Composting of separated solid swine manure

Abstract

Abstract A study was conducted to investigate the efficiency of the composting process when the initial moisture content is higher than the generally recommended limit of 65%. Solids separated from swine manure with very high moisture content were composted in small reactors with and without the addition of bulking agent. The initial moisture content in the compost containing swine manure solids alone was 79%. This was reduced to 71% in the compost mix with swine manure solids and sawdust in a 5:1 ratio by weight. Corresponding air contents were measured to be 68% in the unmixed manure and 70% in the manure/sawdust mixture. Both materials underwent composting under thermophilic conditions with or without the use of forced aeration. The results suggest that composting may be feasible even if the moisture content exceeds the limit of 65% for as long as there is enough air content in the compost pile to satisfy the oxygen needs of microbes. Volatile fatty acids were not detected in the manure/sawdust compost mix but they were evidently present in the compost pile with the unmixed swine manure solids. These indicate that as the water content increases and the air content decreases, the likelihood of localized occurrence of anaerobic composting increases. The headspace‐gas chromatograph technique proved to be a simple and effective means of detecting volatile fatty acids in active compost piles.