Fermentation properties of agro-residues, leaf biomass and urban market garbage in a solid phase biogas fermenter

The decomposition and gas production pattern of eight unprocessed biomass f eedstocks representing annual weeds, leaf litter, agro residues and market wastes were monitored in this laboratory study. Solid phase fermentation wa s effected with a weekly fed biomass bed sprinkled twice daily with recycle d fermenter liquid to initiate and sustain biogas production from the decom posing biomass bed. Fermenters were fed from the top with gradually increas ing feed rates to determine maximum feed rates sustainable. Feed rates of 1 g total solids (TS) l(-1)d(-1) was possible which lead to pseudo steady st ate gas production rates between 0.26-0.98 1 l(-1) d(-1) at specific gas yi elds of 0.18-0.44 1 g(-1) TS at 35-75% volatile solids (VS) destruction. Fe edstocks such as paper mulberry (Broussenetia), Parthenium, Synedrella and urban garbage lost > 50% VS in 30 d while paddy straw, bagasse and sugarcan e trash exhibited lower VS loss (greater than or equal to 35%) in this peri od. During decomposition, bulky biomass feedstocks underwent compaction and obviated the need for a pretreatment step. Bulk densities rose manifold to reach between 150-350 g l(-1) within 20 d. A higher decomposition rate, pr ocess optimization and use of pre-compacted feedstocks have the potential t o increase the feed rates (0.96-1.93 g TS l(-1)d(-1)), quantity of feedstoc k held in the reactor as well as gas production rates. The current gas prod uction rates and space economy in these fermenters compare well with Indian cattle dung fermenters (0.3-0.5 l l(-1) d(-1)) and is attractive. (C) 1999 Elsevier Science Ltd. All rights reserved.