Role of nano-Fe3O4 particle on improving membrane bioreactor (MBR) performance: Alleviating membrane fouling and microbial mechanism

Leveraging almost hydrophobic PVDF membrane and in-situ ozonation in O3/UF/BAC system for superior anti-fouling and rejection performance in drinking water treatment

The almost hydrophobic PVDF membrane (PVDF matrix) commonly exhibited excellent performance in pollutant rejection but with poor anti-fouling performance. This study intended to develop the rejection performance and enhance anti-fouling of the PVDF membrane in an O3/UF/BAC system for high quality water production through leveraging the advantages of in-situ ozonation and the nature of the PVDF membrane. Reduced density gradient (RDG) analysis demonstrated that the PVDF membrane exhibited excellent ozone resistance by reducing hydrogen bonds and electrostatic interactions between the membrane surface and ozone. Consequently, the physicochemical properties of the PVDF membrane remained unchanged in the laboratory continuous flow experiment with in-situ ozonation at 2.86 mg/L. The almost hydrophobicity of the PVDF membrane not only resisted fouling but also facilitated the reaction between ozone and foulants of higher concentrations locally at membrane surface, leading to dynamic changes in membrane fouling, with TMP/TMP0 initially increasing, then decreasing and stable. Therefore, the Rtotal, Rcake and Rgel of the PVDF membrane decreased by 47.40 %, 46.79 % and 50.99 % as compared to the UF/BAC system, respectively, in the O3/UF/BAC system. In-situ ozonation transformed macromolecular substances into micromolecules, particularly organic matter with lignin/carboxylic-rich alicyclic molecules and aromatic structures. The majority of these micromolecules were either rejected by the deposited foulants layer through Van der Waals interaction and utilized as a carbon source by membrane surface microorganisms (eg., Curvibacter and Methyloversatilis), or further degraded by microorganism in the BAC unit. This resulted in a 19.34 % and 40.58 % reduction in CODMn concentrations in the UF and BAC effluents, respectively. The system's anti-fouling and water purification performance observed in laboratory experiments was confirmed in a pilot test, providing new insights into the use of in-situ ozonation and organic membranes.

Integration of manganese ores with activated carbon into constructed wetland for greenhouse gas emissions reduction

Manganese oxide and activated carbon (AC) are widely employed in constructed wetlands (CWs) to remove nutrients and reduce greenhouse gas (GHG) emissions, however, the effect and mechanism of AC combined with manganese ores (MO) on GHG emissions remain unclear. In this study, the mechanisms of nutrient removal and GHG emissions reduction were investigated by three vertical subsurface-flow CWs: gravel (CW-B), manganese ores (MO) uniformly mixing with gravel (CW-M), or activated carbon (CW-MC). The average removal efficiencies of chemical oxygen demand, total nitrogen and total phosphorus in CW-MC were markedly improved compared to CW-B and CW-M, reaching 82.72%, 95.72% and 93.43%, respectively. Moreover, the global warming potential (CO2 equivalent) of CW-MC was reduced by 52.80% and 36.88% relative to CW-B and CW-M, respectively. Mixing of MO with AC reduced the loss of manganese and further enhanced the manganese cycling process by X-ray photoelectron spectroscope and concentration of Mn(Ⅱ) in CWs analysis. The introduction of MO and AC enhanced the PN/PS ratio of extracellular polymeric substances and facilitated extracellular electron transfer (EET). Furthermore, metagenomic analysis showed that the abundances of denitrifying, manganese oxidizing and electroactive bacteria genera were enhanced in the CW-MC, which promoted the transformation of nitrogen and manganese. Meanwhile, high abundances of denitrification and EET related genes were observed in CW-MC, improving denitrification efficiency and reducing N2O emission. This study elucidated the impacts and mechanisms of MO and AC on GHG emissions, providing a new insight to improve manganese-based CW performance.

