Kinetic analysis of forced aeration composting - II. Application of multilayer analysis for the prediction of biological degradation

Extensive pilot-scale composting tests for organic solid waste were conducted under different modes of aeration, to investigate vertical temperature distributions and their effect on biological degradation at different heights of the composting mass. The modes of aeration applied were upflow, downflow, alternate upflow/downflow, and internal air recirculation. Temperatures at different heights of the composting mass were continuously monitored. Results show that (i) significant variation in temperature and biodegradable volatile solids (BVS) degradation occur in the composting mass along the vertical direction when unidirectional aeration is applied; (ii) application of alternate upflow/downflow aeration or periodic mixing greatly reduces vertical gradients in temperature and biodegradable volatile solids (BVS) degradation; and (iii) the rate and extent of degradation in different layers of the composting mass can be quantitatively predicted by applying a combination of multilayer analysis and a previously established temperature-dependent first-order reaction model.