Mechanism and kinetics of organic matter degradation based on particle structure variation during pig manure aerobic composting.

Characterization of the dynamic structure of composting particles may facilitate our understanding of the mechanisms of organic matter degradation during pig manure–wheat straw aerobic composting. In this study, changes in the size, shape, pores, chemical compositions, and crystal structures of pig manure particles during composting were investigated. The results showed that the median diameter ( D 50 ) decreased exponentially, while the particle aspect ratio and sphericity were unchanged, suggesting that particles were degraded uniformly along different radial directions. Pores had a mean diameter of 15–30 μm and were elliptical. The particle porosity increased linearly mainly because of hemicellulose degradation. Furthermore, the influence of particle structure variation on the first order rate constant ( k ) of organic matter degradation was corrected, which may facilitate the optimization of operation conditions. The k value was proportional to the reciprocal of D 50 according to the specific surface area of particles, and it decreased with increased porosity due to the stabilized chemical compositions and crystal structures of particles. However, the applicability of these data to other composting materials should be verified. [ABSTRACT FROM AUTHOR]