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What bacteria cause membrane biofouling in engineering practice? This is the fundamental question in the research on biofouling, which is the Achilles' heel of the reverse osmosis (RO) system. If this question is not addressed clearly, the subsequent research on mechanism interpretation and possible control technologies is questionable due to the lack of appropriate research objects. However, a uniform conclusion has not yet been given, as it varied considerably in different studies. Here, to better cope with RO membrane biofouling introduced by microbiomes, 46 genera of residual microorganisms that tend to adhere to the surface of RO membranes were summarized. Interestingly, disinfection-resistant bacteria (DRB) accounted for 75 % of those reported with high and medium frequency. From the perspective of frequency of occurrence, phylogenetic relationship, and co-occurrence network analysis of membrane-attached residual microorganisms, the fundamental characteristics were identified to recognize the priority bacteria in common. Further, a series of undesirable risks posed by DRB on the level of harmful genes transfer were highlighted. Correspondingly, feasible control strategies to effectively alleviate biofouling and their application in RO systems were discussed. This work identified priority species and their detrimental effects on RO membrane biofouling and provided new insights to solve the inevitable issue. [Display omitted] • Priority bacteria causing biofouling of RO membranes were identified at genera level. • The contribution and potential risks of DRB to biofouling were emphasized. • The enhanced transfer of harmful genes by DRB was discussed. • Corresponding control strategies against priority bacteria were proposed. [ABSTRACT FROM AUTHOR]

A novel approach is investigated for preventing biofouling of spacer filaments, which are an essential part of spiral-wound modules used in membrane-based desalination. Biofouling, caused by the growth and multiplication of microorganisms on the membrane surface, can significantly impact the efficiency and cost-effectiveness of the desalination process. Herein, a method is proposed for fabricating modified feed spacers based on oil-infused slippery substrates made of polydimethylsiloxane (PDMS). These feed spacers, when infused with silicone oil, create a stable, extremely slippery interface that exhibits exceptionally low bacterial adhesion and prevents biofilm formation, especially under flow conditions. By examining the effect of the silicone oil's viscosity, we determined the optimal ratio of the curing agent for fabricating the oil-infused feed spacer. Results showed a substantial reduction of bacterial adhesion to the surface for all tested oil viscosities, particularly under dynamic conditions. Furthermore, even where bacterial adhesion occurred, primarily on samples infused with lower-viscosity oil, it could be easily removed by simple rinsing. Overall, the oil-infused feed spacer demonstrated exceptional biofilm inhibition, providing preliminary indication of the potential offered by this promising approach. • Oil-impregnated PDMS spacers used to test biofouling prevention • PDMS stiffness and oil viscosity affect oil uptake and retention. • Reduced and easily removable biofilm growth on oily substrate • E. coli biofilm mitigation demonstrated on oil-infused PDMS spacer • Lower viscosity oil and lower stiffness PDMS demonstrate best performance. [ABSTRACT FROM AUTHOR]

Biofouling is still an important factor limiting ultrafiltration further application, and previous mechanism analyses were mainly focused on extracellular polymeric substances (EPS) composition and concentration. In this study, both biofouling and alleviation mechanisms were further investigated in detail with three typical microorganisms, particularly toward the microbial interaction energy. The results showed that a stronger fouling degree was induced by Pseudomonas putida (rod-shaped) than that induced by Staphylococcus aureus and Enterococcus faecalis (sphere). The computational fluid dynamics results suggested that the larger membrane filtration resistance caused by P. putida was due to more EPS secretion. EPS composition and confocal laser scanning microscopy analysis indicated that polysaccharide in EPS played greater roles on the biofouling than protein. According to the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, higher interaction energy was induced because of higher content of polysaccharide (e.g., hydroxyl groups) and protein (e.g., aggregated strands of amide I band) in EPS from P. putida , resulting in a thicker biofilm and stronger biofouling degree than that caused by S. aureus and E. faecalis. In addition, both EPS secretion and microbial interaction energy were inhibited by UV pretreatment, resulting in fouling alleviated. This work will be beneficial for further biofouling control in actual water treatment plants. [Display omitted] • Pseudomonas putida induced severe UF membrane fouling due to high content of EPS. • The polysaccharide composition in EPS was mainly contributed to the fouling degree. • Polysaccharide and protein showed good relation with microbial interaction energy. • The microbial interaction energy was positively correlated with fouling degree. • UV reduced biofouling by both restraint of EPS secretion and microbial interaction. [ABSTRACT FROM AUTHOR]

