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• The FO-MSTD process can simultaneously achieve thickening and digestion of WAS. • HRT affected the swift thickening or profound digestion of sludge in the FO-MSTD. • 1 M NaCl draw solution showcased enhanced thickening and digestion capabilities. • The FO-MSTD sequential experience fully aerobic and local anaerobic digestion. • DO change led to microbial community transformation and the two-stage digestion. This study delved into the efficacy of sludge digestion and the mechanisms involved in sludge destruction during the implementation of forward osmosis process for sludge thickening and digestion (FO-MSTD). Utilizing a lab-scale FO membrane reactor for the thickening and digestion of waste activated sludge (WAS), the investigation explored the effects of sludge thickening and digestion in FO-MSTD processes using draw solutions of varying concentrations. The findings underscored the significance of hydraulic retention time (HRT) as a pivotal parameter influencing the swift thickening or profound digestion of sludge. Consequently, tailoring the HRT to specific processing objectives emerged as a key strategy for achieving desired treatment outcomes. In the investigation, the use of a 1 M NaCl draw solution in the FO-MSTD process showcased enhanced thickening and digestion capabilities. This specific setup raised the concentration of mixed liquor suspended solids (MLSS) to over 30 g/L and achieved a 42.7% digestion efficiency of mixed liquor volatile suspended solids (MLVSS) within an operational timeframe of 18 days. Furthermore, the research unveiled distinct stages in the sludge digestion process of the FO-MSTD system, characterized by fully aerobic digestion and aerobic-local anaerobic co-existing digestion. In the fully aerobic digestion stage, the sludge digestion rate exhibited a steady increase, leading to the breakdown of sludge floc structures and the release of a substantial amount of nutrients into the sludge supernatant. The predominant microorganisms during this stage were typical functional microorganisms found in wastewater treatment systems. Transitioning into the aerobic-local anaerobic co-existing digestion stage, both MLSS concentration and MLVSS digestion efficiency continued to rise, accompanied by a decreasing dissolved oxygen (DO) concentration. More organic matter was released into the supernatant, and sludge microbial flocs tended to reaggregate. The localized anaerobic environment within the FO-MSTD reactor fostered an increase in the relative abundance of bacteria with nitrogen and phosphorus removal functions, thereby positively impacting the mitigation of total nitrogen (TN) and total phosphorus (TP) concentrations in the sludge supernatant. The results of this research enhance comprehension of the advanced FO-MSTD technology in the treatment of WAS. [Display omitted] [ABSTRACT FROM AUTHOR]

Membrane-based technologies are increasingly used for water and wastewater treatment; however, biofouling, the adhesion of microorganisms to the membrane and subsequent formation of biofilm, remains a major obstacle in real applications. In this study, we report a novel method to fabricate a highly antibiofouling membrane by grafting quaternary ammonium compounds (QAC) onto a silica-decorated membrane via alkoxysilane polycondensation reaction. A controlled architecture was created by initially coating polydopamine (PDA)/polyethylenimine (PEI) layer, followed by in situ synthesizing a hydrophilic silica nanoparticle layer through silification reaction and then immobilizing QAC on the silica-decorated membrane to form an antibacterial surface. Although the QAC modified membrane exhibited comparable surface roughness, hydrophilicity and water permeability with the pristine membrane, the former displayed clear antibacterial effects against both Gram-positive and Gram-negative bacteria compared to the pristine membrane, i.e., ~93% and ~92% inhibition of S. aureus and E. coli , respectively. The excellent biofouling resistance imparted by the QAC layer was further confirmed by filtration experiment, showing lower water flux decline compared to the control. In addition, QAC-modified membranes exhibited high stability during repeated chemical cleaning cycles. This grafting protocol for QAC provides a new dimension to modify a wide range of water and wastewater treatment membranes for mitigating biofouling. [ABSTRACT FROM AUTHOR]

Efficient removal of toxic metals using low-pressure membrane processes from contaminated waters is an important but challenging task. In the present work, a conducting microfiltration membrane prepared by embedding a stainless steel mesh in the active layer of a polyvinylidene fluoride membrane is developed to remove Cu(II) ions from contaminated waters. Results showed that the conducting membrane had favorable electrochemical properties and stability as cathode. Batch tests showed that Cu(II) removal efficiency increased with the increase of voltages and leveled off with the further enhancement of electric field. The optimal voltages were determined to be 1.0 V and 2.0 V for the influent Cu(II) concentrations of 5 mg/L and 30 mg/L, respectively. X-ray photoelectron spectroscopy and X-ray diffraction results demonstrated the presence of Cu(0) and Cu(OH) 2 on the membrane surface. The removal mechanisms involved the intrinsic adsorption of membrane, electrosorption of membrane, adsorption of deposited layer, chemical precipitation of Cu(OH) 2 and deposition of Cu(0) which were aided by electrophoresis and electrochemical oxidation-reduction. Long-term tests showed that the major contributors for Cu(II) removal were the deposition of Cu(0) by electrochemical reduction-oxidation (47.3% ± 8.5%) and chemical precipitation (41.1% ± 0.2%), followed by electrosorption, adsorption by the fouling layer and membrane intrinsic sorption. [ABSTRACT FROM AUTHOR]

Widespread applications of membrane technology call for the development of antibiofouling membranes. For the in-situ membrane surface modification, the antibiofouling efficacy is always hindered by the inefficient presence of antimicrobial agents on membrane surface since they are blended with the polymers and distributed into the bulk membrane matrix. In this study, a compatible carbon carrier was adopted to assemble the quaternary ammonium compound (QAC@Carbon) for enhancing its surface segregation of polyvinylidene fluoride (PVDF) microfiltration membranes and simultaneously controlling QAC release, thereby improving the efficiency in mitigating biofouling. The results indicated that carbon carrier was capable of driving surface segregation of QAC without deteriorating the physicochemical properties of membranes. The QAC concentration on surface of the membrane modified by QAC@Carbon (MCQ) was 2.5-fold of membrane blended with QAC alone (MQ). Meanwhile, carbon carrier was capable of improving QAC stability in membrane matrix to ensure a lasting antibiofouling efficacy for engineering applications. Batch tests clearly exhibited that both MCQ and MQ had antibiofouling efficiency, while MCQ membrane under cross-flow filtration demonstrated better antibiofouling behaviors compared to MQ. This is mainly attributed to the reduced accumulation of microbial biomass and improved membrane physicochemical properties (higher permeability and porosity) compared to MQ. These findings highlight the potential of introducing QAC@Carbon into polymeric membranes as an effective strategy for fabricating antibiofouling membranes. [ABSTRACT FROM AUTHOR]