Magnetite-mediated shifts in denitrifying consortia in bioelectrochemical system: Insights into species selection and metabolic dynamics

Conductive materials, such as magnetite, are recognized for their ability to enhance electron transfer and stimulate microbial metabolic activities. This study aimed to elucidate the metabolic potential and species interactions of dominant microbial species within complex communities influenced by magnetite. It indicated that the optimal dosage of magnetite at 4.5 mg/cm², would significantly improve denitrification efficiency and then reduce the time for removing 50 mg/L nitrate by 24.33 %. This enhancement was attributed to the reduced charge transfer resistance and the promoted formation of extracellular polymeric substances (EPS) facilitated by magnetite. Metagenomic analysis revealed that magnetite addition mitigated the competition among truncated denitrifiers for downstream nitrogen species, diminished the contribution of bacteria with complete nitrogen metabolism pathways to denitrification, and fostered a transition towards co-denitrification through interspecies cooperation, consequently leading to decreased nitrite accumulation and increased tolerance to nitrate shock loads. Furthermore, an in-depth study on a key species, Geobacter anodireducens JN93 within the bioelectrochemical system revealed that while magnetite with varying Fe(II) and Fe(III) ratios improved denitrification performance, the metabolic potential of Geobacter sp. varied for different nitrogen metabolism pathways. Collectively, this research provides insights into the microecological effects of magnetite on denitrifying consortia by shifting interspecific interactions via enhanced electron transfer.

Enhancing volatile fatty acids production from waste activated sludge: The role of pretreatment by N,N-bis(carboxymethyl)-l-glutamate (GLDA)

N,N-bis(carboxymethyl)-l-glutamate (GLDA) is an eco-friendly chelating agent that effectively extracts multivalent metal ions from waste activated sludge (WAS) flocs, which could potentially alter their structure. However, the effect of GLDA on the production of volatile fatty acids (VFAs) from WAS is not well known. Here, we demonstrate that pretreatment with GLDA at a concentration of 200 mmol per kg VSS results in a significant increase of 142% in extractable extracellular polymeric substances and enhances the total VFAs yield by 64% compared to untreated samples. We reveal GLDA's capability to mobilize organic-binding multivalent metal ions within sludge flocs. Specifically, post-pretreatment analyses showed the release of 69.1 mg L-1 of Ca and 109.8 mg L-1 of Fe ions from the flocs, leading to a more relaxed floc structure and a reduced apparent activation energy (10.6 versus 20 kJ mol-1) for WAS solubilization. Molecular dynamic simulations further demonstrate GLDA's preferential binding to Fe3+ and Ca2+ over Mg2+. Our study suggests that GLDA pretreatment causes minimal disruption to reactor stability, thereby indicating the stability of microbial community composition. GLDA has emerged as a viable pretreatment agent for enhancing volatile fatty acids production from waste activated sludge.

Anaerobic membrane bioreactors for municipal wastewater: Progress in resource and energy recovery improvement approaches

Anaerobic membrane bioreactor (AnMBR) offer promise in municipal wastewater treatment, with potential benefits including high-quality effluent, energy recovery, sludge reduction, and mitigating greenhouse gas emissions. However, AnMBR face hurdles like membrane fouling, low energy recovery, etc. In light of net-zero carbon target and circular economy strategy, this work sought to evaluate novel AnMBR configurations, focusing on performance, fouling mitigation, net-energy generation, and nutrients-enhancing integrated configurations, such as forward osmosis (FO), membrane distillation (MD), bioelectrochemical systems (BES), membrane photobioreactor (MPBR), and partial nitrification-anammox (PN/A). In addition, we highlight the essential role of AnMBR in advancing the circular economy and propose ideas for the water-energy-climate nexus. While AnMBR has made significant progress, challenges, such as fouling and cost-effectiveness persist. Overall, the use of novel configurations and energy recovery strategies can further improve the sustainability and efficiency of AnMBR systems, making them a promising technology for future sustainable municipal wastewater treatment.

Mini critical review: Membrane fouling control in membrane bioreactors by microalgae

Membrane bioreactors (MBRs) hold significant promise for wastewater treatment, yet the persistent challenge of membrane fouling impedes their practical application. One promising solution lies in the synergy between microalgae and bacteria, offering efficient nutrient removal, reduced energy consumption, and potential mitigation of extracellular polymeric substances (EPS) concentrations. Inoculating microalgae presents a promising avenue to address membrane fouling in MBRs. This review marks the first exploration of utilizing microalgae for membrane fouling control in MBR systems. The review begins with a comprehensive overview of the evolution and distinctive traits of microalgae-MBRs. It goes further insight into the performance and underlying mechanisms facilitating the reduction of membrane fouling through microalgae intervention. Moreover, the review not only identifies the challenges inherent in employing microalgae for membrane fouling control in MBRs but also illuminates prospective pathways for future advancement in this burgeoning field.