Abstract: Anaerobic membrane bioreactors (AnMBRs) show great promise for wastewater treatment. However, membrane fouling is still a major limiting factor for industrial application. There is little information focusing on membrane fouling of AnMBRs treating low-strength municipal wastewater. The food-to-microorganism (F/M) ratio is a controllable parameter found to significantly influence system performance and fouling in aerobic membrane bioreactors (MBRs). In this study, two lab-scale AnMBRs (named as HAnMBR and LAnMBR) were comparably run under high and low F/M ratios of 3.8gCOD/gMLSS.d and 0.1gCOD/gMLSS.d, respectively. The impact of the F/M ratio on the performance of AnMBRs was systematically evaluated, especially with regard to fouling. The results showed that cake resistance was responsible for over 98% of the total fouling, and membrane fouling in the HAnMBR was more severe than that in the LAnMBR. HAnMBR had higher amounts of soluble microbial products and higher tightly-bound to loosely-bound extracellular polymeric substance ratio in its cake layer accounted for a higher cake resistance. The larger amount of fine particles in the HAnMBR also contributed to more serious fouling. Membrane filtration deteriorated sludge bioflocculation, which in turn accelerated fouling. [Copyright &y& Elsevier]

Abstract: Interests on the polarity reversal have increased to prevent or minimize membrane fouling and scaling during the operation of electromembrane processes. In this study, the influence of the operation conditions on the process efficiency was investigated in the electrodeionization reversal (EDIR) system with an electrodeionization with the polarity reversal. The removal efficiencies of divalent cations (Mg2+ and Ca2+) kept high value without scale formation on the membrane surface. Through the EDIR operation, the process performance was affected by polarity reversal periods, and the operating polarity reversal period was determined to 40min or shorter in this study. In the long term EDIR experiments with different cation exchange membranes, the homogeneous membranes showed marginally higher removal efficiency compared to the heterogeneous membrane. The scale powders and the surface of scaled membrane were analyzed using electron microscopes and it was observed that the scales formed as carbonate of divalent cations. The EDIR results showed the feasibility of the EDIR system for use in water softening process without significant scale formation even in a relatively high concentration. [Copyright &y& Elsevier]

Abstract: In the last decade osmotically driven membrane processes have attracted growing interest in wastewater treatment, desalination and power generation. A hybrid forward osmosis–nanofiltration (FO–NF) system designed for brackish water desalination was systematically investigated in this study. The hybrid FO–NF process was also compared with a stand-alone reverse osmosis (RO) process in brackish water desalination. It is found that the hybrid FO–NF process has many advantages over the stand-alone RO process in brackish water desalination, such as lower hydraulic pressure, less flux decline caused by membrane fouling and higher flux recovery after cleaning. Other benefits like no pre-treatment requirement, higher permeate quality and no need for chemical cleaning in brackish water desalination can also be achieved by the hybrid FO–NF system. Therefore, the proposed FO–NF system using a divalent draw solute (e.g. Na2SO4 or MgSO4) can be a useful alternative to stand-alone RO processes in brackish water desalination. [Copyright &y& Elsevier]

Abstract: One of the critical issues in the application of membrane filtration to drinking water treatment is fouling by natural organic matter (NOM). In order to better understand fouling, Aldrich humic substances (AHSs), a surrogate NOM, were fractionated into hydrophilic fraction (HPIF) and hydrophobic fraction (HPOF) using DAX-8 resin and then fed into an electro-ultrafiltration (EUF) system. The fractionation performance was validated by contact angle measurement. Results showed that the HPIF deposited membrane had a lower contact angle than the HPOF deposited one. The EUF cell was operated in a constant pressure mode for 5h with and without electric voltage. It was observed that in the absence of an electric field, HPIF caused more severe fouling than HPOF. After applying the electrical voltage, the flux decline decreased due to electrokinetic interactions. In addition, HPOF had a lower flux decline and higher total permeate volume than HPIF, indicating a higher electrophoretic mobility of HPOF. Due to the relatively low apparent electrophoretic mobility (AEM) of HPIF, the flux decline was the highest after applying electricity. Furthermore, the removal efficiency of total organic carbon (TOC) increased by more than 10%, 30% and 13% for the un-fractionated, HPOF, and HIPF, respectively, at 2985V/m. [Copyright &y& Elsevier]

