The management of excess activated sludge imposes great cost on wastewater treatment plants and represents significant technical challenges. This paper investigates a new technology, sonication and cryptic growth, to reduce the amount of excess sludge from the wastewater treatment system. Subsequent Biological Reactors (SBRs) were used for the study. The results show that the amount of excess sludge could be reduced by 58.8%. The optimal sludge sonication ratio was 1/7, the ultrasonic intensity was 1.6 W/mL, the irradiation time was 15 min and the ultrasonic frequency was 25 kHz. The SBR sludge characteristics, settlability, activity, size and organic content, were stable. The effluent Chemical Oxygen Demand (COD) and Total Nitrogen (TN) concentrations were stable. However, increase in phosphorus concentration in the effluent was observed.
Keywords: ultrasound, cryptic growth, waste activated sludge, P-release, wastewater treatment, sonication, subsequent biological reactors, SBRs, effluent concentrations, chemical oxygen demand, COD, total nitrogen, phosphorous