Utilization of high solid waste activated sludge from small facilities by anaerobic digestion and application as fertilizer.

Anaerobic co-digestion of sewage sludge with organic wastes has recently gained attention in small facilities. For small facilities, high solids sludge is suitable for transportation to a centralized co-digester, and direct utilization of the digested sludge as liquid fertilizer is recommended. Effects of high solid and hyperthermophilic pretreatment (80 °C, 24 hr) on anaerobic digestion at low temperatures and utilization as fertilizer are investigated by anaerobic/aerobic digestion and paddy soil incubation experiments. The volatile solids (VS)/total solids (TS) ratio decreases to 0.57(-), and the VS removal rate is approximately 0.7 (-) after long-term aerobic digestion. This is possibly the limitation of biodegradation, even with pretreatment, within engineering time. Substrate TS of 16% (not diluted), 10% and 5% are compared. The effect of substrate TS on biogas production performance (0.2-0.3 NL/gVS-added) is not statistically observed. Laboratory-scale paddy soil incubation experiments are performed fed with anaerobically digested pretreated or not pretreated dewatered sludge as liquid fertilizer. Pretreatment promotes nitrogen mineralization before use as fertilizer, which is helpful to prevent an outflow of surplus ammonia to the environment. The effect of soil type on microbial communities is more significant than that of anaerobically digested sludge conditions.