Development of a novel membrane-based quorum-quenching microbial isolator for biofouling control: Process performance and microbial mechanism

Quorum quenching (QQ) can mitigate biofouling in membrane bioreactors (MBRs) by inhibiting cell-to-cell communication. However, it is difficult to maintain long-term QQ activity. Here, a novel microbial isolator composed of tubular microfiltration membranes was developed to separate QQ bacteria (Rhodococcus sp. BH4) from sludge. The time to reach a transmembrane pressure of 50 kPa was delayed by 69.55 % (p = 0.002, Student's t test) in MBR with QQ microbial isolator (MBR-Q), compared to that in the control MBR (MBR-C) during stable operation. The concentration of proteins in the extracellular polymeric substances of sludge was reduced by 20.61 % in MBR-Q relative to MBR-C. The results of the bacterial community analyses indicated less enrichment of fouling-associated bacteria (e.g., Acinetobacter) but a higher abundance of QQ enzymes in MBR-Q than in MBR-C. This environmentally friendly technique can decrease the cleaning frequency and increase the membrane lifespan, thus improving the sustainability of MBR technology.

Elimination of Pathogen Biofilms via Postbiotics from Lactic Acid Bacteria: A Promising Method in Food and Biomedicine

Pathogenic biofilms provide a naturally favorable barrier for microbial growth and are closely related to the virulence of pathogens. Postbiotics from lactic acid bacteria (LAB) are secondary metabolites and cellular components obtained by inactivation of fermentation broth; they have a certain inhibitory effect on all stages of pathogen biofilms. Postbiotics from LAB have drawn attention because of their high stability, safety dose parameters, and long storage period, which give them a broad application prospect in the fields of food and medicine. The mechanisms of eliminating pathogen biofilms via postbiotics from LAB mainly affect the surface adhesion, self-aggregation, virulence, and QS of pathogens influencing interspecific and intraspecific communication. However, there are some factors (preparation process and lack of target) which can limit the antibiofilm impact of postbiotics. Therefore, by using a delivery carrier and optimizing process parameters, the effect of interfering factors can be eliminated. This review summarizes the concept and characteristics of postbiotics from LAB, focusing on their preparation technology and antibiofilm effect, and the applications and limitations of postbiotics in food processing and clinical treatment are also discussed.

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.

Treatment of volatile organic compounds and other waste gases using membrane biofilm reactors: A review on recent advancements and challenges

This article provides a comprehensive review of membrane biofilm reactors for waste gas (MBRWG) treatment, focusing on studies conducted since 2000. The first section discusses the membrane materials, structure, and mass transfer mechanism employed in MBRWG. The concept of a partial counter-diffusion biofilm in MBRWG is introduced, with identification of the most metabolically active region. Subsequently, the effectiveness of these biofilm reactors in treating single and mixed pollutants is examined. The phenomenon of membrane fouling in MBRWG is characterized, alongside an analysis of contributory factors. Furthermore, a comparison is made between membrane biofilm reactors and conventional biological treatment technologies, highlighting their respective advantages and disadvantages. It is evident that the treatment of hydrophobic gases and their resistance to volatility warrant further investigation. In addition, the emergence of the smart industry and its integration with other processes have opened up new opportunities for the utilization of MBRWG. Overcoming membrane fouling and developing stable and cost-effective membrane materials are essential factors for successful engineering applications of MBRWG. Moreover, it is worth exploring the mechanisms of co-metabolism in MBRWG and the potential for altering biofilm community structures.

