Abstract
Following results were obtained from the trials conducted to clarify fundamental conditions for composting pig excreta:
1) When excreta were piled up intact for the composting, it was found desirable to adjust the moisture content in the excreta for composting by adding to them some adequate moisture adjusting materials. If the moisture content was too low, temperature rise of the excreta was rapid at the initial stage, but the high temperature did not last so long and the composting process tended to be incomplete. In contrast, if the moisture content was too high, fermentation for composting did not proceed due to lack of oxygen. However, if a bulky material was added to the excreta for adjustment of moisture content, the fermentation proceeded smoothly despite the fairly high moisture content because the total materials for composting became more porous.
2) Decrease in the weight of the compost does not mean drying of the compost because water and carbon dioxide are formed as the final decomposition products of carbohydrates following the fermentation for composting.
3) If the excreta was turned up occasionally to bring in fresh air into the piled excreta, the fermentation for composting was more accelerated than the case without the turning-up. In addition, it helped release and disperse moisture from the excreta under fermentation. When active fermentation at a high temperature was under way, oxygen brought into the excreta by the turning-up was consumed out within about one hour.
4) A forcible aeration step for the excreta proved to be an effective means for supply of oxygen to it, especially so when the material for fermentation had a higher moisture. Hower, if the air supply to the excreta was excessive during the composting step, it tended to be unfavorable because moisture and heat were overly taken away. It was estimated that the optimum air supply to the excreta at the peak of its fermentation would be approx. 200ml per minute per kg of the material piled up for composting step.
5) It was verified that, even if the excreta was liquid by adding 4 times as much water to it, decomposition by fermentation comparable to that of normal composting step could be achieved if supply of oxygen was attempted properly by exposure to air.
