Nisargruna biogas plant

Transcription

1 Nisargruna biogas plant Sharad P. Kale Nuclear Agriculture and Biotechnology Division Bhabha Atomic Research Centre Mumbai NISARGRUNA plants are designed for handling and processing the biodegradable waste materials generated in kitchens, vegetable markets, slaughter houses, food and fruit processing industries, agro-waste and biomass in a decentralized manner. These plants serve following purposes. 1. Environment friendly disposal of biodegradable waste, which is need of hour considering mass pollution everywhere. 2. Generation of fairly good amount of fuel gas, which will definitely support the dwindling energy resources. 3. Generation of high quality manure, which would be weed-less and an excellent soil conditioner. This is very important for replenishing fast decreasing resources of productive soils. 4. It would reduce the menace of street dogs and other nuisance animals and pathogens, as major portion of biodegradable waste on dumping yards would no more be available for their feeding. 5. Employment generation 6. Environmental protection by helping in maintenance of elemental cycles in the nature Who will be benefited? NISARGRUNA plants would be useful for Municipal Corporations, urban local bodies, hospitals, hotels, housing societies, government establishments, abattoirs, Grampanchayats, and farmers. What are the capacities of NISARGRUNA plants? NISARGRUNA plants can be installed for handling 1, 2, 3, 4, 5, 10, 25 MT of segregated biodegradable waste per day. Who installs these plants? The technology is developed by Bhabha Atomic Research Centre (BARC), Mumbai. BARC has transferred this technology to 30 private entrepreneurs so far on non-exclusive basis. Their addresses are given in Appendix A. What are government incentives for this project? Government of India has enacted Municipal solid waste (Management and handling) rules, 2000 under the provision of environment Protection Act, 1986 to regulate the management

2 of Municipal solid waste (MSW). It specifies that the Municipal authorities shall adopt suitable technology for minimizing the burden on land fills. Nuclear agricultural and biotechnology division, BARC has developed a technology of bio degradation of solid waste based on biomethanisation process. Technology named as NISARGRUNA produces organic manure (soil conditioner) and produces biogas (consisting methane) which can be used as fuel or can be utilized to generate power. It may be mentioned here that this technology is applicable to the organic biodegradable portion of the Municipal solid waste. It may be mentioned here that the Government also gives various incentives for employing the suitable technology for municipal solid waste (MSW) disposal. These are: 1) Capital subsidy of Rs. 3 Crore per MW exportable electricity for one plant based on each technology ( notification is awaited ) 2) Interest subsidy of Rs. 2 Crore per MW exportable electricity to other plants. 3) 100% depreciation in first year of operation. 4) Purchase of electricity by State Electricity Boards at Rs per KWH (base price in ) with 5% escalation per year (The purchase rate for is Rs per KWH), Transmission losses at 2% from 3 rd year of operation and wheeling charges of 2% from first year of operation and banking for one year. Further this is modified by Maharashtra Electricity Regulatory Commission (MERC) as per notification dated April 6, 2004 presented in Annexure IV to suit the local condition. 5) MSW supply at site free of charge. 6) Land on lease of 30 years at nominal lease rent of Rs. 1 / 10 m 2 / year. In addition to above State Government gives following incentives: 1. Octroi exemption 2. Permission to mortgage the land for project finance. 3. Permission for third party sale of electricity. As per MERC guidelines, first choice of purchase is for local Municipal Corporation. Further under Kyoto Protocol, the project may be able to derive financial benefits under carbon trading as per Clean Development Mechanism (CDM). What are the types of wastes that can and cannot be processed in NISARGRUNA plants? The biodegradable waste that can be processed in the NISARGRUNA plant includes: Stale and unused portion of cooked food from households, hotels and industrial canteens Vegetable refuses either from vegetable markets or kitchens

