An overview of quorum sensing in shaping activated sludge forms: Mechanisms, applications and challenges.

Activated sludge method is an effective method for the wastewater treatment and has been widely applied. Activated sludge usually exists in various forms such as activated sludge floc, biofilm and granule. Due to the different character and function for each sludge type, the role and mechanism in the wastewater treatment process are also different, but all were crucial. The quorum sensing (QS) /quorum quenching (QQ) have been demonstrated and proved to regulate the group behavior by secreting signaling molecules among microorganisms and thus affect the manifestation of sludge. However, the complex mechanisms and regulatory strategies of QS/QQ in sludge forms have not been systematically summarized. This review provided an overview on the mechanism of QS/QQ shaping sludge forms from macro to micro (Explore it through signaling molecules, extracellular polymeric substances and microorganisms). In addition, the application and challenges of QS/QQ regulating sludge forms in various wastewater treatment processes including biofilm batch reactor, granule sludge and membrane bioreactor were discussed. Finally, some suggestions for further research and development of effective and economical QS/QQ strategies are put forward.

Effects of microplastics on sedimentary geochemical properties and microbial ecosystems combined with hydraulic disturbance.

Microplastics (MPs) pollution is widely investigated owing to its potential threats to river ecosystems. However, it remains unclear whether hydraulic disturbance deepens or mitigates the effects of MPs-contaminated sediments on the river environment. Herein, we studied the impact of sediment aggregates, organic matter, and enzyme activity, with emphasis on microbial community structure and function in sediments exposed to MPs (1 %, 5 %, and 10 % w/w) in conjunction with hydraulic disturbance. The experimental results showed that the influence of MPs on the sediment under hydraulic disturbance is more significant than that of static culture, especially for various environmental factors (MWD, MBC, and sucrase activity etc.). The proportions of the >0.05 mm-fraction aggregates increased from 74-76 % to 82-88 % in the sediment throughout the entire disturbance process. It has been found that the disturbance generally promotes the interaction between MPs and sediments. FAPROTAX analysis demonstrated that the disturbance reduced the difference in effects on microbial functional genes between the control group and the MPs-added groups by up to 10 times, suggesting that the effects of disturbance on MPs-contaminated sediments are relatively complex. This work provides new insights into the effects of hydraulic disturbance on physicochemical properties and microbial communities of MPs-contaminated sediment.

Isolation and application of Bacillus thuringiensis LZX01: Efficient membrane biofouling mitigation function and anti-toxicity potential.

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.

Recent advances on microplastic aging: Identification, mechanism, influence factors, and additives release.

Microplastics pollution has attracted worldwide attention in recent years due to their wide distribution and severe threat to biota. Additionally, microplastics will undergo serious aging effects after being discarded into the environment. Aging can change surface properties and affect the environmental behavior of microplastics. However, information on the aging process and influencing factors of microplastics are still limited. This review summarized recently reported characterization methods, and aging means of microplastics. Subsequently, the corresponding aging mechanisms (abrasion, chemical oxidation, light irradiation, and biodegradation) and the intervention mechanism of environmental factors are revealed, which is helpful to understand the environmental aging processes and ecological risks of microplastics. Besides, to further comprehend the potential environmental toxicity of microplastics, the article also outlined the release of additives during aging. This paper provides reference directions for further study on aging microplastics through a systematic review. Future research works should further facilitate the development of technologies to identify aged microplastics. And more attention needs to focus on narrowing the gap between laboratory aging simulation and the natural environment, thereby enhancing research authenticity and environmental relevance.

Enhancing quorum quenching media with 3D robust electrospinning coating: A novel biofouling control strategy for membrane bioreactors.

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.

Impact of microplastics on lead-contaminated riverine sediments: Based on the enzyme activities, DOM fractions, and bacterial community structure.

