High frequency ultrasound-induced sequence batch reactor as a practical solution for high rate wastewater treatment

•A high frequency ultrasound-augmented SBR treating dairy wastewater was developed.•The performance of two SBRs (with and without ultrasound) were compared.•Effect of high frequency ultrasound on biological activity of biomass was studied.•Effect of high frequency ultrasound on physical properties of sludge was studied.•Response surface methodology was applied to model the biological systems.

In practice, operation of conventional treatment systems with high biomass concentration is limited due to difficulty in the sludge sedimentation in clarifiers. In this study, high frequency ultrasound wave (1.7 MHz) was applied to enhance the sludge settling at high biomass concentration. Hence, performance of two sequence batch reactors (SBR) (with and without ultrasound) treating a synthetic dairy wastewater were compared. Experiments were conducted based on a central composite face-centered design and analyzed using response surface methodology. Aeration time (2–24 h), mixed liquor volatile suspended solids (2000–6000 mg/l), and CODin (500–1500 mg/l) were selected as the operating variables to analyze, optimize and model the process. The results showed that high frequency ultrasound led to considerable increase in sludge settling velocity at high MLSS. COD removal and final turbidity were almost similar in the both systems, indicating that the ultrasound applied has not had any adverse effect on the microbial activity.