FERMENTATION AND METHANOGENIC CHARACTERISTICS OF LEAFY BIOMASS FEEDSTOCKS IN A SOLID-PHASE BIOGAS FERMENTER

Biomass feedstocks, such as leaf litter weeds and agro-residues, have been considered as alternative feedstocks to meet rural energy needs i n India. Six different types of biomass substrates representing common ly available fresh and dry feedstocks were studied for their decomposi tion pattern and methanogenic activities in order to arrive at optimum design parameters for solid phase digestion. Broussenetia papyrifera, Parthenium hysterophorus, Synedrella nodiflora (fresh leaf biomass fe edstocks), and paddy straw underwent a rapid initial decomposition los ing 30-40% volatile solids (VS) within 10 d. This decomposition patter n appeared to favour growth and colonization of hydrogenotrophic metha nogens in the latter three feedstocks. Stable biogas production was fo und whet-ever approximately similar rates of aceticlastic and hydrogen otrophic methanogenic activity were recorded on decomposing biomass fe edstocks. Inadequate colonization by aceticlastic methanogens was foun d to be the main cause of a poor start-up and lower daily gas producti on rates, especially in the presence of rapid VS destruction. Two dry feedstocks, cane trash and bagasse were found to have an acidogenesis- limited decomposition pattern with <40% VS destruction in 45 d. These results suggested that proper start-up procedures were needed to ensur e adequate build-up of aceticlastic methanogens, and the use of a mixe d biomass feedstock comprised of fresh and dry biomass had a better ch ance of stable biogas production, conversion efficiency and gas yield. (C) 1997 Elsevier Science Ltd.