Abstract
Two-phase anaerobic digestion process, consisting of hyperthermophilic acidification and thermophilic methane fermentation, coupled with subcritical water process as a pretreatment of thickened excess sludge was examined, aiming at enhancement of methane production ratio and anaerobic digestion efficacy. Batch experiments reveiled that subcritical water process at a 180 °C of temperature and 1 MPa of pressure for 60 min., was able to solubilize 50% of CODCr, 60 to 70% of protein, and 70% of total suger, and that improvement of solubilization and acid production increased methane production in an early stage in the following methan fermentation process. A continuous experiment also reveiled that the pretreatment by subcritical water process was able to improve removal ratios of CODCr, TS and VS, which means enhancement of sludge treatment efficacy. Adding a small amount of kitchen garbage, about 10 %, to thickened excess sludge treated by subcritical water process achieved more stable operation.
