient bradyrhizobial strains in soil, soybean inoculation at that time resulted in bumper crops but incessant inoculation during the last four decades by US farmers has resulted in the build up of a plethora of inefficient strains in soil whose replacement by efficient strains of bradyrhizobia has become an insurmountable problem.

Azotobacter

Of the several species of Azotobacter, A. chroococcum happens to be the dominant inhabitant in arable soils capable of fixing N2 (2-15 mg N2 fixed /g of carbon source) in culture media.

The bacterium produces abundant slime which helps in soil aggregation. The numbers of A. chroococcum in Indian soils rarely exceeds 105/g soil due to lack of organic matter and the presence of antagonistic microorganisms in soil.

Azospirillum

Azospirillum lipoferum and A. brasilense (Spirillum lipoferum in earlier literature) are primary inhabitants of soil, the rhizosphere and intercellular spaces of root cortex of graminaceous plants. They perform the associative symbiotic relation with the graminaceous plants.

The bacteria of Genus Azospirillum are  N2 fixing organisms isolated from the root and above ground parts of a variety of crop plants. They are Gram negative, Vibrio or Spirillum having abundant accumulation of polybetahydroxybutyrate (70 %) in cytoplasm.

Five species of Azospirillum have been described to date A. brasilense, A.lipoferum, A.amazonense, A.halopraeferens and A.irakense.  The organism proliferates under both anaerobic and aerobic conditions but it is preferentially micro-aerophilic in the presence or absence of combined nitrogen in the medium.

Apart from nitrogen fixation, growth promoting substance production (IAA), disease resistance and drought tolerance are some of the additional benefits due to Azospirillum inoculation.

Cyanobacteria

Both free-living as well as symbiotic cyanobacteria (blue green algae) have been harnessed in rice cultivation in India. A composite culture of BGA having heterocystous Nostoc, Anabaena, Aulosira etc. is given as primary inoculum in trays, polythene lined pots and later mass multiplied in the field for application as soil based flakes to the rice growing field at the rate of 10 kg/ha. The final product is not free from extraneous contaminants and not very often monitored for checking the presence of desiredalgal flora.

Once so much publicized as a biofertilizer for the rice crop, it has not presently attracted the attention of rice growers all over India except pockets in the Southern States, notably Tamil Nadu. The benefits due to algalization could be to the extent of 20-30 kg N/ha under ideal conditions but the labour oriented methodology for the preparation of BGA biofertilizer is in itself a limitation. Quality control measures are not usually followed except perhaps for random checking for the presence of desired species qualitatively.

Azolla

Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaena azollae. Azolla fronds consist of sporophyte with a floating rhizome and small overlapping bi-lobed leaves and roots. Rice growing areas in South East Asia and other third World countries have recently been evincing increased interest in the use of the symbiotic N2 fixing water fern Azolla either as an alternate nitrogen sources or as a supplement to commercial nitrogen fertilizers. Azolla is used as biofertilizer for wetland rice and it is known to contribute 40-60 kg N/ha per rice crop.

Phosphate solubilizing microorganisms(PSM)

Several soil bacteria and fungi, notably species of Pseudomonas, Bacillus, Penicillium, Aspergillus etc. secrete organic acids and lower the pH in their vicinity to bring about dissolution of bound phosphates in soil. Increased yields of wheat and potato were demonstrated due to inoculation of peat based cultures of Bacillus polymyxa and Pseudomonas striata. Currently, phosphate solubilizers are manufactured by agricultural universities and some private enterprises and sold to farmers through governmental agencies. These appear to be no check on either the quality of the inoculants marketed in India or the establishment of the desired organisms in the rhizosphere.

AM fungi

The transfer of nutrients mainly phosphorus and also zinc and sulphur from the soil milleu to the cells of the root cortex is mediated by intracellular obligate fungal endosymbionts of the genera Glomus, Gigaspora, Acaulospora, Sclerocysts and Endogone which possess vesicles for storage of nutrients and arbuscles for funneling these nutrients into the root system. By far, the commonest genus appears to be Glomus, which has several species distributed in soil.

Availability for pure cultures of AM (Arbuscular Mycorrhiza) fungi is an impediment in large scale production despite the fact that beneficial effects of AM fungal inoculation to plants have been repeatedly shown under experimental conditions in the laboratory especially in conjunction with other nitrogen fixers.

                                          
Silicate solubilizing bacteria (SSB)

Microorganisms are capable of degrading silicates and aluminum silicates. During the metabolism of microbes several organic acids are produced and these have a dual role in silicate weathering. They supply H+ ions to the medium and promote hydrolysis and the organic acids like citric, oxalic acid, Keto acids and hydroxy carbolic acids which from complexes with cations, promote their removal and retention in the medium in a dissolved state.

The studies conducted with a Bacillus sp. isolated from the soil of granite crusher yard showed that the bacterium is capable of dissolving several silicate minerals under in vitro condition. The examination of anthrpogenic materials like cement, agro inputs like super phosphate and rock phosphate exhibited silicate solubilizing bacteria to a varying degree. The bacterial isolates made from different locations had varying degree of silicate solubilizing potential. Soil inoculation studies with selected isolate with red soil, clay soil, sand and hilly soil showed that the organisms multiplied in all types of soil and released more of silica and the available silica increased in soil and water. Rice responded well to application of organic sliceous residue like rice straw, rice husk and black ash @ 5 t/ha. Combining SSB with these residues further resulted in increased plant growth and grain yield. This enhancement is due to increased dissolution of silica and nutrients from the soil.

Plant Growth Promoting Rhizobacteria (PGPR)

The group of bacteria that colonize roots or rhizosphere soil and beneficial to crops are referred to as plant growth promoting rhizobacteria (PGPR).

The PGPR inoculants currently commercialized that seem to promote growth through at least one mechanism; suppression of plant disease (termed Bioprotectants), improved nutrient acquisition (termed Biofertilizers), or phytohormone production (termed Biostimulants). Species of Pseudomonas and Bacillus can produce as yet not well characterized phytohormones or growth regulators that cause crops to have greater amounts of fine roots which have the effect of increasing the absorptive surface of plant roots for uptake of water and nutrients. These PGPR are referred to as Biostimulants and the phytohormones they produce include indole-acetic acid, cytokinins, gibberellins and inhibitors of ethylene production.

Recent advances in molecular techniques also are encouraging in that tools are becoming available to determine the mechanism by which crop performance is improved using PGPR and track survival and activity of PGPR organisms in soil and roots. The science of PGPR is at the stage where genetically modified PGPR can be produced. PGPR with antibiotic, phytohormone and siderophore production can be made.

Despite of promising results, biofertilizers has not got widespread application in agriculture mainly because of the variable response of plant species or genotypes to inoculation depending on the bacterial strain used. Differential rhizosphere effect of crops in harbouring a target strain or even the modulation of the bacterial nitrogen fixing and phosphate solubilizing capacity by specific root exudates may account for the observed differences. On the other hand, good competitive ability and high saprophytic competence are the major factors determining the success of a bacterial strain as an inoculant.

Studies to know the synergistic activities and persistence of specific microbial populations in complex environments, such as the rhizosphere, should be addressed in order to obtain efficient inoculants. In this regards, research efforts are made at Agricultural College and Research Institute, Madurai to obtain appropriate formulations of microbial inoculants incorporating nitrogen fixing, phosphate- and silicate- solubilizing bacteria and plant growth promoting rhizobacteria which will help in promoting the use of such beneficial bacteria in sustainable agriculture.

Liquid Biofertilizers

Biofertilizers are such as Rhizobium, Azospirillum and Phosphobacteria  provide nitrogen  and phosphorous nutrients to crop plants through nitrogen fixation and phosphorous solubilization processes. These Biofertilizers could be effectively utilized for rice, pulses, millets, cotton, sugarcane, vegetable and other horticulture crops.

Biofertilizers  is one of the prime input in organic farming not only enhances the crop growth and yield but also improves the soil health and sustain soil fertility.

At  present, Biofertilizers  are supplied to the farmers as carrier based  inoculants. As an alternative, liquid formulation technology has been developed in the Department of Agricultural  Microbiology, TNAU, Coimbatore which has more advantages than the carrier inoculants.

Benefits

The advantages of Liquid Bio-fertilizer over conventional carrier based Bio-fertilizers are listed below:

  • Longer shelf life -12-24 months.
  • No contamination.
  • No loss of properties due to storage upto 45º c.
  • Greater potentials to fight with native population.
  • High populations can be maintained more than 109 cells/ml upto 12 months to 24 months.
  • Easy identification by typical fermented smell.
  • Cost saving on carrier material, pulverization, neutralization, sterilization, packing and transport.
  • Quality control protocols are easy and quick.
  • Better survival on seeds and soil.
  • No need of running Bio-fertilizer production units through out the year.
  • Very much easy to use by the farmer.
  • Dosages is 10 time less than carrier based powder Bio-fertilizers.
  • High commercial revenues.
  • High export potential.
  • Very high enzymatic activity since contamination is nil.

Characteritistics of different liquid Bio-fertilizers

Rhizobium

This belongs to bacterial group and the classical example is symbiotic nitrogen fixation. The bacteria infect the legume root and form root nodules within which they reduce molecular nitrogen to ammonia which is reality utilized by the plant to produce valuable proteins, vitamins and other nitrogen containing compounds. The site of  symbiosis is within the root nodules. It has been estimated that 40-250 kg N / ha / year is fixed by different legume crops by the microbial activities of Rhizobium. The percentage of nodules occupied, nodules dry weight, plant dry weight and the grain yield per plant the multistrain inoculant was highly promising Table-2 shows the N fixation rates.

Quantity of biological N fixed by Liqiud Rhizobium in different crops

Host Group Rhizobium Species Crops N fix kg/ha
Pea group Rhizobium leguminosarum Green pea, Lentil 62- 132
Soybean group R.japonicum Soybean 57-  105
Lupini Group R. lupine orinthopus Lupinus 70- 90
Alfafa grp.Group R.mellilotiMedicago Trigonella Melilotus 100- 150
Beans group R. phaseoli Phaseoli 80- 110
Clover group R. trifoli Trifolium 130
Cowpea group R. species Moong, Redgram, Cowpea, Groundnut 57- 105
Cicer group R. species Bengal gram 75- 117

Physical features of liquid Rhizobium

  • Dull white in colour
  • No bad smell
  • No foam formation, pH 6.8-7.5

Azospirllium

It belongs to bacteria and is known to fix the considerable quantity of nitrogen in the range of 20- 40 kg N/ha in the rhizosphere in non- non-leguminous plants such as cereals, millets, Oilseeds, cotton etc. The efficiency of Azospirillium as  a  Bio-Fertilizer has increased because of its ability of inducing abundant roots in several pants like rice, millets and oilseeds even in upland conditions. Considerable quantity of nitrogen fertilizer up to 25-30 % can be saved by the use of Azospirilluminoculant. The genus Azospirillum has three species viz., A. lipoferum, A. brasilense and A. amazonense. These species have been commercially exploited for the use as nitrogen supplying Bio-Fertilizers.

One of the characteristics of Azospirillum is its ability to reduce nitrate and denitrify. Both A. lipoferum,and A. brasilense may comprise of strains which can actively or weakly denitrify or reduce nitrate to nitrite and therefore, for inoculation preparation, it is necessary to select strains which do not possess these characteristics.Azospirllium lipoferum present in the roots of some of tropical forage grasses uch as Digitaria, Panicum, Brachiaria, Maize, Sorghum, Wheat and Rye.

Physical  features of liquid Azospirillum

  • The colour of the liquid may be blue or dull white.
  • Bad odours confirms improper liquid formulation and may be concluded as mere broth.
  • Production of yellow gummy colour materials comfirms the quality product.
  • Acidic pH always confirms that there is no Azospirillum bacteria in the liquid.

N2 fixing capacity of Azospirillum in the roots of several plants and the amount of N2 fixed by them.

Plant Mg N2  fixed /g of substrate
Oryza sativa (Paddy) 28
Sorghum bicolour (Sorghum) 20
Zea mays (Maize) 20
Panicum sp. 24
Cynodon dactylon 36
Setaria sp 12
Amaranthus spinosa 16

Production of growth hormones

Azospirillum cultures synthesize considerable amount of biologically active substances like vitamins, nicotinic acid, indole acetic acids giberllins. All these hormones/chemicals helps the plants in better germination, early emergence, better root development.

Role of Liquid Azospirillum under field conditions

  • Stimulates growth and imparts green colour which is a characteristic of a healthy plant.
  • Aids utilization of potash, phosphorous and other nutrients.
  • Encourage plumpness and succulence of fruits and increase protein percentage.

Sign of non functioning of Azospirillum in the field

  • No growth promotion activity
  • Yellowish green colour of leaves, which indicates no fixation of Nitrogen

Azotobacter

It is the important and well known free living nitrogen fixing aerobic bacterium. It is used as a Bio-Fertilizer for all non leguminous plants especially rice, cotton, vegetables etc. Azotobacter cells are not present on the rhizosplane but are abundant in the rhizosphere region. The lack of organic matter in the soil is a limiting factor for the proliferation of Azotobaceter in the soil.

Field experiments were conducted in 1992, 1993 and 1994 during the pre-kharif wet seasons to find out the influence on rice grain yield by the combined use of N- fixing organisms and inorganic nitrogen fertilizer which recorded increase in was yield.

Physical features of liquid Azotobacter

The pigmentation that is produced by Azotobacter in aged culture is melanin which is due to oxidation of tyrosine by tyrosinase an enzyme which has copper. The colour can be noted in liquid forms. Some of the pigmentation are described below-

  • A. chroococcum: Produces brown-black pigmentation in liquid inoculum.
  • A. beijerinchii: Produces yellow- light brown pigementation in liquid inoculum
  • A. vinelandii: Produces green fluorescent pigmentation in liquid inoculum.
  • A. paspali: Produces green fluorescent pigmentation in liquid inoculum.
  • A. macrocytogenes: Produces, pink pigmentation in liquid inoculum.
  • A. insignis: Produces less, gum less, grayish-blue pigmentation in liquid inoculum.
  • A. agilies: Produces green-fluorescent pigmentation in liquid inoculum.

Role of liquid Azotobacter in tissue culture

The study was conducted by Dr. Senthil et al (2004) on sugarcane variety CO 86032 in Tissue culture Laboratories of Rajashree Sugars and Chemicals Ltd, Varadaraj nagar, Theni, Tamilnadu. The liquid bioinoculants were provided by Dr. Krishnan Chandra, Regional Director, RCOF, Bangalore to evaluate their growth promoting effects on sugarcane micropropagation. He recorded Biometric observations like Plant height, leaf length, width, root length, no of roots. Chemical parameters –Protein, Carbohydrates, N, P,K total biomass and concluded as follows:

  • The performance of Azotobacter liquid inoculant was c
  • omparatively better than all the treatments in 10 % MS medium followed Azospirillum.
  • The performance of Azotobacter liquid inoculant was comparatively better than all the treatments followed by Azosopirillum for the growth of the polybag sugarcane seedlings.

Role of liquid Azotobacter as a Bio-control agent

Azotobacter have been found to produce some antifungal substance which inhibits the growth of some soil fungi like Aspergillus, Fusarium, Curvularia, Alternaria, Helminthosporium, Fusarium etc.

Acetobaceter

This is a sacharophillic bacteria and associate with sugarcane, sweet potato and sweet sorghum plants and fixes 30 kgs/ N/ ha year. Mainly this bacterium is commercialized for sugarcane crop. It is known  to increase yield by 10-20 t/ acre and sugar content by about  10-15 percent.

Effect of liquid Acetobacter diazotrophicus on sugarcane

In South India use of Azospirillum and Phospho-bacterium on the cash crop sugarcane is a regular practice for the past few years with a saving of nearly 20 % of chemical nitrogen and phosphate applications. Now, it has been reported that a bacteria Acetobacter diazotrophicus  which is present in the sugarcane stem, leaves, soils have a capacity to fix up to 300 kgs of nitrogen. This bacteria first reported in brazil where the farmers cultivate sugarcane in very poor sub-soil fertilized with Phosphate, Potassium and micro elements alone, could produce yield for three consecutive harvests, without any nitrogen fertilizer. They have recorded yield 182- 244 tones per ha. This leads to the assumption that active nitrogen fixing bacteria has associated within the plant.

Do’s and Don’t for Entrepreneurs, Dealers and farmers

Do

Don’t

Keep Bio-fertilizers bottles away from direct heat and sunlight. Store it in cool and dry place. Don’t store Bio-fertilizers bottles under heat and sunlight
Sell only Bio-fertilizers bottles which contain batch number, the name of the crop on which it has to be used, the date of manufacture and expiry period. Don’t sell Bio-fertilizers bottles after their expiry period is over.
If the expiry period is over, then discard it as it is not effective. Don’t prick holes into the bottles or puncture them to pour the content
Keep Bio-fertilizers bottles away from fertilizer or pesticide containers and they should not be mixed directly. Do not mix the Bio-fertilizers with fungicides, insecticides, herbicides, herbicides and chemical fertilizers.

Liquid  Bio-fertlizer application methodology
There are three ways of using Liquid Bio-fertilizers

  1. Seed treatment
  2. Root dipping
  3. Soil application

Seed Treatment

Seed Treatment is a most common method adopted for all types of inoculants. The seed treatment is effective and economic. For small quantity of seeds (up to 5 kgs quantity) the coating can done in a plastic bag. For this purpose, a plastic bag having size (21” x 10”) or big size can be used. The bag should be filled with 2 kg or more of seeds. The bag should be closed in such a way to trap the airs as much as possible. The bag should be squeezed for 2 minutes or more until all the seed are uniformly wetted. Then bag is opened, inflated again and shaked gently. Stop shaking after each seeds gets a uniform layer of culture coating. The bag is opened and the seed is dried under the shade for 20-30 minutes. For large amount of seeds coating can be done in a bucket and inoculant can be mixed directly with hand. Seed Treatment with Rhizobium, Azotobacter, Azospirillum, along with PSM can be done.