Potential role of AgNPs within wastewater in deteriorating sludge floc structure and settleability during activated sludge process: Filamentous bacteria and quorum sensing

Excellent sludge floc structure and settleability are essential to maintain the process stability and excellent effluent quality during the activated sludge process. The underlying effect of silver nanoparticles (AgNPs) within wastewater on sludge floc structure and settleability is still unclear. The potential role of AgNPs in promoting filamentous bacterial proliferation and deteriorating sludge floc structure and settleability based on quorum sensing (QS) were investigated in this study. The results indicated that N-acyl homoserine lactose (AHL) concentration sharply increased from 23.56 to 108.41 ng/g VSS in the sequencing batch reactor with 1 mg/L AgNPs. AgNPs strengthened communication between filamentous bacteria, which triggered the filamentous bacterial QS system involving the synthetic gene hdtS and sensing genes traR and lasR. Filamentous bacterial proliferation was promoted by the triggered QS via positively regulating its cell cycle progression including chromosomal replication and divisome formation. In addition, extracellular protein production was obviously increased from 43.56 to 97.91 mg/g VSS through QS by regulating arginine and tyrosine secretion during filamentous bacterial proliferation under 1 mg/L AgNPs condition, which led to an increase in the negative charge and hydrophily at the cell surface. AgNPs resulted in an obvious increase in the surface energy barrier (WT) between bacteria. The change in the physicochemical properties of extracellular polymeric substance (EPS) induced by QS among filamentous bacteria obviously inhibited bacterial aggregation between filamentous bacteria and floc-forming bacteria under AgNPs condition, thus resulting in serious deterioration of the sludge floc structure and settleability. This study provided new insights into the microcosmic mechanism for the effect of AgNPs on sludge floc structure and settleability.

Role of Nano-Fe3O4 for enhancing nitrate removal in microbial electrolytic cells: Characterizations and microbial patterns of cathodic biofilm

Conductive magnetite nanoparticle (Nano-Fe3O4) can facilitate numerous biological reduction reactions as an outstanding electron mediator for electron transfer. The positive role of Nano-Fe3O4 for nitrate removal has gradually gained attention recent years, however, it has not been clarified for the persistence of the promoting effect under different concentrations addition. Performance of nitrogen removal and characteristics of cathodic biofilm were evaluated in this study after Nano-Fe3O4 addition with gradient concentration of 100∼500 mg L-1 in microbial electrolytic cells (MEC). Our study illustrated that the optimal concentration was 200 mg L-1 as the removal rate of nitrate increased by 24.76% and the removal rate of total dissolved nitrogen by 29.72%. At the optimal concentration, Nano-Fe3O4 increased cathodic biofilm DNA concentration by 61.04%, enhanced electron transport system activity, enriched iron redox bacteria, denitrifying bacteria and genes, as well as increased extracellular polymeric substances (EPS) amount, especially the protein content of soluble-EPS. However, promoting effect on nitrate removal was not visible in high concentration (500 mg L-1) addition, its electron transport system activity and EPS content were even declined. XPS results indicated that high concentration of Nano-Fe3O4 may reduce the availability of electrons to cathodic biofilm by competing for electrons, which inhibit nitrate removal.

Bioelectrochemical anaerobic membrane bioreactor enables high methane production from methanolic wastewater: Roles of microbial ecology and microstructural integrity of anaerobic biomass

The disintegration of anaerobic sludge and blockage of membrane pores has impeded the practical application of anaerobic membrane bioreactor (AnMBR) in treating methanolic wastewater. In this study, bioelectrochemical system (BES) was integrated into AnMBR to alleviate sludge dispersion and membrane fouling as well as enhance bioconversion of methanol. Bioelectrochemical regulation effect induced by BES enhanced methane production rate from 4.94 ± 0.52 to 5.39 ± 0.37 L/Lreactor/d by accelerating the enrichment of electroactive microorganisms and the agglomeration of anaerobic sludge via the adhesive and chemical bonding force. 16 S rRNA gene high-throughput sequencing demonstrated that bioelectrochemical stimulation had modified the metabolic pathways by regulating the key functional microbial communities. Methanogenesis via the common methylotrophic Methanomethylovorans was partially substituted by the hydrogenotrophic Candidatus_Methanofastidiosum, etc. The metabolic behaviors of methanol are bioelectrochemistry-dependent, and controlling external voltage is thus an effective strategy for ensuring robust electron transfer, low membrane fouling, and long-term process stability.

