BIOGAS - AN IDEAL SOURCE OF ENERGY Dr . Sarbjit Singh Sooch Director, School of Energy Studies for Agriculture,

1. BIOGAS - AN IDEAL SOURCE OF ENERGY • Dr. Sarbjit Singh Sooch • Director, School of Energy Studies for Agriculture, • Punjab Agricultural University, Ludhiana-141004, Punjab, India • E-mail: Email: sssooch@rediffmail.com • Phone no.: 98720-84513, 95010-34513

2. Introduction • The anaerobic sludge digestion process is well known and is often practiced in municipal sewage treatment plants. • Now it has been extensively applied to the treatment of livestock and crop wastes. • On a moderate scale it has been tried in Europe and in Africa. The experimental production of biogas was first attempted at the Indian Agricultural Research Institute (IARI) in 1939 in India. • The gas can be put to various uses like cooking, lighting, running dual-fuel engines, power generation etc.

3. Materials and Methods • The amount of gas production as well as the fertilizer value of the final product of digestion depend to a great extent on the physical, chemical and biological properties of animal wastes. • These properties, in turn, depend upon the characteristics (size, sex and breed) of the animal, the nature of the feed ration (its digestibility, the content of protein, fiber and other elements) and the environment. • Nitrogen contained in proteins vary in digestibility depending on the source of protein. • The animal wastes will contain all the ingredients of the feed, some of them in their original and some in chemically simpler form. • On the average about 75 % of the nitrogen, 80 % of the phosphorous (as P2S5), 85 % of the potassium (as K2O) and about 40 to 50 % of the organic matter of the feed can be recovered in the manure. • Although the moisture content of the excreta is 70 to 80 %, ruing constitute 40 to 70 % of the fertilizer value of the total excrement.

4. The Digestion Process • The anaerobic digestion is a complex biological process during which the organic matter is decomposed by anaerobic bacterial organisms. • It is neither necessary to use a pure culture for inoculation nor to maintain such a culture for inoculation. • The bacteria capable of decomposing organic substances and of producing methane gas are found universally and abundantly in nature, particularly in decaying matter, e.g. human and animal excreta. • The organic substrate need not be pure-any kind of mixture of organic substance is decomposed if the process is allowed to continue long enough. • The entire substrate — carbohydrates, fats and proteins — with the possible exception of a small amount of fiber is broken during the digestion process and yields methane and carbon dioxide.

5. During the digestion of organic matter, two phases of decomposition occur - These are the liquefaction stage and the gasification stage. • The first stage is brought about by a highly mixed culture of bacteria (the acid fermenters), the majority of which are saprophytes. • These bacteria are capable of rapid reproduction and are not as sensitive to changes in environment as the bacteria responsible for the gasification stage. • Extra cellular enzymes excreted by a saprophytes bring about the liquefaction of the organic matter. • Complex carbohydrates are converted to simple sugars and alcohols; and fatty acids and proteins to peptides and amino acids. • The first culture of bacteria carries the decarboxylation even future by converting all the alcohols, fatty acids and amino acids to volatile acids and water.

6. The gasifying organisms (the methane fermentrers) are also a mixed culture of bacteria. • They are strict anaerobics, the majority of them are nonmotile have low rates of reproduction, are extremely sensitive to pH and temperature changes and require carbon dioxide for the reduction of the volatile acids to methane. • The conversion of acids to methane is accomplished with interacellular enzymes secreted by the methane forming bacteria. • In the absence of methane bacteria, the digestion process succeeds only in liquefying the sludge, often rendering it more offensive than the raw sludge.

7. On the other hand, if under certain conditions, liquefaction proceeds at a faster rate than gasification, the resultant accumulation of acids inhibits further the methane bacteria, and the digestion process malfunctions. • Thus both type of bacteria must be in proper balance. However, the optimum conditions for the gasifying bacteria are also suitable for the liquefying bacteria. • Anaerobic digestion, in contrast to most fermentations, is a continuous process. • Once the process starts, it is possible to feed the raw waste at one point and withdraw sludge from another continuously, while methane and carbon dioxide are given off at a steady rate.

8. Optimum Conditions for Gas Production • The quantity and the composition of gas produced is greatly affected by temperature, the loading rate, the consistency of the waste fed to the digester, the accessibility of the substrate, the detention period, and the concentration of volatile acids in the digester. • The optimum temperature for gas production is about 95°F (35°C). • Digestion is not affected materially by an increase in temperature, but a small drop in temperature may result in an excessive accumulation of volatile acids and in digester failure. Maintenance of constant temperature is essential. • The loading rate of a digester is expressed as the weight in Kgs of volatile (organic) solids fed per day per m3 of digester capacity and usually varies from 25 Kg/day/m3 to 30 Kg/day/m3.

9. Mixing of the digester contents aids the digestion process by establishing uniform distribution of bacteria and food and by breaking up the floating scum layer formed from the accumulation of fibrous material at the top of the digester. • The objection to the scum layer is that it constitutes a zone of substrate in which a high concentration of volatile acids develop. • Usually if the volatile acids concentration rises much above, 200 mg/litre as acetic acid, methane gas formation drops and digestion ceases within two to three days. • The optimum detention period is the digestion time required to obtain maximum gas production and figure of 40 days is often used. • The range of solid concentration for satisfactory digestion is 8 to 10 % and the optimum pH range is 7 to 9. • Presence of toxic substances in excessive quantities is detrimental to digestion because the growth of bacteria is retarded.