The seed treatment can be done with any of two or more bacteria. There is no side (antagonistic) effect. The important things that has to be kept in mind are that the seeds must be coated first with Rhizobium, Azotobacter or Azospirillum. When each seed get a layer of above bacteria then PSM inoculant has to be coated as outer layer. This method will provide maximum number of each bacteria required for better results. Treatments of seed with any two bacteria will not provide maximum number of bacteria on individual seed.

Root dipping

For application of Azospirillum/ /PSM on paddy transplating/ vegetable crops this method is used. The required quantity of Azospirillum/ /PSM has to be mixed with 5-10 litres of water at one corner of the field and the roots of seedlings has to be dipped for a minimum of half-an-hour before transplantation.

Soil application

Use 200ml of PSM per acre. Mix PSM with 400 to 600 kgs of Cow dung FYM along with ½ bag of rock phosphate if available. The mixture of PSM, cow dung  and rock phosphate have to be kept under any tree or under shade for over night and maintain 50% moisture. Use the mixture as soil application in rows or during leveling of soil.

Dosage of liquid Bio-fertilizers in different crops

Recommended Liquid Bio-fertilizers and its application method, quantity to be used for different crops are as follows:

Crop

Recommended Bio-fertilizer

Application method

Quantity to be used

Field crops
Pulses
Chickpea, pea, Groundnut, soybean, beans, Lentil, lucern, Berseem, Green gram, Black gram, Cowpea and pigeon pea
Rhizobium Seed treatment 200ml/acre
Cereals
Wheat, oat, barley
Azotobacter/Azospirillum Seed treatment 200ml/acre
Rice Azospirillum Seed treatment 200ml/acre
Oil seeds
Mustard, seasum, Linseeds, Sunflower, castor
Azotobacter Seed treatment 200ml/acre
Millets
Pearl millets, Finger millets, kodo millet
Azotobacter Seed treatment 200ml/acre
Maize and Sorghum Azospirillum Seed treatment 200ml/acre
Forage crops and Grasses
Bermuda grass, Sudan grass, Napier Grass , ParaGrass, StarGrass etc.
Azotobacter Seed treatment 200ml/acre
Other Misc. Plantation Crops
Tobacco
Azotobacter Seedling treatment 500ml/acre
Tea, Coffee Azotobacter Soil treatment 400ml/acre
Rubber, Coconuts Azotobacter Soil treatment 2-3 ml/plant
Agro-ForestRY/Fruit Plants
All fruit/agro-forestry (herb,shrubs, annuals and perennial) plants for fuel wood fodder, fruits,gum,spice,leaves,flowers,nuts and seeds puppose
Azotobacter Soil treatment 2-3 ml/plant at nursery
Leguminous plants/ trees Rhizobium Soil treatment 1-2 ml/plant

Note:

Doses recommended when count of inoculum is 1 x 108 cells/ml then doses will be ten times more besides above said Nitrogen fixers, Phosphate solubilizers and potash mobilizers at the rate of 200 ml/ acre could be applied for all crops.

Equipments required for Biofertilizer production

In biofertilizer production industry, equipments are the major infrastructure, which involves 70 percent of capital investment. Any compromise on the usage  of the following mentioned equipments may finally decline in the quality of biofertilizer.After studying the principle behind the usage of all instruments, some of the instruments can be replaced with a culture room fitted with a U.V.Lamp. Autoclaves, Hot Air Oven, Incubators and sealing machines are indigenously made with proper technical specifications. The correct use of equipments will give uninterrupted introduction with quality inoculum.

Essential equipments

Autoclave

It is an apparatus in which materials are sterilized by air free saturated steam (under pressure) at a temperature above 100OC. If the steam pressure inside the autoclave is increased to 15 psi,  the temperature will rise to 121°C. this is sufficient to destroy all vegetative cells. Normally all growth medium are sterilized in the autoclave.

Laminar air flow chamber

Laminar air flow chamber provides a uniform flow of filtered air. This continuous flow of air will prevent settling of particles in the work area.Air borne contamination is avoided in this chamber. Culture transfers and inoculation can be done here.

BOD incubators 

Incubators providing controlled conditions (light, temperature, humidity, etc.) required for the growth and development of microorganisms. Multiplication of starter culture can be done in this instrument.

Rotary shaker

It is used for agitating culture flasks by circular motion under variable speed control. Shaking provides aeration for growth of cultures. Shakers holding upto 20-50 flasks are generally used. The capacity of the shaker may be increased if it is a double- decker type.

Hot air oven

Hot air oven is meant for sterilizing all glassware materials. Dry heat is used in this apparatus to sterilize the materials. Normally 180OC is used for two hours for sterilizing glasswares.

pH meter

An instrument for measuring pH of the solution using a 0-14 scale in which seven represents neutral points, less than seven is acidity (excess of H‘  over OH-) and more than seven is alkality  (excess of OH- over H‘  ) useful in adjusting the pH of the growth medium.

Refrigerator

This equipment is used preserving all mother cultures used for biofertilizer production. The mother culture is periodically sub-cultured and stored in the refrigerator for long- term usage.

Fermentor

A fermentor is the equipment, which provides the proper environment for the growth of a desired organism.

It is generally a large vessel in which, the organism may be kept at the required temperature, pH , dissolved oxygen concentration and substrate concentration. Different models of fermentors are available depending upon the necessity.

A simple version model contains steam generator, sterilization process devices and agitator.

A sophisticated fermentor contains pH regulator, oxygen level regulator, anti-foam device, temperature  controller, etc.


3. Mass production of   Bacterial Biofertilizer

Azospirillum Rhizobium Phosphobacteria Azotobacter

Biofertilizers are carrier based preparations containing efficient strain of nitrogen fixing or phosphate solubilizing microorganisms. Biofertilizers are formulated usually as carrier based inoculants. The organic carrier materials are more effective for the preparation of bacterial inoculants. The solid inoculants carry more number of bacterial cells and support the survival of cells for longer periods of time.

  • The mass production of carrier based bacterial biofertilizers involves three stages.
  • Culturing of microorganisms
  • Processing of carrier material
  • Mixing the carrier and the broth culture and packing

Culturing of Microorganisms

Although many bacteria can be used beneficially as a biofertilizer the technique of mass production is standardizedfor Rhizobium, Azospirillum, Azotobacter and phosphobacteria.
The media used for mass culturing are as follows:

Rhizobium : Yeast extract mannitol broth.

Growth on Congo red yeast extract mannitol agar medium

Mannitol 10.0 g
K2 HPO4 0.5 g
Mg So4 7H2 O 0.2 g
NaCl 0.1 g
Yeast extract 0.5 g
Agar 20.0 g
Distilled water 1000.0 ml

Add 10 ml of Congo red stock solution (dissolve 250 mg of Congo  red  in 100ml water) to 1 liter after adjusting the PH to 6.8 and before adding agar.

Rhizobium forms white, translucent, glistening, elevated and comparatively small colonies on this medium. Moreover, Rhizobium colonies do not take up the colour of congo red dye added in the medium. Those colonies which readily take up the congo red stain are not rhizobia but presumably Agrobacterium, a soil bacterium closely related to Rhizobium.

Azospirillum : Dobereiner’s malic acid broth with NH4Cl (1g per liter)

Composition of the N-free semisolid malic acid medium

Malic acid 5.0g
Potassium hydroxide 4.0g
Dipotassium hydrogen orthophosphate 0.5g
Magnesium sulphate 0.2g
Sodium chloride 0.1g
Calcium chloride 0.2g
Fe-EDTA (1.64% w/v aqueous) 4.0 ml
Trace element solution 2.0 ml
BTB (0.5% alcoholic solution) 2.0 ml
Agar 1.75 g
Distilled water 1000 ml
pH 6.8
Trace element solution
Sodium molybdate 200 mg
Manganous sulphate 235 mg
Boric acid 280 mg
Copper sulphate 8 mg
Zinc sulphate 24 mg
Distilled water 200 ml

Waksman medium No.77 (N-free Mannitol Agar Medium for Azotobacter)

Mannitol : 10.0 g
Ca CO3 : 5.0 g
K2HPO4 : 0.5 g
Mg SO4.7H2O : 0.2 g
NaCl : 0.2 g
Ferric chloride : Trace
MnSO4.4H2O : Trace
N-free washed Agar : 15.0 g
pH : 7.0
Distilled Water : 1000 ml

Phosphobacteria : Pikovskaya’s Broth

Glucose : 10.0 g
Ca3(PO4)2 : 5.0 g
(NH4)2SO4 : 0.5 g
KCl : 0.2 g
MgSO4. 7H2O : 0.1 g
MnSO4 : Trace
FeSO4 : Trace
Yeast Extract : 0.5 g
Distilled Water : 1000 ml

The broth is prepared in flasks and inoculum from mother culture is transferred to flasks. The culture is grown under shaking conditions at 30±2°C as submerged culture. The culture is incubated until maximum cell population of 1010 to 1011 cfu/ml is produced. Under optimum conditions this population level could be attained with in 4 to 5 days for Rhizobium; 5 to 7 days for Azospirillum; 2 to 3 days for phosphobacteria and 6-7 days for Azotobacter. The culture obtained in the flask is calledstarter culture. For large scale production of inoculant, inoculum from starter culture is transferred to large flasks/seed tank fermentor and grown until required level of cell count is reached.

Inoculum preparation

  • Prepare appropriate media for specific to the bacterial inoculant in 250 ml, 500 ml, 3 litre and 5 litre conical flasks and sterilize.
  • The media in 250 ml flask is inoculated with efficient bacterial  strain under aseptic condition
  • Keep the flask under room temperature in rotary shaker (200 rpm) for 5- 7 days.
  • Observe the flask for growth of the culture and estimate the population, which serves as the starter culture.
  • Using the starter culture (at log phase) inoculate the larger flasks (500 ml, 3 litre and 5 litre) containing the media, after obtaining growth in each flask.
  • The above media is prepared in large quantities in fermentor, sterilized well, cooled and kept it ready.
  • The media in the fermentor is inoculated with the log phase culture grown in 5 litre flask. Usually 1 -2 % inoculum is sufficient, however inoculation is done up to 5% depending on the growth of the culture in the larger flasks.
  • The cells are grown in fermentor by providing aeration (passing sterile air through compressor and sterilizing agents like glass wool, cotton wool, acid etc.) and given continuous stirring.
  • The broth is checked for the population of inoculated organism and contamination if any at the growth period.
  • The cells are harvested with the population load of 109 cells ml-1 after incubation period.
  • There should not be any fungal or any other bacterial contamination at 10-6 dilution level
  • It is not advisable to store the broth after fermentation for periods longer than 24 hours. Even at 4o C number of viable cells begins to decrease.

Processing of carrier material

The use of ideal carrier material is necessary in the production of good quality biofertilizer. Peat soil, lignite, vermiculite, charcoal, press mud, farmyard manure and soil mixture can be used as carrier materials. The neutralized peat soil/lignite are found to be better carrier materials for biofertilizer production The following points are to be considered in the selection of ideal carrier material.

  • Cheaper in cost
  • Should be locally available
  • High organic matter content
  • No toxic chemicals
  • Water holding capacity of more than 50%
  • Easy to process, friability and vulnerability.

Preparation of carrier material

  • The carrier material (peat or lignite) is powdered to a fine powder so as to pass through 212 micron IS sieve.
  • The pH of the carrier material is neutralized with the help of calcium carbonate (1:10 ratio) , since the peat soil / lignite  are acidic in nature (  pH of 4 – 5)
  • The neutralized carrier material is sterilized in an autoclave to eliminate the contaminants.

Mixing the carrier and the broth culture and packing

Inoculant packets are prepared by mixing the broth culture obtained from fermentor with sterile carrier material as described below:

Preparation of Inoculants packet

  • The neutralized, sterilized carrier material is spread in a clean, dry, sterile metallic or plastic tray.
  • The bacterial culture drawn from the fermentor is added to the sterilized carrier and mixed well by manual (by wearing sterile gloves) or by mechanical mixer. The culture suspension is to be added to a level of 40 – 50% water holding capacity depending upon the population.
  • The inoculant packet of 200 g quantities in polythene bags, sealed with electric sealer and allowed for curing for 2 -3 days at room temperature ( curing can be done by spreading the inoculant on a clean floor/polythene sheet/ by keeping in open shallow tubs/ trays with polythene covering for 2 -3 days at room temperature before packaging).

Schematic representation of mass production of bacterial biofertilizers

Specification of the polythene bags

  • The polythene bags should be of low density grade.
  • The thickness of the bag should be around 50 – 75 micron.
  • Each packet should be marked with the name of the manufacturer, name of the product, strain number, the crop to which recommended, method of inoculation, date of manufacture, batch number, date of expiry, price, full address of the manufacturer and storage instructions etc.,

Storage of biofertilizerpacket

  • The packet should be stored in a cool place away from the heat or direct sunlight.
  • The packets may be stored at room temperature or in cold storage conditions in lots in plastic crates or polythene / gunny bags.
  • The population of inoculant in the carrier inoculant packet may be determined at 15 days interval. There should be more than 109 cells / g of inoculant at the time of preparation and107 cells/ g on dry weight basis before expiry date.

Mass production of Mycorrhizal biofertilizer

The commercial utilization of mycorrhizal fungi has become difficult because of the obligate symbiotic nature and difficulty in culturing on laboratory media. Production of AM inoculum has evolved from the original use of infested field soils to the current practice of using pot culture inoculum derived from the surface disinfected spores of single AM fungus on a host plant grown in sterilized culture medium. Several researches in different parts of the world resulted in different methods of production of AM fungal inoculum as soil based culture as well as carrier based inoculum. Root organ culture and nutrient film technique provide scope for the production of soil less culture.

As a carrier based inoculum, pot culture is widely adopted method for production. The AM inoculum was prepared by using sterilized soil and wide array of host crops were used as host. The sterilization process is a cumbersome one and scientists started using inert materials for production of AM fungi. The researchers tried use of perlite, montmorillonite clay etc., In TNAU vermiculite was tried as substrate for the replacement of soil sterilization, which resulted in the best method of inoculum production.

Method of production

1. Tank for mass multiplication of AM    2. Sprinkling of water in tank with vermiculite     3. Making of furrows to sow maize seeds
4. Sowing the seeds in furrows 5. View of the maize sown AM pit 6. Vermiculite contained raised AM infected maize plants
  • A trench (1m x 1m x 0.3m) is formed and lined with black polythene sheet to be used as a plant growth tub.
  • Mixed 50 kg of vermiculite and 5 kg of sterilized soil and packed in the trench up to a height of 20 cm
  • Spread 1 kg of AM inoculum (mother culture) 2-5 cm below the surface of vermiculite
  • Maize seeds surface sterilized with 5% sodium hypochlorite for 2 minutes are sown
  • Applied 2 g urea, 2 g super phosphate and 1 g muriate of potash for each trench at the time of sowing seeds.  Further 10 g of urea is applied twice on 30 and 45 days after sowing for each trench
  • Quality test on AM colonization in root samples is carried out on 30th and 45th day
  • Stock plants are grown for 60 days (8 weeks).  The inoculum is obtained by cutting all the roots of stock plants.  The inoculum produced consists of a mixture of vermiculite, spores, pieces of hyphae and infected root pieces.
  • Thus within 60 days 55 kg of AM inoculum could be produced from 1 sq meter area.  This inoculum will be sufficient to treat 550 m2 nursery area having 11,000 seedlings.

AM fungi

Nursery application: 100 g bulk inoculum is sufficient for one metre square. The inoculum should be applied at 2-3 cm below the soil at the time of sowing. The seeds/cutting should be sown/planted above the VAM inoculum to cause infection.

For polythene bag raised crops: 5 to 10 g bulk inoculum is sufficient for each packet. Mix 10 kg of inoculum with 1000 kg of sand potting mixture and pack the potting mixture in polythene bag before sowing.

For out –planting: Twenty grams of VAM inoculum is required per seedling. Apply inoculum at the time of planting.
For existing trees: Two hundred gram of VAM inoculum is required for inoculating one tree. Apply inoculum near the root surface at the time of fertilizer application.

Mass production and field application of cyanobacteria

Blue green algal inoculation with composite cultures was found to be more effective than single culture inoculation. A technology for mass scale production of composite culture of blue green algae under rice field condition was developed at TNAU and the soil based BGA inoculum could survive for more than 2 years.

At many sites where algal inoculation was used for three to four consecutive cropping seasons, the inoculated algae establish well and the effect persisted over subsequent rice crop. Technologies for utilizing nitrogen fixing organisms in low land rice were the beneficial role of blue green algal inoculation in rice soils of Tamil Nadu.

The blue green algal inoculum may be produced by several methods viz., in tubs, galvanized trays, small pits and also in field conditions.  However the large-scale production is advisable under field condition which is easily adopted by farmers.

I. Multiplication in trays

  • Big metallic trays (6’x 3’x 6”lbh) can be used for small scale production
  • Take 10 kg of paddy field soil, dry powder well and spread
  • Fill water to a height of 3”
  • Add 250 g of dried algal flakes (soil based) as inoculum
  • Add 150 g of super phosphate and 30 g of lime and mix well with the soil
  • Sprinkle 25 g carbofuran to control the insects
  • Maintain water level in trays
  • After 10 to 15 days, the blooms of BGA will start floating on the water sources
  • At this stage stop watering and drain. Let the soil to dry completely
  • Collect the dry soil based inoculum as flakes
  • Store in a dry place.  By this method 5 to 7 kg of soil based inoculum can be obtained.

