How does separate collection efficiency influence biological stability of commingled Italian municipal solid waste?

Italy developed over the last two decades a fairly efficient separate collection system but still about 30% of municipal solid waste (MSW) collected is destined to landfilling. Italian Regulation adopts the Dynamic Respirometric index (DRI) as the key parameter for evaluating the waste biological stability of MSW prior to landfilling. On the basis of a recent literature survey, this paper aims at evaluating how much DRI (used as aerobic waste stability index) and the biochemical methane potential (used as anaerobic waste stability index) of commingled (mixed) waste, respectively before and after a simulated biological treatment, are influenced by separate collection. Experimental data confirm that enhanced separate collection results in a reduction of the putrescible content of commingled waste. However, the reduction of DRI due to separate collection only (about 20%) is insufficient to approve direct landfilling without any biological pretreatment since the required standard is not achieved, while its implementation decreases efficiently both indices in the order of 50–75%. It is also delineated that only the joint use of an aerobic and an anaerobic index gives complete and reliable information on commingled waste stability, which optimizes the treatment of municipal waste for increasing the overall sustainability of the system.