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[Display omitted] • A core–shell QQ-encapsulated structure was prepared by a standardized method. • SIPN shell enables excellent biocontainment with physical and chemical stability. • The anti-biofouling and phosphorus removal were enhanced in QQ microcapsule MBR. • QQ microcapsule promoted the application of QQ media for anti-biofouling in MBR. Microbial quorum quenching (QQ) has been proven to be a sustainable anti-biological fouling strategy for membrane bioreactors (MBR), but the long-term stability and practical application in MBR were uncertain. We reported a novel semi-interpenetrating network (SIPN) hydrogels-based design of QQ bacteria (Rhodococcus sp. BH4) encapsulation for both biofouling control and enhancement of organic pollutants removal in MBR. The microcapsule included the alginate core, chitosan thin intermediate compartment and SIPN (sodium alginate / polyacrylamide) shell, which exhibited near-perfect biocontainment, including preventing detectable QQ bacteria escape and improving mechanical strength. The QQ-microcapsules in the MBR demonstrated its significant anti-biofouling effect for treating synthetic wastewater (i.e., membrane fouling was delayed by 233%-280% compared to the control MBR membrane). Meanwhile, the efficiency of phosphorus removal was developed in QQ-microcapsule MBR because of the enhanced phosphorus removal triggered by the flocculation of polyacrylamide (PAM) fraction in SIPN. This promising QQ media brings the broad potential for biofouling control and long-term efficient operation in actual MBR wastewater treatment. [ABSTRACT FROM AUTHOR]

• 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]

Graphical abstract Highlights • Polyacrylonitrile layer can enhance chemical stability. • Polyacrylonitrile layer can lengthen service life of microcapsules. • Anti-biofouling ability of microcapsules with polyacrylonitrile layer was superior. • Chitosan layer can protect bacteria from damage caused by toxic casting solution. • Biofouling was mitigated by quorum quenching microcapsules during MBR operation. Abstract Quorum quenching (QQ) has been proved to be an efficient method to mitigate biofouling in membrane bioreactors (MBRs). In this paper, in order to enhance practicability of QQ microcapsules, we prepared three types microcapsules with same alginate cores (SAs). The microcapsules with polyacrylonitrile (PAN) layer showed excellent performance in preventing cell leakage from the microcapsules, increasing service life and improving mechanical strength. And confocal laser scanning microscopy images demonstrated that there were very little dead bacteria in the microcapsules with both chitosan and PAN layer than microcapsules with only PAN layer because chitosan layer can protect bacteria entrapped in cores from the hurt caused by poisonous PAN solution. At the same time, the microcapsules with PAN layer presented more efficient anti-biofouling ability in the physical washing test. At last, the bacterial microcapsules coated with both chitosan and PAN layer showed an obvious biofouling mitigation during the MBRs operation. [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]

[Display omitted] • The BH4 immobilized media were prepared using nano-silica and silica beads as core reinforcements. • The inclusion of two types of silicon in the beads ensured they were ready for prolonged use. • The application of two quorum quenching media effectively mitigated MBR biofouling. Quorum quenching (QQ) is a strategy to alleviate membrane biofouling in membrane bioreactors (MBRs). As a stable inorganic material with a large specific surface area, silica is often used to prepare of microbial immobilization composites. This study selected two different sizes of silica materials (silica beads and Nano-silica) to make the core encapsulate a QQ bacterial strain (Rhodococcus sp. BH4). The compressive strength and stability under extreme environments were characterized, and the positive effect of silica on QQ beads was verified. The results showed that both QQ beads could resist the impact of high pressure, acid, alkali, salt and EDTA buffer. It was proved that they have the potential to quench effectively continuously. Both beads were still more than 70 % QQ activity after five months of use. In the lab-scale continuous MBR experiment, the time of transmembrane pressure (TMP) reaching 50 kPa in both experimental groups was more than 3 times that in the blank group. The TMP contamination time was extended from 5 to 6 days in the blank group to 18–19 days. Among them, silica beads greatly improve the compressive strength of the beads, and also have a better performance in QQ. [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]

[Display omitted] • Double-layer gel beads were prepared to promote the synergistic effect of QQ bacteria and PAC. • The surface of the porous shell-with PAC layer was rough and uneven. • The core part QQ bacteria embedded was a dense sponge structure. • The addition of PAC into the shell can improve the mass transfer conditions and adsorption capacity. Quorum quenching (QQ) has been proven to be an effective method to reduce MBR membrane biological contamination. In this paper, a novel and efficient QQ-PAC core-shell beads were prepared for mitigating the membrane contamination. The bead was composed of two parts: QQ bacteria embedded in the core and PAC in the shell. The microstructure of the bead was observed by scanning electron microscopy (SEM) and the functional groups were revealed by Fourier transform infrared spectroscopy (FTIR). Meanwhile, the mechanical strength, swelling property, penetration property and QQ activity of the core bead, the core shell-without PAC bead and the core shell-with PAC bead were compared. The core shell-with PAC structure improved the adsorption capacity under good mass transfer conditions. Besides, the combined effect of QQ bacteria and PAC enhanced the QQ effect and alleviated the process of MBR membrane biological contamination consequently. Therefore, the QQ-PAC core-shell beads have a potential possibility in MBR membrane fouling control as the immobilization technology of QQ bacteria. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new quorum quenching strain LZX01 was isolated and produce intracellular lactonase. • LZX01 can rapidly degrade AHL and effectively mitigated membrane biofouling. • LZX01 decreased activated sludge TB-EPS and enhances its hydrophilicity. • LZX01 affected the growth of biofilm-associated bacteria but not MBR performance. • LZX01 still has high QQ activity in the environment rich in some toxic substances. Significant progress has been made in mitigating membrane biofouling by microbial quorum quenching (QQ). More efficient and survivable QQ strains need to be discovered. A new strain named Bacillus thuringiensis LZX01 was isolated in this study using a low carbon source concentration "starving" method from a membrane bioreactor (MBR). LZX01 secreted intracellular lactonase to enable QQ behavior and was capable of degrading 90 % of C8-HSL (200 ng/mL) within 30 min, which effectively delayed biofouling by inhibiting the growth of bacteria associated with biofouling and improving the hydrophilicity of bound extracellular polymeric substances. As a result, the membrane biofouling rate of MBR adding LZX01 was four times slower than that of the control MBR. Importantly, LZX01 maintains its QQ activity even in environments contaminated with typical toxic pollutants. Therefore, with high efficiency, toxicity resistance, and easy culture, LZX01 holds great potential and significant promise for biofouling control applications. [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]