Bioresource Technology 48 (1994) 203 -207 © 1994 Elsevier Science Limited Printed in Great Britain. All fights reserved 0960-8524/94/$7,00 ELSEVIER SOLID-STATE ANAEROBIC DIGESTION OF CATTLE DUNG AND AGRO-RESIDUES IN SMALL-CAPACITY FIELD DIGESTERS M. Shyam* Agricultural Energy &Power Division, Central Institute of Agricultural Engineering, Nabibagh, Berasia Road, Bhopal: 462 018, India & P. K. Sharma Division of Agricultural Engineering, Indian Agricultural Research Institute, Pusa, New Delhi: 110 012, India (Received 4 August 1993; revised version received 15 November 1993; accepted 23 December 1993) Abstract centration in the digesters. The effluent discharged Anaerobic fermentation of cattle dung alone or with from the plants is spread on to the ground for drying paddy straw, mango leaves or foliage of Parthenium before transportation to fields for use as manure. Solid- hysterophorus in uninsulated, small capacity, batch- state anaerobic fermentation requires a much smaller type out-door digesters of cylindrical and cuboid shapes quantity of water, makes handling of digested slurry gave encouraging results at initial total solids (TS) con- easier, can utilize a variety of agro-residues as substrate centrations of 16-19%. The gas yield on a unit digester and conserves plant nutrients in the final product. The volume basis varied from 202"2 to 499.3 litres/day/m~for site can also look much cleaner, and this may help to 7 weeks retention period and 196.2-407.7 litres/day/m 3 overcome the farmers' reluctance to locate the plant jor 10 weeks retention period as compared to 204-372 near their houses. litres/day/m ~in the case of semicontinuous type conven- Anaerobic digestion of cattle dung and many other tional digesters that used water-diluted cattle dung at agro-residues at initial total solids (TS) concentration 8-9% TS concentration at 7 weeks retention time. Gas varying from 16 to 25% in small, batch type, digesters yield per kg of TS fed was, however, significantly lower under laboratory conditions has been reported to be than from a semicontinuous type, conventional, satisfactory (Pathak & Jain, 1985; Rajsekharan & digester. The digestion process was, in general, severely Prasad Reddy, 1991; Shyam, 1991 ). Solid-state anaer- affected at TS concentrations in excess of 19%. The gas obic digestion of wheat straw at 35°C (Jewell, 1982) yield was also affected by season of the year and pre- and a mixture of corn stalks and cattle dung at treatment of the agro-residues used. The substrate at the 55-35°C (Molnar & Bartha, 1989) in thermally-insu- end of the trials was loaded straight on to a trolley and lated, batch-type, plants has also been demonstrated transported to fields for use as manure. Seeds of parthe- successfully. Anaerobic digestion of a mixture of paddy nium passed through the plant were found non-viable straw and cattle dung in 2 : 1 ratio at TS concentration after retention for 93 days. of 20-25% in batch-type, field digesters gave satisfac- tory gas yields during the summer and rainy seasons in Key words: Solid-state anaerobic digestion, anaerobic North India (Anon., 1990). However, the gas yield was digestion, cattle dung, agro-residues, mango leaves, reported to be negligible for about five winter months paddy straw, Parthenium hysterophorus, biogas, of the year when the ambient temperature was low. Experimental details and results of a study on anaer- obic digestion of cattle dung, paddy straw, mango INTRODUCTION leaves and green foliage of Parthenium hysterophorus in small capacity, batch-type, uninsulated, field diges- Biogas plants in India use cattle dung mixed with an ters conducted in Central India, where the ambient equal quantity of water to maintain 8-9% solids con- temperature during the winter months remains moder- *To whom correspondence should be addressed, ate, are reported here. 203