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In recent years, biogas production through anaerobic digestion of animal manures has received renewed interest. The present state of the art has been re viewed by several researchers (Hashimoto et al. 1980 Smith 1980). Most of the existing on-farm anaerobic digester feed materials are in the range of 8-12% total solids (TS). At these levels, many are having material-handling problems typified by difficulties in manure slurry pumping and solids settling out in the digesters due to inadequate mixing (Abeles et al. 1978). Additional water is sometimes added in an attempt to solve these problems, resulting in an increase in digester volume requirements and hence a higher capital cost. In the conventional anaerobic digestion process, the volatile solids (VS) break down is usually in the range of 15-30% (Hills 1980 National Academy of Sciences-National Research Council 1977). It is logical to assume that the principal organic fraction being metabolized consists of the organic molecules which are already in solution and the very fine particles having a high surface to volume ratio which are readily attacked by bacterial enzymes. If it is hypothesized that a very high percentage of the VS fraction which is destroyed in most digesters is contained in this liquid fraction, then a liquid-solid separation pre-treatment of the waste should produce a filtrate which on digestion will still yield a high volume of biogas but which will not have the same material handling problems. It would also be expected that the size of digester needed to treat the waste from a given number of animals would be smaller with only a small decrease in total biogas production. The objective of this project was to determine the feasibility of reducing the digester volume per animal unit or per litre of biogas produced by removing a portion of the VS in the waste via screening.
biogas production from dairy manure and its filtrate
Lo, K. V., Bulley, N. R. and P. H. Liao 1983. BIOGAS PRODUCTION FROM DAIRY MANURE AND ITS FILTRATE. Canadian Agricultural Engineering 25(1):59-62.
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