II. Multiplication under field condition

Materials

  • Rice field
  • Super phosphate
  • Carbofuran
  • Composite BGA starter culture

Procedure

Select an area of 40 m2 (20m x 2m) near a water source which is directly exposed to sunlight.
Make a bund all around the plot to a height of 15 cm and give it a coating with mud to prevent loss of water due to percolation.

  • Plot is well prepared and levelled uniformly and water is allowed to a depth of 5-7.5 cm and left to settle for 12 hrs.
  • Apply 2 kg of super phosphate and 200 g lime to each plot uniformly over the area.
  • The soil based composite starter culture of BGA containing 8-10 species @ 5 kg / plot is powdered well and broadcasted.
  • Carbofuran @ 200 g is also applied to control soil insects occurring in BGA.
  • Water is let in at periodic intervals so that the height of water level is always maintained at 5 cm.
  • After 15 days of inoculation, the plots are allowed to dry up in the sun and the algal flakes are collected and stored.

Observations

The floating algal flasks are green or blue green in colour.  From each harvest, 30 to 40 kg of dry algal flakes are obtained from the plot.

Method of inoculation of BGA in rice field

Blue green algae may be applied as soil based inoculum to the rice field following the method described below.

  • Powder the soil based algal flakes very well.
  • Mix it with 10 kg soil or sand (10kg powdered algal flakes with 10 kg soil / sand).
  • BGA is to be inoculated on 7-10 days after rice transplanting.
  • Water level at 3-4” is to be maintained at the time of BGA inoculation and then for a month so as to have maximum BGA development.

Observation

A week after BGA inoculation, algal growth can be seen and algal mat will float on the water after 2-3 weeks. The algal mat colour will be green or brown or yellowish green.

Mass production and field application of Azol

Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaena azollae. Azolla fronds consist of sporophyte with a floating rhizome and small overlapping bi-lobed leaves and roots. Rice growing areas in South East Asia and other third World countries have recently been evincing increased interest in the use of the symbiotic N2 fixing water fern Azolla either as an alternate nitrogen sources or as a supplement to commercial nitrogen fertilizers.  Azolla is used as biofertilizer for wetland rice and it is known to contribute 40-60 kg N ha-1 per rice crop. The agronomic potential ofAzolla is quite significant particularly for rice crop and it is widely used as biofertilizer for increasing rice yields. Rice crop response studies with Azolla biofertilizer in the People’s Republic in China and in Vietnam have provided good evidence that Azolla incorporation into the soil as a green manure crop is one of the most effective ways of providing nitrogen source for rice.

The utilization of Azolla as dual crop with wetland rice is gaining importance in Philippines, Thailand, Srilanka and India. The important factor in using Azolla as a biofertilizer for rice crop is its quick decomposition in soil and efficient availability of its nitrogen to rice. In tropical rice soils the applied Azolla mineralizes rapidly and its nitrogen is available to the rice crop in very short period. The common species of Azolla are A. microphylla, A. filiculoides, A. pinnata, A. caroliniana, A. nilotica, A. rubra and A. mexicana.

I.  Mass multiplication of Azolla under field conditions

A simple Azolla nursery method for large scale multiplication of Azolla in the field has been evolved for easy adoption by the farmers.

Materials

  • One cent (40 sq.m) area plot
  • Cattle dung
  • Super phosphate
  • Furadan
  • Fresh Azolla inoculum

Procedure

  • Select a wetland field and prepare thoroughly and level uniformly.
  • Mark the field into one cent plots (20 x 2m) by providing suitable bunds and irrigation channels.
  • Maintain water level to a height of 10 cm.
  • Mix 10 kg of cattle dung in 20 litres of water and sprinkle in the field.
  • Apply 100 g super phosphate as basal dose.
  • Inoculate fresh Azolla biomass @ 8 kg to each pot.
  • Apply super phosphate @ 100 g as top dressing fertilizer on 4th and 8th day after Azolla inoculation.
  • Apply carbofuran (furadan) granules @ 100 g/plot on 7th day after Azolla inoculation.
  • Maintain the water level at 10 cm height throughout the growth period of two or three weeks.
  • Observations
  • Note the Azolla mat floating on the plot. Harvest the Azolla, drain the water and record the biomass.

II.  Method of  inoculation of Azolla to rice crop

The Azolla biofertilizer may be applied in two ways for the wetland paddy.  In the first method, fresh Azolla biomass is inoculated in the paddy field before transplanting and incorporated as green manure.  This method requires huge quantity of fresh Azolla. In the other method, Azolla may be inoculated after transplanting rice and grown as dual culture with rice and incorporated  subsequently.

A.  Azolla  biomass incorporation as green manure for rice crop

  • Collect the fresh Azolla biomass from the Azolla nursery plot.
  • Prepare the wetland well and maintain water just enough  for easy incorporation.
  • Apply fresh Azolla biomass (15 t ha-1) to the main field and incorporate the Azolla by using implements or tractor.

B.  Azolla inoculation as dual crop for rice

  • Select a transplanted rice field.
  • Collect fresh Azolla  inoculum from Azolla nursery.
  • Broadcast the fresh Azolla in the transplanted rice field on 7th day after planting (500 kg / ha).
  • Maintain water level at 5-7.5cm.
  • Note the growth of Azolla mat four weeks after transplanting and incorporate the  Azolla biomass by using implements or tranctor or during inter-cultivation practices.
  • A second bloom of Azolla will develop 8 weeks after transplanting which may be incorporated again.
  • By the two incorporations, 20-25 tonnes of Azolla can be incorporated in one hectare rice field.

4. Application of Biofertilizers

1. Seed treatment or seed inoculation
2. Seedling root dip
3. Main field application

Seed treatment

One packet of the inoculant is mixed with 200 ml of rice kanji to make a slurry. The seeds required for an acre are mixed in the slurry so as to have a uniform coating of the inoculant over the seeds and then shade dried for 30 minutes. The shade dried seeds should be sown within 24 hours. One packet of the inoculant (200 g) is sufficient to treat 10 kg of seeds.

Seedling root dip

This method is used for transplanted crops. Two packets of the inoculant is mixed in 40 litres of water. The root portion of the seedlings required for an acre is dipped in the mixture for 5 to 10 minutes and then transplanted.

Main field application

Four packets of the inoculant is mixed with 20 kgs of dried and powdered farm yard manure and then broadcasted in one acre of main field just before transplanting.

Rhizobium

For all legumes Rhizobium is applied as seed inoculant.

Azospirillum/Azotobacter

In the transplanted crops, Azospirillum is inoculated through seed, seedling root dip and soil application methods. For direct sown crops, Azospirillum is applied through seed treatment and soil application.

Phosphobacteria

Inoculated through seed, seedling root dip and soil application methods as in the case of Azospirillum.
Combined application of bacterial biofertilizers.

Phosphobacteria can be mixed with Azospirillum and Rhizobium. The inoculants should be mixed in equal quantities and applied as mentioned above.

Points to remember

  • Bacterial inoculants should not be mixed with insecticide, fungicide, herbicide and fertilizers.
  • Seed treatment with bacterial inoculant is to be done at last when seeds are treated with fungicides.

Biofertilizers recommendation (one packet – 200 g)

Crop Seed Nursery Seedling dip Main field Total requirement of packets per ha
Rice 5 10 5 10 30
Sorghum 3 10 13
Pearl millet 3 10 13
Ragi 3 5 10 18
Maize 3 10 13
Cotton 3 10 13
Sunflower 3 10 13
Castor 3 10 13
Sugarcane 10 36
(3 split)
46
Turmeric 24
(2 split)
24
Tobacco 1 3 10 g/pit 14
Papaya 2 10
Mandarin
Orange
2 10 g/pit
Tomato 1 10 14
Banana 5 10 g/pit

Rhizobium (only seed application is recommended)

Crop Total requirement of packets per ha
Soybean 5
Groundnut 5
Bengalgram 5
Blackgram 3
Greengram 3
Redgram 3
Cowpea 3

Phosphobacteria
The recommended dosage of Azospirillum is adopted for phosphobacteria inoculation; for combined inoculation, both biofertilizers as per recommendations are to be mixed uniformly before using.


5. Azolla – The best feed for cattle and poultry

Azolla is a free floating water fern that floats in water and fixes nitrogen in association with the nitrogen fixing blue green algae, Anabaena azollae. Azolla is considered to be a potential biofertilizer in terms of nitrogen contribution to rice. Long before its cultivation as a green manure, Azolla has been used as a fodder for domesticated animals such as pigs and ducks. In recent days, Azolla is very much used as a sustainable feed substitute for livestock especially dairy cattle, poultry, piggery and fish.

Azolla contains 25 – 35 per cent protein on dry weight basis and rich in essential amino acids, minerals, vitamins and carotenoids including the antioxidant b carotene. Cholorophyll a, chlorophyll b and carotenoids are also present in Azolla, while the cyanobiont Anabaena azollae contains cholorophyll a, phycobiliproteins and carotenoids. The rare combination of high nutritive value and rapid biomass production make Azolla a potential and effective feed substitute for live stocks.

Inputs required

Azolla fronds, Polythene sheet, Super phosphate and Cow dung.

Methodology

The area selected for Azolla nursery should be partially shaded. The convenient size for Azolla is 10 feet length, 2 feet breadth and 1 feet depth. The nursery plot is spread with a polythene sheet at the bottom to prevent water loss. Soil is applied to a depth of 2 cm and a gram of super phosphate is applied along with 2 kg of vermicompost or cow dung in the nursery for quick growth. Azolla mother inoculum is introduced @ 5 kg/plot.

The contents in the plot are stirred daily so that the nutrients in the soil dissolve in water for easy uptake by Azolla. Azolla is harvested fifteen days after inoculation at the rate of 50-80 kg / plot. One third of Azolla should be left in the plot for further multiplication. Five kg cow dung slurry should be sprinkled in the Azolla nursery at  ten days intervals. Neem oil can be sprayed over the Azolla at 0.5 5 level to avoid pest incidence.

Animal Dosage / day
Adult cow , Buffalo, Bullock 1.5-2  kg
Layer, Broiler birds 20 – 30 grams
Goat 300 – 500 grams
Pig 1.5 – 2.0 kg
Rabbit 100 gram

Value of the technology

The egg yield is increased in layer birds due to Azolla feeding. The Azolla fed birds register an overall egg productivity of 89.0 per cent as against 83.7 per cent recorded by the birds fed with only concentrated feed. The average daily intake  of concentrated feed is considerably low (106.0 g) for birds due to Azolla substitution as against 122.0 g in the control birds. More impotantly Azolla feeding shows considerable amount of savings in the consumption of concentrated feed (13.0 %) leading to reduced operational cost. By considering the average cost of the concentrated feed  as Rs. 17/ Kg, a 13.0 % saving in the consumption ultimately leads to a feed cost savings of 10.0 paise /day/ bird and hence a layer unit maintaining 10,000 birds could cut down its expense towards feed to a tune of rs.1000/day.

Benefits
The Azolla feeding to layer birds increase egg weight, albumin, globulin and carotene contents. The total protein content of the eggs laid by the Azolla fed birds is high and the total carotene content of Azolla eggs(440 g 100 g-1 of edible portion)is also higher than the control. The rapid biomass production due to the high relative growth rate, increased protein and carotene contents and good digestability of the Azolla hybrid Rong ping favour its use as an effective feed supplement to poultry birds.

Effect of Azolla hybrid Rong Ping on the nutritional value of egg

Parameters Azolla egg Control percentage increase over control
Egg weight (g) 61.20 57.40 6.62
Albumin (g /100 g of edible portion) 3.9 3.4 14.70
Globulin (g /100 g of edible portion) 10.1 9.5 6.31
Total protein (g/ 100 g of edible portion) 14.0 12.9 8.52
Carotenes (µg / 100 g of edible portion) 440 405 8.64

Application

In Indian conditions, agriculture is very much coupled with poultry farming. Azolla is an important low cost input, which plays a vital role in improving soil quantity in sustainable rice farming. The twin potentials as biofertilizer and animal feed make the water fern Azolla as an effective input to both the vital components of integrated farming, agricultural and animalo husbandry.

Limitation

Azolla is a water fern and requires a growth temperature of 35-38º C. The multiplication of Azolla is affected under elevated temperature. Hence adopting this technology in dry zones where the temperature exceeds 40ºc is difficult.

Achievements

Azolla hybrid Rong ping had been selected to supply to the tribal population. Azolla mother inoculum nursery was  laid out in villages with the help of Krishi Vigyan Kendra, TNAU, Coimbatore and Krishi Vigyan Kendra, Karamadai,  women entrepreneurs were selected and one day training  was imparted to them  on the cultivation of Azolla. Wet biomass (Starter inoculm) were supplied at free of cost @ 10 kg/women entrepreneur during the training so as to enable them to initiate commercial Azolla cultivation in their backyards.

Azolla multiplication plots had been laid out in Narasipuram. Azolla mass production training was conducted to the SHG in Narasipuram village with the help of Kalaimagal Arts and Science College, Narasipuram, Sappanimadai (tribal village) and Avinashilingam KVK, Karamadai. With the help of Avinashilingam KVK, Karamadai Azolla trainings were conducted to women volunteers and we have established Azolla village in Karamadai. The Avin milk producers union Coimbatore and the poultry owners association,  Namakkal have been contacted and explained the importance of Azolla as feed supplement.

The Milk Producers Union also involved in the training and marketing of Azolla. They are purchasing Azolla fronds from the village level Azolla growers both under wet and dry conditions. Around 400 rural women and 370 tribal people have been trained on the cultivation of Azolla through this project. The Azolla laboratory and the Azolla germplasm center at AC& RI, TNAU, Coimbatore helped us in the maintenance of germplasm by providing the mother inoculum. The Animal Husbandry Unit at AC&RI, TNAU, Coimbatore  helped us in standardizing the Azolla and concentrated feed mixing ratio.

Azolla mass multiplication in pits Feeding Azolla to Rabbit
Feeding Azolla to Poultry Feeding Azolla to Livestock
Inoculating Super phosphate and Cow dung in Azolla pit

EE-Unit-V Biofuels

A biofuel is defined as any fuel whose energy is obtained through a process of biological carbon fixation. That definition serves to make our understanding of biofuels as clear as mud, so let’s unpack it a bit.

Biological Carbon Fixation

Carbon fixation is a process that takes inorganic carbon (in the form of things like CO2) and converts it into organic compounds. In other words, any process that converts carbon dioxide into a molecule that would be found in a living organism is carbon fixation. If this process occurs in a living organism, it is referred to as ‘biological carbon fixation’.

Fuel

The next part of the definition of a biofuel involves fuel. A fuel is nothing more than something from which we humans can get energy. Carbon fixation can lead to a number of different compounds, like proteins, fats, and alcohols (just to name a few). If any of those molecules can be used to provide energy in a mechanical setting, we call it a fuel.

The Real Definition of a Biofuel and the Practical Definition

A biofuel is a hydrocarbon that is made BY or FROM a living organism that we humans can use to power something. This definition of a biofuel is rather formal. In practical consideration, any hydrocarbon fuel that is produced from organic matter (living or once living material) in a short period of time (days, weeks, or even months) is considered a biofuel. This contrasts with fossil fuels, which take millions of years to form and with other types of fuel which are not based on hydrocarbons (nuclear fission, for instance).

What makes biofuels tricky to understand is that they need not be made by a living organism, though they can be. Biofuels can also be made through chemical reactions, carried out in a laboratory or industrial setting, that use organic matter (called biomass) to make fuel. The only real requirements for a biofuel are that the starting material must be CO2 that was fixed (turned into another molecule) by a living organism and the final fuel product must be produced quickly and not over millions of years.

Biomass

Biomass is simply organic matter. In others words, it is dead material that was once living. Kernels of corn, mats of algae, and stalks of sugar cane are all biomass. Before global warming related to burning fossil fuels became a major factor in determining where energy came from, the major concern was that fossil fuels, which are considered limited in supply, would run out over the next century. It was thought that if we could produce hydrocarbons another way, and quickly, then we could meet our energy demands without much problem. This leads to one of the major separating factors between a biofuel and a fossil fuel – renewability.

A fossil fuel is not considered renewable because it takes millions of years to form and humans really can’t wait that long. Biofuel, on the other hand, comes from biomass, which can be produced year after year through sustainable farming practices. This means biomass and biofuel are renewable (we can replace used biofuel over a very short period of time).

It is important to note that ‘renewable’ energy is not the same thing as ‘green’ energy. Renewable energy simply won’t run out any time soon, like biofuels, hydroelectric, wind, and solar. A “green” energy is one that is also good for the planet because it does not harm ecosystems, contribute to acid rain, or worsen global warming. Solar energy is a ‘green’ energy. All ‘green’ energy is considered renewable, but not all renewable energy is green. Biofuels are examples of renewable energy sources that aren’t always green because they produce greenhouse gases.

Types of Biofuels

The chemical structure of biofuels can differ in the same way that the chemical structure of fossil fuels can differ. For the most part, our interest is in liquid biofuels as they are easy to transport. The table below compares various biofuels with their fossil fuel counterparts.

Biofuel Fossil Fuel Differences
Ethanol Gasoline/Ethane Ethanol has about half the energy per mass of gasoline, which means it takes twice as much ethanol to get the same energy. Ethanol burns cleaner than gasoline, however, producing less carbon monoxide. However, ethanol produces more ozone than gasoline and contributes substantially to smog. Engines must be modified to run on ethanol.
Biodiesel Diesel Has only slightly less energy than regular diesel. It is more corrosive to engine parts than standard diesel, which means engines have to be designed to take biodiesel. It burns cleaner than diesel, producing less particulate and fewer sulfur compounds.
Methanol Methane Methanol has about one third to one half as much energy as methane. Methanol is a liquid and easy to transport whereas methane is a gas that must be compressed for transportation.
Biobutanol Gasoline/Butane Biobutanol has slightly less energy than gasoline, but can run in any car that uses gasoline without the need for modification to engine components.

