Effective quorum quenching bacteria dose for anti-fouling strategy in membrane bioreactors utilizing fixed-sheet media

Quorum quenching (QQ) has been recognized as an emerging anti-biofouling strategy for membrane bioreactors (MBRs), but studies on effective QQ bacterial doses are needed. Therefore, in this study, the QQ efficacy for sheet-type media containing different amounts of QQ bacteria (i.e., Rhodococcus sp. BH4) with respect to biofouling control during MBR treatment of synthetic and real municipal wastewaters was investigated. The QQ sheets with well-embedded BH4 bacteria were distinctly effective at alleviating biofouling, but their efficacy was highly dependent on the QQ bacterial dose. The activity of the QQ sheet increased with the QQ bacterial density and its pseudo-first order rate constant reached 3.52 h⁻¹ with 100 mg BH4 per liter of reactor volume. No QQ activity loss occurred with long-term use of the QQ sheets. The relationship between QQ dose and fouling delay had a strong, linear correlation. Fouling retardation was more pronounced with real wastewater because it had less biofouling propensity owing to its inferior organics and nutrients. In fact, the MBRs fed with real wastewater experienced a dramatic decrease in extracellular polymeric substance (EPS) content responsible for biofouling. QQ suppressed the EPS secretion leading to fouling mitigation, but with no impact on biological treatment performances.