Antifouling membranes are of great importance to the applications of membrane technologies for water and wastewater treatment. Blending with hydrophilic polymer to provide enhanced antifouling properties for polymeric membranes is regarded as a facile method, while in preparation process the compatibility of membrane materials and blending agents may cause changes in casting solution stability, thus significantly affecting the physicochemical properties of modified membranes. However, the relationship of membrane materials compatibility and casting solution stabilities remains unanswered. In this study, for the first time, the relations of polymers compatibility and casting solution stability are disclosed in fabricating poly(vinylidene fluoride)/poly(vinyl alcohol) (PVDF/PVA) membranes. Results showed that there existed a strong correlation of compatibility with solution stability, and that the increase of incompatibility between PVDF and PVA resulted in deterioration of casting solution stability as revealed by multiple light scattering spectroscopy (MLiSSP). The critical Turbiscan stability index (TSI) was determined to be 4.3 based on the nexus of compatibility-stability (the enthalpy≤10×10 −3 cal/mol); otherwise, a TSI value higher than 4.3 might cause the deterioration in properties of formed membrane. Casting solution with 0.1 wt% PVA showed favorable stability and compatibility of blend polymers, and the formed membrane exhibited better intrinsic membrane properties and enhanced antifouling behavior. The obtained results highlight the nexus of compatibility-stability to be an important factor in fabricating polymeric membranes via addition of hydrophilic polymer. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) hold a great potential in preparing low-fouling and robust membranes for water and wastewater treatment due to their hierarchical structures and multiple functionalities. In this work, a facile approach was proposed for in-situ preparation of polyvinylidene fluoride (PVDF) and carbon nanosphere (CNS) MMMs (PVDF/CNS MMMs) during phase-inversion process for enhancing anti-fouling ability. This protocol, dipping casted films into various dosages of CNS sol as coagulation bath, allowed the formation of membranes and immobilization of CNS onto membrane surfaces simultaneously. Results showed that MMMs had enhanced surface physicochemical properties such as decreased contact angle and increased negatively-charged potential with the increase of CNS dosages from 0 mg/L to 400 mg/L. X-ray photoelectron spectroscopy (XPS) analysis and electrochemical measurements confirmed the immobilization of CNS on MMMs. However, the further increase of CNS dosage to 800 mg/L resulted in an evident decrease in porosity and permeability for MMMs. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory evaluation and batch filtration experiments demonstrated improved anti-fouling behaviors for MMMs, which was further confirmed by the long-term membrane bioreactor (MBR) tests, with the best anti-fouling performance for MMM at a CNS dosage of 400 mg/L. XPS analysis also showed that the immobilized CNS on membrane surfaces had satisfactory stability (no significant release) during the long-term operation in MBR. [ABSTRACT FROM AUTHOR]

Widespread applications of membrane technology call for the development of antifouling membranes, and preparation of mixed matrix membranes (MMMs) by mixing nanoparticles (NPs) into polymeric membrane matrix has attracted much attention. In this work, polyvinylidene fluoride (PVDF) MMMs were prepared by two TiO 2 sols with different NPs size (one from hydrolysis and condensation with an average size of 5 nm, and the other from dispersion of TiO 2 nanoparticles with a particle size of 21 nm), and comparison of their antifouling behaviours was conducted. Compared to the pristine PVDF membrane (N0) and membrane (N1) modified by TiO 2 sol from dispersion of TiO 2 NPs, the surface pore size, porosity and permeability of modified membrane (N2) by TiO 2 sol from hydrolysis and condensation were slightly decreased, while the hydrophilicity and the absolute value of Zeta potential were obviously improved. Moreover, the N2 membrane showed a higher surface energy barrier, smaller frequency shift in quartz crystal microbalance with dissipation monitoring, and higher relative flux than N1, indicating a better antifouling performance. The abundant hydroxyl groups and the increased Ti and O elements on the membrane surface accounted for the enhanced hydrophilicity and antifouling ability. Scanning electron microscope (SEM) images clearly show that TiO 2 particles were uniformly distributed for N2; however, the severe agglomeration and sedimentation were observed for N1. Multiple light scattering spectroscopy (MLiSSP) analysis showed that N2 casting solution had a higher stability as revealed by the negligible backscattering change, decreased demixing thickness and low turbiscan stability index (TSI) value. The different stability of casting solutions might result in the different NPs’ behaviours during membrane formation process, accounting for the discrepancy in the physicochemical properties and antifouling ability between N1 and N2 membranes. [ABSTRACT FROM AUTHOR]

While microalgae have been suggested as a promising substitute to conventional fossil fuels, their cost effective cultivation and harvesting constitutes a major challenge. In the work described here, a novel photosynthetic microbial fuel cell (PMFC) in which a stainless steel mesh with biofilm formed on it serves as both the cathode and filtration material has been developed. Results of this study reveal that, in addition to inducing oxygen reduction reactions under illumination, the biocathode is effective in preventing the washout of algae during continuous operation, resulting in retained biomass concentrations reaching 3.5–6.5 g L −1 . The maximum output current density reached ∼200 mA m −2 under irradiation, which is comparable with recent PMFC studies. Microbial diversity analyses targeting 16S and 18S rRNA genes indicated that the eukaryotic species belonging to the genus Chlorella was able to sustain its community dominance (>96%) over other competing species over the course of the studies. In the absence of catalysts such as Pt, a consortium of photosynthetic organisms including plant growth-promoting bacteria such as Azospirillum and Rhizobium were overrepresented in the biofilm, with these organisms most likely contributing to cathodic electron transfer. Energy flow analysis suggested that the PMFC system held the potential to achieve theoretical energy balance in simultaneous algae production and wastewater treatment. [ABSTRACT FROM AUTHOR]

Biofouling is one of the major obstacles to the widespread application of membrane technology in water and wastewater treatment, and use of anti-biofouling membrane materials is an effective approach to suppress biofouling. In this study, anti-biofouling polyvinylidene fluoride (PVDF) membranes were prepared by blending quaternary ammonium compound (QAC). Effects of QAC dosages on the physicochemical properties and anti-biofouling behaviours of the modified membranes were systematically investigated. The results showed that QAC was successfully present on the membrane surfaces, as revealed by X-ray photoelectron spectroscopy, Zeta potential and contact angle analyses. Anti-fouling tests using individual organic model foulants showed that the modified membranes had higher membrane fouling rate against organic matters, which is consistent with the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. In contrast, the modified membranes demonstrated evident anti-bacterial behaviours when individual model bacteria were used, which cannot be evaluated by this theory. Interestingly, the modified membrane showed a clear anti-fouling activity in a membrane bioreactor (the sludge mixture contained both organic foulant and microorganisms), suggesting its concurrent efficiency in controlling fouling induced by both organic matters and bacteria. This might be attributed to the contact-killing effects of QAC and the dual interactions between bacteria and organic foulants in the mixed liquor of membrane bioreactor. The study offers an effective way to enhance membrane anti-biofouling ability through the addition of antibacterial agent QAC. [ABSTRACT FROM AUTHOR]

Sodium hypochlorite (NaClO) is a commonly used reagent for membrane cleaning in membrane bioreactors (MBRs), while it, being a kind of disinfectant (oxidant), may impair viability of microbes or even totally inactivate them upon its diffusion into mixed liquor during membrane cleaning. In this study, we systematically examine the effects of NaClO on microorganisms in terms of microbial cell integrity, metabolism behaviours (key enzymes), and intracellular reactive oxygen species (ROS) under various NaClO concentrations. Different proportions of microbial cells in activated sludge were damaged within several minutes dependent on NaClO dosages (5–50 mg/g-SS), and correspondingly organic matters were released to bulk solution. Inhibition of key enzymes involved in organic matter biodegradation, nitrification and denitrification was observed in the presence of NaClO above 1 mg/g-SS, and thus organic matter and nitrogen removal efficiencies were decreased. It was also demonstrated that intracellular ROS production was increased with the NaClO dosage higher than 1 mg/g-SS, which likely induced further damage to microbial cells. [ABSTRACT FROM AUTHOR]

A novel and cost-effective electrochemical membrane bioreactor (EMBR) was proposed for low-strength wastewater treatment. In this system, influent organic matter could act as electron donor in the anode chamber and then denitrification was driven on the cathodes. During 270 days of operation, a positive and time-lag correlation was found between temperature and exoelectrogenesis process. At lower temperatures (<10∼15 °C), power production in the EMBR was negligible and therefore the integration did not improve the reactor performance. With the rebound of water temperatures over 15∼20 °C, efficient redox reactions were achieved in the EMBR, which subsequently resulted in sludge reduction (27.3% lower than the control MBR) and membrane fouling alleviation. Due to the capture of electrons that were then used at the cathode to drive the denitrification process, the total nitrogen removal efficiency of the EMBR averaged 78.2% at high temperatures, despite the decrease of organic loading rate of the feed for heterotrophic denitrification. Pyrosequencing revealed that the denitrifiers of Denitratisoma , Ottowia , Sulfuritalea and Thiobacillus were notably enriched in the cathode biofilm of the EMBR at high temperatures, and 6.05% of the sequences in the activated sludge were assigned into the denitrification related phylotypes, which was 65% higher compared to that of the control MBR. The enrichment of versatile nitrate/nitrite reducers could be conducive to the autotrophic and heterotrophic denitrification processes. Energy balance analysis also indicated that the total energy consumption of the EMBR was decreased by 20% compared to that of the CMBR (0.386 kWh/m 3 wastewater). Overall, the obtained results clearly demonstrate that this novel EMBR is capable of providing superior effluent quality, alleviating membrane fouling and incorporating into existing treatment facilities for improving the sustainability of wastewater treatment. [ABSTRACT FROM AUTHOR]

