Optimization of the operating parameters for online ultrasonic on controlling membrane fouling in SMBR

In this study, bi-frequency online ultrasound was applied to a submerged membrane bioreactor (SMBR–US) to mitigate the membrane fouling. The transmembrane pressure (TMP) was used as an indicator of membrane fouling, and it was observed at different ultrasound parameters to investigate the alleviating effect of membrane fouling. The wastewater treatment experiments were then carried out to explore the effects of online ultrasound on effluent quality and activated sludge concentrations in SMBR system. The results show that the TMP were relatively low when the ultrasonic cleaning time continued for three minutes with an ultrasonic frequency at 50 kHz, or bi-frequency of 25–50 kHz, or tri-frequency of 25–50–90 kHz and an ultrasonic power of 200 or 300 W. The results of wastewater treatment experiments show that both the SMBR–US and the SMBR-Control system had high COD, ammonia, and TN removal efficiency, indicating that the ultrasound did not have a negative influence on the properties of activated sludge and effluent quality. The mixed liquor suspended solids (MLSS) in SMBR–US system decreased apparently, about 7.1% when comparing to the SMBR-Control system, after 40-day operation, which suggested that the ultrasound can reduce extra sludge production.