The chart above is only a limited list of the biofuels available, covering only the most popular and widely used. It is worth nothing that ethanol is found in almost all gasoline mixtures. In Brazil, gasoline contains at least 95% ethanol. In other countries, ethanol usually makes up between 10 and 15% of gasoline.

Biofuel versus Fossil Fuel

Biofuels are not new. In fact, Henry Ford had originally designed his Model T to run on ethanol. There are several factors that decide the balance between biofuel and fossil fuel use around the world. Those factors are cost, availability, and food supply.

All three factors listed above are actually interrelated. To begin, the availability of fossil fuels has been of concern almost from day one of their discovery. Pumping fuel from the ground is a difficult and expensive process, which adds greatly to the cost of these fuels. Additionally, fossil fuels are not renewable, which means they will run out at some point. As our ability to pump fossil fuels from the ground diminishes, the available supply will decrease, which will inevitably lead to an increase in price.

It was originally thought that biofuels could be produced in almost limitless quantity because they are renewable. Unfortunately, our energy needs far out-pace our ability to grown biomass to make biofuels for one simple reason, land area. There is only so much land fit for farming in the world and growing biofuels necessarily detracts from the process of growing food. As the population grows, our demands for both energy and food grow. At this point, we do not have enough land to grow both enough biofuel and enough food to meet both needs. The result of this limit has an impact on both the cost of biofuel and the cost of food. For wealthier countries, the cost of food is less of an issue. However, for poorer nations, the use of land for biofuels, which drives up the cost of food, can have a tremendous impact.

The balance between food and biofuel is what keeps the relatively simple process of growing and making biofuels from being substantially cheaper than fossil fuel. When this factor is combined with an increased ability (thanks to advances in technology) to extract oil from the ground, the price of fossil fuel is actually lower than that of biofuel for the most part.

The Carbon Equation: Would Biofuels Contribute to Global Warming?

Assuming we can overcome the problem of biofuels interrupting the food supply (such as growing algae in the ocean), can we overcome the problem of biofuels contributing to global warming? The answer, surprisingly, may be yes.

It is true that biofuels produce carbon dioxide, which is a potent greenhouse gas and the one most often blamed for global warming. However, it is also true that growing plants consumes carbon dioxide. Thus, the equation becomes a simple balancing act. If the plants we grow utilize the same amount of carbon dioxide that we produce, then we will have a net increase of zero and no global warming. How realistic is this view?

It may seem like a simple matter to only produce as much carbon dioxide as plants use. After all, couldn’t we only burn biofuels and thus keep the equation balanced? Well, the math actually doesn’t quite add up. Research has shown that energy must be invested into producing crops and converting them into biofuels before any energy is obtained. A 2005 study from Cornell University found that producing ethanol from corn used almost 30% more energy than it produced. In other words, you can’t produce a perpetual motion machine using biofuels because you lose the energy you invest in creating them in the first place. In fact, you can’t even break even.

The other problem that we run into with biofuels is that carbon dioxide is not the only greenhouse gas we have to worry about. Other chemicals, like nitrous oxide, are also greenhouse gases and growing plants using fertilizer produces a lot of nitrous oxide. Basically, fertilizer contains nitrogen, which plants need to grow. However, most plants cannot convert molecular nitrogen into the elemental nitrogen they need. For this process, plants rely on bacteria. As it turns out, bacteria not only produce nitrogen that plants can use, they also produce nitrogen products like nitrous oxide, and probably more than was previously thought. The net result is that we may be balancing the CO2 ­ equation by using biofuels, but we are unbalancing the N2O part of the equation and still causing global warming.

The Future of Biofuel

A decade ago, subsidies for biofuel growth and development in many countries (especially the U.S.) were high. However, better understanding of global warming, increased awareness of the fragility of the food supply, and a general trend toward “greener” alternatives have all led to a decline in the popularity of biofuels. In 2011, The U.S. Senate voted 73 to 27 to end tax credits and trade protections for corn-based ethanol production. As the second largest producer of ethanol, this is a substantial move that reflects the changing pressures on our energy needs and shifted focus to environmentally friendly energy sources.

Biodiversity and Biofuels

There is one last problem presented by biofuels that needs to be addressed: biodiversity. Biodiversity refers to the variety of different living things in an environment. For instance, if you grow only sweet corn in a field, you have low biodiversity. If, however, you grow sweet corn, dent corn, flint corn, flour corn, and popcorn, then you have high biodiversity. Why should we care?

Growing a single type of corn is easier for producing biofuels because we can select that type that yields the best raw product, is easiest to grow, and which requires the least amount of water and other resources. This sounds great, but then down side to this is that pests that eat this type of corn will begin to proliferate. What is worse, if we spray with pesticide to kill these pests, some will inevitably be resistant to the pesticide. Over time, these pests will grow in number and we will be left with pests that are resistant to our chemical defenses. In the end, we have a bigger problem that what we started with and probably no corn because the new “super pest” ate it all.

Biodiversity is important to ensuring that pests do not grow out of control. The type of farming needed to produce large quantities of biofuels is generally not amendable to high levels of biodiversity. This presents a fundamental problem in producing biofuels that is enhanced by the fact that “super pests” produced in the effort to grow biofuels can also threaten food crops.

EE-Unit-V Environmental Biotechnology

Environmental biotechnology is a system of scientific and engineering knowledge related to the use of microorganisms and their products in the prevention of environmental pollution through biotreatment of solid, liquid, and gaseous wastes, bioremediation of polluted environments, and biomonitoring of environment and treatment processes. The advantages of biotechnological treatment of wastes are as follows: biodegradation or detoxication of a wide spectrum of hazardous substances by natural microorganisms; availability of a wide range of biotechnological methods for complete destruction of hazardous wastes; and diversity of the conditions suitable for biodegradation. The main considerations for application of biotechnology in waste treatment are technically and economically reasonable rate of biodegradability or detoxication of substances during biotechnological treatment, big volume of treated wastes, and ability of natural microorganisms to degrade substances. Type of biotreatment is based on physiological type of applied microorganisms, such as fermenting anaerobic, anaerobically respiring (anoxic), microaerophilic, and aerobically respiring microorganisms. All types of biotechnological treatment of wastes can be enhanced using optimal environmental factors, better availability of contaminants and nutrients, or addition of selected strain(s) biomass. Bioaugmentation can accelerate start-up or biotreatment process in case microorganisms, which are necessary for hazardous waste treatment, are absent or their concentration is low in the waste; if the rate of bioremediation performed by indigenous microorganisms is not sufficient to achieve the treatment goal within the prescribed duration; when it is necessary to direct the biodegradation to the best pathway of many possible pathways; and to prevent growth and dispersion in waste treatment system of unwanted or nondetermined microbial strain which may be pathogenic or opportunistic one. Biosensors are essential tools in biomonitoring of environment and treatment processes. Combinations of biosensors in array can be used to measure concentration or toxicity of a set of hazardous substances. Microarrays for simultaneous qualitative or quantitative detection of different microorganisms or specific genes in the environmental sample are also useful in the monitoring of environment.

Environmental protection using Biotechnology 

  1. The surroundings around us are termed as ‘environment’. Our environment includes the abiotic component (the non living) and biotic component (the living). The abiotic environment includes air, water and soil; and the biotic environment consists of all living organisms such as plants, animals and microorganisms. Environmental pollution broadly refers to the presence of undesirable substances in the environment which are harmful to man and other organisms. There has been a significant increase in the levels of harmful environmental pollution mostly due to direct or indirect human activities in recent past. The major sources of environmental pollution are industries, agricultural and other anthropogenic and biogenic sources etc. The pollutants are chemical, biological and physical in nature.
  2. Controlling the environmental pollution and the conservation of environment and biodiversity and controlling environmental pollution are the major focus areas of all the countries around the world. In this context, the importance and impact of biotechnological approaches and the implications of biotechnology has to be thoroughly evaluated. There have been serious concerns regarding the use of biotechnological products and the impact assessment of these products due to their interaction with the environmental factors. A lobby of the environmentalists has expressed alarm on the release of genetically engineered organisms in the atmosphere and have stressed on thorough investigation and proper risk assessment of theses organisms before releasing them in to the environment. The effect of the effluents from biotechnological companies is also a cause of concern for everyone. The need of the hour is to have a proper debate on the safety of the use of the biotechnological products. The efforts are not only on to use biotechnology to protect the environment from pollution but also to use it to conserve the natural resources. As we all know that microorganisms are known natural scavengers so the microbial preparations (both natural as well as genetically engineered) can be used to clean up the environmental hazards.
  3. Biotechnology is being used to provide alternative cleaner technologies which help to further reduce the hazardous environmental implications of the traditional technologies. Some of the well known examples and mechanisms are:

(i) Some fermentation technologies have some serious environmental implications. Various biotechnological processes have been devised in which all nutrients introduced for fermentation are retained in the final product, which ensures high conversion efficiency and low environmental impact.

(ii) In paper industry, the pulp bleaching technologies are being replaced by more environmentally friendly technologies involving biotechnology. The pulp processing helps to remove the lignin without damaging valuable cellulosic fibres but the available techniques suffer from the disadvantages of high costs, high energy use and corrosion. A lignin degrading and modifying enzyme (LDM) was isolated from Phanerochaete chrysosporum and was used, which on one hand, helped to reduce the energy costs and corrosion and on the other hand increased the life of the system. This approach helped in reducing the environmental hazards associated with bleach plant effluents.

(iii) In Plastic industry, the conventional technologies use oil based raw materials to extract ethylene and propylene which are converted to alkene oxides and then polymerized to form plastics such as polypropylene and polyethylene. There is always the risk of these raw materials escaping into the atmosphere thereby causing pollution. Using biotechnology, more safer raw materials like sugars (glucose) are being used which are enzymatically or through the direct use of microbes converted into alkene oxides.e.g. Methylococcus capsulatus has been used for converting alkene into alkene oxides.

(iv) Bioremediation is defined as ‘the process of using microorganisms to remove the environmental pollutants where microbes serve as scavengers. The removal of organic wastes by microbes leads to environmental cleanup. The other names/terms used for bioremediation are bio-treatment, bio-reclamation, and bio-restoration. The term “Xenobiotics” (xenos means foreign) refers to the unnatural, foreign and synthetic chemicals such as pesticides, herbicides, refrigerants, solvents and other organic compounds. The microbial degradation of xenobiotics also helps in reducing the environmental pollution. Depending on the method followed to clean up the environment, the bioremediation is carried out in two ways:

(a) In situ bioremediation – involves a direct approach for the microbial degradation of xenobiotics at the site of pollution which could be soil, water etc. The in situ bioremediation is generally used for clean up of oil spillages, beaches etc.;

(b) Ex-situ bioremediation – In this the waste and the toxic material is collected from the polluted sites and the selected range of microorganisms carry out the bioremediation at designed place. This process is an improved method over the in situ bioremediation method.

(v) Pseudomonas which is a soil microorganism effectively degrades xenobiotics. Different strains of Pseudomonas that are capable of detoxifying more than 100 organic compounds (e.g. phenols, biphenyls, organophosphates, naphthalene etc.) have been identified. Some other microbial strains are also known to have the capacity to degrade xenobiotics such as Mycobacterium, Alcaligenes, Norcardia etc.

  1. In recent years, efforts have been made to create genetically engineered microorganisms to enhance bioremediation. This is done to overcome some of the limitations and problems in bioremediation. These problems are: a) Sometimes the growth of microorganisms gets inhibited or reduced by the xenobiotics. b) No single naturally occurring microorganisms has the capability of degrading all the xenobiotics present in the environmental pollution. c) The microbial degradation is a very slow process. d) Sometimes certain xenobiotics get adsorbed on to the particulate matter of soil and thus become unavailable for microbial degradation.
  2. As the majority of genes responsible for the synthesis of enzymes with biodegradation capability that are located on the plasmids, the genetic manipulations of plasmids can lead to the creation of new strains of bacteria with different degradative pathways. Well known example of genetic manipulations of plasmids is development of ‘Superbug’, which is used for degrading a number of hydrocarbons of petroleum simultaneously such as camphor, octane, xylene, naphthalene etc.
  3. We all know that, carbon dioxide (CO2) is the main cause of green house effect and rise in the atmospheric temperature. There is a steady increase in the CO2 content due to continuous addition of CO2 from various sources particularly from industrial processes. It is very clear that the reduction in atmospheric CO2 concentration assumes significance. Biotechnological methods have been used to reduce the atmospheric CO2 content at two levels:

(a) Photosynthesis- Plants utilize CO2 during the photosynthesis which reduces the CO2 content in the atmosphere;

(b) Biological Calcification- Certain deep sea organisms like corals, green and red algae store CO2 through a process of biological calcification. As the CaCO3 gets precipitated, more and more atmospheric CO2 can be utilized for its formation.

  1. The sewage is treated to get rid of these undesirable substances by subjecting the organic matter to biodegradation by microorganisms. The biodegradation involves the degradation of organic matter to smaller molecules, such as CO2, NH3, PO4 etc., and requires constant supply of oxygen. The process of supplying oxygen is expensive, tedious, and requires a lot of expertise and manpower. These problems are overcome by growing micro-algae in the ponds and tanks where sewage treatment is carried out. The algae release the O2 while carrying out the photosynthesis which ensures a continuous supply of oxygen for biodegradation. The algae are also capable of adsorbing certain heavy toxic metals due to the negative charges on the algal cell surface which can take up the positively charged metals. The algal treatment of sewage also supports fish growth as algae are a good source of food for fishes.
  2. The environmental impact assessment system requires proponents to foresee possible environmental impacts when a development project is being planned, and to conduct an environmental assessment. However, debate continues on exactly what kinds of environmental protection measures are needed and how they should be integrated into a given project to achieve desirable environmental results. Actions to deal with global warming and to prevent ozone layer depletion are gaining momentum, but currently available technologies may not be enough to meet the required targets. Technological advances are needed in order to make progress in solving these issues, as well as with the problem of dioxins. New developments are also needed in technologies for pollution removal and environmental restoration, in cases where environmental pollution has already been generated or is already accumulating in the environment.
Environmental biotechnology – serving the future

Like white biotechnology, environmental biotechnology, often referred to as “grey biotechnology”, also focuses on sustainability. For instance, environmental biotechnology deals with the treatment of sewage water, the purification of exhaust gas or the decontamination of soils or ground water using specific microorganisms.

The use of organisms for the removal of contamination or pollutants is generally referred to as bioremediation. Originally, bioremediation was mainly used in cleanup operations, including the decomposition of spilt oil or slagheaps containing radioactive waste. In addition, bioremediation is also the method of choice when solvents, plastics or heavy metals and toxic substances like DDT, dioxins or TNT need to be removed.

Bioadsorption processes using newly developed bioadsorbers made from renewable materials are currently being developed. These adsorbers function as ion exchangers and are used in the elimination and disposal of toxic heavy metals. The industrial use of mineral resources leads to the drastic accumulation of these pollutants in the biosphere. The new bioadsorbers are used for the elimination of heavy metals and radionuklids from industrial wastewater, ore mine wastewater, seepage water from dumpsites or wastewater from nuclear power stations.

EE-Unit-IV Noise Pollution

Sound, a normal feature of our life, is the means of communication and enter­tainment in most animals, including human beings. It is also a very effective alarm system. A low sound is pleasant whereas a loud sound is unpleasant and is commonly referred to as ‘noise’. Noise can be defined as an unpleasant and unwanted sound.

Whether a given sound is as pleasant as music or as unpleasant as noise de­pends on its loudness, duration, rhythm and the mood of the person. But loud­ness is definitely the most significant criterion which converts sound into noise. Exposure to loud noise is indeed annoying and harmful too.

Noise is a physical form of pollution and is not directly harmful to the life sup­porting systems namely air, soil and water. Its effects are more directly on the receiver i.e. man. Noise pollution is the result of modern industrialized urban life and congestion due to over population.

Even though noise pollution is not fatal to human life, yet its importance cannot be overlooked because repeated exposure to noise reduces the sleeping hours and productivity or efficiency of a human being. It affects the peace of mind and invades the privacy of a human being. The importance of noise pollution as environmental problem is being recog­nised as the ill effects of noise on human health and environment are becoming evident with each passing day.

Sources of Noise Pollution:

Major causes / sources of noise pollution are:

(i) Industrial Sources:

Progress in technology (industrialization) has resulted in creating noise pollu­tion. Textile mills, printing presses, engineering establishments and metal works etc. contribute heavily towards noise pollution. In industrial cities like Kolkata, Ludhiana, Kanpur etc., often the industrial zones are not separated from the residential zones of the city especially in the case of small scale industries.

These operate from workshops located on the ground floors of the residential areas and cause annoyance, discomfort and irri­tation to the residents exposed to the noise that is inevitably produced. The situation is much better in modern planned cities like Chandigarh where the industrial area is kept away from the residential areas and both are sepa­rated from each other by a sufficiently wide green belt.

(ii) Transport Vehicles:

Automobile revolution in urban centers has proved to be a big source of noise pollution. Increasing traffic has given rise to traffic jams in congested areas where the repeated hooting of horns by impatient drivers pierce the ears of all road users.

Noise from airplanes constitutes an increasing serious problem in big cities like Delhi & Mumbai. Airport situated in the vicinity of population centres and the air planes pass over residential areas. Heavy trucks, buses trains, jet-planes, motor-cycles, scooters, mopeds, jeeps—the list of vehicles is endless but the outcome is same — noise pollution.