New insight into the irreversible membrane fouling in different pore-sized ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater treatment

Despite great achievements in ceramic membrane bioreactor applications, membrane fouling, which decreases the permeability and separation performance of bioreactors and is associated with increased operational costs and energy consumption, remains a problem. The aim of this study was to expand our understanding of the fouling behavior in the long-term performance of ultrafiltration ceramic membrane bioreactors (UCMBRs) for high-strength textile wastewater reclamation. Using real textile wastewater effluent, the effects of ultrafiltration (UF) membrane pore sizes, cleaning strategies, and foulant distribution were systematically evaluated over more than three months of continuous operation. The results showed that UCMBR system achieved chemical oxygen demand and total nitrogen removal efficiencies as high as 91-95% and 39-43%, respectively. The high PN concentration can easily increase the viscosity of mixed liquor samples, contributing to a fouling layer on the membrane surface. In addition, the fouling layer formed on the surface of small-pore-sized ceramic UF membranes was not completely reversible but was difficult to eliminate by simple physical cleaning. Soluble extracellular polymeric substances, especially proteins and low molecular weight neutrals, remained, resulting in irreversible fouling on the UF membrane. However, saturated CO₂ backwash showed great potential for enhancing the system through efficient fouling control without using environmentally unfriendly cleaning chemicals. The cake-intermediate and complete-standard models were suitable for explaining the fouling mechanism in the large- and small-pore-sized UF membranes, respectively.

Impact of sandwich-type composite anodic membrane on membrane fouling and methane recovery from sewage sludge and food waste via electrochemical anaerobic membrane bioreactor

Membrane fouling presents a big challenge for the real-world implementation of anaerobic membrane bioreactors (AnMBRs) in digesting high-solid biowastes. In this study, an electrochemical anaerobic membrane bioreactor (EC-AnMBR) with a novel sandwich-type composite anodic membrane was designed and constructed for controlling membrane fouling whilst improving the energy recovery. The results showed that EC-AnMBR produced a higher methane yield of 358.5 ± 74.8 mL/d, rising by 12.8% compared to the AnMBR without applied voltage. Integration of composite anodic membrane induced a stable membrane flux and low transmembrane pressure through forming an anodic biofilm while total coliforms removal reached 97.9%. The microbial community analysis further provided compelling evidence that EC-AnMBR enriched the relative abundance of hydrolyzing (Chryseobacterium 2.6%) bacteria and methane-producing (Methanobacterium 32.8%) archaea. These findings offered new insights into anti-biofouling performance and provided significant implications for municipal organic waste treatment and energy recovery in the new EC-AnMBR.

Effects of High Pharmaceutical Concentrations in Domestic Wastewater on Membrane Bioreactor Treatment Systems: Performance and Microbial Community

Despite pharmaceuticals being widely detected in water-bodies worldwide, what remain unclear are the effects of high pharmaceutical concentrations on the treatment efficiency of biological wastewater treatment processes, such as membrane bioreactor (MBR) systems. This study investigated the efficiency of MBR technology in the treatment of synthetic wastewater containing a mixture of five typical pharmaceuticals (ofloxacin, sulfamethoxazole, sulfamethylthiadiazole, carbamazepine and naproxen) with a total concentration of 500 µg/L. Both the control MBR (MBRc) without pharmaceutical dosing and the MBR operated with high influent pharmaceutical concentrations (MBRe) were operated under room temperature with the same hydraulic retention time of 11 h and the same sludge retention time of 30 d. The removal efficiency rates of total nitrogen and total phosphorus were 83.2% vs. 90.1% and 72.6% vs. 57.8% in the MBRc vs. MBRe systems, and both MBRs achieved >98% removal of organics for a 180-day period. The floc size decreased, and membrane fouling became more severe in the MBRe system. Microbial diversity increased in the MBRe system and the relative abundances of functional microbe differed between the two MBRs. Furthermore, the total relative abundances of genes involved in glycolysis, assimilating nitrate reduction and nitrification processes increased in the MBRe system, which could account for the higher organics and nitrogen removal performance. This work provides insights for MBR operation in wastewater treatment with high pharmaceutical concentrations.

