Effect of ultrasonic pretreatment on secondary sludge and anaerobic biomass to enhance biogas production

Anaerobic digestion studies were carried out with tannery excess secondary sludge obtained from common effluent treatment plant. The excess sludge as a feed was disintegrated by ultrasonic homogenizer, to solubilize the intracellular compounds to overcome the rate-limiting hydrolysis step. The anaerobic biomass was subjected to diligent disintegration with the aim of increasing the maintenance energy requirements thereby enhancing its microbial activity. To achieve maximum gas production, the percentage treatment volume of feed and biomass were chosen as dynamic variables and the optimization of these variables was carried out by RSM technique. A 2² full factorial central composite design was used for experimental design and analysis. It was observed that the percentage treatment volume of biomass was found to be most significant variable that of feed and the interaction effects of these two variables found to be insignificant. Based on experimental results, quadratic model was arrived and the variables were optimized for maximum gas production. In addition, response surface for maximum gas production was obtained as a function of two dynamic variables for identification. In the present study, the influence of pretreatment was observed only in biogas production and COD removal, but the methane content remains unchanged.