3 Shredded paper Abattoir waste especially the cattle intestinal materials Gobar, night soil Lawn cuttings, dry leaves, algal or plant materials recovered from water bodies like lakes, rivers or wells Certain materials are to be strictly avoided. They include Coconut and egg shells Coconut coir Feathers, hair Green twigs, wood The straw and sugarcane bagasse can be processed but only if effective grinding is available. These materials will have to be chopped very finely before processing. Design of NISARGRUNA plants may be classified under following two categories depending on segregation of waste received and its quality:- SEGREGATED AND CONTROLLED Under this category the material delivered would contain more than 85-90% of the bio-degradable material and remaining 15-10% waste would be manually segregated. Among the bio-degradable material, more than 80% of material would either be cooked waste or the green leafy vegetables which would require no extensive chopping or disintegration. The plants built for this category of material would employ nominal manual segregation and a simple low duty mixer to prepare the slurry. Probable sources for this type of MSW are hotels, vegetable markets and directly collected segregated waste from the residences in the vicinity. SEGREGATED BUT UNCONTROLLED Under this category the material delivered would contain more than 85-90% of the bio-degradable material and remaining 15-10% waste would be manually segregated. The bio-degradable material would not be controlled and may have all types of material like fruits, hard vegetables like jackfruit, white gourd, sugar cane remains etc. The plants built for this category of material would employ nominal manual segregation, but would employ elaborate chopping and disintegration equipment in addition to mixer to prepare the slurry. Probable sources for this type of MSW are vegetable markets, food processing industry wastes etc.

4 Science of Nisargruna process The principle of Nisargruna technology is as follows, it produces organic manure ( soil conditioner) and biogas based on the process of Biomethanation. The organically rich biodegradable portion of solid waste is mixed with recycled water to form slurry. The slurry is then aerobically digested in predigester, where organic matter is converted to organic acids. The Predigestion is accentuated by addition of hot water and intermittent aeration. Predigestion reactions are exothermic and temperature rises to 40 ºC by itself. Hot water obtained using solar energy is added to raise the temperature to 50 ºC. If sunlight is not sufficient especially during winter, provision can be made to use part of the biogas generated to heat the required quantity of hot water using methane stoves. Their main role is to digest proteins and low molecular weight carbohydrates to produce volatile fatty acids. K itche n was te. B io gas us e d fo r co o king. Water re c ycling Crus her Water sump The rmo philic Ae ro bic Diges te r Anae robic Diges ter Manure P it The smaller molecules like proteins and simple carbohydrates are degraded during Predigestion. The ph of the feed slurry to predigester is around 7-8. the retention time (Hydraulic time) of 4 days is maintained in the predigester. After the Predigestion the ph reduces to 4-5 ph units. The predigested slurry is further digested under anaerobic conditions for about 15 days. The process of methanogenesis takes place in this digester. Methane and carbon dioxide are the terminal products of this process. Methane is produced from two primary substrates viz. Acetate and Hydrogen/ Carbon dioxide (Formate). At this stage the organic acids are converted by consortium of methane bacteria to methane and carbon dioxide.

5 The undigested lignocelluloses and hemi celluloses then flow out as high quality organic manure slurry. The ph of this slurry ranges from since the waste is processed at higher temperature, weed seeds are killed completely and the manure becomes weed free. The three steps of Biogas production are as follows; 1) Hydrolysis 2) Acidification and 3) Methanogenesis. Various bacteria are involved in these processes. Hydrolysis In the first step (hydrolysis), the organic matter is enzymolyzed externally by extra cellular enzymes (cellulase, amylase, protease and lipase) of microorganisms in the predigester tank. Converting solid waste into liquid form in the mixer stimulates this step. Bacteria start decomposing the long chains of the complex carbohydrates, proteins and lipids into shorter parts. Proteins are split into peptides and amino acids. Simple carbohydrates and proteins are degraded completely. Acidification Acid-producing bacteria involved in the second step convert the intermediates of fermenting bacteria into acetic acid (CH 3 COOH), hydrogen (H 2 ) and carbon dioxide (CO 2 ) in the predigester. These bacteria, of the genus bacillus, are aerobic and facultatively anaerobic, and can grow under acidic conditions. An air compressor maintains aerobic conditions in the predigester. To produce acetic acid, the bacteria use the oxygen dissolved in the solution or bonded oxygen. Hereby, the acid-producing bacteria reduce the compounds with a low molecular weight into alcohols, organic acids, amino acids, carbon dioxide, hydrogen sulphide and traces of methane. The ph of the raw slurry falls from 7.5 to about 4.5 to 5.5 in the pre-digester. It appears that in the predigester, various zones are formed and different bacteria dominate these zones. Addition of hot water helps in eliminating the mesophilic bacteria and selection of thermophilic bacteria. But these thermophilic bacteria can operate at lower temperatures also. Hence hot water added even once a day should be sufficient for maintaining the pure consortium in the predigester. However if it is possible to maintain the temperature of predigester in the range of 50-55oC throughout the day, the performance of predigester will definitely be better and the holding time may be further reduced. The hot water helps in hygienization of the slurry by killing the enteric bacteria that may be present in the waste. Some Gram negative Enterobacteria and Coliform bacteria have been isolated in the raw slurry. However in the second zone these bacteria are totally eliminated. From the predigester tank, the slurry enters the main tank where it undergoes anaerobic degradation by