Microplastics (MPs) are able to interact with diverse contaminants in sediments. However, the impacts of MPs on sediment properties and bacterial community structure in heavy metal-contaminated sediments remain unclear. In this study, we investigated the adsorption of Pb(II) by sediment-MPs mixtures and the effects of different concentration MPs on sediment enzyme activities, DOM fractions, and Pb bioavailability in riverine sediments, and further explored the response of sediment microbial community to Pb in the presence of MPs. The results indicated that the addition of MPs significantly decreased the adsorption amount of Pb(II) by sediments, especially decreased by 12.6% at 10% MPs treatment. Besides, the changes in enzyme activities, DOM fractions exhibited dose-dependent effects of MPs. The higher level of MPs (5% and 10%) tends to transform Pb into more bioavailable fractions in sediments. Also, MPs amendment was observed to alter sediment bacterial community structures, and community differences were evident in the uncontaminated and lead-contaminated sediments. Therein, significant increase of Bacteroidota, Proteobacteria and decrease of Firmicutes abundance in Pb-contaminated sediment at the phylum level were observed. These findings are expected to provide comprehensive information for assessing the combined ecological risks of heavy metals and MPs in riverine sediments.

Construction of PDIsa/BiOBr type-I scheme heterojunction for efficient ciprofloxacin photocatalytic degradation.

Fabrication of heterojunction photocatalysts is a promising strategy for enhancing photocatalytic activity. However, the study about traditional type-I heterojunction still remains to be developed. Herein, a PDIsa/BiOBr traditional type-I heterojunction was constructed by electrostatic self-assembly method, which owned improved light absorption capacity and photogenerated charge separation efficiency. The interfacial electric field and the polarization electric field of PDIsa impelled the separation of excitons. The degradation rate of ciprofloxacin (CIP) was improved by 3.2 times over the optimal PDIsa/BiOBr composite than pure BiOBr. In addition, the TOC removal efficiency reached 67.34% within 120 min. Trapping experiments and electron spin resonance (ESR) tests showed that superoxide radical (•O2-) was the most active species, and singlet oxygen (1O2) and hole (h+) played a secondary role. The work may furnish a new reference for designing BiOBr-based type-I heterojunction.

Long-term impacts of polyethylene terephthalate (PET) microplastics in membrane bioreactor.

Due to the mass production and daily use of plastic products, the potential toxicity of microplastics to the water environment has attracted worldwide attention. In this work, the effect of typical microplastics (PET) on the performance of activated sludge from membrane bioreactors (MBR) was evaluated. The impacts on biological removal efficiency were unconspicuous with continuous dosing of 60 particles/L. However, further investigations revealed that PET particle accumulation caused adverse impacts on settleability and dewaterability. The SVI value increased from 53.3 ml/g MLSS to 69.9 ml/g MLSS and the CST in the PET reactor increased by 22%. Nevertheless, hydrophobicity was reduced by 49.2%. Mechanism studies exposed that the PET microplastics accumulation improved extracellular polymeric substances (EPS) from 116.96 mg/L to 138.70 mg/L and caused cell membrane damage. The abundance and diversity of microbial community reduced in activated sludge in PET reactor compared with control reactor. These phenomena revealed a possible hypothesis that the microplastic particles increased EPS and cytotoxicity of activated sludge. However, the rate of transmembrane pressure (TMP) build-up was significantly mitigated in PET-MBR compared to that in a control-MBR (1.27 folds), which attributes that physical scour of particles may still alleviate membrane contamination in MBR.

Investigation of the adsorption behavior of Pb(II) onto natural-aged microplastics as affected by salt ions.

