CHANGES IN MICROBIOLOGICAL PROPERTIES DURING IN-SITU COMPOSTING OF PIG MANURE

A 10-month study was carried out in an experimental farm in Hong Kong to examine the microbial densities and activities of the mesophilic in-situ composting process of pig manure under a 'Pig-on-litter' (POL) system. The effects of the commercial bacterial product recommended by this POL system (treated group) were evaluated and compared with the control pig pens (without any bacterial inoculation). The results show that there was no significant difference between the treated and control groups, both had very high microbial populations, including total aerobic heterotrophs, nitrifying and denitrifying bacteria, and microbial activities, in terms of oxygen consumption rate, content of ATP and microbial biomass C and N. These parameters were low at the beginning of the study as well as during the idle periods when no pigs were kept, but increased rapidly when pigs were kept within the pig pens and the pig manure started to deposit directly onto and mixed with the bedding material. It is clear that the pig manure and sawdust bedding were important in maintaining such substantial bacterial population and activities.