(iii) Household:

The household is an industry in itself and is a source of many indoor noises such as the banging of doors, noise of playing children, crying of infants, moving of furniture, loud conversation of the inhabitants etc. Besides these are the entertainment equipment in the house, namely the radio, record-players and television sets. Domestic gadgets like the mixer-grinders, pressure cookers, desert coolers, air- conditioners, exhaust fans, vacuum cleaners, sewing and washing machines are all indoor sources of noise pollution.

(iv) Public Address System:

In India people need only the slightest of an excuse for using loud speakers. The reason may be a religious function, birth, death, marriage, elections, dem­onstration, or just commercial advertising. Public system, therefore, contrib­utes in its own way towards noise pollution.

(v) Agricultural Machines:

Tractors, thrashers, harvesters, tube wells, powered tillers etc. have all made agriculture highly mechanical but at the same time highly noisy. Noise level 90 dB to 98 dB due to running of farm machines have been recorded in the state of Punjab.

(vi) Defence Equipment:

A lot of noise pollution is added to the atmosphere by artillery, tanks, launching of rockets, explosions, exercising of military airplanes and shooting practices. Screams of jet engines and sonic booms have a deafening impact on the ears and in extreme cases have been known to shatter the window panes and old dilapidated buildings.

(vii) Miscellaneous Sources:

The automobile repair shops, construction-works, blasting, bulldozing, stone crushing etc. are other sources of noise pollution.

Effects of Noise:

Noise is generally harmful and a serious health hazard. It has far-reaching consequences and has many physical, physiological as well as psychological ef­fects on human beings.

(i) Physical Effects:

The physical manifestation of noise pollution is the effect on hearing ability. Repeated exposure to noise may result in temporary or permanent shifting of the hearing threshold of a person depending upon the level and duration of exposure. The immediate and acute effect of noise pollution is impairment of hearing (i.e. total deafness.)

Human ears have sensory cells for hearing. If these cells are subjected to re­peated sounds of high intensity before they have an opportunity to recover fully, they can become permanently damaged leading to impairment of hearing. Be­sides the sensory cells, the delicate tympanic membrane or the ear drum can also be permanently damaged by a sudden loud noise such as an explosion.

(ii) Physiological Effects:

The physiological manifestations of noise pollution are several as mentioned be­low:

(a) Headache by dilating blood vessels of the brain.

(b) Increase in the rate of heart-beat.

(c) Narrowing of arteries.

(d) Fluctuations in the arterial blood pressure by increasing the level of choles­terol in the blood.

(e) Decrease in heart output.

(f) Pain in the heart.

(g) Digestive spasms through anxiety and dilation of the pupil of the eye, thereby causing eye-strain.

(h) Impairment of night vision.

(i) Decrease in the rate of colour perception.

(j) Lowering of concentration and affect on memory,

(k) Muscular strain and nervous breakdown.

(l) Psychological Effect

The psychological manifestations of noise pollution are:

(a) Depression and fatigue which considerably reduces the efficiency of a person.

(b) Insomnia as a result of lack of undisturbed and refreshing sleep

(c) Straining of senses and annoyance as a result of slow but persistent noise from motorcycles, alarm clocks, call bells, telephone rings etc.

(d) Affecting of psychomotor performance of a person by a sudden loud sound

(e) Emotional disturbance

For a talkative person, the most important effect of noise pollution would in­variably be that noise interferes with our conservation. So, noise is annoying and the annoyance depends on many factors not merely the intensity of the sound but also repetition, because even a sound of small intensity (e.g. dripping tap or clicking of clock) may become annoying, simply by repetition.

Some of the well- known effects of noise on human beings and the relation of noise pollution level and its harmful effects are shown in Table 1

Table 1. Noise Pollution Level and its Harmful Effects:

Level (in db) Effects
up to 23 ……………………….. No disturbance
30—60 ……………………….. Stress, tension, psychological (illness, heart attact) effects especially at upper range.
60—90 ……………………….. Damage to health, psychological and vegetative (disturbance in stomach-gall function, pains in muscles, high blood pressure, disturbance in sleep­ing)
60—120 ……………………… Damages to health and ontological (ear diseases) ef­fects
Above 120 ……………………. Painful effects in long run.

EE-Unit-IV Composting

Composting is the natural process of ‘rotting’ or decomposition of organic matter by microorganisms under controlled conditions. Raw organic materials such as crop residues, animal wastes, food garbage, some municipal wastes and suitable industrial wastes, enhance their suitability for application to the soil as a fertilizing resource, after having undergone composting.

Compost is a rich source of organic matter. Soil organic matter plays an important role in sustaining soil fertility, and hence in sustainable agricultural production. In addition to being a source of plant nutrient, it improves the physico-chemical and biological properties of the soil. As a result of these improvements, the soil: (i) becomes more resistant to stresses such as drought, diseases and toxicity; (ii) helps the crop in improved uptake of plant nutrients; and (iii) possesses an active nutrient cycling capacity because of vigorous microbial activity. These advantages manifest themselves in reduced cropping risks, higher yields and lower outlays on inorganic fertilizers for farmers.

Types of composting

Composting may be divided into two categories by the nature of the decomposition process. In anaerobic composting, decomposition occurs where oxygen (O) is absent or in limited supply. Under this method, anaerobic micro-organisms dominate and develop intermediate compounds including methane, organic acids, hydrogen sulphide and other substances. In the absence of O, these compounds accumulate and are not metabolized further. Many of these compounds have strong odours and some present phytotoxicity. As anaerobic composting is a low-temperature process, it leaves weed seeds and pathogens intact. Moreover, the process usually takes longer than aerobic composting. These drawbacks often offset the merits of this process, viz. little work involved and fewer nutrients lost during the process.

Aerobic composting takes place in the presence of ample O. In this process, aerobic microorganisms break down organic matter and produce carbon dioxide (CO2), ammonia, water, heat and humus, the relatively stable organic end product. Although aerobic composting may produce intermediate compounds such as organic acids, aerobic micro-organisms decompose them further. The resultant compost, with its relatively unstable form of organic matter, has little risk of phytotoxicity. The heat generated accelerates the breakdown of proteins, fats and complex carbohydrates such as cellulose and hemi-cellulose. Hence, the processing time is shorter. Moreover, this process destroys many micro-organisms that are human or plant pathogens, as well as weed seeds, provided it undergoes sufficiently high temperature. Although more nutrients are lost from the materials by aerobic composting, it is considered more efficient and useful than anaerobic composting for agricultural production. Most of this publication focuses on aerobic composting.

Composting objectives may also be achieved through the enzymatic degradation of organic materials as they pass through the digestive system of earthworms. This process is termed vermicomposting.

The aerobic composting process

The aerobic composting process starts with the formation of the pile. In many cases, the temperature rises rapidly to 70-80 °C within the first couple of days. First, mesophilic organisms (optimum growth temperature range = 20-45 °C) multiply rapidly on the readily available sugars and amino acids (Figure 1). They generate heat by their own metabolism and raise the temperature to a point where their own activities become suppressed. Then a few thermophilic fungi and several thermophilic bacteria (optimum growth temperature range = 50-70 °C or more) continue the process, raising the temperature of the material to 65 °C or higher. This peak heating phase is important for the quality of the compost as the heat kills pathogens and weed seeds.

The active composting stage is followed by a curing stage, and the pile temperature decreases gradually. The start of this phase is identified when turning no longer reheats the pile. At this stage, another group of thermophilic fungi starts to grow. These fungi bring about a major phase of decomposition of plant cell-wall materials such as cellulose and hemi-cellulose. Curing of the compost provides a safety net against the risks of using immature compost such as nitrogen (N) hunger, O deficiency, and toxic effects of organic acids on plants.

Eventually, the temperature declines to ambient temperature. By the time composting is completed, the pile becomes more uniform and less active biologically although mesophilic organisms recolonize the compost. The material becomes dark brown to black in colour. The particles reduce in size and become consistent and soil-like in texture. In the process, the amount of humus increases, the ratio of carbon to nitrogen (C:N) decreases, pH neutralizes, and the exchange capacity of the material increases.

FIGURE 1
Temperature changes and fungi populations in wheat straw compost

Note:
Solid line = temperature; broken line = mesophilic fungi population; dotted line = thermophilic fungi population; left y-axis = fungal populations (logarithm of colony forming units (cfu) per gram of compost plated onto agar); right y-axis = temperature in centre of compost. a, b, c and d = heating phases.
Source: http://helios.bto.ed.ac.uk/bto/microbes/thermo.htm

Factors affecting aerobic composting

Aeration

Aerobic composting requires large amounts of O, particularly at the initial stage. Aeration is the source of O, and, thus, indispensable for aerobic composting. Where the supply of O is not sufficient, the growth of aerobic micro-organisms is limited, resulting in slower decomposition. Moreover, aeration removes excessive heat, water vapour and other gases trapped in the pile. Heat removal is particularly important in warm climates as the risk of overheating and fire is higher. Therefore, good aeration is indispensable for efficient composting. It may be achieved by controlling the physical quality of the materials (particle size and moisture content), pile size and ventilation and by ensuring adequate frequency of turning.

Moisture

Moisture is necessary to support the metabolic activity of the micro-organisms. Composting materials should maintain a moisture content of 40-65 percent. Where the pile is too dry, composting occurs more slowly, while a moisture content in excess of 65 percent develops anaerobic conditions. In practice, it is advisable to start the pile with a moisture content of 50-60 percent, finishing at about 30 percent.

Nutrients

Micro-organisms require C, N, phosphorus (P) and potassium (K) as the primary nutrients. Of particular importance is the C:N ratio of raw materials. The optimal C:N ratio of raw materials is between 25:1 and 30:1 although ratios between 20:1 and 40:1 are also acceptable. Where the ratio is higher than 40:1, the growth of micro-organisms is limited, resulting in a longer composting time. A C:N ratio of less than 20:1 leads to underutilization of N and the excess may be lost to the atmosphere as ammonia or nitrous oxide, and odour can be a problem. The C:N ratio of the final product should be between about 10:1 and 15:1.

Temperature

The process of composting involves two temperature ranges: mesophilic and thermophilic. While the ideal temperature for the initial composting stage is 20-45 °C, at subsequent stages with the thermophilic organisms taking over, a temperature range of 50-70 °C may be ideal. High temperatures characterize the aerobic composting process and serve as signs of vigorous microbial activities. Pathogens are normally destroyed at 55 °C and above, while the critical point for elimination of weed seeds is 62 °C. Turnings and aeration can be used to regulate temperature.

Lignin content

Lignin is one of the main constituents of plant cell walls, and its complex chemical structure makes it highly resistant to microbial degradation (Richard, 1996). This nature of lignin has two implications. One is that lignin reduces the bioavailability of the other cell-wall constituents, making the actual C:N ratio (viz. ratio of biodegradable C to N) lower than the one normally cited. The other is that lignin serves as a porosity enhancer, which creates favourable conditions for aerobic composting. Therefore, while the addition of lignin-decomposing fungi may in some cases increase available C, accelerate composting and reduce N loss, in other cases it may result in a higher actual C:N ratio and poor porosity, both of which prolong composting time.

Polyphenols

Polyphenols include hydrolysable and condensed tannins (Schorth, 2003). Insoluble condensed tannins bind the cell walls and proteins and make them physically or chemically less accessible to decomposers. Soluble condensed and hydrolysable tannins react with proteins and reduce their microbial degradation and thus N release. Polyphenols and lignin are attracting more attention as inhibiting factors. Palm et al. (2001) suggest that the contents of these two substances be used to classify organic materials for more efficient on-farm natural resource utilization, including composting.

pH value

Although the natural buffering effect of the composting process lends itself to accepting material with a wide range of pH, the pH level should not exceed eight. At higher pH levels, more ammonia gas is generated and may be lost to the atmosphere.

EE-Unit-IV Solid Waste Management

Solid waste management is a polite term for garbage management. As long as humans have been living in settled communities, solid waste, or garbage, has been an issue, and modern societies generate far more solid waste than early humans ever did.

Daily life in industrialized nations can generate several pounds of solid waste per consumer, not only directly in the home, but indirectly in factories that manufacture goods purchased by consumers.

Garbage: many broad categories of garbage are:

i. Organic waste: kitchen waste, vegetables, flowers, leaves, fruits.

ii. Toxic waste: old medicines, paints, chemicals, bulbs, spray cans, fertilizer and pesticide containers, batteries, shoe polish.

iii. Recyclable: paper, glass, metals, plastics.

iv. Hospital waste such as cloth with blood

1. Types & Source of Solid Wastes:

Basically solid waste can be classified into different types depending on their source:

 

2. Effects of Solid Waste Pollution:

Municipal solid wastes heap up on the roads due to improper disposal system. People clean their own houses and litter their immediate surroundings which affects the community including themselves.

This type of dumping allows biodegradable materials to decompose under uncontrolled and unhygienic conditions. This produces foul smell and breeds various types of insects and infectious organisms besides spoiling the aesthetics of the site. Industrial solid wastes are sources of toxic metals and hazardous wastes, which may spread on land and can cause changes in physicochemical and biological characteristics thereby affecting productivity of soils.

Toxic substances may leach or percolate to contaminate the ground water. In refuse mixing, the hazardous wastes are mixed with garbage and other combustible wastes. This makes segregation and disposal all the more difficult and risky.

Various types of wastes like cans, pesticides, cleaning solvents, batteries (zinc, lead or mercury), radioactive materials, plastics and e-waste are mixed up with paper, scraps and other non-toxic materials which could be recycled. Burning of some of these materials produces dioxins, furans and polychlorinated biphenyls, which have the potential to cause various types of ailments including cancer.

3. Methods of Solid Wastes Disposal:

i. Sanitary Landfill

ii. Incineration

iii. Composting

iv. Pyrolysis

i. Sanitary Land Filling:

In a sanitary landfill, garbage is spread out in thin layers, compacted and covered with clay or plastic foam. In the modern landfills the bottom is covered with an impermeable liner, usually several layers of clay, thick plastic and sand. The liner protects the ground water from being contaminated due to percolation of leachate.

Leachate from bottom is pumped and sent for treatment. When landfill is full it is covered with clay, sand, gravel and top soil to prevent seepage of water. Several wells are drilled near the landfill site to monitor if any leakage is contaminating ground water. Methane produced by anaerobic decomposition is collected and burnt to produce electricity or heat. Sanitary Landfills Site Selection:

i. Should be above the water table, to minimize interaction with groundwater.

ii. Preferably located in clay or silt.

iii. Do not want to place in a rock quarry, as water can leech through the cracks inherent in rocks into a water fracture system.

iv. Do not want to locate in sand or gravel pits, as these have high leeching. Unfortunately, most of Long Island is sand or gravel, and many landfills are located in gravel pits, after they were no longer being used.

v. Do not want to locate in a flood plain. Most garbage tends to be less dense than water, so if the area of the landfill floods, the garbage will float to the top and wash away downstream.

A large number of adverse impacts may occur from landfill operations. These impacts can vary:

i. Fatal accidents (e.g., scavengers buried under waste piles).

ii. Infrastructure damage (e.g., damage to access roads by heavy vehicles).

iii. Pollution of the local environment (such as contamination of groundwater and/or aquifers by leakage and residual soil contamination during landfill usage, as well as after landfill closure).

iv. Off gassing of methane generated by decaying organic wastes (methane is a greenhouse gas many times more potent than carbon dioxide, and can itself be a danger to inhabitants of an area).

v. Harbouring of disease vectors such as rats and flies, particularly from improperly operated landfills.

ii. Incineration:

The term incinerates means to burn something until nothing is left but ashes. An incinerator is a unit or facility used to burn trash and other types of waste until it is reduced to ash. An incinerator is constructed of heavy, well-insulated materials, so that it does not give off extreme amounts of external heat.

The high levels of heat are kept inside the furnace or unit so that the waste is burned quickly and efficiently. If the heat were allowed to escape, the waste would not burn as completely or as rapidly. Incineration is a disposal method in which solid organic wastes are subjected to combustion so as to convert them into residue and gaseous products. This method is useful for disposal of residue of both solid waste management and solid residue from waste water management. This process reduces the volumes of solid waste to 20 to 30 per cent of the original volume.

Incineration and other high temperature waste treatment systems are sometimes described as “thermal treatment”. Incinerators convert waste materials into heat, gas, steam and ash. Incineration is carried out both on a small scale by individuals and on a large scale by industry. It is used to dispose of solid, liquid and gaseous waste. It is recognized as a practical method of disposing of certain hazardous waste materials. Incineration is a controversial method of waste disposal, due to issues such as emission of gaseous pollutants.

iii. Composting:

Due to shortage of space for landfill in bigger cities, the biodegradable yard waste (kept separate from the municipal waste) is allowed to degrade or decompose in a medium. A good quality nutrient rich and environmental friendly manure is formed which improves the soil conditions and fertility.

Organic matter constitutes 35%-40% of the municipal solid waste generated in India. This waste can be recycled by the method of composting, one of the oldest forms of disposal. It is the natural process of decomposition of organic waste that yields manure or compost, which is very rich in nutrients.

Composting is a biological process in which micro-organisms, mainly fungi and bacteria, convert degradable organic waste into humus like substance. This finished product, which looks like soil, is high in carbon and nitrogen and is an excellent medium for growing plants.

The process of composting ensures the waste that is produced in the kitchens is not carelessly thrown and left to rot. It recycles the nutrients and returns them to the soil as nutrients. Apart from being clean, cheap, and safe, composting can significantly reduce the amount of disposable garbage.

