Centralized anaerobic digestion of dewatered sludge from small scale wastewater treatment plants and other waste biomass such as kitchen garbage is a promising energy recovery technology. Anaerobic digestion at lower temperatures can reduce operational cost. Hyperthermophilic pre-treatment at 80°C possibly upgrades anaerobic digestion performance. The applicability of dewatered sewage sludge (DS) from oxidation ditch processes to anaerobic digestion was investigated by continuous and batch experiments under different temperature conditions. Total solids (TS) and volatile solids (VS) of DS were 15.6% and 12.8%, respectively, and DS was diluted to TS 5% before feeding. The organic loading rate was 0.94 kgVS/(m~3·d). Biogas production from DS at a mesophilic condition (35°C) was 0.20 NL/gVS-added. Under anaerobic digestion conditions at 25, 30 and 35°C with hyperthermophilic pretreatment, biogas production was higher than 0.20 NL/gVS-added. An ammonia concentration of the digested sludge with pretreatment was higher than that of the digested sludge without pretreatment. This is possibly due to higher protein degradation performance by the pretreatment. These results proved that the centralized anaerobic digestion system under the various temperature conditions is useful for sludge management in local cities with decentralized small facilities.
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