Recently, thin film composite (TFC) polyamide forward osmosis (FO) membranes have received attention for their potential water- and energy-related applications. TFC FO membranes have been shown to achieve both higher water flux and better solute rejection than cellulose triacetate (CTA) FO membranes. One of the major obstacles in widespread membrane use is the irreversible fouling that occurs during long-term filtration processes such as wastewater treatment. The development of proper chemical cleaning protocols for TFC FO membranes holds the key to achieving sustainable operation of FO processes. In this study, virgin membrane samples were exposed to chemical cleaning agents to determine their effects on membrane properties. In Addition, the water flux recovery efficiency of selected chemical agents was investigated by measuring the change in water flux following chemical cleaning of fouled membrane samples. Exposure of TFC membranes to commercial cleaning detergents (0.8% EDTA and 1% Alconox mixture) resulted in a dramatic increase in water and solute fluxes. Alkaline soaking led to a slight increase in the relative water and solute fluxes, while acid exposure led to a decrease in these fluxes. It was also found that the changes in membrane properties caused by Alconox exposure were irreversible, while the impacts of alkaline exposure were reversible, demonstrating that the Alconox exposure caused damage to TFC membranes. Various cleaning protocols were then developed and tested on wastewater-fouled TFC membranes. Results indicate that the use of 0.1% NaOH/0.1% sodium dodecyl sulfate (SDS) mixture cleaning followed by acid cleaning with either 2% citric acid or 0.5% HCl was the most effective cleaning strategy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Anaerobic dynamic membrane bioreactor was used for landfill leachate treatment. [•] 62.2% of COD removal efficiency was achieved at the influent COD 13,000mg/L. [•] Average methane yield was 0.34L/g CODremoved at OLR 4.87kg COD/(m3 d). [•] Archaeal community was stable while changes occurred in the bacterial community. [•] Genus Methanosarcina was identified as the dominant methanogen in the system. [Copyright &y& Elsevier]

Abstract: In membrane bioreactors (MBRs), soluble microbial products (SMPs) are a key factor in membrane fouling. In this study, the production, characteristics, and fouling potential of SMPs in the presence of zinc oxide (ZnO) nanoparticles (NPs) were investigated in order to clarify the impact of environmental nanoparticle pollutants (ENPs) on SMP behavior in MBRs. Batch tests showed that the SMP production was elevated as both NP concentration and exposure time increased. It was also found that the increase of SMPs was mainly due to the enhanced production of biomass-associated products (BAPs). Further examination of bound extracellular polymeric substances (EPS) demonstrated that the release of intracellular polymeric substances (IPS) occurred, which subsequently caused the production of BAPs in the presence of NPs. Chemical analysis and Fourier transform infrared (FTIR) spectroscopy confirmed the increased production of polysaccharides and proteins of SMPs while no significant changes were observed in EPS concentration and composition. Quartz crystal microbalance with dissipation monitoring (QCM-D) analysis indicated that the increase of adsorption abilities was attributed to the elevation of SMP concentration in presence of ZnO NPs rather than the change of fluidity. Filtration tests showed that membrane fouling worsened with elevated SMP and NP concentrations. Scanning electron microscopy (SEM) demonstrated that a slime gel layer with NPs scattered within was formed on membrane surfaces in high NP concentrations. Energy dispersive X-ray (EDX) microanalysis and X-ray mapping (XRM) indicated that more NPs were present during membrane surface fouling when ZnO concentrations were increased. The escalation of membrane fouling may not only be due to elevated SMP concentration under the presence of ZnO NPs, but also be due to the complex interactions with SMPs and subsequent NP aggregation in organic matters to form a dense fouling layer on membrane surfaces. [Copyright &y& Elsevier]

Abstract: Ultrasonication has been widely used for bound extracellular polymeric substance (EPS) extraction. However, the used ultrasonic power density is quite different in literature, which makes their results non-comparable. In this study, the effects of different ultrasonic power densities on extracting bound EPS were assessed via analyzing carbohydrates, proteins, humic acids and DNA. Experimental results proved that ultrasonication power density had a significant effect on loosely bound EPS (LB-EPS) extraction, and an appropriate power density termed critical power density was found to be 35W/10mL according to the variations of DNA which represented the intactness or damage of cell membrane. Nevertheless, carbohydrates, proteins and humic acids did not change obviously in tightly bound EPS (TB-EPS) until a very high power density was applied. The critical power density was determined as 65W/10mL for TB-EPS extraction. The results indicated that a critical power density should be used in order to extract maximal EPS but not to damage cell membrane intactness. [Copyright &y& Elsevier]

Abstract: Fouling caused by soluble microbial products (SMP) in membrane bioreactors (MBRs) is a critical problem, and a general understanding on SMP fouling behaviors has not been well established due to the complex interactions between SMP and membranes. In the present work, alginate solution was chosen as a model SMP foulant, and the effects of solution chemistry on the interaction energy between alginate and polymeric membranes were assessed by the extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. The results showed that the pH and ionic strength levels of the solution had significant effects on the solution properties and the interaction energy between alginate and membranes. The free energy of cohesion of alginate was maximal at pH 6.5 and ionic strength 10mM. Either increase or decrease of pH could lessen its cohesion free energy. Increase of ionic strength reduced the free energy of cohesion and made alginate solution more unstable and hydrophobic. Energy barrier between alginate and membranes was reduced under higher ionic strength and acidic condition, which was supported by fouling filtration experiments. It was also found that after the formation of initial fouling layer onto membranes, membrane fouling was controlled by cohesion free energy between approaching alginate and alginate-modified surfaces. This study demonstrated that XDLVO-model is sufficient to assess short-range membrane–foulant interactions and to predict SMP fouling in MBRs. [Copyright &y& Elsevier]

Highlights: [•] Alkaline pH values greatly enhanced disintegration and VFA production of MBR sludge. [•] The optimal condition for VFA production was under pH 11.0 and digestion time 4d. [•] High pH stimulated organic matter transfer from the inner to the outer of microbes. [•] Bound EPS were involved in organic matter transformation and VFA production. [ABSTRACT FROM AUTHOR]

In this study, an approach using influent COD/N ratio reduction was employed to improve process performance and nitrification efficiency in a membrane bioreactor (MBR). Besides sludge reduction, membrane fouling alleviation was observed during 330 d operation, which was attributed to the decreased production of soluble microbial products (SMP) and efficient carbon metabolism in the autotrophic nitrifying community. 454 high-throughput 16S rRNA gene pyrosequencing revealed that the diversity of microbial sequences was mainly determined by the feed characteristics, and that microbes could derive energy by switching to a more autotrophic metabolism to resist the environmental stress. The enrichment of nitrifiers in an MBR with a low COD/N-ratio demonstrated that this condition stimulated nitrification, and that the community distribution of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) resulted in faster nitrite uptake rates. Further, ammonia oxidation was the rate-limiting step during the full nitrification. [ABSTRACT FROM AUTHOR]

