Performance of different systems for the composting of the source-selected organic fraction of municipal solid waste

Performance of three pile composting systems at field-scale were studied and compared in the composting of source-selected organic fraction of municipal solid waste (OFMSW): turned pile (TP), static forced-aerated pile (SAP) and turned forced-aerated pile (TAP). Routine parameters such as temperature, oxygen content, moisture and porosity were monitored. Temperature was found to be higher in turned systems whereas oxygen content was higher in forced-aerated systems. Although the initial air-filled porosity (AFP) for all mixtures was high, around 70%, the material tended to compact in the static system. A high degree of heterogeneity was found in the non-turned system. Extent of biodegradation was measured by respiration techniques (from 5.3 to 1.1 mg [O2] g [organic matter {OM}]−1 h−1 in TP and from 4.7 to 0.7 mg [O2] g [OM]−1 h−1 in turned forced-aerated pile). The non-turned compost showed a low level of stability (3.6 mg [O2] g [OM]−1 h−1) and the lowest maturity grade (I) measured by the self-heating test. In forced-aerated systems a low intermittent aeration rate of 1 l kg [volatile solids {VS}]−1 min−1 (5 min on, 30 min off) proved to be excessive, causing major water losses and hampering moisture control. Comparison of the results obtained for TP and TAP demonstrated that the investment cost in a forced-aeration system is not necessary for this waste. Hence, turned systems are recommended for OFMSW pile composting.