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• An indigenous QQ bacteria is efficient on biofouling control in the short-period MBR. • The QQ bacteria has an inhibiting effect on EPS and SMP in MBR mixed liquor. • EPS and SMP contents are linearly dependent on AHLs concentration in mixed liquor. • QQ bacteria has an effect on the variation of TMP at different stages. In this paper, the immobilized quorum quenching (QQ) bacteria – microbial bag was added to a short-period membrane bioreactor (MBR) and its antifouling ability and mechanism were studied by monitoring the changes in transmembrane pressure (TMP), along with the production of N-acyl-homoserine lactones (AHLs), extracellular polymeric substance (EPS) and soluble microbial products (SMP). The QQ bacteria showed efficient mitigation of TMP increase in different membrane fouling stages. In the control MBR group, the TMP reached 43 kPa on the 4th day, while in the experimental group, TMP of QQ-MBR was only 18 kPa at the same time. The detection result of EPS and SMP content of protein and polysaccharide in MBRs showed that QQ bacteria had significant inhibitory effects on EPS and SMP. Also, the QQ bacterial exhibited excellent AHLs degradation rate in MBR reaction tank. [ABSTRACT FROM AUTHOR]

Objective: A modified method was used for cell entrapped beads (CEBs) preparation and two aeration intensities (low and high aeration intensity) was supplied as factors to investigate the change of quorum quenching performance for membrane biofouling in membrane bioreactor (MBR).Results: Dehydrogenase activity and growth trend of activated sludge were improved at high aeration intensity. Compared with C-MBR (with vacant beads), QQ-MBR (with CEBs) had more stable quorum quenching activity and longer application time at high aeration intensity, in which the proteins and polysaccharides were reduced by 15 and 20%, respectively. The difference of EPS concentration in mixed liquor was attributed to the protein concentration controlled by quorum quenching bacteria, meanwhile sufficient organics was necessary to maintain the process.Conclusions: The better settleability, greater stability and relatively lower hydrophobicity of activated sludge properties was achieved with quorum quenching. The scouring effect of CEBs was promoted at high aeration intensity, further controlling the membrane biofouling. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: Quorum sensing (QS) could regulate gene expression so as to mediate some bacterial behaviors such as the production of extracellular polymeric substances (EPS) and biofilm formation. In this study, a quorum quenching (QQ) bacterium was isolated from an indigenous lab‐scale membrane bioreactor (MBR) and encapsulated in a dumpling‐shaped microbial bag for biofouling control. RESULTS: This QQ bacteria has a higher genetic homology with Acinetobacter bereziniae strain. The effect of time and temperature on the QQ activity of the microbial bag was tested by degrading N‐acyl homoserine lactone (AHL). The results showed the degradation of C8‐HSL (N‐Octanoyl‐DL‐homoserine lactone) and C6‐HSL (N‐Hexanoyl‐L‐homoserine lactone) could reach equilibrium within 2 h. In addition, a suitable temperature for AHL degradation was 20 °C, at which the rate of degradation of C6‐HSL and C8‐HSL by the microbial bag was 88% and 69%, respectively. The antifouling efficiency of the microbial bag was investigated by a constant pressure filtration system. With the microbial bag added, the decrease of permeability was obviously improved. After 14 days, the permeability with QQ decreased to 18% while the control experiment exhibited almost no permeability. CONCLUSION: The excellent AHL degradation rate and the filtration test showed that this QQ bacteria has an excellent antifouling potential in membrane filtration systems. © 2017 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

• A novel method of electrospinning was employed to enhance quorum quenching hydrogel. • QQ-ECHB performs excellent physical stability and environmental-tolerance. • Stable and long-lasting quorum quenching can be effected at low dosage of QQ-ECHB. • MBR biofouling greatly mitigated and extended service cycle with QQ media addition. Bacterial quorum quenching (QQ) is an effective strategy for controlling biofouling in membrane bioreactor (MBR) by interfering the releasing and degradation of signal molecules during quorum sensing (QS) process. However, due to the framework feature of QQ media, the maintenance of QQ activity and the restriction of mass transfer threshold, it has been difficult to design a more stable and better performing structure in a long period of time. In this research, electrospun fiber coated hydrogel QQ beads (QQ-ECHB) were fabricated by using electrospun nanofiber coated hydrogel to strengthen layers of QQ carriers for the first time. The robust porous PVDF 3D nanofiber membrane was coated on the surface of millimeter-scale QQ hydrogel beads. Biocompatible hydrogel entrapping quorum quenching bacteria (sp.BH4) was employed as the core of the QQ-ECHB. In MBR with the addition of QQ-ECHB, the time to reach transmembrane pressure (TMP) of 40 kPa was 4 times longer than conventional MBR. The robust coating and porous microstructure of QQ-ECHB contributed to keeping a lasting QQ activity and stable physical washing effect at a very low dosage (10g beads/5L MBR). Physical stability and environmental-tolerance tests also verified that the carrier can maintain the structural strength and keep the core bacteria stable when suffering long-term cyclic compression and great fluctuations in sewage quality. [Display omitted] [ABSTRACT FROM AUTHOR]

Quorum sensing (QS) is a communication process between cells, in which bacteria secrete and sense the specific chemicals, and regulate gene expression in response to population density. Quorum quenching (QQ) blocks QS system, and inhibits gene expression mediating bacterial behaviors. Given the extensive research of acyl-homoserine lactone (AHL) signals, existences and effects of AHL-based QS and QQ in biological wastewater treatments are being subject to high concern. This review summarizes AHL structure, synthesis mode, degradation mechanisms, analytical methods, environmental factors, AHL-based QS and QQ mechanisms. The existences and roles of AHL-based QS and QQ in biomembrane processes, activated sludge processes and membrane bioreactors are summarized and discussed, and corresponding exogenous regulation strategy by selective enhancement of AHL-based QS or QQ coexisting in biological wastewater treatments is suggested. Such strategies including the addition of AHL signals, AHL-producing bacteria as well as quorum quenching enzyme or bacteria can effectively improve wastewater treatment performance without killing or limiting bacterial survival and growth. This review will present the theoretical and practical cognition for bacterial AHL-based QS and QQ, suggest the feasibility of exogenous regulation strategies in biological wastewater treatments, and provide useful information to scientists and engineers who work in this field. [ABSTRACT FROM AUTHOR]

In order to improve the antifouling properties of quorum quenching (QQ) bacteria immobilized beads, the mechanical strength and permeability of QQ beads were modified by adding powdered activated carbon (PAC) based on traditional polyvinyl alcohol (PVA)-boric acid method. Optimal PAC concentration was investigated through measuring the mechanical strength, permeability and N -octanoyl-DLhomoserine lactone (C8-HSL) removal ratio of the PAC-PVA beads. Particularly, the enhanced antifouling effects of the optimal PAC-PVA beads were compared with those of original QQ beads through a membrane filtration experiment under constant pressure. The optimal concentration of PAC was 1% (w/v), under that PAC concentration, the mechanical strength, permeability and removal ratio of C8-HSL increased by 11.3%, 29.3% and 12.4% respectively. Synergistic effect between adsorption and biodegradation of 1% PAC-PVA beads was also observed. In membrane filtration experiment, membrane permeability with the 1% PAC-QQ beads decreased to 55.4% after 14 days, while the membrane permeability with 0% PAC-QQ beads decreased to 39.9%. The addition of PAC (1%) increased the antifouling efficiency of the QQ beads 15.5%. This paper demonstrated PAC-PVA bead as a QQ bacteria immobilized method had a great potential for biofouling control in membrane bioreactors (MBRs). [ABSTRACT FROM AUTHOR]