Abstract: 454 high-throughput pyrosequencing was employed to investigate microbial communities in bulk sludge (BS) and cake layer (CL) in an anaerobic dynamic membrane bioreactor (AnDMBR). Pyrosequencing produced 7402 and 7026 high-quality V1–V3 tags of the 16S rRNA-gene for the BS and CL samples, and the number of total OTUs estimated by Chao1 was 2906 (BS) and 2532 (CL) at a 3% distance. Phylogenetic spectrum and Venn diagrams revealed that the bacterial phyla in the two samples were nearly identical, and that the predominant microorganisms of them exhibited a high homology. Nevertheless, population distribution was different between them. Proteobacteria were the most dominant in the BS, while Bacteroidetes, Firmicutes and Spirochaetes were highly enriched in the CL, accounting for 57.6% of the total microbes. The main microbial groups in the CL were highly functionally organized. Bacteroides, Clostridia and Delta-proteobacteria were likely the pioneers for surface colonization on membranes in the AnDMBR. [Copyright &y& Elsevier]

Abstract: An upflow dynamic membrane separation (DMS) process was developed for organic matter recovery from low-strength municipal wastewater. During the operation of 300days, 81.6% of organic matter recovery rate on average was achieved at a high membrane flux of 60L/(m2 h). Chemical analyses and batch assays revealed that the recovered organic matter (ROM) had larger carbon to nitrogen mass ratio (C/N) and higher fermentation potential compared to the waste activated sludge. The transformation of the organic matter occurred in the DMS process, which was related to the polyferric sulfate (PFS) coagulation, anaerobic metabolism and membrane retention. The recovery of soluble organic matter was facilitated by the coagulation, and the transformation was observed in the sludge zone due to the anaerobic metabolism. Although the dynamic membrane was less efficient to remove the small molecules, it allowed a sound retention of particulate fractions and biopolymers, enabling a relatively high ROM recovery in the DMS process. Furthermore, the net operation expenditure for the novel wastewater treatment paradigm employing the DMS process was about 0.24kWh/m3, much lower than that (1.10kWh/m3) for the conventional membrane bioreactor treatment technology. These results indicated that the upflow DMS process was a promising approach for sustainable wastewater treatment. [Copyright &y& Elsevier]

Abstract: For understanding of the microbial community structure and composition under different aeration intensities, 454 high-throughput pyrosequencing was applied to analyze the 16S rRNA gene of bacteria in two submerged membrane bioreactors (MBRs) under low (RL) and high aeration (RH) conditions. In total, 7818 (RL) and 9353 (RH) high-quality reads were obtained, and 1230 (RL) and 924 (RH) operational taxonomic units (OTUs) were generated at 3% cutoff level, respectively. 454 pyrosequencing could also reveal the minority bacteria that were hardly detected by the conventional molecular methods. Although the core populations were shared with highly functional organization (>80%), clear differences between the samples in the two MBRs were revealed by richness–diversity indicators and Venn analyses. Notably, microbial diversity was decreased under high aeration condition, and the evolution of the populations was observed mainly in the shared OTUs. Moreover, specific comparison down to the class and genus level showed that the relative abundances of β-Proteobacteria and γ-Proteobacteria in the RH community were respectively decreased by 41.5% and 66.6%, consistent with the observed membrane fouling mitigation during the reactor operation. It was also found that Nitrospira and Nitrosomonas, being nitrite oxidizing bacteria (NOB) and ammonium oxidizing bacteria (AOB), were the dominant phylogenetic groups at the genus level of both reactors, and that the high ratio of NOB to AOB populations well supported the complete ammonium oxidation performance in the two reactors. Although some populations of NOB and AOB decreased with the increase of aeration intensity, the functional stability of the nitrification process was less affected, probably due to the low influent substrate concentration and the high level of functional organization. [Copyright &y& Elsevier]

Membrane fouling is one of the major obstacles for wide applications of MBRs. Over the past decade, the behaviors of colloidal and soluble substances have attracted much attention, and intensive efforts have been dedicated to the clarification of their role in membrane fouling. However, to date, the conclusions are often different and even controversial. The review is attempted to clarify their interrelations and to eliminate some confusions by reviewing the recent literature. The similarities and differences of those potential foulants are analyzed through comparing definitions, extraction methods, fouling indicators, and fouling behaviors. The implications of future research directions are also discussed in this paper. [ABSTRACT FROM PUBLISHER]

ABSTRACT In this study, D417 resin was characterized using scanning electron microscopy, Fourier transform infrared spectrometry and thermogravimetric analysis (TGA). Batchwise experiments were carried out to evaluate the thermodynamic and kinetic behaviors of the aqueous nitrate adsorption onto D417 resin. Response surface methodology (RSM) with Box-Behnken design (BBD) was employed to analyze the competition disturbance and matrix effects in terms of pH, organic matter concentration, contact time (CT) and salinity. Test results revealed that the resin was composed of the quaternary ammonium functional group and exhibited a considerable adsorption capacity of 23.46 to 22.81 mg·g−1 at the temperature ranging from 293.15 to 313.15 K. Mean free energy of adsorption calculated from the Dubinin-Radushkevich model showed that the adsorption was realized through ion-exchange pathway. Gibbs free energy change, enthalpy change and entropy change illustrated that the aqueous nitrate sorption was feasible and spontaneous. It was also found that the pseudo-second-order model could well describe the adsorption kinetics, and the intraparticle diffusion was the main rate-limiting step. RSM with BBD showed that CT and salinity had significant effects on aqueous nitrate adsorption, whereas the impacts of pH and dissolved organic matter were negligible. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Polyvinylidene fluoride (PVDF)-based microfiltration membranes applied in membrane bioreactor for wastewater treatment were prepared by immersion-precipitation method. The effects of different solvent compositions such as N-N dimethylformamide (DMF), N-N dimethylacetylamide (DMAC), triethyl phosphate (TEP), dimethyl sulphoxide (DMSO) and the mixed solvents on physicochemical characteristics of the final membranes were studied. The membrane permeability and fouling performance were assessed via pure water flux and critical flux experiments, respectively. Experimental results proved that the formation of the top-layer of the PVDF membranes prepared from different solvents was controlled by the equilibrium thermodynamics, whereas the sub-layer of those membranes was dominated by the diffusion rate of solvent-nonsolvent. Furthermore, the mixture of reagents facilitated the formation of porous top-layer and the finger-like pore except for DMF and TEP. There was no significant correlation found between the solvent compositions and the hydrophilicity of the membranes. However, the membranes prepared with DMSO as the solvent or part of the solvents exhibited more negative charge and greater permeability than the membranes without DMSO in the casting solution, and these properties were supposed to improve the critical flux value and mitigate the membrane fouling potential. [Copyright &y& Elsevier]

Abstract: In this study, polyacrylonitrile (PAN) flat-sheet membranes were prepared using phase inversion method for the wastewater treatment by membrane bioreactor (MBR). Twelve processing factors in the membrane preparation were investigated by Plackett–Burman design (PBD) in order to prepare high-performance membranes. Test results showed that none of the twelve processing factors had a significant effect on membrane pore size. The casting thickness, non-woven fabric type and casting speed were found to have substantial negative effects on the pure water flux values, and were identified as the significant factors determining the membrane pure water flux. It was also found that the non-woven fabric type, casting speed and casting thickness had significant positive effects on the fouling rate. Moreover, the model using membrane fouling rate as a response value was more credible and in good linear correlation within the tested range. [Copyright &y& Elsevier]

Abstract: Two distinct fouling layers, i.e., a gel layer and a sludge cake layer were observed in two MBRs operated under same constant fluxes but different aeration rates. The formation mechanisms and properties of the two fouling layers were systematically analyzed. It was found that the gel layer had lower porosity and higher specific resistance (α c ) compared to the sludge cake layer. The mean particle size of the gel layer was smaller than that of the sludge cake layer. Soluble microbial products (SMP) were found to be the major soluble organic materials in both fouling layers. Mg, Ca and Al were the major inorganic elements in solid state of the foulants, and the monovalent elements such as Na and K were mainly detectable in the soluble component of the foulants. SMP and tightly bound extracellular polymeric substances (EPS) of both fouling layers featured macromolecular characters. The molecular weight (MW) of gel foulants was larger than that of cake foulants. The loosely bound EPS and the fouling layers had very similar MW distribution profiles. Only the peaks associated with protein-like fluorophores were detectable in gel foulants, while besides the protein-like materials the humic acid-like substances were present in sludge cake foulants. [Copyright &y& Elsevier]

