Effects of Combined Pretreatment of Sewage Sludge on Biogas Production in Anaerobic Digestion Process

Biogas recovery by anaerobic digestion was seen as an ideal way to treat biomass waste-sewage sludge, but has some limitations, such as the low efficient biogas production. In this paper, the combined (alkaline and ultrasonic) pretreatment was proposed for effective sludge anaerobic digestion and the effect of these pretreatments was investigated. It can be seen that this treatment effectively led to the increase of soluble chemical oxygen demand (SCOD) and volatile fatty acids (VFA) concentration. The high concentration of VFA led to an increase in biogas production. Under the optimum combined pretreatment condition (under 6000 kJ/kg TS and with 0.15 mol/L NaOH), the biogas production was nearly 8 times higher than the raw sample. Besides, the SV of sludge was reduced and the settling characteristics of sludge were improved. The results indicated that the combined pretreatment could be an effective method for improving biogas yield.