6 a consortium of archaebactereacea belonging to Methanococcus group. These bacteria are naturally present in the alimentary canal of ruminant animals (cattle). They produce methane from the cellulosic materials in the slurry. The undigested lignocellulosic and hemicellulosic materials are then passed on to the settling tank. After about a month, high quality manure can be dug out from the settling tanks. There is no odour in the manure and the organic content is high, which can improve the quality of humus in soil. Methane formation Methane-producing bacteria, involved in the third step, decompose compounds with a low molecular weight. Under natural conditions, methane-producing microorganisms occur to the extent that anaerobic conditions are provided, for instance under water (in marine sediments), in ruminant stomachs and in marshes. They are anaerobic and very sensitive to environmental changes. In contrast to acidogenic and acetogenic bacteria, methanogenic bacteria belong to the archaebacteria group, a group of bacteria with a very heterogeneous morphology and a number of common biochemical and molecular-biological properties that distinguish them from all other bacterial genera. It is advisable to circulate the generated biogas back into the system using a small compressor. This would enhance the reduction of Carbon dioxide to methane and enrichment of methane fraction in the biogas. The separation of two stages in methane production helps in improving the purity of methane gas, thereby increasing its fuel efficiency. However, the average composition round the year would depend on how effectively pre-digester temperatures can be maintained. It is taken through a GI pipeline to utility points. Drains for condensed water vapor are provided online. The biogas burns with a blue flame and is ideal for cooking. Alternately, it can be used to produce electricity in a dual fuel biogas-diesel engine.

7 Nisargruna helps in maintenance of elemental carbon

8 Byproducts in Nisargruna process The two by-products of biomethanation process are the 1) Biogas & 2) Organic manure i. Nisargjyoti (Biogas) In Nisargruna technology, 1MT/day of waste material generates around m3 of biogas depending on type of waste material (Table 11-1). Table 11-1: Quantity of biogas generated from various types of waste materials Type of waste material Biogas quantity (m3) Kitchen (Food) waste material Vegetable waste material Abattoir waste material Cattle dung Poultry manure ii) Organic manure Most solids not converted into Methane settle out in the digester as a liquid sludge. Depending upon the raw materials used and the conditions of digestion, this sludge contains many elements essential to the plant life Nitrogen, Phosphorous, Potassium plus small amount of salts ( trace elements), indispensable for plant growth such as boron, calcium, copper, iron, magnesium, sulphur, zinc, etc. The C:N ratio of organic manure is between 12:1 to 16:1. It is a good source of all the essential elements needed for restoring the soils cropping ability. The organic manure generated by Nisargruna process has been tested for its constituents and the elemental composition of the organic manure is given in the figure no.1 The benefits of the organic manure as follows; 1) Since the process occurs at higher temperature it is weed-less.

9 2) It is an eco friendly fertilizer which has all the essential nutrient needed to improve the soil quality. 3) It restores the water holding capacity of soil. 4) It helps maintaining the elemental cycle of nature. Commissioning of Nisargruna plant Nisargruna plant is based on microbial activities. The initial microbial culture development is therefore becomes extremely important for successful commissioning of the plant. There are two digesters. The microbial culture in the predigester builds up naturally. It will start building up only after biodegradable waste is processed. Before this happens, it is necessary to build up inoculum in the main digester. This is achieved by seeding with cattle dung. Usually 15-20% by volume seed is required. Fresh cattle dung is preferred. It is to be mixed with 1:1 water and proper slurry is made. The floating straw has to be removed. It is recommended that 80% of this slurry is put directly into the main digester while remaining 20% is passed through primary digester. This is required to provide some base material before waste is actually processed. It takes about days for establishment of culture in the main digester. In hot summer this may be 5-6 days, in winter it would tale more than 20 days. The rising of dome would be an indication of establishment of culture. The first filling of dome contains very less quantity of methane. Hence when dome fully rises, it is recommended to open the valve fully and drive out all the gas contents. After this evacuation, methane will start filling in larger quantities and can be effectively used. Still it would take few more weeks to reach the expected purity of methane. The capacity build up is very tricky in the operation of Nisargruna plant. It must be remembered that the whole operation depends upon microorganisms. The various cultures have to develop and coexist in tandem for successful processing of a variety of biodegradable wastes. The conditions required for their optimum activities have to be carefully monitored. Following clauses should be strictly adhered to while making the plant operational. The first waste feeding of the plant will begin after 15 days of gobar seeding. The feeding should be as per the schedule given in following table. It would be different for different capacity plants and generally table given at the end of this section should be followed strictly. There is a need to monitor the type of waste being processed. Generally the ph of the raw slurry entering the predigester should be around 7-8. If this ph is too acidic,