Abstract: Filtration performances and fouling behaviours of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) membranes were studied in a pilot-scale membrane bioreactor. Results showed that removable fouling was dominant for both membranes while irremovable fouling of the PVDF membrane was severer than that of the PAN membrane. The PAN membrane could reject more soluble microbial products (SMP) than the PVDF membrane due to different pore sizes. The PVDF membrane rejected more carbohydrates and fewer proteins than the PAN membrane. The mean particle size of surface foulants on the PAN membrane was smaller than that on the PVDF membrane. Gel filtration chromatography analysis indicated that the surface foulants of the PVDF membrane were comprised of larger molecular weight molecules than those of the PAN membrane. Three-dimensional excitation–emission matrix fluorescence spectroscopy analysis showed that soluble microbial by-product-like substances were the key factor causing membrane fouling of the two membranes. Hydrophobic humic-like substances played a more important role in forming irremovable fouling of the PAN membrane whereas protein-like substances were the main contributor to the irremovable fouling of the PVDF membrane. Hydrophobic fraction had the largest fouling propensity for the PAN membrane, while neutral hydrophilic fraction demonstrated the strongest fouling potential for the PVDF membrane. [Copyright &y& Elsevier]

Abstract: An anaerobic dynamic membrane bioreactor (AnDMBR) treating municipal wastewater with a high flux of 65L/(m2 h) was operated for 11 months. Organic and inorganic membrane foulants and bulk sludge characteristics were investigated using particle size distribution analyzer, three-dimensional excitation–emission matrix fluorescence spectroscopy and X-ray fluorescence analysis. The fouling layers exhibited a double-layered structure, i.e., a loosely bound outer layer and a tightly bound internal layer. Besides that, there were foulants in membrane chambers due to the imperfect interception effect of solid particles by the dynamic membranes. Compared with the bulk sludge, membrane foulants in the internal layer and in the membrane chamber were found to have more fine particles. The Dacron mesh with large pore size could not achieve a good rejection of soluble macromolecules, which led to low soluble microbial products and extracellular polymeric substances contents in the membrane fouling layers but high contents in the foulants in membrane chambers. Microorganism activity and abundance analyses showed that the membrane foulants had some different communities and lower activities compared with the bulk sludge, which was attributed to the suppressed mass transfer in the foulants. [Copyright &y& Elsevier]

Abstract: Membrane foulants including external foulants and internal foulants were systematically characterized in a full-scale membrane bioreactor (MBR) for supermarket wastewater treatment in this study. Three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analyzer were used to characterize the membrane foulants. The results indicated that the organic substances with fluorescence characteristics in both external and internal foulants were identified as protein-like substances and soluble microbial by-product-like materials by EEM technology. The GFC analysis exhibited that the external foulants had much broader distributions of molecular weight (MW) than the effluent and the internal foulants. Analyses of MW distributions suggest that the external and internal foulants were formed due to distinct fouling mechanisms. Besides proteins and polysaccharides, the oil substances were identified on the fouled membranes by the FT-IR analysis. SEM and EDX analyses indicated that the foulants covering the membrane surfaces comprised not only organic substances but also inorganic elements including Mg, Ca, Na, Al, K, and Si. [Copyright &y& Elsevier]

Abstract: An anaerobic dynamic membrane bioreactor with a high flux of 65L/(m2 h) was used to treat municipal wastewater. Particle size distribution, scanning electron microscopy, gel filtration chromatography (GFC), and three-dimensional excitation–emission matrix (EEM) were used to investigate the components of the cake layer formed on the membrane surface and the interception effect of the dynamic membrane. Test results showed that the dynamic membrane was formed by suspended solids (SS) in the settling zone and the soluble contents such as soluble microbial products (SMP) and extracellular polymeric substances (EPS). According to the index of SS/cake volume, the formation of dynamic membrane can be divided into three stages, i.e., the formation of separation layer, the stable growth stage, and the fouling stage. The accumulation rates of SS, SMP and EPS were of some differences at each stage. The secondary membrane was not entirely formed until the 7th day, and the dynamic membrane demonstrated a weak interception effect of dissolved organic matters after the 20th day. From EEM and GFC analyses of SMP in the cake layer, it was found that the fluorescence intensity ratio of Peak B/Peak A in the EEM fluorescence spectra had a similar changing tendency with large molecules of MW>5000kDa. They both increased with operation time before the 20th day, probably due to the soluble by-products secreted by the microorganism in the cake layer. [Copyright &y& Elsevier]

Abstract: Traditionally, the chemical cleaning is unanimously considered to be an effective means to restore membrane permeability. However, the chemical solutions can also be responsible for changes in membrane properties and thus affect the life-span of membranes. The aim of this study was to gain a better understanding of the effect of sodium hypochlorite cleaning solutions on the changes of physiochemical characteristics of microfiltration (MF) flat sheet membranes made from polyvinylidene fluoride (PVDF). A pilot-scale MBR was operated for 63 d and frequent and high dose sodium hypochlorite cleaning was carried out. The properties of the original and cleaned membranes were compared by pure water flux evaluation, contact angle measurement, mechanical testing, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra analysis. Effective removal of the foulant from the membrane surface resulted in more severe fouling. The pure water flux decayed faster with the extension of operation time and the membrane became more and more hydrophilic. The deterioration of ultimate tensile strength and the improvement of the ultimate elongation of membranes showed that membrane became more weak and flexible after hypochlorite cleaning. The results of ATR-FTIR indicated that the sodium hypochlorite cleaning had no vital damage to the chemical structure of PVDF membrane, but exerted impacts on its surface properties. [ABSTRACT FROM AUTHOR]

Abstract: Two membrane bioreactors (MBRs) with different operation conditions were employed to investigate the role of dissolved organic matter (DOM) in membrane fouling. DOM characteristics and their correlations with membrane fouling in the MBR systems were studied by using three-dimensional excitation-emission matrix (EEM) fluorescence technology, gel filtration chromatography (GFC) analysis, and column chromatographic method for DOM fractionation, etc. The three-dimensional EEM fluorescence spectroscopy analysis indicated that the fluorescence intensity of protein-like peaks in DOM samples collected from the MBR zones showed positive correlations with membrane fouling. The fluorescence spectra of membrane foulants also exhibited two protein-like peaks, confirming that proteins played an important role in membrane fouling. The DOM samples collected from MBR zones were fractionated into four components, i.e., hydrophobic (HPO), transphilic (TPI), charged hydrophilic (HPI-C) and neutral hydrophilic fractions (HPI-N). It was found that HPI-N was the most abundant fraction in all the samples, accounting for 42.0–48.9% of the total DOM. Test results also showed that HPI-N had the highest fouling potential, which could be attributed to the high molecular weight (MW) distribution and the high membrane rejection rate of macromolecules. [Copyright &y& Elsevier]

Abstract: A pilot-scale submerged membrane bioreactor (MBR) for the treatment of real municipal wastewater was operated in this study under various sludge retention time (SRT) in order to verify the correlations of fluorescent dissolved organic matter (DOM) with membrane fouling. The fluorescent DOM determined by three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy and the trans-membrane pressure (TMP) under different SRT operation were investigated, and the correlations between them were analyzed. The results showed that the variations of fluorescent DOM (Peaks B and C) in the sludge supernatants correlated well with the variations of EEM spectra signal of bound extracellular polymeric substances (EPS) even though they were different in nature, i.e., the bound EPS were found to be more non-biodegradable than DOM. The fluorescent intensity (FI) variations of Peaks A and B in the EEM spectra of DOM were closely related to the TMP increase rate (membrane fouling) in the MBR, suggesting that they might be used to monitor the DOM variations and to indicate MBR performance. Through the EEM spectra analysis, it was confirmed in this work that the DOM in the sludge supernatants was not only originated from the bound EPS but also from the influent wastewater. [Copyright &y& Elsevier]

