Stratification of Free Air Space and Its Dynamics in the Process of Co-Composting
混合堆肥过程中自由空域(FAS)的层次效应及动态变化

Co-composting of sewage sludge and pig manure was studied. Free air space (FAS) in the whole composting pile was 26.2% at the temperature rising stage and 42.3% at the stage of high temperature composting. FAS in the upper portion of composting pile was higher than that in the lower, where the air was enough for microorganism to live on for two stages above. The FAS was 52.4% at the stage of the cooling, when the effect of stratification of FAS was significant. The FAS in the upper pile was bigger than that in the middle, which was bigger than that in the lower. At the stage of maturing, FAS was 54.7% and its stratified effect weakened, but the capability of aeration in the upper and in the middle of the pile was larger than that in the lower. At the different stages of composting, the degree of difference of FAS was of the order: the cooling stage > the high temperature stage > maturing stage > the temperature rising stage. The difference in the pile for every stage of composting was as follows: the upper > the middle > the lower. The change of FAS agreed with two-order kinetics.