CO-DIGESTION OF WASTE ORGANIC-SOLIDS - BATCH STUDIES

Anaerobic digestion is a well established process for treating many ty pes of organic waste, both solid and liquid. As such, the digestion of cattle slurries and of the organic fraction of municipal solid waste has been evaluated and has been successful. Attempts to apply the proc ess to other types of solid organic waste, for example, to chicken man ure, have met with limited success. In many areas of the UK, intensive chicken farming is leading to solids disposal problems. It has been p roposed that co-digestion with cattle slurry could be a possible dispo sal route for chicken manure. In this study, cattle slurries were mixe d with a range of solid wastes and allowed to digest in 1-1 batch dige sters. The criteria for judging the success of a co-digestion were vol atile solids (VS) reduction, total methane production and methane yiel d. In terms of the VS reductions (%), there was little difference betw een the various digestions. In terms of the cumulative methane product ion (1) the co-digestions with fruit and vegetable waste, the fish off al and the dissolved air flotation sludge were more effective than the digestion with cattle slurry alone. In terms of the specific methane yield (m(3) CH4 kg(-1) VS removed), the co-digestions containing fish offal and the brewery sludge gave higher values than the control diges tion with cattle slurry alone. Compared with their control (cattle slu rry alone), both co-digestions with poultry manure (7.5 and 15% TS) ga ve higher cumulative productions of methane and the system with the lo wer concentration of poultry manure gave a higher specific methane yie ld. However, there was some evidence of ammonia inhibition. (C) 1998 E lsevier Science Ltd. All rights reserved.