10 then materials responsible for acidity (mainly lemon and citrus skins, pickles, soured foods) may be segregated and processed in smaller aliquots by mixing with larger volumes of non-acidic materials. Floating materials in the raw slurry may be collected and reprocessed in the mixer. This is to ensure uniform homogenization of the waste material. It would also help in reducing the scum formation. Providing a strainer at the predigester entry point can ensure this. The addition of hot water is an important step. Everyday two additions of 500L hot water (85-90 o C) each are recommended for a five tonne plant. If the solar heater is not efficient due to weather conditions, it is recommended that part of methane generated in the plant may be used for provision of hot water. The heating system may be provided and included in the initial design. The microorganisms in predigester are mainly aerobic. Hence it is necessary to maintain aeration intermittently using compressed air. Generally aeration at 2-3 intervals of 1-hour duration during a day through a 3 HP compressor would serve this purpose. The ph of the slurry entering the main digester is about 5-6. If it is in the range of 4-4.5, it is recommended that the ph of raw slurry may be checked. If the raw slurry were maintained at ph 7-8, there would not be any problem of ph maintenance. However careful monitoring of ph at these two levels is absolutely important for efficient running of the plant. Schedule for capacity build up in a Nisargruna plant First seeding 0 day No feeding 1-15 days 500 Kg waste/day days 1 tonne waste/day days 1.5 tonne/day days 2 tonne/day days 3 tonne/day days 4 tonne/day days 5 tonne/day 180 days 10 tonne/day 300 days 25 tonne/day 450 days

11 The ph of manure slurry flowing into manure pits must be more than 7. If it is acidic, it means there is a problem in digestion process. Intervention at right time would ensure smooth running of the plant. The intervention may be either controlling the ph of raw slurry or addition of gobar (usually 5% of digester volume). The latter alternative may be tried immediately after noticing the indigestion in main digester. This would be evident by sour and foul smell of the manure slurry. The appearance of insect larvae in manure pits are another indication of improper digestion. DO S AND DON T S DO S The safety rules should be followed strictly. Uniform code should be strictly followed. Appropriate aprons should be provided to the workers. The workers must always examine the plant for any abnormalities around the plant for eg., leakage of methane gas, over flow of the water outlet etc. The leakage should be repaired immediately. The waste for high capacity plant i.e., more than 5 ton/day, should be received at plant in installments to prevent stagnation of waste. The aesthetics of the plant is very important. At no stage NISAR RUNA plant should even appear as waste disposal plant. The gas holder should be painted periodically to prevent rusting. The water seal around the gas dome should be overlaid with oil to prevent mosquito breeding There should be posters providing all the necessary information about the plant, explaining all the benefits, details of the Nisargruna plant. The plant operators must undergo regular medical checkups. The slurry in the aerobic digester must be stirred (agitated) and aerated several times a day to enhance gas production. All the openings at the plant must be closed to avoid falling of any individuals..

12 Scented flowered plant like, Parijatak, Mogra, Raat rani etc. must be cultivated at the periphery of the plant. The fly repellent tube lights will have to installed on segregating platform. DON T S No smoking near the plant area. Do not lit any kind of flame near the plant. Workers must not enter any underground tank without supervision and safety belts. Do not climb on dome. Do not put stones, non-degradable items in the plant for processing. Do not leave the plant premises until all the stoves, generator, electricity are switched off. Do not touch the gas meters, they are very sensitive. Do not operate the instruments if you don t know how to operate them. Never aerate the main digester (anaerobic digester). It would instantly kill the culture. Do not handle the waste without wearing gloves and face mask Never inhale Methane Gas to avoid health hazards. Never aerate the main digester (anaerobic digester). It would instantly kill the culture. Do not use water from the manure pit for cleaning purposes or for watering plants. It contains residual amounts of methane.