Effect of the Sonophotocatalytic Pretreatment on the Volume Reduction of Sewage Sludge and Enhanced Recovery of Methane and Phosphorus

In this study, the sonophotocatalytic process, i.e., combination of ultrasonic irradiation (US) and photocatalytic reaction, was proposed as a pretreatment process for the anaerobic digestion of organic sludge in order to drastically reduce the amount of sludge and promote the recovery of methane and phosphorus. Several series of experiments employing different techniques, i.e., sonophotocatalysis (SPC), US, photocatalysis (PC), and thermal treatment, were conducted by using a batch type apparatus. The results of the SPC treatment showed a decrease in sludge volume by about 50% and the synergetic effects of US and PC treatments which were clearly observed as increases in dissolved chemical oxygen demand of sludge filtrate and in phosphorus compounds dissolution from sludge particles. In the SPC process of sewage sludge, the photocatalytic reaction was enhanced by the sufficient disintegration of sludge flocks due to the US treatment. Any pretreatments applied promoted the anaerobic digestion process, however, there was little synergetic effect and the long time SPC treatment resulted in a decrease in the reaction rate.