10. Properties of Biogas • Biogas is a mixture of methane, carbon dioxide, nitrogen and hydrogen sulphide gases as well as some water vapours. • The actual ratio of these gases depend upon the organic material used in the digestion. • On an average, gas contains 55-60 % methane, 30-35 % carbon dioxide and 5 % nitrogen and hydrogen sulphide. • The calorific value of the biogas is about 4700 Kcal. • One m3 of biogas is equivalent 3.50 Kg of wood, 12.30 Kg of dung cakes, 1.60 Kg of coal, 0.62 litres of kerosene oil, 0.43 Kg of LPG, 0.52 litre of diesel etc.

11. Properties of Manure Left after Digestion • The manure obtained after the anaerobic digestion of organic wastes is superior to the farm yard manure in several ways in the preparation of farm yard manure by the usual methods, losses of organic matter of the order of 50 per cent are known to take place, and over of the original nitrogen is also lost to the temperature. • By digestion in the gas plant about 25% of the dry matter of the dung is converted into combustible gas and there is no loss of nitrogen. • The digested manure contains 1.5 to 1.8 per cent nitrogen as compared to 0.5 per cent in farm manure. • The farm yard manure as obtained from compost pits is a source of weeds. All weeds are, however, destroyed during the digestion process in the gas plant. • Also the digested manure is available in only 30-40 days while it takes 4 to 6 months to compost it in the usual manner.

12. Discussion • According to the information available from Ministry of New and Renewable Energy (MNRE), New Delhi, at present number of family size biogas plants installed in India are 45.45 Lakh and that in Punjab are 1.25 Lakh. • The capacity of these plants vary from 2 m3 to 6 m3 of biogas per day and almost all of them are fixed dome type biogas plants. • Larger plants have also been installed in India for power generation, bottling of biogas and thermal application of biogas for cooking/Industrial use. • At present, in Punjab around 100 biogas plants of larger capacity of fixed dome type (designed by PAU) have been operating for decentralized power generation applications at the dairy farms. • One bigger biogas plant of capacity 1MW grid power generation has been operating at Ludhiana since the year 2000 and one more bigger biogas plant of capacity 4MW capacity grid power generation is under construction in Hoshiarpur District.

13. Similarly two bigger biogas plants (one of capacity 600 m3/day at Abohar and one of capacity 1000 m3/day at Mukatsar) have been operating for bottling of biogas for the last 2-3 years and one more biogas plant of capacity 5000 m3/day for bottling of biogas is under construction at Bathinda. • Main problems which restricts the use of such a technology • The cost of installing such a plant is high. The recent (March, 2013) experience at the Punjab Agricultural University (P.A.U) shows that the cost may beyond Rs. 35,000/- for a 4 m3/day capacity plant. • Since the gas is supplied at atmospheric temperature and pressure, the gas supply system gets cumbersome and inconvenient very soon as the distance of the plant from the point of use. • This may either not be available in the residential area or it may not be preferred by the inhabitants. • The sources of wastes and water should also be close to the site of the gas plant.

14. The products of digestion contains water vapours. These condense into the gas delivery pipe and clog it. Care must, therefore, be taken that this water be removed in some suitable manner. • The use of biogas is limited to cooking purposes. The large percentage of CO2 present in the biogas must he removed if it is to be efficiency used for producing mechanical energy. • The disposal of slurry from the digestion pit is another problem. Either it must be dried which means more space for drying beds is needed or it must be transported in the fluid from to the field which is not easy except when the plant is located close to the field and at such elevation that the slurry can flow to the field by gravity.

15. Conclusion • The relevance of the biogas in the modem technological World stems from considerations of energy scarcity and environmental protection both of which have become important recently. • The digestion process for producing biogas has the following main advantages: • Methane gas which has commercial value is produced during the process. • The organic content of the waste is reduced by 50%. • The digested waste is a thick free-flowing fluid with no offensive order. • The waste is well stabilized and thus, needs no further treatment before final disposal. • The fertilizing constitutions of the raw waste are conserved and the fertilizer value of the digested solids is higher than that of the raw waste. Weeds in the waste are completely destroyed. • Rodents and files are not attracted to the end product of digestion.

16. References Mittal, K.M. 1996 Biogas Systems : Principles and Applications, New Age International (P) limited Publishers, New Delhi. Biogas – A Rural Energy Source. (1985), Ministry of Non-Conventional Energy Sources Publication, New Delhi. Grewal N.S., Sooch S.S., Ahluwalia S and Brar G.S. 2000. Hand Book Biogas Tech, PAU, Ludhiana. Sooch S.S. 2010. Biogas Plants for Rural Masses. School of Energy Studies for Agriculture, PAU, Ludhiana. AkshyayUrja 2012. Energing the re way, Ministry of Renewable Energy Government of India, 5 (6). www.mnre.gov.in.