Accelerated biogas production without leachate recycle

The economics of biogas production remain marginal, even on 'free' substrat es such as wastes. However, new insights into the fundamental processes of solid-state digestion promise a much faster and more predictable process. T his holds the future prospect of profitable biogas production from anaerobi c composters fed with a range of solid substrates, including food industry wastes and biomass crops. A novel process model proposes that reaction occurs at a well-defined but m obile interface between raw and depleted wastes, forming the boundary of an independent expanding microreactor. Very small seed particles cannot estab lish such micro-reactors. The present paper explores the implications for s eeding practice. Leachate recycle might do no more than compensate for erra tic seeding, by transporting nutrients into well-seeded zones. Inoculating the waste with well-distributed seed particles of viable size could be more effective - and a great deal simpler and cheaper. (C) 2001 Elsevier Scienc e Ltd. All rights reserved.