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This study addresses membrane biofouling in membrane bioreactors (MBRs) by exploring fungal-to-bacterial quorum quenching (QQ) strategies. While most research has been focused on bacterial-to-bacterial QQ tactics, this study identified fungal strain Vanrija sp. MS1, which is capable of degrading N-acyl-homoserine lactones (signaling molecules of Gram-negative bacteria). To determine the benefits of fungal over bacterial strains, after immobilization on fluidizing spherical beads in an MBR, MS1 significantly reduced the fouling rate by 1.8-fold compared to control MBR, decreased extracellular polymeric substance levels in the biofilm during MBR operation, and favorably changed microbial community and bacterial network, resulting in biofouling mitigation. It is noteworthy that, unlike Rhodococcus sp. BH4, MS1 enhanced QQ activity when switching from neutral to acidic conditions. These results suggest that MS1 has the potential for the effective treatment of acidic industrial wastewater sources such as semiconductor and secondary battery wastewater using MBRs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Membrane fouling is a significant obstacle to applying membrane bioreactors (MBRs) for wastewater treatment. Here we report the impact of sunlight irradiation on membrane fouling, biopolymers, signal molecules, and microbial communities in MBRs. The degradation of signal molecules, which induce membrane biofouling, occurred through solar photolysis in batch tests. However, MBR sludge exposed to sunlight exhibited different biological behaviors creating more soluble microbial products (SMP) and signal molecules (particularly autoinducer-2). Cell lysis and deflocculation occurred when the MBR mixed liquor was exposed to sunlight. MBR fouling rates coincided with the temporal concentration profiles of SMP and signal molecules. Sunlight caused drastic changes in the MBR microbial community, stimulating the preferential growth of specific bacteria (e.g., Deinococcus Runella , Flavitalea , Glaiimonas , and Rurimicrobium). The nonmetric multidimensional scaling analysis of the MBR community structures with and without sunlight irradiation showed two distinct microbial community clusters and their reversibility. Network analysis based on Spearman's rank correlations revealed that with sunlight irradiation, fouling rates had significant positive connections with SMP proteins and the Flavitalea genus. The findings of this study demonstrate that sunlight is a considerable factor affecting membrane fouling and microbial ecology in MBRs, needing shade for fouling mitigation and sustainable operation. [Display omitted] • The effects of sunlight on membrane biofouling and microbial ecology were investigated. • The signal molecules in batch reactors degraded well when sunlight irradiation was applied. • Sunlight irradiation of biological mixed liquor exacerbated membrane fouling. • The concentration of soluble organics and autoinducer-2 increased with sunlight irradiation. • Sunlight irradiation caused drastic changes in microbial communities and their networks. [ABSTRACT FROM AUTHOR]

[Display omitted] • The direct dosing of quorum quenching (QQ) bacteria for biofouling control was investigated. • The degree of fouling mitigation was proportional to QQ bacteria doses. • Probiotic QQ effects were responsive to BH4 injection, halting, and re-injection. • Thiothrix became less abundant in the probiotic reactor during QQ bacteria injection. • Cell-bound biopolymers were not the major cause of biofouling, but soluble parts were. In membrane bioreactors (MBRs), N -acyl homoserine lactones (AHLs)-related quorum sensing (QS) has been described as one of the main causes of biofouling during wastewater treatment. Quorum-quenching (QQ) bacteria for the mitigation of QS in MBRs have been applied but limited to entrapping methods only. Thus, this study investigates the direct injection of different doses (0–77.2 mg/d) of unentrapped QQ strains (Rhodococcus sp. BH4) into a probiotic QQ MBR (i.e., bioaugmented reactor) while monitoring the changes in fouling rates as well as microbial communities, biopolymers, signal molecules, and treatment performances. The QQ bacteria show effective biofouling mitigation in diverse MBR phases, but a halt in QQ bacteria injection leads to increased fouling rates in the probiotic QQ MBR. The QQ bacteria exhibit a noticeable AHL degradation rate during BH4 inoculation as opposed to when inoculation is halted. They also have significant inhibitory effects on the generation of soluble carbohydrates and proteins. However, cell-bound extracellular polymeric substance (EPS) concentrations are relatively higher in the probiotic QQ reactor despite decreased fouling rates. This can be ascribed to the production of EPS by injected BH4, as revealed in pure BH4 batch cultures. Probiotic QQ has impacts on both the relative bacterial abundance and the overall microbial composition. Thiothrix is identified as the most dominant genus in the mixed liquor of both MBRs; however, its relative abundance becomes low in the probiotic MBR during QQ bacteria injection. These findings provide valuable information that will foster the development of improved QQ strategies in MBRs. [ABSTRACT FROM AUTHOR]

• Membrane reciprocation paired with quorum quenching (QQ) combats fouling. • Service time is boosted six-fold through membrane reciprocation and QQ methods. • Synergy reduces physically reversible resistance, enhancing membrane performance. • QQ curbs biofouling, degrading signal molecules but maintaining microbial community. • The combined approach saves > 80 % of energy and minimizes membrane fouling. Membrane bioreactors (MBRs) play a crucial role in wastewater treatment, but they face considerable challenges due to fouling. To tackle this issue, innovative strategies are needed. This study investigated the effectiveness of membrane reciprocation and quorum quenching (QQ) to control fouling in MBRs. The study compared MBRs using membrane reciprocation (30 rpm) and QQ (injecting media containing 100 or 200 mg/L BH4) with conventional MBRs employing different air-scouring intensities. The results demonstrated that combining membrane reciprocation (30 rpm) with QQ (200 mg/L BH4) significantly extended the service time of MBRs, making it approximately six times longer than conventional methods. Moreover, this approach reduced physically reversible resistance. The reduction in signal molecules related to biofouling due to QQ showcased its critical role in controlling biofouling, even under high shear caused by membrane reciprocation. However, the impact of QQ on microbial community structure appeared relatively insignificant when compared to factors such as operation time, aeration intensity, and membrane reciprocation. By combining membrane reciprocation and QQ, the study achieved a remarkable 81 % energy saving compared to extensive aeration (103 s−1 in velocity gradient), in addition to the extended service time. Importantly, this combined antifouling approach did not negatively affect microbial characteristics and wastewater treatment, emphasizing its effectiveness in MBRs. Overall, the findings of this study offer valuable insights for developing synergistic fouling control strategies in MBRs, significantly improving the energy efficiency of the wastewater treatment process. [Display omitted] [ABSTRACT FROM AUTHOR]