Impact of Encapsulated Quorum-Quenching Bacterial Dose and Feed Type on Biofouling Control in Membrane Bioreactors

Quorum quenching (QQ) vessels have been used as an effective method of biofouling control for membrane bioreactors (MBRs), but further studies on the effect of entrapped QQ bacterial levels on the antibiofouling efficacy and stability of the QQ vessel are needed. In the present study, we investigated the efficacy and stability of QQ vessels containing different doses of QQ bacteria (i.e., Rhodococcus sp. BH4) during long-term MBR operation fed with synthetic and real municipal wastewater. It was found that the degradation rate of signal molecules (e.g., N-acyl homoserine lactones; AHLs) depended on the numbers of BH4 bacteria in the QQ vessel. The QQ vessel supplying a dose of 135 mg/L of BH4 to the reactor improved fouling mitigation while slowing down the build-up of transmembrane pressure. Biofilm formation on the membrane surface was alleviated by quenching the AHL-based signaling among microorganisms. The delay in membrane fouling had a strong linear correlation with the QQ activity rate constant, and this was more pronounced for the MBR treating real municipal wastewater with lower carbon and nutritional content. The activity of the QQ vessel supplying a dose of 135 mg/L of BH4 gradually increased over time (>1,200 days), confirming that it has the potential for stable long-term use. These results demonstrate that QQ vessels are effective and stable for biofouling control in MBRs treating synthetic and real wastewater.