Abstract: Two identical submerged membrane bioreactors (MBRs) for synthetic wastewater treatment were operated in parallel under different dissolved oxygen (DO) levels for over 3 months in this study. The digital biological microscopy, particle size distribution (PSD) analysis, gel filtration chromatography (GFC), three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, and column chromatographic method, etc. were used to identify the difference between bulking sludge (BS) caused by filamentous bacteria (low DO operation, about 0.4mg/L) and normal sludge (NS) (high DO operation, about 4.0mg/L) and to obtain a comprehensive insight into the behaviours of filamentous bacteria in MBRs. Test results showed that the MBR with bulking sludge (BS-MBR) exhibited a better filtration performance and a reduced membrane fouling compared to the MBR with normal sludge (NS-MBR). It was found that the mitigation of membrane fouling by the abundant filamentous bacteria in the BS-MBR could be attributed to the larger PSD, lower hydrophobic contents in SMP, and the retention effects of a special fouling layer induced by filamentous bacteria. [Copyright &y& Elsevier]

Abstract: Membrane foulants were systematically characterized in an anaerobic membrane bioreactor (AnMBR), in which non-woven fabric was used as the membrane material. In this study, three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analyzer were used to analyze the membrane foulants. The results indicated that the organic substances with fluorescence characteristics in the extracellular polymeric substances (EPS) extracted from the membrane foulants were identified as proteins and visible humic acid-like substances by EEM technology. The GFC analysis exhibited that the EPS had much broader distributions of molecular weight (MW) and a larger weight-average molecular weight (M w) compared with the influent wastewater and the effluent. Proteins and clay materials were also identified in the fouling layer by the FT-IR analysis. The examination by EDX demonstrated that Mg, Al, Ca, Si, and Fe were the major inorganic elements in the fouling cake. Furthermore, the results suggested that bridging between deposited biopolymers and inorganic compounds could enhance the compactness of fouling layer. During the operation of AnMBR, the protein-like and visible humic acid-like substances, which were main components of the organic matters with fluorescence characteristics in the influent, were partly removed. And the large MW organics (>4000Da) in the influent were partly metabolized into low MW organics by microorganisms combined with the separation function of the cake layer and the membrane pores. [Copyright &y& Elsevier]

Membrane bioreactor (MBR) has been deemed to be a promising technology for wastewater treatment and reclamation; however, the MBR filtration performance inevitably decreases with filtration time attributed to the deposition of soluble and particulate materials onto and into the membrane under the interactions between activated sludge components and the membrane. Cake layer formation on membrane surfaces has been a major challenge in the operation of MBRs under supra-critical flux operation, and/or caused by uneven distribution of aeration intensities, etc.; however, it was argued that a thin cake layer might improve filtration operation by some researchers. This paper provides a critical review on the formation mechanisms, properties, the role of sludge cake in membrane filtration, and the corresponding strategies of controlling cake fouling in MBRs. Drawbacks and benefits of the formation of sludge cake were also discussed in order to better understand the characteristics and role of sludge cake formation in MBRs. [ABSTRACT FROM AUTHOR]

Abstract: The distribution and transformation of molecular weight (MW) of organic matters in a pilot-scale submerged membrane bioreactor (MBR) and a conventional activated sludge (CAS) process was studied in order to better understand organic pollutant behaviours and removal mechanisms in the two processes. Gel filtration chromatography (GFC) images of the CAS process showed that the influent wastewater had relatively large MW molecules and a narrow MW distribution while the dissolved organic matters (DOM) in the anaerobic, anoxic, oxic basins and the effluent water demonstrated a broad MW distribution. MW distribution in the MBR system illustrated that the organic matters with high MW molecules were degraded into relatively low MW organic substances, whereas DOM in the oxic basin had a little part of high MW molecules produced by microorganisms during the metabolism of substrates. There is a lack of those high MW molecules in the effluent water due to the retention of the macromolecules by the membrane. Test results also showed that in both the CAS process and the MBR the majority of molecules in the influent wastewater with MW between 100kDa and 500kDa were mainly transformed into the molecules with MW between 10kDa and 100kDa. [Copyright &y& Elsevier]

A pilot-scale submerged membrane bioreactor (MBR) for real municipal wastewater treatment was operated for over one year in order to investigate extracellular polymeric substances (EPS) properties and their role in membrane fouling. The components and properties of bound EPS were examined by the evaluation of mean oxidation state (MOS) of organic carbons, Fourier transform infrared (FT-IR) spectroscopy, three-dimensional excitation¿emission matrix (EEM) fluorescence spectroscopy, and gel filtration chromatography (GFC), etc. Test results showed that MOS of organic carbons in the bound EPS was ranging from ¿0.14 to ¿0.51, and major components could be assessed as proteins and carbohydrates. FT-IR analysis confirmed the presence of proteins and carbohydrates in the bound EPS. The organic substances with fluorescence characteristics in the bound EPS were identified as proteins, visible humic acid-like substances and fulvic acid-like substances by EEM technology. GFC analysis demonstrated that EPS had part of higher MW molecules and a broader MW distribution than the influent wastewater. It was also found that a high shear stress imposed on mixed liquor could result in the release of EPS, which would in turn influence membrane fouling in MBRs. Bound EPS solution was observed to have a stronger potential of fouling than mixed liquor. During long-term operation of the MBR, bound EPS demonstrated positive correlations with membrane fouling while temperature was verified as a negative factor affecting EPS concentration. Compared to tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) showed more significant correlations with membrane fouling. This critical investigation would contribute towards a better understanding of the behavior, composition and fouling potential of EPS in MBR operation. [Copyright &y& Elsevier]

Three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy was employed to characterize dissolved organic matter (DOM) in a submerged membrane bioreactor (MBR). Three fluorescence peaks could be identified from the EEM fluorescence spectra of the DOM samples in the MBR. Two peaks were associated with the protein-like fluorophores, and the third was related to the visible humic acid-like fluorophores. Only two main peaks were observed in the EEM fluorescence spectra of the extracellular polymeric substance (EPS) samples, which were due to the fluorescence of protein-like and humic acid-like matters, respectively. However, the EEM fluorescence spectra of membrane foulants were observed to have three peaks. It was also found that the dominant fluorescence substances in membrane foulants were protein-like substances, which might be due to the retention of proteins in the DOM and/or EPS in the MBR by the fine pores of the membrane. Quantitative analysis of the fluorescence spectra including peak locations, fluorescence intensity, and different peak intensity ratios and the fluorescence regional integration (FRI) analysis were also carried out in order to better understand the similarities and differences among the EEM spectra of the DOM, EPS, and membrane foulant samples and to further provide an insight into membrane fouling caused by the fluorescence substances in the DOM in submerged MBRs. [Copyright &y& Elsevier]

Abstract: Membrane foulants and gel layer formed on membrane surfaces were systematically characterized in a submerged membrane bioreactor (MBR) under sub-critical flux operation. The evaluation of mean oxidation state (MOS) of organic carbons and Fourier transform infrared (FT-IR) spectroscopy demonstrated that membrane foulants in gel layer were comprised of not only extracellular polymeric substances (EPS) (proteins, polysaccharides, etc.) but also other kinds of organic substances. It was also found that fine particles in mixed liquor had a strong deposit tendency on the membrane surfaces, and membrane foulants had much smaller size than mixed liquor in the MBR by particle size distribution (PSD) analysis. Gel filtration chromatography (GFC) analysis showed that membrane foulants and soluble microbial products (SMP) had much broader distributions of molecular weight (MW) and a larger weight-average molecular weight (M w) compared with the influent wastewater and the membrane effluent. Scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analysis indicated that membrane surfaces were covered with compact gel layer which was formed by organic substances and inorganic elements such as Mg, Al, Fe, Ca, Si, etc. The organic foulants coupled the inorganic precipitation enhanced the formation of gel layer and thus caused membrane fouling in the MBR. [Copyright &y& Elsevier]