In this study, the adsorption behavior of Pb(II) on natural-aged and virgin microplastics in different electrolyte solutions was investigated. The results demonstrated that natural-aged microplastics exhibited higher adsorption capacity for Pb(II) compared to virgin ones, and the addition of CaCl2 strongly inhibited the adsorption amount of Pb(II). The adsorption kinetics of Pb(II) adsorption were better fitted by the pseudo-second order model and Elovich equation, and were slowed down greatly at higher ionic strength. The rate-limiting steps of adsorption process were dominated by intra-particle diffusion. The adsorption isotherm of Pb(II) onto microplastics affected by salt ions can be well described by Freundlich model, the greater adsorption efficiency of natural-aged microplastics proved that adsorption process was multilayer and heterogeneous. In addition, pH significantly influenced the adsorption of Pb(II) due to the changes electrostatic interactions. The effect of fulvic acid in the electrolyte solutions was also revealed and attributed to the complexation with Na+ and Ca2+. Furthermore, the higher pH and ionic strength in different environmental water dramatically decreased adsorption capacity onto microplastics. Finally, it's confirmed that the adsorption mechanisms affected by salt ions mainly involve electrostatic interaction, surface complexation, and ionic exchange. These findings indicate that salt ions exert an important influence on the adsorption of heavy metals for MPs, which should be further concerned.

Microplastics as a vehicle of heavy metals in aquatic environments: A review of adsorption factors, mechanisms, and biological effects.

Microplastics (MPs) have recently attracted much attention due to their widespread distribution in the aquatic environment. Microplastics can act as a vector of heavy metals in the aquatic environment, causing a potential threat to aquatic organisms and human health. This review mainly summarized the occurrence of microplastics in the aquatic environment and their interaction with heavy metals. Then, we considered the adsorption mechanisms of MPs and heavy metals, and further critically discussed the effects of microplastics properties and environmental factors (e.g., pH, DOM, and salinity) on the adsorption of heavy metals. Finally, the potential risks of combined exposure of MPs and heavy metals to aquatic biota were briefly evaluated. This work aims to provide a theoretical summary of the interaction between MPs and heavy metals, and is expected to serve as a reference for the accurate assessment of their potential risks in future studies.

Construction of MoO3 nanopaticles /g-C3N4 nanosheets 0D/2D heterojuntion photocatalysts for enhanced photocatalytic degradation of antibiotic pollutant.

A new type of 0D-2D Z-scheme heterojunction photocatalyst (MoO3/g-C3N4) was successfully prepared via simple hydrothermal calcination method. The catalytic activities of MoO3/g-C3N4 was evaluated by the degradation effect of tetracycline. The results indicated that the 0D-2D MoO3/g-C3N4 Z-scheme heterojunction was significantly better than that of original g-C3N4. Especially, the optimal 0.5 wt% MoO3/g-C3N4 could reach 85.9% removal efficiency within 100 min under visible light irradiation (λ > 420 nm), and its degradation rate constant was 2.3 times higher than that of g-C3N4·In addition, the effects of real water matrix, natural sunlight irradiation on tetracycline removal were examined. Reactive-species-trapping experiments show that both photo-generated •O2- and h+ are the main active species in the photocatalytic process. Besides, the results of •O2- and •OH detection further indicated that the yield amount of •O2- and •OH in MoO3/g-C3N4 case showed enhancement when compared with g-C3N4. Moreover, the quite stable crystal structure and excellent recycling ability endowed the MoO3/g-C3N4 composite with a great potential for applying in photocatalytic fields.

QQ-PAC core-shell structured quorum quenching beads for potential membrane antifouling properties.

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.

Role of concentration polarization in cross flow micellar enhanced ultrafiltration of cadmium with low surfactant concentration.

Concentration polarization is an important issue in micellar enhanced ultrafiltration (MEUF) of wastewater containing heavy metal ions at low surfactant concentrations. In this paper, we studied removal of Cd(Ⅱ) by cross flow MEUF at low sodium dodecyl sulfate (SDS) concentration levels, and the role of concentration polarization in flux decline and Cd(Ⅱ) rejection was emphasized. Concentration polarization resistance and SDS concentration near membrane were calculated to characterize concentration polarization. The results showed that SDS concentration near membrane was 13 mM when feed concentration was merely 0.8 mM. By combining phase diagram of SDS, structures of SDS micelles in concentration polarization layer were deduced and thin layer structure transformed to porous structure formed by accumulated globular micelles when SDS concentration increased. Although micelles formed in concentration polarization layer was responsible for flux decline, they also provided adsorption sites for Cd(Ⅱ).