Existing Filtration Treatment on Drinking Water Process and Concerns Issues

Water is one of the main sources of life's survival. It is mandatory to have good-quality water, especially for drinking. Many types of available filtration treatment can produce high-quality drinking water. As a result, it is intriguing to determine which treatment is the best. This paper provides a review of available filtration technology specifically for drinking water treatment, including both conventional and advanced treatments, while focusing on membrane filtration treatment. This review covers the concerns that usually exist in membrane filtration treatment, namely membrane fouling. Here, the parameters that influence fouling are identified. This paper also discusses the different ways to handle fouling, either based on prevention, prediction, or control automation. According to the findings, the most common treatment for fouling was prevention. However, this treatment required the use of chemical agents, which will eventually affect human health. The prediction process was usually used to circumvent the process of fouling development. Based on our reviews up to now, there are a limited number of researchers who study membrane fouling control based on automation. Frequently, the treatment method and control strategy are determined individually.

Bioaugmentation with an aerobic denitrifying bacterium with quorum quenching activity for improved nitrogen removal and reduced membrane fouling in anoxic/oxic membrane bioreactor

In this study, an aerobic denitrifying bacterium with quorum quenching activity, Acinetobacter sp. WZL728, was inoculated into the anoxic/oxic membrane bioreactor (A/O-MBR) to study its effects on A/O-MBR performance. The pollutant removal and membrane fouling between A/O-MBR with WZL728 (EMBR) and A/O-MBR without WZL728 (CMBR) were compared. WZL728 increased the total nitrogen removal efficiency from 75.05% in CMBR to 91.03% in EMBR and extended the filtration cycle from 5.44 days in CMBR to 9.57 days in EMBR, which indicated that WZL728 improved the pollutant removal performance and mitigated membrane fouling of A/O-MBR. The concentration of N-acyl-homoserine lactones in the biocake of EMBR (EMBRB) was 11.23% of that in the biocake of CMBR (CMBRB). The content of extracellular polymeric substances (EPS) in EMBRB was 69.00% of that in CMBRB. The abundance of bacteria associated with EPS secretion (Alpthaproteobacteria) decreased and the abundance of bacteria associated with EPS degradation (Clostridia) increased in EMBRB. Valine, alanine and uridine diphosphate-N-acetylgalactosamine associated with protein and polysaccharide synthesis were significantly lower in EMBRB than those in CMBRB, which revealed the reason for the decrease of protein and polysaccharide content of EPS within EMBRB. This study provides useful information for improving A/O-MBR performance by probiotics.

Mechanism of HMBR in Reducing Membrane Fouling under Different SRT: Effect of Sludge Load on Microbial Properties

Extracellular polymeric substances (EPS) are the main causative agents of membrane fouling, and the use of a hybrid membrane bioreactor (HMBR) can mitigate this by reducing the EPS content. Four bench scale sets of HMBRs were used simultaneously to treat domestic wastewater. The effect of sludge retention times (SRT) on membrane fouling in HMBRs and the underlying mechanism were investigated by comparing and analyzing the changes in sludge load, microbial characteristics, EPS distribution characteristics, and transmembrane pressure under different SRTs. Results revealed that, among the four SRTs (10 d, 20 d, 30 d, and 60 d), the best removal rates of chemical oxygen demand and total nitrogen were observed for an SRT of 30 d, with average removal rates of 95.0% and 57.1%, respectively. The best results for ammonia nitrogen and total phosphorus removal were observed at an SRT of 20 d, with average removal rates of 84.3% and 99.5%, respectively. SRT can affect sludge load by altering the biomass, which significantly impacts the microbial communities. The highest microbial diversity was observed at an SRT of 30 d (with a BOD sludge load of 0.0310 kg/kg∙d), with Sphingobacteriales exhibiting the highest relative abundance at 19.6%. At this SRT setting, the microorganisms produced the least amount of soluble EPS and loosely bond EPS by metabolism, 3.41 mg/g and 4.52 mg/g, respectively. Owing to the reduced EPS content, membrane fouling was effectively controlled and the membrane module working cycle was effectively enhanced up to 99 d, the longest duration among the four SRTs.

