Abstract
In order to investigate the effect of hydraulic retention time (HRT) on the thermophilic anaerobic digestion of paper-containing organic fraction of municipal solid waste (OFMSW), a lab-scale CSTR was operated. The paper-containing OFMSW consisted of 50% (total solids) of food waste and 50% of paper waste. The HRT in the thermophilic CSTR was shortened from 30 days to 20, 10, 7.5 and 5 days. The performance was evaluated on process stability, biogas yield and organic removal efficiency. The result shows that thermophilic methanogenesis was stable when the HRT was longer than 7.5 days, with high organic removal efficiencies and methane production. When HRT was 30 days, the TS, VS, COD, carbohydrate and protein removal were 78.1%, 79.0%, 78.9%, 91.5% and 29.5%, respectively. No significant decrease in organic removals was observed during the stable operation. The biogas production rate increased in proportion to the organic loading rate and the maximum biogas production rate of 8.51±1.24 L/L/d was obtained at HRT 7.5 days. Whereas, when the HRT was 5 days, the process failed due to the acidification. The first-order kinetic constants and anaerobic reaction rates indicated that the washing-out of propionate-degraders was the cause of process failure in the thermophilic anaerobic digestion of paper-containing OFMSW at 5 days.
