Combined effects of ultrasound power and DO on nitrogen removal in a low-intensity ultrasound (LIU)-assisted sequencing batch biofilm reactor

Abstract

Ultrasonication is a sustainable biophysical technology used in sludge treatment. Studies show it enhances microbial activity and pollutant removal from wastewater under optimal conditions. This study examines ultrasonic irradiation's effect on nitrogen removal efficiency and extracellular polymeric substances (EPS) formation in Sequencing Batch Biofilm Reactors (SBBRs). Four reactors with different ultrasonic powers (0 W, 180 W, 270 W, and 360 W) and dissolved oxygen (DO) concentrations were tested to explore the interaction between ultrasonic treatment and nitrogen transformation. Results show that moderate ultrasonic power (180 W and 270 W) significantly improves ammonia nitrogen and total nitrogen (TN) removal rates, reaching up to 99.4% and 91.7% at a 2 mg/L DO concentration. Higher power (360 W) increased EPS production, especially tightly bound EPS, enhancing biofilm stability and microbial protection, but did not improve nitrogen removal. Thus, balancing ultrasonic intensity and DO is crucial for optimal performance. Microbial analysis indicates ultrasonic treatment alters microbial diversity, promoting species and aiding nitrification and denitrification. This study shows that controlled ultrasonic irradiation can enhance SBBR efficiency by adjusting microbial activity and biofilm structure, improving wastewater treatment.