[Stratification of volatile solid content and its dynamics in the process of co-composting]

Co-composting of sewage sludge and pig manure was conducted and it was indicated that, at the stages of temperature starting and high temperature composting, the difference of organic decomposition in the upper portion was largest among three portions of composting pile. The difference was largest in the lower part of the pile and the stratification effect of volatile solid (VS) content was formed at the stage of cooling, while it was largest in the middle and the stratification effect was still remarkable at the stage of maturity. At different stages of composting, the difference of VS content in the pile was of the order: the cooling > or = the maturity > the high temperature > the temperature starting. At each stage of composting, the difference of organic decomposition in the pile was as follows: the upper > the middle > the lower. The change of VS content met with first-order kinetics equation and decomposition rate of VS was 0.3 kg x d(-1) while average loss of VS content was 8.2% in the whole process of composting.