Effect of Moisture Content on the Composting of Pig-Manure Sawdust Litter Disposed From the Pig-on-Litter (POL) System

Abstract

The pig-on-litter system, known as in-situ composting, has been developed as one of the recommended methods in Hong Kong to treat pig waste. The system utilizes a mixture of sawdust and a commercial bacterial product as the bedding material on which the pigs are raised, and the pig excreta are decomposed within the bedding material. After 10-13 weeks, the spent pig-manure sawdust litter is removed from the pig pens. This spent litter contains high concentrations of organic matter, nitrogen, phosphorus, potassium and trace elements, and also a significant amount of active microbial biomass, which is similar to an immature compost. In order to improve the quality of the spent litter, further composting to reach maturity is essential. Moisture is one of the most critical factors in controlling the rate of composting and the maturity of the product. Water provides a medium for the transport of dissolved nutrients for the metabolic and physiological activities of microorganisms. Very low initial moisture values would mean early dehydration of the pile which will arrest the biological process giving a physically stable but biologically unstable compost (Bertoldi et al., 1983). On the other hand, high moisture values may produce anaerobic conditions due to water logging. However, the effect of different moisture contents on composting of spent litter and their changes throughout the composting process are not yet understood. Therefore, the study aimed (1) to investigate the changes in the nutrients and organic matter of the spent litter at different stages of composting, and (2) to evaluate the effect of different initial moisture content of the spent litter on this composting process.