Abstract: In the past 15 years, remarkable progress has been achieved on the research and commercial applications of membrane bioreactor (MBR) technology in China. The objective of this paper is then to critically review the research achievements and to specifically present commercial applications of MBR in China. A total of 722 scientific papers published in peer-reviewed journals (600 Chinese papers and 122 English papers) written by Chinese authors from 1991 to 2006 and 254 full-scale MBR plants constructed in China were used as the analysis database. The number of articles published in journals together with organizations involved in MBR research saw a significant increase from 2001 to 2006, and much research progress was made during this period. From geographic distribution of these studies, it was found that the majority of the studies were carried out in North China, East China and North-East China. The research mainly focused on biomass separation MBR (BSMBR) with limited studies on extractive MBR (EMBR) and membrane aeration bioreactor (MABR), etc., and research contents included MBR configuration and type, membrane material and module, membrane fouling and control, characteristics of various wastewater treatment and other aspects like gas removal and microbial fermentation, etc. For commercial applications in China, a total of 254 MBR plants for municipal and industrial wastewater treatment were constructed by a lot of home-grown companies such as Tianjin Motimo Membrane Technology Co., Ltd. and Beijing Origin Water Technology Co., Ltd. and overseas-funded companies like Toray (Japan), Zenon (Canada), Mitsubishi-Rayon (Japan), etc. MBR plants with large treatment capacity will be built in future especially in North China due to the great need of water reclamation and reuse. Potential areas of MBR application include surface/drinking water treatment, gas diffusion and removal, membrane assisted fermentation for biological substance transformation and production, etc. [Copyright &y& Elsevier]

Abstract: Critical flux is an important concept in membrane bioreactor (MBR) process for wastewater treatment, and the study on it could enhance the understanding of MBR process and facilitate its application. In this study, the effects of various factors, such as sludge concentration, aeration intensity, soluble chemical oxygen demand (SCOD) of the mixed liquors, and measurement parameters including initial flux, step length and step height, and membrane properties including membrane materials and membrane history, on critical flux were critically investigated. Test results showed that the critical flux decreased with the increase of sludge concentration and it could be enhanced by improving aeration intensity. SCOD, which was used to indicate sludge characteristics, was found to have a negative effect on critical flux. It was also observed that the increase of step length or step height would lower the critical flux; however, the variations of initial fluxes did not clearly affect critical flux. In addition, membrane materials also had significant influences on critical flux, and membrane M3 had a higher critical flux value, which was more suitable for the application to the submerged MBR compared to M1 and M2 membranes. Membrane history was found to have negative impacts on membrane critical flux, and the critical flux decreased as the membrane operation prolonged. [Copyright &y& Elsevier]

To address global pollution caused by contaminants in water bodies, it is crucial to develop an efficient and environmentally friendly treatment process for wastewater from various industries. Advanced oxidation processes (AOPs) have proven to be highly effective in wastewater treatment due to their high oxidation efficacy and the absence of secondary pollutants. Different methods such as ozone, Fenton, electrochemical, photolysis, and sonolysis can be used in AOPs to degrade emerging pollutants that are resistant to conventional methods. In recent years, nanotechnology has emerged as a viable solution, with various nanomaterials being developed for wastewater treatment. Among them, copper‐based nanocatalysts have shown great potential in AOPs. This review focuses on the progress and mechanisms of copper‐based nanocatalysts in wastewater treatment via AOPs. It also discusses the challenges associated with oxidation, electrochemistry, Fenton, and photocatalysis in wastewater treatment processes. Copper‐based nanocatalysts can be modified to enhance their catalytic activity, selectivity, and stability, leading to improved performance in wastewater treatment. They have shown promising results in degrading pollutants like pharmaceuticals, pesticides, and dyes. However, the practical application of these nanocatalysts still faces challenges, including the high cost of synthesis, potential nanoparticle toxicity, and scalability issues. More research is needed to address these challenges and improve the utilization of copper‐based nanocatalysts in wastewater treatment. In addition, Cu‐based catalysts with magnetic properties offer the advantage of easy recovery and reusability in wastewater treatment. They can also be incorporated into catalytic membranes, forming efficient systems for recycling. Heterogeneous catalysts with diverse structures, including ternary or quaternary systems, are widely used. However, challenges remain in identifying suitable coupling pairs and understanding the complex processes involved in constructing heterogeneous interfaces without generating defects. Therefore, a thorough understanding of the catalyst's band structure is crucial for developing efficient heterogeneous structures. Furthermore, cost implications of synthesis methods and raw materials should be considered in the preparation of transition metal catalysts, and relevant cost analysis data is needed for optimizing the degradation of pollutants. In conclusion, copper‐based nanocatalysts hold great potential in AOPs for wastewater treatment. With their magnetic properties, Cu‐based catalysts offer the advantage of easy recovery and reusability. However, challenges such as high synthesis costs, nanoparticle toxicity, and scalability issues need to be addressed. Further research is needed to overcome these challenges and optimize the utilization of copper‐based nanocatalysts in wastewater treatment processes. [ABSTRACT FROM AUTHOR]

In this study, the different graphene derivatives, graphene oxide (GO), carboxylic acid‐modified graphene (G‐COOH), and amine‐modified graphene (G‐NH2), were used to prepare polyvinylidene fluoride (PVDF) composite membranes. The membrane modification performance was evaluated using the extended Derjaguin–Landau–Verwey–Overbeek theory and quartz crystal microbalance dissipation monitoring. The results show that the addition of low‐dose GO and G‐NH2 can improve membrane surface porosity and permeability. The hydrophilicity and electron donor monopolarity of PVDF/GO composite membranes were enhanced by adding more than 0.024 wt% GO, thus improving its antifouling ability. In addition, the enhancement of hydrophilicity, free energy of cohesion, and antifouling ability of composite membrane modified with G‐COOH and G‐NH2 was more significant compared with that of GO with the same dosage, which implies the important role of functional group in additives. This study provides new insights for the blending modification of PVDF membranes by systematically comparing the addition of graphene derivatives with different functional groups. Practitioner points: The comprehensive comparison of membrane modification with different graphene derivatives was investigated.The enhancement of hydrophilicity and antifouling ability of membranes modified with G‐COOH and G‐NH2 was more significant than that of GO.The free energy of cohesion of nanocomposite membrane was affected by the functional group of additives.G‐NH2 composite membrane had the best comprehensive performance with great hydrophilicity, permeability, and antifouling performance. [ABSTRACT FROM AUTHOR]