Roles of surfactants in pressure-driven membrane separation processes: a review.

Surfactants widely exist in various kinds of wastewaters which could be treated by pressure-driven membrane separation (PDMS) techniques. Due to the special characteristics of surfactants, they may affect the performance of membrane filtration. Over the last two decades, there are a number of studies on treating wastewaters containing surfactants by PDMS. The current paper gives a review of the roles of surfactants in PDMS processes. The effects of surfactants on membrane performance were discussed via two aspects: influence of surfactants on membrane fouling and enhanced removal of pollutants by surfactants. The characteristics of surfactants in solution and at solid-liquid interface were summarized. Surfactants in membrane filtration processes cause membrane fouling mainly through adsorption, concentration polarization, pore blocking, and cake formation, and fouling degree may be influenced by various factors (feed water composition, membrane properties, and operation conditions). Furthermore, surfactants may also have a positive effect on membrane performance. Enhanced removal of various kinds of pollutants by PDMS in the presence of surfactants has been summarized, and the removal mechanism has been revealed. Based on the current reports, further studies on membrane fouling caused by surfactants and enhanced removal of pollutants by surfactant-aided membrane filtration were also proposed.

The role of quorum sensing in granular sludge: Impact and future application: A review.

Quorum sensing (QS) is a process widely exist in bacteria, which refers to the cell-cell communication through secretion and sensing the specific chemical signal molecules named autoinducers. This review demonstrated recent research progresses on the specific impacts of signal molecules in the granular sludge reactors, such corresponding exogenous strategies contained the addition of QS signal molecules, QS-related enzymes and bacteria associated with QS process. Accordingly, the correlation between QS signaling molecule content and sludge granulation (including the formation and stability) was assumed, the comprehensive conclusion elucidated that some QS signals (acyl-homoserine lactone and Autoinducer 2) can accelerate the growth of particle diameter, the production of extracellular polymeric substance (EPS), microbial adhesion and change the microbiome structure. But diffusable signal factor (DSF) acted as a significant disincentive to the formation and stability of GS. As a result, it deserved serious attention on the value and role of QS signals in the GS. This review attempts to illuminate the potential method for addressing the main bottleneck: to accelerate the formation of granules and keep the high stability of GS for a long-term reactor. Therefore, review discussed the possible trends of GS: QS and intercellular/intracellular signaling which can lay a theoretical foundation for mechanism of GS formation and stability, would be of practical significance for further application in the future.

Evaluation of self-cleaning performance of the modified g-C3N4 and GO based PVDF membrane toward oil-in-water separation under visible-light.

Photocatalytic membranes (PMs), coupling of membrane filtration and photocatalysis, have exhibited the potential for application in the wastewater treatment. In this study, we firstly adopted the supramolecular aggregates of melamine (M), cyanuric acid (C), and urea (U) in specific dimethyl sulfoxide (DMSO) as precursors to prepare carbon nitride MCU-C3N4 with high photocatalytic performance, and a kind of novel-designed photocatalytic membrane was prepared via filtrating the mixture of graphene oxide (GO) nanosheets and MCU-C3N4 on PVDF membrane supports, and then crosslinked using glutaraldehyde (GA) to construct a steady coating on the GO/MCU-C3N4/PVDF membrane. GO/MCU-C3N4/PVDF composite membrane exhibited higher permeation flux than that of GO/PVDF membrane and exhibited excellent separation performance for oil-in-water emulsion. A visible light-driven self-cleaning four-stage filtration by a self-built dead-end filtration system was carried out to evaluate membrane antifouling property, and GO/MCU-C3N4/PVDF membrane (M2) possessed higher flux recovery ratio (FRR) (∼92.36%) and lower irreversible fouling resistance (Rir) ratio (∼8%) under 30min visible-light irradiation, maintaining relatively higher FRR (>72%) during 4 cycling of four-stage filtrating experiments. GO/MCU-C3N4/PVDF PMs are equipped with high permeation flux, separation performance, anti-fouling property and stability, indicating potential application in water treatment.