Study on the performance and mechanism of bio-electrochemical system to mitigate membrane fouling in bioreactors

To alleviate membrane fouling, a membrane of the membrane bioreactor was directly used as the anode of the bio-electrochemical system. On the 14th day, the control group had blocked, while the experimental group with a current of 0.44 mA, the increase in ΔTMP was only 2.2 kPa. The polysaccharide and protein concentrations in the open-circuit group were 4.2 and 2.9 times higher than those in the closed-circuit group, respectively. Three-dimensional fluorescence spectroscopy and gas chromatography mass spectrometry showed that most of the deposition in the control group contained high-molecular-weight compounds, especially long-chain ester derivatives, phenols, and complex hydrocarbons, whereas the experimental group was the opposite. Therefore, current (electrons) can change the composition of the cake layer. High-throughput sequencing indicated that a significantly higher abundance of electroactive microorganisms on the experimental than control group. Two-dimensional correlation spectroscopy showed that electrons promote the degradation of polysaccharides, thereby alleviating membrane fouling.

Nanomaterials in membrane bioreactors: Recent progresses, challenges, and potentials

The use of nanomaterials (NMs) in the fabrication and modification of membranes as well as the coupling of nanomaterial-based processes with membrane processes have been attracted many researchers today. The NMs due to a wide range of types, different chemistry, the possibility of various kinds of functionality, different properties like antibacterial activity, hydrophilicity, and large surface area were applied to enhance the membrane properties. In the membrane bioreactors (MBRs) as a highly successful process of membrane technology in wastewater treatment, the NMs have been applied for improving the efficiency of MBR process. This review assessed the application of NMs both as the modifiers of membrane and as the effective part of hybrid techniques with MBR system for wastewater treatment. The efficiency of NMs blended membranes in the MBR process has been reviewed in terms of antifouling and antibacterial improvement and removal performance of the pollutants. Novel kinds of NMs were recognized and discussed based on their properties and advantages. The NMs-based photocatalytic and electrochemical processes integrated with MBR were reviewed with their benefits and drawbacks. In addition, the effect of the presence of mobilized NPs in the sludge on MBR performance was surveyed. As a result of this review, it can be concluded that nanomaterials generally improve MBR performance. The high flux and antifouling properties can be obtained by adding nanomaterials with hydrophilic and antibacterial properties to the membrane, and further studies are required for photocatalytic NMs applications. In addition, this review shows that the low amounts of NMs in the membrane structure could have an effective influence on the MBR process. Besides, since many studies in the literature are carried out at the laboratory scale, it is thought that pilot and real-scale studies should be carried out to obtain more reliable data.

Effects of polysaccharides' molecular structure on membrane fouling and the related mechanisms

Fouling behaviors of polysaccharides vary with their structure, while the mechanisms underlying this phenomenon remain unexplored. This work was carried out to explore the thermodynamic fouling mechanisms of polysaccharides with different structure. Carrageenan and xanthan gum were selected as the model polysaccharides with structure of straight and branch chains, respectively. Batch filtration experiments showed that xanthan gum solution corresponded to a more rapid flux decline trend, and specific filtration resistance (SFR) of xanthan gum (2.32 × 10¹⁵ m^-1 kg^-1) was over 10 times than that of carrageenan (2.21 × 10¹⁴ m^-1 kg^-1). It was found that, xanthan gum possessed a more disordered structure and a rather higher viscosity (15.03 mPa·s V.S. 1.98 mPa·s for carrageenan). Calculation of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed higher adhesion energy of xanthan gum (-42.82 my m^-2 V.S. -23.26 mJ m^-2 for carrageenan). Scanning electron microscopy (SEM) analyses showed that xanthan gum gel layer had a more homogenous structure and rigid polymer backbone, indicating better mixing with water to form a gel. As verified by heating experiments, such a structure tended to contain more bound water. According to this information, Flory-Huggins lattice theory was introduced to build a bridge between polymeric structure and SFR. It was revealed that branch structure corresponded to higher chemical potential change during gel layer formation, and higher ability to carry bound water, resulting in higher filtration resistance during filtration process. This work revealed the fundamental thermodynamic mechanism of membrane fouling caused by polysaccharides with different structure, deepening understanding of membrane fouling.