Enhancement of biochemical methane potential from excess sludge with low organic content by mild thermal pretreatment

Abstract

Excess sludge with low organic content always led to the failure of anaerobic digestion for methane production. Recently, the mild thermal pretreatment, which is usually operated at temperatures below 120°C, has drawn much attention due to less energy consumption and no chemical addition. In this study the effect of mild thermal pretreatment (50–120°C) on the solubilization and methane potential of excess sludge with a low concentration of organic matters was investigated. Experimental results showed that the concentration of soluble organic matters increased gradually with temperature during the mild thermal pretreatment of excess sludge. Biochemical methane potential experiments demonstrated that the potential of methane production from excess sludge was greatly enhanced by mild thermal pretreatment, and under the conditions of pretreatment temperature 100°C and digestion time 20 d the methane yield was as high as 142.6±2.5mL/g of volatile solids. Mechanism investigation on the enhancement of methane production from excess sludge exhibited that the consumptions of sludge protein and carbohydrate, the adenosine 5′-triphosphate content of anaerobic microorganisms, the activities of key enzymes related to anaerobic digestion, and the amount of methanogens were all improved by mild thermal pretreatment, in correspondence with the production of methane.