Reduction of Excess Sludge Using Different Methods in SBR Process for Biological Wastewater Treatment (Emphasizing on Ultrasonic Usage)

The activated sludge process is the most widely used biological wastewater treatment for both domestic and industrial plants in the world. One of the drawbacks of conventional activated sludge (CAS) processes is high sludge production. Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. In this paper the usability of different sludge reduction processes such as, ozone, ultrasonic, thermal lysis, and high DO concentration to be linked with low load are investigated. Each process was tested under the following conditions to improve yield coefficient in sequence batch reactors (SBRs): ultrasonic (3500 Kj / kg VSS, 20 KHz, 100 w), ozonation (25 mg O3 /g VSS), thermal lysis (80°C for 180 min.), and high DO concentration liked with low load (6 mg/l DO, 0.19 Kg BOD5/m³.day). The investigated processes induced the organic matter solubilisation and yield coefficient reduction (total suspended solids): ultrasonic (78%), ozone (63%), thermal lysis (49%), and high DO concentration (37%). In our experimental conditions, ultrasonic and ozone led to the best sludge production improvement after disintegration of 30 percent of total sludge volume and return it to the reactor. COD removal efficiency and specific oxygen uptake rate (SOUR), in the all investigated processes reduced slightly, but in ultrasonic and thermal lysis methods, sludge settle ability improved and sludge volume index (SVI) decreased to 82 and 95 respectively.