Reducing excess sludge volume in sequencing batch reactor by integrating ultrasonic waves and ozonation

The effects of ultrasonic waves and ozonation on the reduction of produced sludge in the sequencing batch reactor (SBR) system were investigated in laboratory-scale experiments. For this purpose, the optimal ozone dosage was determined by measuring soluble chemical oxygen demand (SCOD), protein concentration, turbidity level, and biomass yield coefficient. Next, the effect of its integration with different levels of ultrasonic specific energy was evaluated. Based on the results, the minimum excess sludge production in the SBR system was achieved at the ozone dosage of 11 mg O₃/g MLSS followed by ultrasonic specific energy of 12000 kJ/kg TS. In this case, the biomass yield coefficient decreased from 0.75 in the control reactor to 0.34 mg MLSS/mg COD in the test reactor, which was equal to a 54% reduction in excess sludge production in the SBR system. In these circumstances, the removal efficiencies of COD, total nitrogen, and total phosphorus were measured as 90%, 82%, and 81%, respectively.