Fermentation and methanogenic characteristics of leafy biomass feedstocks in a solid phase biogas fermentor

Biomass feedstocks, such as leaf litter, weeds and agroresidues, have been considered as alternative feedstocks to meet rural energy needs in India. Six different types of biomass substrates representing commonly available fresh and dry feedstocks were studied for their decomposition 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 feedstocks), and paddy straw, underwent a rapid initial decomposition losing 30–40% volatile solids (VS) within 10 d. This decomposition pattern appeared to favour growth and colonization of hydrogenotrophic methanogens in the latter three feedstocks. Stable biogas production was found wherever approximately similar rates of aceticlastic and hydrogenotrophic methanogenic activity were recorded on decomposing biomass feedstocks. Inadequate colonization by aceticlastic methanogens was found to be the main cause of a poor start-up and lower daily gas production 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 ensure adequate build-up of aceticlastic methanogens, and the use of a mixed biomass feedstock comprised of fresh and dry biomass had a better chance of stable biogas production, conversion efficiency and gas yield.