Membrane fouling is one of the major obstacles that hinder the widespread applications of anerobic membrane bioreactors (AnMBRs) for wastewater treatment. Due to the intrinsic complexity of membrane fouling, identifying critical fouling factors and predicting fouling behavior are of great significance in membrane fouling control. Herein, artificial intelligence (AI) algorithms and their modeling framework were developed to predict membrane fouling behaviors in AnMBRs. Operating parameters, biomass properties, and membrane characteristics were considered as input variables for membrane fouling prediction. The results of hyper-parameter optimization showed that the optimal architecture of artificial neural network (ANN) model for membrane fouling prediction was "14-9-6-1" while the best hyper-parameters of random forest (RF) model were n_trees = 1200 and n_features = 14. After hyper-parameter adjusting, RF had more robustness of predictive capabilities (R 2=0.906, mean squared error (MSE) = 0.061) for membrane fouling than the ANN model (R 2=0.800, MSE = 0.118). More importantly, the feature importance and Shapley additive explanations analysis indicated SMPp/SMPc (0.281) > EPSp/EPSc (0.110) > organic loading rate (0.106), which were the most critical factors affecting membrane fouling. Partial dependence plot analysis further verified the marginal and interaction effects of various input features on membrane fouling. The revealed partial dependence relationships of critical variables can provide theoretical reference for optimization of practical operation. Overall, this study established a novel AI-based approach for predicting membrane fouling and comprehensively understanding the complicated effects of various influencing factors on membrane fouling while overcoming the "black-box" nature of conventional models. [Display omitted] • AI-based algorithms accurately predicts and interprets membrane fouling in AnMBRs. • RF model (R 2=0.906) demonstrates better prediction capabilities than ANN model. • Interpretable analysis shows that SMPp/SMPc is the most critical fouling factor. • PDP analysis reveals the partial dependence relationships of contributing factors. [ABSTRACT FROM AUTHOR]

• AAMBR combining anaerobic acidification and MF membrane was firstly proposed. • AAMBR recovered organic matter in terms of VFAs from municipal wastewater. • FO concentrating municipal wastewater enhanced VFAs production of AAMBR. • FO process effectively concentrated VFAs and nutrients in AAMBR effluent. • FO-AAMBR-FO simultaneously recovered VFAs and struvite from municipal wastewater. In order to meet the demand of municipal wastewater for low-carbon treatment and resource recovery, a novel process of anaerobic acidification membrane bioreactor (AAMBR) assisted with a two-stage forward osmosis (FO) (FO-AAMBR-FO) was developed for simultaneously recovering organic matter and nutrients from municipal wastewater. The results indicated that the first FO process concentrated the municipal wastewater to one tenth of the initial volume. The corresponding chemical oxygen demand (COD), ammonia nitrogen (NH 4 +-N) and total phosphorus (TP) concentration reached up to 2800, 200 and 33 mg/L, respectively. Subsequently, the AAMBR was operated at pH value of 10 for treating the concentration of municipal wastewater, in which the organic matter was successfully converted to acetic acid and propionic acid with a total volatile fatty acids (VFAs) concentration of 1787 mg COD/L and a VFAs production efficiency of 62.36 % during 47 days of stable operation. After that, the NH 4 +-N and TP concentration in the effluent of the AAMBR were further concentrated to 175 and 36.7 mg/L, respectively, by the second FO process. The struvite was successfully recovered with NH 4 +-N and TP recovery rate of 94.53 % and 98.59 %, respectively. Correspondingly, the VFAs, NH 4 +-N and TP concentrations in the residual solution were 2905 mg COD/L, 11.8 and 7.92 mg/L, respectively, which could be used as the raw material for the synthesis of polyhydroxyalkanoate (PHA). Results reported here demonstrated that the FO-AAMBR-FO is a promising wastewater treatment technology for simultaneous recovery of organic matter (in form of VFAs) and nutrients (in form of struvite). [Display omitted] [ABSTRACT FROM AUTHOR]

Osmotically driven membrane processes (ODMPs) have gained renewed interests in recent years as an emerging separation/desalination process. However, fouling, specifically biofouling, is still an inevitable and crucial issue for long-term application of FO processes. Due to the limited studies on biofouling in ODMPs, the formation and control of biofouling are still not fully understood. This brief review focuses on the insights into the analysis techniques, formation mechanisms, and uniqueness of biofouling in FO processes. Furthermore, the control strategies of biofouling on FO membranes are highlighted and future perspectives are presented. [ABSTRACT FROM AUTHOR]

Quaternary ammonium compounds (QACs) are emerging contaminants with the extensive applications in a variety of fields. However, little is known about their potential impacts on activated sludge and performance of biological wastewater treatment processes. In this work, the effects of benzalkonium chloride (BAC, a kind of QACs) on acute and chronic responses of microorganisms and on MBR performance were systematically investigated. The results showed that a low concentration (0.5–2.0 mg BAC/g SS) caused no significant effects on activated sludge property. In contrast, an elevated concentration of BAC led to severer inhibition on activated sludge and key enzyme activity (e.g., dehydrogenase activity) in both short-term and long-term exposure, thus deteriorating the pollutant removal efficiency. Compared with the control MBR (R1) and the reactor with 0.5 mg/L BAC (R2), the removal efficiency of ammonia in R3 with 5.0 mg/L BAC at identical hydraulic retention time (4.3 h) and sludge retention time (30 d) was decreased, i.e., ammonium removal efficiency in R1∼R3 was 95.4 ± 6.1, 93.4 ± 8.1 and 89.3 ± 17.6%, respectively. Moreover, MBR tests showed that membrane fouling was aggravated in the presence of high-concentration BAC. Long-term exposure to BAC reduced microbial community diversity and enriched the BAC-resistant microbes. For instance, the abundance of Pseudomonas genus in R3 was increased from 0.02% to 14.9% with the increase of operation time. Microbial community structure was changed to resist the environmental stress induced by BAC during long-term exposure, thus decreasing the inhibition effects. [ABSTRACT FROM AUTHOR]

Sodium hypochlorite (NaOCl) is a widely used cleaning reagent for membrane separation processes to recover membrane permeability; however, the competitive interactions of different chlorine species with fouling layers have not been adequately elucidated. In this work, we investigated the pH-dependent diffusion of the active chlorine species and reactions involved in the consequent dissociation and/or destruction of the fouling layers. The hypochlorite conductivity and dynamic diffusion tests showed that an increase in pH facilitated the uneven and fast diffusion of active chlorine via relaxing the matrix structure of the fouling layer. Under the synergetic effects of oxidation, hydrolysis and hydraulic shearing, the enhanced diffusion resulted in an uneven but massive removal of the foulants rather than a layer-by-layer dissociation, leading to a higher membrane cleaning efficiency. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added into the cleaning solution to further validate the diffusion-dependent cleaning mechanisms. With a faster diffusion process aided by SDS, the cleaning efficiency was significantly improved. These findings provide new insight into the chemical cleaning mechanisms, which are of great importance to the optimisation of cleaning efficiency for various membrane-based processes. [ABSTRACT FROM AUTHOR]

Anaerobic osmotic membrane bioreactor (AnOMBR) has gained increasing interests in wastewater treatment owing to its simultaneous recovery of biogas and water. However, the forward osmosis (FO) membrane fouling was severe during a long-term operation of AnOMBRs. Here, we aim to recover the permeability of fouled FO membranes by chemical cleaning. Specifically speaking, an optimal chemical cleaning procedure was searched for fouled thin film composite polyamide FO (TFC-FO) membranes in a novel microfiltration (MF) assisted AnOMBR (AnMF-OMBR). The results indicated that citric acid, disodium ethylenediaminetetraacetate (EDTA-2Na), hydrochloric acid (HCl), sodium dodecyl sulfate (SDS) and sodium hydroxide (NaOH) had a low cleaning efficiency of less than 15%, while hydrogen peroxide (H 2 O 2 ) could effectively remove foulants from the TFC-FO membrane surface (almost 100%) through oxidizing the functional group of the organic foulants and disintegrating the colloids and microbe flocs into fine particles. Nevertheless, the damage of H 2 O 2 to the TFC-FO membrane was observed when a high cleaning concentration and a long duration were applied. In this case, the optimal cleaning conditions including cleaning concentration and time for fouled TFC-FO membranes were selected through confocal laser scanning microscope (CLSM) and scanning electron microscopy (SEM) images and the flux recovery rate. The results suggested that the optimal cleaning procedure for fouled TFC-FO membranes was use of 0.5% H 2 O 2 at 25 °C for 6 h, and after that, the cleaned TFC-FO membrane had the same performance as a virgin one including water flux and rejection for organic matters and phosphorus during the operation of AnMF-OMBR. [ABSTRACT FROM AUTHOR]