The organic fertilizer can be used instead of chemical fertilizers and is better specially when used for vegetables. It increases the soil’s ability to hold water and makes the soil easier to cultivate. It helped the soil retain more of the plant nutrients.

Vermi-composting has become very popular in the last few years. In this method, worms are added to the compost. These help to break the waste and the added excreta of the worms makes the compost very rich in nutrients. In the activity section of this web site you can learn how to make a compost pit or a vermi-compost pit in your school or in the garden at home.

To make a compost pit, you have to select a cool, shaded corner of the garden or the school compound and dig a pit, which ideally should be 3 feet deep. This depth is convenient for aerobic composting as the compost has to be turned at regular intervals in this process.

Preferably the pit should be lined with granite or brick to prevent nitrite pollution of the subsoil water, which is known to be highly toxic. Each time organic matter is added to the pit it should be covered with a layer of dried leaves or a thin layer of soil which allows air to enter the pit thereby preventing bad odour. At the end of 45 days, the rich pure organic matter is ready to be used. Composting: some benefits

i. Compost allows the soil to retain more plant nutrients over a longer period.

ii. It supplies part of the 16 essential elements needed by the plants.

iii. It helps reduce the adverse effects of excessive alkalinity, acidity, or the excessive use of chemical fertilizer.

iv. It makes soil easier to cultivate.

v. It helps keep the soil cool in summer and warm in winter.

vi. It aids in preventing soil erosion by keeping the soil covered.

vii. It helps in controlling the growth of weeds in the garden.

iv. Pyrolysis:

Pyrolysis is a form of incineration that chemically decomposes organic materials by heat in the absence of oxygen. Pyrolysis typically occurs under pressure and at operating temperatures above 430 °C (800 °F).

In practice, it is not possible to achieve a completely oxygen-free atmosphere. Because some oxygen is present in any pyrolysis system, a small amount of oxidation occurs. If volatile or semi-volatile materials are present in the waste, thermal desorption will also occur.

Organic materials are transformed into gases, small quantities of liquid, and a solid residue containing carbon and ash. The off-gases may also be treated in a secondary thermal oxidation unit. Particulate removal equipment is also required. Several types of pyrolysis units are available, including the rotary kiln, rotary hearth furnace, and fluidized bed furnace. These units are similar to incinerators except that they operate at lower temperatures and with less air supply.

Limitations and Concerns:

i. The technology requires drying of soil prior to treatment.

ii. Limited performance data are available for systems treating hazardous wastes containing polychlorinated biphenyls (PCBs), dioxins, and other organics. There is concern that systems that destroy chlorinated organic molecules by heat have the potential to create products of incomplete combustion, including dioxins and furans. These compounds are extremely toxic in the parts per trillion ranges. The MSO process reportedly does not produce dioxins and furans.

iii. The molten salt is usually recycled in the reactor chamber. However, depending on the waste treated (especially inorganics) and the amount of ash, spent molten salt may be hazardous and require special care in disposal.

iv. pyrolysis is not effective in either destroying or physically separating in organics from the contaminated medium. Volatile metals may be removed as a result of the higher temperatures associated with the process, but they are not destroyed. By-products containing heavy metals may require stabilization before final disposal.

v. When the off-gases are cooled, liquids condense, producing an oil/tar residue and contaminated water. These oils and tars may be hazardous wastes, requiring proper treatment, storage, and disposal.

EE-Unit-IV Solid Waste Management

Solid-waste management, sanitary landfill [Credit: iStockphoto/Thinkstock]the collecting, treating, and disposing of solid material that is discarded because it has served its purpose or is no longer useful. Improper disposal of municipal solid waste can create unsanitary conditions, and these conditions in turn can lead to pollution of the environment and to outbreaks of vector-borne disease—that is, diseases spread by rodents and insects. The tasks of solid-waste management present complex technical challenges. They also pose a wide variety of administrative, economic, and social problems that must be managed and solved.

Historical background

Early waste disposal

In ancient cities, wastes were thrown onto unpaved streets and roadways, where they were left to accumulate. It was not until 320 bce in Athens that the first known law forbidding this practice was established. At that time a system for waste removal began to evolve in Greece and in the Greek-dominated cities of the eastern Mediterranean. In ancient Rome, property owners were responsible for cleaning the streets fronting their property. But organized waste collection was associated only with state-sponsored events such as parades. Disposal methods were very crude, involving open pits located just outside the city walls. As populations increased, efforts were made to transport waste farther out from the cities.

After the fall of Rome, waste collection and municipal sanitation began a decline that lasted throughout the Middle Ages. Near the end of the 14th century, scavengers were given the task of carting waste to dumps outside city walls. But this was not the case in smaller towns, where most people still threw waste into the streets. It was not until 1714 that every city in England was required to have an official scavenger. Toward the end of the 18th century in America, municipal collection of garbage was begun in Boston, New York City, and Philadelphia. Waste disposal methods were still very crude, however. Garbage collected in Philadelphia, for example, was simply dumped into the Delaware River downstream from the city.

Developments in waste management

A technological approach to solid-waste management began to develop in the latter part of the 19th century. Watertight garbage cans were first introduced in the United States, and sturdier vehicles were used to collect and transport wastes. A significant development in solid-waste treatment and disposal practices was marked by the construction of the first refuse incinerator in England in 1874. By the beginning of the 20th century, 15 percent of major American cities were incinerating solid waste. Even then, however, most of the largest cities were still using primitive disposal methods such as open dumping on land or in water.

Technological advances continued during the first half of the 20th century, including the development of garbage grinders, compaction trucks, and pneumatic collection systems. By mid-century, however, it had become evident that open dumping and improper incineration of solid waste were causing problems of pollution and jeopardizing public health. As a result, sanitary landfills were developed to replace the practice of open dumping and to reduce the reliance on waste incineration. In many countries waste was divided into two categories, hazardous and nonhazardous, and separate regulations were developed for their disposal. Landfills were designed and operated in a manner that minimized risks to public health and the environment. New refuse incinerators were designed to recover heat energy from the waste and were provided with extensive air pollution control devices to satisfy stringent standards of air quality. Modern solid-waste management plants in most developed countries now emphasize the practice of recycling and waste reduction at the source rather than incineration and land disposal.

Solid-waste characteristics

Composition and properties

The sources of solid waste include residential, commercial, institutional, and industrial activities. Certain types of wastes that cause immediate danger to exposed individuals or environments are classified as hazardous; these are discussed in the article hazardous-waste management. All nonhazardous solid waste from a community that requires collection and transport to a processing or disposal site is called refuse or municipal solid waste (MSW). Refuse includes garbage and rubbish. Garbage is mostly decomposable food waste; rubbish is mostly dry material such as glass, paper, cloth, or wood. Garbage is highly putrescible or decomposable, whereas rubbish is not. Trash is rubbish that includes bulky items such as old refrigerators, couches, or large tree stumps. Trash requires special collection and handling.

Construction and demolition (C&D) waste (or debris) is a significant component of total solid waste quantities (about 20 percent in the United States), although it is not considered to be part of the MSW stream. However, because C&D waste is inert and nonhazardous, it is usually disposed of in municipal sanitary landfills (see below).

Another type of solid waste, perhaps the fastest-growing component in many developed countries, is electronic waste, or e-waste, which includes discarded computer equipment, televisions, telephones, and a variety of other electronic devices. In 2006 e-waste made up 5 percent of the total solid waste stream, and the United Nations Environment Programme estimated that developed countries would triple their output of e-waste by 2010. Concern over this type of waste is escalating. Lead, mercury, andcadmium are among the materials of concern in electronic devices, and governmental policies may be required to regulate their recycling and disposal.

Solid-waste characteristics vary considerably among communities and nations. American refuse is usually lighter, for example, than European or Japanese refuse. In the United States paper and paperboard products make up close to 40 percent of the total weight of MSW; food waste accounts for less than 10 percent. The rest is a mixture of yard trimmings, wood, glass, metal, plastic, leather, cloth, and other miscellaneous materials. In a loose or uncompacted state, MSW of this type weighs approximately 120 kg per cubic metre (200 pounds per cubic yard). These figures vary with geographic location, economic conditions, season of the year, and many other factors. Waste characteristics from each community must be studied carefully before any treatment or disposal facility is designed and built.

Generation and storage

Rates of solid-waste generation vary widely. In the United States, for example, municipal refuse is generated at an average rate of approximately 2 kg (4.4 pounds) per person per day. Japan generates roughly half this amount, yet in Canada the rate is 3 kg (almost 7 pounds) per person per day. In some developing countries (e.g., India) the average rate can be lower than 0.5 kg (1 pound) per person per day. These data include refuse from commercial, institutional, and industrial as well as residential sources. The actual rates of refuse generation must be carefully determined when a community plans a solid-waste management project.

Most communities require household refuse to be stored in durable, easily cleaned containers with tight-fitting covers in order to minimize rodent or insect infestation and offensive odours. Galvanized metal or plastic containers of about 115-litre (30-gallon) capacity are commonly used, although some communities employ larger containers that can be mechanically lifted and emptied into collection trucks. Plastic bags are frequently used as liners or as disposable containers for curbside collection. Where large quantities of refuse are generated—such as at shopping centres, hotels, or apartment buildings—dumpsters may be used for temporary storage until the waste is collected. Some office and commercial buildings use on-site compactors to reduce the waste volume.

Solid-waste collection

Collecting and transporting

Proper solid-waste collection is important for the protection of public health, safety, and environmental quality. It is a labour-intensive activity, accounting for approximately three-quarters of the total cost of solid-waste management. Public employees are often assigned to the task, but sometimes it is more economical for private companies to do the work under contract to the municipality or for private collectors to be paid by individual home owners. A driver and one or two loaders serve each collection vehicle. These are typically trucks of the enclosed, compacting type, with capacities up to 30 cubic metres (40 cubic yards). Loading can be done from the front, rear, or side. Compaction reduces the volume of refuse in the truck to less than half of its loose volume.

The task of selecting an optimal collection route is a complex problem, especially for large and densely populated cities. An optimal route is one that results in the most efficient use of labour and equipment, and selecting such a route requires the application of computer analyses that account for all the many design variables in a large and complex network. Variables include frequency of collection, haulage distance, type of service, and climate. Collection of refuse in rural areas can present a special problem, since the population densities are low, leading to high unit costs.

Refuse collection usually occurs at least once per week because of the rapid decomposition of food waste. The amount of garbage in the refuse of an individual home can be reduced by garbage grinders, or garbage disposals. Ground garbage puts an extra load on sewerage systems, but this can usually be accommodated. Many communities now conduct source separation and recycling programs, in which homeowners and businesses separate recyclable materials from garbage and place them in separate containers for collection. In addition, some communities have drop-off centres where residents can bring recyclables.

Transfer stations

If the final destination of the refuse is not near the community in which it is generated, one or more transfer stations may be necessary. A transfer station is a central facility where refuse from many collection vehicles is combined into a larger vehicle, such as a tractor-trailer unit. Open-top trailers are designed to carry about 76 cubic metres (100 cubic yards) of uncompacted waste to a regional processing or disposal location. Closed compactor-type trailers are also available, but they must be equipped with ejector mechanisms. In a direct discharge type of station, several collection trucks empty directly into the transport vehicle. In a storage discharge type of station, refuse is first emptied into a storage pit or onto a platform, and then machinery is used to hoist or push the solid waste into the transport vehicle. Large transfer stations can handle more than 500 tons of refuse per day.

Solid-waste treatment and disposal

Once collected, municipal solid waste may be treated in order to reduce the total volume and weight of material that requires final disposal. Treatment changes the form of the waste and makes it easier to handle. It can also serve to recover certain materials, as well as heat energy, for recycling or reuse.

Incineration

FURNACE OPERATION

Burning is a very effective method of reducing the volume and weight of solid waste. In modern incinerators the waste is burned inside a properly designed furnace under very carefully controlled conditions. The combustible portion of the waste combines with oxygen, releasing mostly carbon dioxide, water vapour, and heat. Incineration can reduce the volume of uncompacted waste by more than 90 percent, leaving an inert residue of ash, glass, metal, and other solid materials called bottom ash. The gaseous by-products of incomplete combustion, along with finely divided particulate material called fly ash, are carried along in the incinerator airstream. Fly ash includes cinders, dust, and soot. In order to remove fly ash and gaseous by-products before they are exhausted into the atmosphere, modern incinerators must be equipped with extensive emission control devices. Such devices include fabric baghouse filters, acid gas scrubbers, and electrostatic precipitators. (See also air pollution control.) Bottom ash and fly ash are usually combined and disposed of in a landfill. If the ash is found to contain toxic metals, it must be managed as a hazardous waste.

Municipal solid-waste incinerators are designed to receive and burn a continuous supply of refuse. A deep refuse storage pit, or tipping area, provides enough space for about one day of waste storage. The refuse is lifted from the pit by a crane equipped with a bucket or grapple device. It is then deposited into a hopper and chute above the furnace and released onto a charging grate or stoker. The grate shakes and moves waste through the furnace, allowing air to circulate around the burning material. Modern incinerators are usually built with a rectangular furnace, although rotary kiln furnaces and vertical circular furnaces are available. Furnaces are constructed of refractory bricks that can withstand the high combustion temperatures.

Combustion in a furnace occurs in two stages: primary and secondary. In primary combustion, moisture is driven off, and the waste is ignited and volatilized. In secondary combustion, the remaining unburned gases and particulates are oxidized, eliminating odours and reducing the amount of fly ash in the exhaust. When the refuse is very moist, auxiliary gas or fuel oil is sometimes burned to start the primary combustion.

In order to provide enough oxygen for both primary and secondary combustion, air must be thoroughly mixed with the burning refuse. Air is supplied from openings beneath the grates or is admitted to the area above. The relative amounts of this underfire air and overfire air must be determined by the plant operator to achieve good combustion efficiency. A continuous flow of air can be maintained by a natural draft in a tall chimney or by mechanical forced-draft fans.

ENERGY RECOVERY

The energy value of refuse can be as much as one-third that of coal, depending on the paper content, and the heat given off during incineration can be recovered by the use of a refractory-lined furnace coupled to a boiler. Boilers convert the heat of combustion into steam or hot water, thus allowing the energy content of the refuse to be recycled. Incinerators that recycle heat energy in this way are calledwaste-to-energy plants. Instead of a separate furnace and boiler, a water-tube wall furnace may also be used for energy recovery. Such a furnace is lined with vertical steel tubes spaced closely enough to form continuous sections of wall. The walls are insulated on the outside in order to reduce heat loss. Water circulating through the tubes absorbs heat to produce steam, and it also helps to control combustion temperatures without the need for excessive air, thus lowering air pollution control costs.

Waste-to-energy plants operate as either mass burn or refuse-derived fuel systems. A mass burn system uses all the refuse, without prior treatment or preparation. A refuse-derived fuel system separates combustible wastes from noncombustibles such as glass and metal before burning. If a turbine is installed at the plant, both steam and electricity can be produced in a process called cogeneration.

Waste-to-energy systems are more expensive to build and operate than plain incinerators because of the need for special equipment and controls, highly skilled technical personnel, and auxiliary fuel systems. On the other hand, the sale of generated steam or electricity offsets much of the extra cost, and recovery of heat energy from refuse is a viable solid-waste management option from both an engineering and an economic point of view. About 80 percent of municipal refuse incinerators in the United States are waste-to-energy facilities.

Composting

Another method of treating municipal solid waste is composting, a biological process in which the organic portion of refuse is allowed to decompose under carefully controlled conditions. Microbes metabolize the organic waste material and reduce its volume by as much as 50 percent. The stabilized product is called compost or humus. It resembles potting soil in texture and odour and may be used as a soil conditioner or mulch.

Composting offers a method of processing and recycling both garbage and sewage sludge in one operation. As more stringent environmental rules and siting constraints limit the use of solid-waste incineration and landfill options, the application of composting is likely to increase. The steps involved in the process include sorting and separating, size reduction, and digestion of the refuse.

SORTING AND SHREDDING

The decomposable materials in refuse are isolated from glass, metal, and other inorganic items through sorting and separating operations. These are carried out mechanically, using differences in such physical characteristics of the refuse as size, density, and magnetic properties. Shredding or pulverizing reduces the size of the waste articles, resulting in a uniform mass of material. It is accomplished with hammer mills and rotary shredders.

DIGESTING AND PROCESSING

Pulverized waste is ready for composting either by the open windrow method or in an enclosed mechanical facility. Windrows are long, low mounds of refuse. They are turned or mixed every few days to provide air for the microbes digesting the organics. Depending on moisture conditions, it may take five to eight weeks for complete digestion of the waste. Because of the metabolic action of aerobic bacteria, temperatures in an active compost pile reach about 65 °C (150 °F), killing pathogenic organisms that may be in the waste material.

Open windrow composting requires relatively large land areas. Enclosed mechanical composting facilities can reduce land requirements by about 85 percent. Mechanical composting systems employ one or more closed tanks or digesters equipped with rotating vanes that mix and aerate the shredded waste. Complete digestion of the waste takes about one week.

Digested compost must be processed before it can be used as a mulch or soil conditioner. Processing includes drying, screening, and granulating or pelletizing. These steps improve the market value of the compost, which is the most serious constraint to the success of composting as a waste management option. Agricultural demand for digested compost is usually low because of the high cost of transporting it and because of competition with inorganic chemical fertilizers.

Sanitary landfill

sanitary landfill [Credit: Encyclopædia Britannica, Inc.]Land disposal is the most common management strategy for municipal solid waste. Refuse can be safely deposited in a sanitary landfill, a disposal site that is carefully selected, designed, constructed, and operated to protect the environment and public health. One of the most important factors relating to landfilling is that the buried waste never comes in contact with surface water or groundwater. Engineering design requirements include a minimum distance between the bottom of the landfill and the seasonally high groundwater table. Most new landfills are required to have an impermeable liner or barrier at the bottom, as well as a system of groundwater-monitoring wells. Completed landfill sections must be capped with an impermeable cover to keep precipitation or surface runoff away from the buried waste. Bottom and cap liners may be made of flexible plasticmembranes, layers of clay soil, or a combination of both.

