Enhancement of sludge digestion via different physicochemical methods

Abstract

Anaerobic digestion (AD) is a common treating process to limit the sludge accumulation. In the present work, four pre-treatment methods (ultrasonic, chemical, thermal, and thermo-chemical) are investigated in order to find their effect on solubilization and biogas production.

Two frequencies of ultrasonic wave were used 30 kHz and 50 kHz during the pre-treatment. Sodium hydroxide was added in different amounts to give three pH values of 9, 10 and 11 in chemical pre-treating processes. The sludge was heated at 60oC and 80oC through thermal pre-treatment experiment. Also, the sludge was treated thermo-chemically at 80oC and pH 11 prior to anaerobic digestion. Maximum biogas production (6009 ml) was obtained at ultrasonic pre-treatment method with 30 kHz. The volumetric ratio of produced biogas to the initial volume of sludge is about 4:1.