Controlled Sewage Sludge Alkaline Fermentation to Produce Volatile Fatty Acids to be Used for Biological Nutrients Removal in WWTPs

In municipal wastewater treatment plants (WWTPs), the disposal of sewage sludge accounts for 20-50% of capital and operating expenses. Therefore, technologies that can simultaneously reduce sludge and generate carbon source for improving biological nutrients removal are in demand. The application of sewage sludge alkaline fermentation can provide the external carbon source that is required to remove nutrients via nitrite for the separate treatment of the supernatant produced from the anaerobic digestion of sewage sludge. Existing studies on sewage sludge fermentation use caustic soda or other chemicals to achieve the desirable pH for alkaline fermentation; this practice increases the cost. In this work, the anaerobic supernatant produced from sewage sludge was used to adjust the pH in the fermentation reactor,while the impact of temperature (30 °C and 55°C), pH (8-11), retention time (1-8 days) and initial total solids (TS = 4.5 and 6.5%) concentration of sludge was examined. The highest volatile fatty acids (VFAs) concentration was achieved at a retention time of 6 days, sludge TS = 6.5%, pH = 10&11 and temperature of 55 C. The addition of pre-aerated anaerobic supernatant achieved similar VFAs as the one of similar pH in which caustic soda adjustment took place.