Subcritical Water Hydrolysis Treatment for Sewage Sludge Reduction and Energy Recovery by High-rate Digestion

This study was a verifying performance of a demonstration plant installed at an existing sewage treatment plant, where it used a continuous forced circulation type subcritical water reactor to hydrolyze sewage sludge and then performed high-rate anaerobic digestion of the treated slurry, in order to reduce the quantity of the sewage sludge. The results show that sewage sludge was reduced by 53-72%(average 62.5%) on suspended solid(SS) basis. The amount of biogas produced by anaerobic digestion was an average of approximately 10.6Nm3/ sludge-m3. This amount of biogas provided the heat energy needed for the subcritical water treatment. The anaerobic digestion was stable after hydraulic retention time(HRT) 5 days, confirming that it is possible to lower the digester capacity below that of a conventional digester.