Two-phase anaerobic digestion of the organic fraction of municipal solid waste: estimation of methane production

Abstract

Energy generation from methane (CH₄) is one of the primary targets of the anaerobic digestion process. Consequently, the focus of this study was to investigate the effect on CH₄ production of total solids (TS) loading (measured as % TS) and hydraulic residence time (HRT) during the treatment of the organic fraction of municipal solid waste (OFMSW). Laboratory-scale, two-phase anaerobic digestion systems were employed with each system consisting of an acidogenic reactor and a methanogenic reactor linked in series. The group A runs in the experiment explored the effect on digester performance of four variations in methanogenic HRT (15, 20, 25 and 30 days) at three different feed TS concentrations (8, 12 and 15%). The group B runs compared the actual methane yield (0.14 to 0.45 L g ${\text{VS}}_{\text{feed}}^{-1}$ ) to that predicted by the Chen–Hashimoto model. Results from the group A runs indicated that acidogenesis improved with an increase in % TS and a decrease in HRT; while, methanogenesis behaved inversely, achieving higher yields at the lower % TS and longer HRT values. In comparison with the group B runs, the Chen–Hashimoto model under-predicted (by an average of 16.5 ± 6.6%) the CH₄ yield obtained from the digestion of OFMSW.