CONSTRUCTING THE LANDFILL

sanitary landfill [Credit: Encyclopædia Britannica, Inc.]The basic element of a sanitary landfill is the refuse cell. This is a confined portion of the site in which refuse is spread and compacted in thin layers. Several layers may be compacted on top of one another to a maximum depth of about 3 metres (10 feet). The compacted refuse occupies about one-quarter of its original loose volume. At the end of each day’s operation, the refuse is covered with a layer of soil to eliminate windblown litter, odours, and insect or rodent problems. One refuse cell thus contains the daily volume of compacted refuse and soil cover. Several adjacent refuse cells make up a lift, and eventually a landfill may comprise two or more lifts stacked one on top of the other. The final cap for a completed landfill may also be covered with a layer of topsoil that can support vegetative growth.

Daily cover soil may be available on-site, or it may be hauled in and stockpiled from off-site sources. Various types of heavy machinery, such as crawler tractors or rubber-tired dozers, are used to spread and compact the refuse and soil. Heavy steel-wheeled compactors may also be employed to achieve high-density compaction of the refuse.

The area and depth of a new landfill are carefully staked out, and the base is prepared for construction of any required liner and leachate-collection system. Where a plastic liner is used, at least 30 cm (12 inches) of sand is carefully spread over it to provide protection from landfill vehicles. At sites where excavations can be made below grade, the trench method of construction may be followed. Where this is not feasible because of topography or groundwater conditions, the area method may be practiced, resulting in a mound or hill rising above the original ground. Since no ground is excavated in the area method, soil usually must be hauled to the site from some other location. Variations of the area method may be employed where a landfill site is located on sloping ground, in a valley, or in a ravine. The completed landfill eventually blends in with the landscape.

CONTROLLING BY-PRODUCTS

Organic material buried in a landfill decomposes by anaerobic microbial action. Complete decomposition usually takes more than 20 years. One of the by-products of this decomposition ismethane gas. Methane is poisonous and explosive when diluted in the air, and it can flow long distances through porous layers of soil. If it is allowed to collect in basements or other confined areas, dangerous conditions may arise. In modern landfills, methane movement is controlled by impermeable barriers and by gas-venting systems. In some landfills the methane gas is collected and recovered for use as a fuel.

A highly contaminated liquid called leachate is another by-product of decomposition in sanitary landfills. Most leachate is the result of runoff that infiltrates the refuse cells and comes in contact with decomposing garbage. If leachate reaches the groundwater or seeps out onto the ground surface, serious environmental pollution problems can occur, including the possible contamination of drinking-water supplies. Methods of controlling leachate include the interception of surface water in order to prevent it from entering the landfill and the use of impermeable liners or barriers between the waste and the groundwater. New landfill sites should also be provided with groundwater-monitoring wells and leachate-collection and treatment systems.

IMPORTANCE IN WASTE MANAGEMENT

In communities where appropriate sites are available, sanitary landfills usually provide the most economical option for disposal of nonrecyclable refuse. However, it is becoming increasingly difficult to find sites that offer adequate capacity, accessibility, and environmental conditions. Nevertheless, landfills will always play a key role in solid-waste management. It is not possible to recycle all components of solid waste, and there will always be residues from incineration and other treatment processes that will eventually require disposal underground. In addition, landfills can actually improve poor-quality land. In some communities properly completed landfills are converted into recreational parks, playgrounds, or golf courses.

Recycling

recycling: role in solid-waste disposal [Credit: Encyclopædia Britannica, Inc.]Separating, recovering, and reusing components of solid waste that may still have economic value is called recycling. One type of recycling is the recovery and reuse of heat energy, a practice discussed separately inIncineration. Composting can also be considered a recycling process, since it reclaims the organic parts of solid waste for reuse as mulch or soil conditioner. Still other waste materials have potential for reuse. These include paper, metal, glass, plastic, and rubber, and their recovery is discussed here.

SEPARATION

refuse disposal system: plastic bins filled with recyclable materials waiting to be picked up [Credit: Ted Russell—Photographer’s Choice/Getty Images]Before any material can be recycled, it must be separated from the raw waste and sorted. Separation can be accomplished at the source of the waste or at a central processing facility. Source separation, also called curbside separation, is done by individual citizens who collect newspapers, bottles, cans, and garbage separately and place them at the curb for collection. Many communities allow “commingling” of nonpaper recyclables (glass, metal, and plastic). In either case, municipal collection of source-separated refuse is more expensive than ordinary refuse collection.

In lieu of source separation, recyclable materials can be separated from garbage at centralized mechanical processing plants. Experience has shown that the quality of recyclables recovered from such facilities is lowered by contamination with moist garbage and broken glass. The best practice, as now recognized, is to have citizens separate refuse into a limited number of categories, including newspaper; magazines and other wastepaper; commingled metals, glass, and plastics; and garbage and other nonrecyclables. The newspaper, other paper wastes, and commingled recyclables are collected separately from the other refuse and are processed at a centralized material recycling facility, or MRF (pronounced “murf” in waste-management jargon). A modern MRF can process about 300 tons of recyclable wastes per day.

At a typical MRF, commingled recyclables are loaded onto a conveyor. Steel cans (“tin” cans are actually steel with only a thin coating of tin) are removed by an electromagnetic separator, and the remaining material passes over a vibrating screen in order to remove broken glass. Next, the conveyor passes through an air classifier, which separates aluminum and plastic containers from heavier glass containers. Glass is manually sorted by colour, and aluminum cans are separated from plastics by an eddy-current separator, which repels the aluminum from the conveyor belt.

REUSE

Recovered broken glass can be crushed and used in asphalt pavement. Colour-sorted glass is crushed and sold to glass manufacturers as cullet, an essential ingredient in glassmaking. Steel cans are baled and shipped to steel mills as scrap, and aluminum is baled or compacted for reuse by smelters. Aluminum is one of the smallest components of municipal solid waste, but it has the highest value as a recyclable material. Recycling of plastic is a challenge, mostly because of the many different polymeric materials used in its production. Mixed thermoplastics can be used only to make lower-quality products, such as “plastic lumber.”

In the paper stream, old newspapers are sorted by hand on a conveyor belt in order to remove corrugated materials and mixed papers. They are then baled or loose-loaded into trailers for shipment to paper mills, where they are reused in the making of more newspaper. Mixed paper is separated from corrugated paper for sale to tissue mills. Although the processes of pulping, de-inking, and screening wastepaper are generally more expensive than making paper from virgin wood fibres, the market for recycled paper should improve as more processing plants are established.

Rubber is sometimes reclaimed from solid waste and shredded, reformed, and remolded in a process called revulcanization, but it is usually not as strong as the original material. Shredded rubber can be used as an additive in asphalt pavements, and discarded tires may be employed as swings and other recreational structures for use by children in “tire playgrounds.” In general, the most difficult problem associated with the recycling of any solid-waste material is finding applications and suitable markets. Recycling by itself will not solve the growing problem of solid-waste management and disposal. There will always be some unusable and completely valueless solid residue requiring final disposal.

EE-Unit-IV Lithosphere

The word lithosphere is derived from the word sphere, combined with the Greek word lithos, meaning rock . The lithosphere is the solid outer section of Earth, which includes Earth’s crust(the “skin” of rock on the outer layer of planet Earth), as well as the underlying cool, dense, and rigid upper part of the upper mantle. The lithosphere extends from the surface of Earth to a depth of about 44–62 mi (70–100 km). This relatively cool and rigid section of Earth is believed to “float” on top of the warmer, non-rigid, and partially melted material directly below.

Earth is made up of several layers. The outermost layer is called Earth’s crust. The thickness of the crust varies. Under the oceans , the crust is only about 3–5 mi (5–10 km) thick. Under the continents, however, the crust thickens to about 22 mi (35 km) and reaches depths of up to 37 mi (60 km) under some mountain ranges. Beneath the crust is a layer of rock material that is also solid, rigid, and relatively cool, but is assumed to be made up of denser material. This layer is called the upper part of the upper mantle, and varies in depth from about 31–62 mi (50–100 km) below Earth’s surface. The combination of the crust and this upper part of the upper mantle, which are both comprised of relatively cool and rigid rock material, is called the lithosphere.

Below the lithosphere, the temperature is believed to reach 1,832°F (1,000°C), which is warm enough to allow rock material to flow if pressurized. Seismic evidence suggests that there is also some molten material at this depth (perhaps about 10%). This zone which lies directly below the lithosphere is called the asthenosphere , from the Greek word asthenes, meaning weak. The lithosphere, including both the solid portion of the upper mantle and Earth’s crust, is carried “piggyback” on top of the weaker, less rigid asthenosphere, which seems to be in continual motion. This motion creates stress in the rigid rock layers above it, forcing the slabs or plates of the lithosphere to jostle against each other, much like ice cubes floating in a bowl of swirlingwater . This motion of the lithospheric plates is known as plate tectonics , and is responsible for many of the movements seen on Earth’s surface today including earthquakes, certain types of volcanic activity, and continental drift.

EE-Unit-IV Land pollution

Land pollution, in other words, means degradation or destruction of earth’s surface and soil, directly or indirectly as a result of human activities. Anthropogenic activities are conducted citing development, and the same affects the land drastically, we witness land pollution; by drastic we are referring to any activity that lessens the quality and/or productivity of the land as an ideal place for agriculture, forestation, construction etc. The degradation of land that could be used constructively in other words is land pollution.

Land Pollution has led to a series of issues that we have come to realize in recent times, after decades of neglect. The increasing numbers of barren land plots and the decreasing numbers of forest cover is at an alarming ratio. Moreover the extension of cities and towns due to increasing population is leading to further exploitation of the land. Land fills and reclamations are being planned and executed to meet the increased demand of lands. This leads to further deterioration of land, and pollution caused by the land fill contents. Also due to the lack of green cover, the land gets affected in several ways like soil erosion occurs washing away the fertile portions of the land. Or even a landslide can be seen as an example.

Causes of Land Pollution

Below are the sources of land pollution:

1. Deforestation and soil erosion: Deforestation carried out to create dry lands is one of the major concerns. Land that is once converted into a dry or barren land, can never be made fertile again, whatever the magnitude of  measures to redeem it are. Land conversion, meaning the alteration or modification of the original properties of the land to make it use-worthy for a specific purpose is another major cause. This hampers the land immensely. Also there is a constant waste of land. Unused available land over the years turns barren; this land then cannot be used. So in search of more land, potent land is hunted and its indigenous state is compromised with.

2. Agricultural activities: With growing human population, demand for food has increased considerably. Farmers often use highly toxic fertilizers and pesticides to get rid off insects, fungi and bacteria from their crops. However with the overuse of these chemicals, they result in contamination and poisoning of soil.

3. Mining activities: During extraction and mining activities, several land spaces are created beneath the surface. We constant hear about land caving in; this is nothing but nature’s way of filling the spaces left out after mining or extraction activity.

4. Overcrowded landfills: Each household produces tonnes of garbage each year. Garbage like aluminum, plastic, paper, cloth, wood is collected and sent to the local recycling unit. Items that can not be recycled become a part of the landfills that hampers the beauty of the city and cause land pollution.

5. Industrialization: Due to increase in demand for food, shelter and house, more goods are produced. This resulted in creation of more waste that needs to be disposed of.  To meet the demand of the growing population, more industries were developed which led to deforestation. Research and development paved the way for modern fertilizers and chemicals that were highly toxic and led to soil contamination.

6. Construction activities: Due to urbanization, large amount of construction activities are taking place which has resulted in large waste articles like wood, metal, bricks, plastic that can be seen by naked eyes outside any building or office which is under construction.

7. Nuclear waste: Nuclear plants can produce huge amount of energy through nuclear fission and fusion. The left over radioactive material contains harmful and toxic chemicals that can affect human health. They are dumped beneath the earth to avoid any casualty.

8. Sewage treatment: Large amount of solid waste is leftover once the sewage has been treated. The leftover material is sent to landfill site which end up in polluting the environment.

Effects of Land Pollution

1. Soil pollution: Soil pollution is another form of land pollution, where the upper layer of the soil is damaged. This is caused by the overuse of chemical fertilizers, soil erosion caused by running water and other pest control measures; this leads to loss of fertile land for agriculture, forest cover, fodder patches for grazing etc.

2. Change in climate patterns: The effects of land pollution are very hazardous and can lead to the loss of ecosystems. When land is polluted, it directly or indirectly affects the climate patterns.

3. Environmental Impact: When deforestation is committed, the tree cover is compromised on. This leads to a steep imbalance in the rain cycle. A disturbed rain cycle affects a lot of factors. To begin with, the green cover is reduced. Trees and plants help balance the atmosphere, without them we are subjected to various concerns like Global warming, the green house effect, irregular rainfall and flash floods among other imbalances.

4. Effect on human health: The land when contaminated with toxic chemicals and pesticides lead to problem of skin cancer and human respiratory system. The toxic chemicals can reach our body through foods and vegetables that we eat as they are grown in polluted soil.

5. Cause Air pollution: Landfills across the city keep on growing due to increase in waste and are later burned which leads to air pollution. They become home for rodents, mice etc which in turn transmit diseases.

6. Distraction for Tourist: The city looses its attraction as tourist destination as landfills do not look good when you move around the city. It leads to loss of revenue for the state government.

7. Effect on wildlife: The animal kingdom has suffered mostly in the past decades. They face a serious threat with regards to loss of habitat and natural environment. The constant human activity on land, is leaving it polluted; forcing these species to move further away and adapt to new regions or die trying to adjust. Several species are pushed to the verge of extinction, due to no homeland.

Other issues that we face include increased temperature, unseasonal weather activity, acid rains etc.  The discharge of chemicals on land, makes it dangerous for the ecosystem too. These chemicals are consumed by the animals and plants and thereby make their way in the ecosystem. This process is called bio magnification and is a serious threat to the ecology.

Solutions for Land Pollution

1. Make people aware about the concept of Reduce, Recycle and Reuse.

2. Reduce the use of pesticides and fertilizers in agricultural activities.

3. Avoid buying packages items as they will lead to garbage and end up in landfill site.

4. Ensure that you do not litter on the ground and do proper disposal of garbage.

5. Buy biodegradable products.

6. Do Organic gardening and eat organic food that will be grown without the use of pesticides.

7. Create dumping ground away from residential areas.

EE_Unit-III Waste Water Treatment

The principal objective of wastewater treatment is generally to allow human and industrial effluents to be disposed of without danger to human health or unacceptable damage to the natural environment. Irrigation with wastewater is both disposal and utilization and indeed is an effective form of wastewater disposal (as in slow-rate land treatment). However, some degree of treatment must normally be provided to raw municipal wastewater before it can be used for agricultural or landscape irrigation or for aquaculture. The quality of treated effluent used in agriculture has a great influence on the operation and performance of the wastewater-soil-plant or aquaculture system. In the case of irrigation, the required quality of effluent will depend on the crop or crops to be irrigated, the soil conditions and the system of effluent distribution adopted. Through crop restriction and selection of irrigation systems which minimize health risk, the degree of pre-application wastewater treatment can be reduced. A similar approach is not feasible in aquaculture systems and more reliance will have to be placed on control through wastewater treatment.

The most appropriate wastewater treatment to be applied before effluent use in agriculture is that which will produce an effluent meeting the recommended microbiological and chemical quality guidelines both at low cost and with minimal operational and maintenance requirements (Arar 1988). Adopting as low a level of treatment as possible is especially desirable in developing countries, not only from the point of view of cost but also in acknowledgement of the difficulty of operating complex systems reliably. In many locations it will be better to design the reuse system to accept a low-grade of effluent rather than to rely on advanced treatment processes producing a reclaimed effluent which continuously meets a stringent quality standard.

Nevertheless, there are locations where a higher-grade effluent will be necessary and it is essential that information on the performance of a wide range of wastewater treatment technology should be available. The design of wastewater treatment plants is usually based on the need to reduce organic and suspended solids loads to limit pollution of the environment. Pathogen removal has very rarely been considered an objective but, for reuse of effluents in agriculture, this must now be of primary concern and processes should be selected and designed accordingly (Hillman 1988). Treatment to remove wastewater constituents that may be toxic or harmful to crops, aquatic plants (macrophytes) and fish is technically possible but is not normally economically feasible. Unfortunately, few performance data on wastewater treatment plants in developing countries are available and even then they do not normally include effluent quality parameters of importance in agricultural use.

The short-term variations in wastewater flows observed at municipal wastewater treatment plants follow a diurnal pattern. Flow is typically low during the early morning hours, when water consumption is lowest and when the base flow consists of infiltration-inflow and small quantities of sanitary wastewater. A first peak of flow generally occurs in the late morning, when wastewater from the peak morning water use reaches the treatment plant, and a second peak flow usually occurs in the evening. The relative magnitude of the peaks and the times at which they occur vary from country to country and with the size of the community and the length of the sewers. Small communities with small sewer systems have a much higher ratio of peak flow to average flow than do large communities. Although the magnitude of peaks is attenuated as wastewater passes through a treatment plant, the daily variations in flow from a municipal treatment plant make it impracticable, in most cases, to irrigate with effluent directly from the treatment plant. Some form of flow equalization or short-term storage of treated effluent is necessary to provide a relatively constant supply of reclaimed water for efficient irrigation, although additional benefits result from storage.