Control of indigenous quorum quenching bacteria on membrane biofouling in a short-period MBR.

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.

Evaluation of self-cleaning and photocatalytic properties of modified g-C3N4 based PVDF membranes driven by visible light.

Recently, the application of membranes faces a big challenge due to membrane fouling, to alleviate this situation, the hybridization of photocatalysis and membrane filtration has aroused significant attention. In this study, we firstly introduced melamine, cyanuric acid and urea in dimethyl sulfoxide (DMSO) as precursors to fabricated the MCU(DMSO)-C3N4 material with excellent photocatalytic performance, and immobilized it on PVDF membranes by vacuum filtration, subsequently adding polyethylene glycol and glutaraldehyde as crosslinkers from MCU-C3N4/PVDF membrane. The results demonstrate that with the MCU-C3N4 ratio increasing, the membrane flux was gradually decreased. Besides, the photocatalytic efficiencies of MCU-C3N4/PVDF for rhodamine B (RhB) and tetracycline hydrochloride (TC) degradation are 84.24% and 71.26% respectively, which are about 8 times higher than that of the original membrane. To evaluate antifouling performance of photocatalytic membranes, we conducted a four-stage filtration system, and the flux recovery ratio (FRR) of MCU-C3N4/PVDF membranes reached over 80% (optimum 91%) under visible light irradiating (λ > 420 nm) for 30 min. Meanwhile, under visible light irradiation reversible fouling (Rr) gradually became the dominant fouling factor instead of the irreversible fouling (Rir), indicating the excellent antifouling performance of MCU-C3N4/PVDF membranes. This novel method to modify membranes with MCU-C3N4 gives insight to photocatalytic and self-cleaning properties of photocatalytic composite membranes, providing theoretical basis for their broad application.

Membrane layers intensifying quorum quenching alginate cores and its potential for membrane biofouling control.

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.

Honeycomb-like carbon nitride through supramolecular preorganization of monomers for high photocatalytic performance under visible light irradiation.

A metal-free modified carbon nitride MCU(DMSO)-C3N4 (3:3:1) with a honeycomb-like morphology was prepared via firstly introducing cyanuric acid and urea into melamine in dimethyl sulfoxide (DMSO) as the precursor for the MCU-C3N4. A variety of characterization methods, including XRD, XPS, FT-IR, SEM, TEM, UV-vis, photoluminescence (PL), and photocurrent generation, were applied to investigate the structure, morphology, optical, and photoelectrochemical properties of the g-C3N4 and MCU-C3N4 (3:3:1). Rhodamine B (RhB), methylene blue (MB), and bisphenol A (BPA) were selected as target pollutants to evaluate photocatalytic activity of the MCU-C3N4 (3:3:1) under visible light irradiation. MCU-C3N4 (3:3:1) exhibits significantly enhanced photocatalytic activity compared with g-C3N4, where 99.49% RhB is removed within 40min, 97.7% MB is removed within 80 min, and 84.37% BPA is removed within 90 min. The improved photodegradation efficiency was mainly due to the larger surface area, the stronger REDOX ability, and the increased separation efficiency of photogenerated electron-hole pairs. The active radical trapping experiments and electron spin resonance tests indicated that h+ and O2- radicals were the dominant active species whereas OH radicals could be a minor factor. A possible photocatalytic mechanism is proposed. This strategy here provides an ideal platform for the design of photocatalysts with large surface area and high porosity for various pollutant controlling applications.