Conventional wastewater treatment processes


1 Preliminary treatment
2 Primary treatment
3 Secondary treatment
4 Tertiary and/or advanced treatment
5 Disinfection
6 Effluent storage
7 Reliability of conventional and advanced wastewater treatment


Conventional wastewater treatment consists of a combination of physical, chemical, and biological processes and operations to remove solids, organic matter and, sometimes, nutrients from wastewater. General terms used to describe different degrees of treatment, in order of increasing treatment level, are preliminary, primary, secondary, and tertiary and/or advanced wastewater treatment. In some countries, disinfection to remove pathogens sometimes follows the last treatment step. A generalized wastewater treatment diagram is shown in Figure 5.

1 Preliminary treatment

The objective of preliminary treatment is the removal of coarse solids and other large materials often found in raw wastewater. Removal of these materials is necessary to enhance the operation and maintenance of subsequent treatment units. Preliminary treatment operations typically include coarse screening, grit removal and, in some cases, comminution of large objects. In grit chambers, the velocity of the water through the chamber is maintained sufficiently high, or air is used, so as to prevent the settling of most organic solids. Grit removal is not included as a preliminary treatment step in most small wastewater treatment plants. Comminutors are sometimes adopted to supplement coarse screening and serve to reduce the size of large particles so that they will be removed in the form of a sludge in subsequent treatment processes. Flow measurement devices, often standing-wave flumes, are always included at the preliminary treatment stage.

2 Primary treatment

The objective of primary treatment is the removal of settleable organic and inorganic solids by sedimentation, and the removal of materials that will float (scum) by skimming. Approximately 25 to 50% of the incoming biochemical oxygen demand (BOD5), 50 to 70% of the total suspended solids (SS), and 65% of the oil and grease are removed during primary treatment. Some organic nitrogen, organic phosphorus, and heavy metals associated with solids are also removed during primary sedimentation but colloidal and dissolved constituents are not affected. The effluent from primary sedimentation units is referred to as primary effluent. Table 1 provides information on primary effluent from three sewage treatment plants in California along with data on the raw wastewaters.

Table 1: QUALITY OF RAW WASTEWATER AND PRIMARY EFFLUENT AT SELECTED TREATMENT PLANTS IN CALIFORNIA

Quality parameters (mg/l, except as otherwise indicated)

City of Davis

San Diego

Los Angeles County Joint Plant

Raw wastewater

Primary effluent

Raw wastewater

Primary effluent

Raw wastewater

Primary effluent

Biochemical oxygen demand,BOD5

112

73

184

134

204

Total organic carbon

63.8

40.6

64.8

52.3

Suspended solids

185

72

200

109

219

Total nitrogen

43.4

34.7

NH3-N

35.6

26.2

21.0

20.0

39.5

NO-N

0

0

Org-N

7.8

8.5

14.9

Total phosphorus

7.5

10.2

11.2

Ortho-P

7.5

11.2

pH (unit)

7.7

7.3

7.3

Cations:
Ca

78.8

Mg

25.6

Na

357

359

K

19

19

Anions:
SO4

160

270

Cl

120

397

Electrical conductivity, dS/m

2.52

2.34

2.19

Total dissolved solids

829

821

1404

1406

Soluble sodium percentage, %

70.3

Sodium adsorption ratio

8.85

6.8

Boron (B)

1.68

1.5

Alkalinity (CaCO3)

322

332

Hardness (CaCO3)

265

In many industrialized countries, primary treatment is the minimum level of preapplication treatment required for wastewater irrigation. It may be considered sufficient treatment if the wastewater is used to irrigate crops that are not consumed by humans or to irrigate orchards, vineyards, and some processed food crops. However, to prevent potential nuisance conditions in storage or flow-equalizing reservoirs, some form of secondary treatment is normally required in these countries, even in the case of non-food crop irrigation. It may be possible to use at least a portion of primary effluent for irrigation if off-line storage is provided.

Primary sedimentation tanks or clarifiers may be round or rectangular basins, typically 3 to 5 m deep, with hydraulic retention time between 2 and 3 hours. Settled solids (primary sludge) are normally removed from the bottom of tanks by sludge rakes that scrape the sludge to a central well from which it is pumped to sludge processing units. Scum is swept across the tank surface by water jets or mechanical means from which it is also pumped to sludge processing units.

In large sewage treatment plants (> 7600 m3/d in the US), primary sludge is most commonly processed biologically by anaerobic digestion. In the digestion process, anaerobic and facultative bacteria metabolize the organic material in sludge (see Example 3), thereby reducing the volume requiring ultimate disposal, making the sludge stable (nonputrescible) and improving its dewatering characteristics. Digestion is carried out in covered tanks (anaerobic digesters), typically 7 to 14 m deep. The residence time in a digester may vary from a minimum of about 10 days for high-rate digesters (well-mixed and heated) to 60 days or more in standard-rate digesters. Gas containing about 60 to 65% methane is produced during digestion and can be recovered as an energy source. In small sewage treatment plants, sludge is processed in a variety of ways including: aerobic digestion, storage in sludge lagoons, direct application to sludge drying beds, in-process storage (as in stabilization ponds), and land application.

3 Secondary treatment

The objective of secondary treatment is the further treatment of the effluent from primary treatment to remove the residual organics and suspended solids. In most cases, secondary treatment follows primary treatment and involves the removal of biodegradable dissolved and colloidal organic matter using aerobic biological treatment processes. Aerobic biological treatment (see Box) is performed in the presence of oxygen by aerobic microorganisms (principally bacteria) that metabolize the organic matter in the wastewater, thereby producing more microorganisms and inorganic end-products (principally CO2, NH3, and H2O). Several aerobic biological processes are used for secondary treatment differing primarily in the manner in which oxygen is supplied to the microorganisms and in the rate at which organisms metabolize the organic matter.

High-rate biological processes are characterized by relatively small reactor volumes and high concentrations of microorganisms compared with low rate processes. Consequently, the growth rate of new organisms is much greater in high-rate systems because of the well controlled environment. The microorganisms must be separated from the treated wastewater by sedimentation to produce clarified secondary effluent. The sedimentation tanks used in secondary treatment, often referred to as secondary clarifiers, operate in the same basic manner as the primary clarifiers described previously. The biological solids removed during secondary sedimentation, called secondary or biological sludge, are normally combined with primary sludge for sludge processing.

Common high-rate processes include the activated sludge processes, trickling filters or biofilters, oxidation ditches, and rotating biological contactors (RBC). A combination of two of these processes in series (e.g., biofilter followed by activated sludge) is sometimes used to treat municipal wastewater containing a high concentration of organic material from industrial sources.

i. Activated Sludge

In the activated sludge process, the dispersed-growth reactor is an aeration tank or basin containing a suspension of the wastewater and microorganisms, the mixed liquor. The contents of the aeration tank are mixed vigorously by aeration devices which also supply oxygen to the biological suspension . Aeration devices commonly used include submerged diffusers that release compressed air and mechanical surface aerators that introduce air by agitating the liquid surface. Hydraulic retention time in the aeration tanks usually ranges from 3 to 8 hours but can be higher with high BOD5 wastewaters. Following the aeration step, the microorganisms are separated from the liquid by sedimentation and the clarified liquid is secondary effluent. A portion of the biological sludge is recycled to the aeration basin to maintain a high mixed-liquor suspended solids (MLSS) level. The remainder is removed from the process and sent to sludge processing to maintain a relatively constant concentration of microorganisms in the system. Several variations of the basic activated sludge process, such as extended aeration and oxidation ditches, are in common use, but the principles are similar.

ii. Trickling Filters

A trickling filter or biofilter consists of a basin or tower filled with support media such as stones, plastic shapes, or wooden slats. Wastewater is applied intermittently, or sometimes continuously, over the media. Microorganisms become attached to the media and form a biological layer or fixed film. Organic matter in the wastewater diffuses into the film, where it is metabolized. Oxygen is normally supplied to the film by the natural flow of air either up or down through the media, depending on the relative temperatures of the wastewater and ambient air. Forced air can also be supplied by blowers but this is rarely necessary. The thickness of the biofilm increases as new organisms grow. Periodically, portions of the film ‘slough off the media. The sloughed material is separated from the liquid in a secondary clarifier and discharged to sludge processing. Clarified liquid from the secondary clarifier is the secondary effluent and a portion is often recycled to the biofilter to improve hydraulic distribution of the wastewater over the filter.

iii. Rotating Biological Contactors

Rotating biological contactors (RBCs) are fixed-film reactors similar to biofilters in that organisms are attached to support media. In the case of the RBC, the support media are slowly rotating discs that are partially submerged in flowing wastewater in the reactor. Oxygen is supplied to the attached biofilm from the air when the film is out of the water and from the liquid when submerged, since oxygen is transferred to the wastewater by surface turbulence created by the discs’ rotation. Sloughed pieces of biofilm are removed in the same manner described for biofilters.

High-rate biological treatment processes, in combination with primary sedimentation, typically remove 85 % of the BOD5 and SS originally present in the raw wastewater and some of the heavy metals. Activated sludge generally produces an effluent of slightly higher quality, in terms of these constituents, than biofilters or RBCs. When coupled with a disinfection step, these processes can provide substantial but not complete removal of bacteria and virus. However, they remove very little phosphorus, nitrogen, non-biodegradable organics, or dissolved minerals. Data on effluent quality from selected secondary treatment plants in California are presented in Table 2.

Table 2: QUALITY OF SECONDARY EFFLUENT AT SELECTED WASTEWATER TREATMENT PLANTS IN CALIFORNIA

Quality parameter (mg/I except as otherwise indicated)

Plant location

Trickling filters

Activated sludge

Chino Basin MWD (No. 1)

Chino Basin MWD (No. 2)

Santa Rosa Laguna

Montecito Sanitary District

Biochemical oxygen demand, BOD5

21

8

11

Chemical oxygen demand

27

Suspended solids

18

26

13

Total nitrogen

NH3-N

25

11

10

1.4

NO3-N

0.7

19

8

5

Org-N

1.7

Total phosphorus

12.5

Ortho-P

3.4

pH (unit)

7.6

Cations:
Ca

43

55

41

82

Mg

12

18

18

33

Na

83

102

94

K

17

20

11

Anions:
HCO3

293

192

165

SO4

85

143

66

192

Cl

81

90

121

245

Electrical conductivity dS/m

1.39

Total dissolved solids

476

591

484

940

Sodium adsorption ratio

2.9

3.1

3.9

3.7

Boron (B)

0.7

0.6

0.6

0.7

Alkalinity (CaCO3)

226

Total Hardness (CaCO3)

156

200

175

265

Source: Asano and Tchobanoglous (1987)

4 Tertiary and/or advanced treatment

Tertiary and/or advanced wastewater treatment is employed when specific wastewater constituents which cannot be removed by secondary treatment must be removed. As shown in Figure 3, individual treatment processes are necessary to remove nitrogen, phosphorus, additional suspended solids, refractory organics, heavy metals and dissolved solids. Because advanced treatment usually follows high-rate secondary treatment, it is sometimes referred to as tertiary treatment. However, advanced treatment processes are sometimes combined with primary or secondary treatment (e.g., chemical addition to primary clarifiers or aeration basins to remove phosphorus) or used in place of secondary treatment (e.g., overland flow treatment of primary effluent).

An adaptation of the activated sludge process is often used to remove nitrogen and phosphorus and an example of this approach is the 23 Ml/d treatment plant commissioned in 1982 in British Columbia, Canada (World Water 1987). The Bardenpho Process adopted is shown in simplified form in Figure 6. Effluent from primary clarifiers flows to the biological reactor, which is physically divided into five zones by baffles and weirs. In sequence these zones are: (i) anaerobic fermentation zone (characterized by very low dissolved oxygen levels and the absence of nitrates); (ii) anoxic zone (low dissolved oxygen levels but nitrates present); (iii) aerobic zone (aerated); (iv) secondary anoxic zone; and (v) final aeration zone. The function of the first zone is to condition the group of bacteria responsible for phosphorus removal by stressing them under low oxidation-reduction conditions, which results in a release of phosphorus equilibrium in the cells of the bacteria. On subsequent exposure to an adequate supply of oxygen and phosphorus in the aerated zones, these cells rapidly accumulate phosphorus considerably in excess of their normal metabolic requirements. Phosphorus is removed from the system with the waste activated sludge.

 

Most of the nitrogen in the influent is in the ammonia form, and this passes through the first two zones virtually unaltered. In the third aerobic zone, the sludge age is such that almost complete nitrification takes place, and the ammonia nitrogen is converted to nitrites and then to nitrates. The nitrate-rich mixed liquor is then recycled from the aerobic zone back to the first anoxic zone. Here denitrification occurs, where the recycled nitrates, in the absence of dissolved oxygen, are reduced by facultative bacteria to nitrogen gas, using the influent organic carbon compounds as hydrogen donors. The nitrogen gas merely escapes to atmosphere. In the second anoxic zone, those nitrates which were not recycled are reduced by the endogenous respiration of bacteria. In the final re-aeration zone, dissolved oxygen levels are again raised to prevent further denitrification, which would impair settling in the secondary clarifiers to which the mixed liquor then flows.

An experimentation programme on this plant demonstrated the importance of the addition of volatile fatty acids to the anaerobic fermentation zone to achieve good phosphorus removal. These essential short-chain organics (mainly acetates) are produced by the controlled fermentation of primary sludge in a gravity thickener and are released into the thickener supernatent, which can be fed to the head of the biological reactor. Without this supernatent return flow, overall phosphorus removal quickly dropped to levels found in conventional activated sludge plants. Performance data over three years have proved that, with thickener supernatent recycle, effluent quality median values of 0.5-1.38 mg/l Ortho-P, 1.4-1.6 mg/l Total nitrogen and 1.4-2.0 mg/l nitrate-N are achievable. This advanced biological wastewater treatment plant cost only marginally more than a conventional activated sludge plant but nevertheless involved considerable investment. Furthermore, the complexity of the process and the skilled operation required to achieve consistent results make this approach unsuitable for developing countries.

In many situations, where the risk of public exposure to the reclaimed water or residual constituents is high, the intent of the treatment is to minimize the probability of human exposure to enteric viruses and other pathogens. Effective disinfection of viruses is believed to be inhibited by suspended and colloidal solids in the water, therefore these solids must be removed by advanced treatment before the disinfection step. The sequence of treatment often specified in the United States is: secondary treatment followed by chemical coagulation, sedimentation, filtration, and disinfection. This level of treatment is assumed to produce an effluent free from detectable viruses. Effluent quality data from selected advanced wastewater treatment plants in California are reported in Table 14. In Near East countries adopting tertiary treatment, the tendency has been to introduce pre-chlorination before rapid-gravity sand filtration and post-chlorination afterwards. A final ozonation treatment after this sequence has been considered in at least one country.

5 Disinfection

Disinfection normally involves the injection of a chlorine solution at the head end of a chlorine contact basin. The chlorine dosage depends upon the strength of the wastewater and other factors, but dosages of 5 to 15 mg/l are common. Ozone and ultra violet (uv) irradiation can also be used for disinfection but these methods of disinfection are not in common use. Chlorine contact basins are usually rectangular channels, with baffles to prevent short-circuiting, designed to provide a contact time of about 30 minutes. However, to meet advanced wastewater treatment requirements, a chlorine contact time of as long as 120 minutes is sometimes required for specific irrigation uses of reclaimed wastewater. The bactericidal effects of chlorine and other disinfectants are dependent upon pH, contact time, organic content, and effluent temperature.

6 Effluent storage

Although not considered a step in the treatment process, a storage facility is, in most cases, a critical link between the wastewater treatment plant and the irrigation system. Storage is needed for the following reasons:

i. To equalize daily variations in flow from the treatment plant and to store excess when average wastwater flow exceeds irrigation demands; includes winter storage.ii. To meet peak irrigation demands in excess of the average wastewater flow.

iii. To minimize the effects of disruptions in the operations of the treatment plant and irrigation system. Storage is used to provide insurance against the possibility of unsuitable reclaimed wastewater entering the irrigation system and to provide additional time to resolve temporary water quality problems.

Table 3: EFFLUENT QUALITY DATA FROM SELECTED ADVANCED WASTEWATER TREATMENT PLANTS IN CALIFORNIA1

Quality parameter (mg/l except as otherwise indicated)

Plant location

Long Beach

Los Coyotes

Pomona

Dublin San Ramon

City of Livermore

Simi Valley CSD

Biochemical oxygen demand, BOD5

5

9

4

2

3

4

Suspended solids

5

1

Total nitrogen

19

NH3-N

3.3

13.6

11.4

0.1

1.0

16.6

NO3-N

15.4

1.1

3

19.0

21.3

0.4

Org-N

2.2

2.5

1.3

0.2

2.6

2.3

Total phosphorus

Ortho-P

30.8

23.9

21.7

28.5

16.5

pH (unit)

6.8

7.1

Oil and grease

3.1

Total coliform bacteria, MPN/100 ml

2

4

Cations:
Ca

54

65

58

Mg

17

18

14

Na

186

177

109

168

178

K

16

18

12

Anions:
SO4

212

181

123

202

Cl

155

184

105

147

178

110

Electrical conductivity, dS/m

1.35

1.44

1.02

1.27

1.25

Total dissolved solids

867

827

570

585

Soluble sodium, %

63.2

59.2

51.7

Sodium adsorption ratio

5.53

4.94

3.37

4.6

5.7

Boron (B)

0.95

0.95

0.66

1.33

0.6

Alkalinity (CaCO3)

256

197

150

Total Hardness (CaCO3)

212

242

206

254

184

1Advanced wastewater treatment in these plants follows high rate secondary treatment and includes addition of chemical coagulants (alum + polymer) as necessary followed by filtration through sand or activated carbon granular medium filters.