Abstract: Ultrafiltration is a widely used technique to remove hazardous pollutants from wastewaters. As ultrafiltration is a dynamic process, non steady-state UF models have been widely investigated and described in the literature. The main equations of most dynamic models found in the literature can be rearranged and simplified into a linear equation. In this work, experimental results from UF tests were expressed in terms of TMP 2 /J P 2 as a function of time to check linearity. Transmembrane pressure (TMP), feed concentration (FC), temperature and crossflow velocity (CFV) were varied during the experiments. The feed consisted in an aqueous solution of polyethylene glycol of 35kg/mol molecular weight. The experimental results confirmed a linear relationship when TMP 2 /J P 2 was plotted vs. time. For severe fouling conditions, the linearity found when plotting experimental values of initial membrane fouling resistance vs. TMP was very high. A linear correlation between the initial membrane fouling resistance and the temperature was also found for the experimental conditions tested. However, it was found that, above 25°C, increasing temperature did not result in a noticeable reduction of the gel layer resistance. The quotient r c /c g as a function of TMP and CFV was also evaluated to check if it followed any pattern. [Copyright &y& Elsevier]

Abstract: Seawater reverse osmosis technology is fully mature at industrial scale which has been installed in all coastal areas around the world with limited natural hydrological resources. There are many technological advances and innovations which are trying to improve the reverse osmosis desalination process. In particular, all pursue to reduce the process energy consumption, as well as to minimize the harmful effects of scaling and fouling on membranes and to obtain higher water flux membranes. This paper presents a comprehensive review of the main innovations and future trends in the design of seawater reverse osmosis desalination technology. These are intended to improve the process performance and the efficiency of this technique for high production. Special focus is placed on the use of renewable energies as an innovation in the medium-term for medium and large production capacities. It supports desalination with renewable energies as an attractive combination in many regions with the possibility of reducing stress on existing water supplies. [Copyright &y& Elsevier]

Abstract: Efficient performance of the combination of treatment processes for oilfield produced water generated from oil tank dewatering was investigated in the study presented below. By-produced wastewater is generated in significant quantity during exploitation of crude oil and gas from onshore and offshore production operations. This wastewater, commonly referred to as “produced water”, has distinctive characteristics, due to their organic and inorganic compounds. However, these characteristics change from well to well. The treatment process investigated here consists of a pre-treatment step utilizing microfiltration (0.1 and 0.2µm pore size filters) and/or a simulated batch dissolved air flotation (DAF), and a multistage post-treatment step utilizing cross-flow ultra- (0.05µm pore size and 20kDa molecular weight cut-off filters), and nanofiltration (1 and 0.75kDa MWCO filters). Filters used were ceramic membranes. To determine the separation capability of the processes described, various parameters, such as trans-membrane pressure varying from 0.5 to 2bar, cross-flow velocity in the range of 0.6 to 1.3m/s, influent oil concentration ranging from 32 to 5420 parts per million (ppm) and different membrane cleaning methods used were investigated. The average permeate flux varied from 3.4 to 3300l/h m2 bar, total oil removal was up to 99.5% and total organic carbon removal reached 49%. [Copyright &y& Elsevier]

Abstract: Fouling and subsequent chemical cleaning are two important issues for sustainable operation of nanofiltration (NF) membranes in water treatment and reuse applications. Fouling strongly depends on the feed water quality, especially the nature of the foulants and ionic composition of the feed water. Consequently, appropriate selection of the chemical cleaning solutions can be seen as a critical factor for effective fouling control. In this study, membrane fouling and chemical cleaning under condition typical to that in water recycling applications were investigated. Fouling conditions were achieved over approximately 18h with foulant cocktails containing five model foulants namely humic acids, bovine serum albumin, sodium alginate, and two silica colloids in a background electrolyte solution. These model foulants were selected to represent four distinctive modes of fouling: humic acid, protein, polysaccharide, and colloidal fouling. Three chemical cleaning solutions (alkaline solution at pH 11, sodium dodecyl sulphate (SDS), and a combination of both) were evaluated for permeate flux recovery efficiency. The results indicated that with the same mass of foulant, organic fouling was considerably more severe as compared to colloidal fouling. While organic fouling caused a considerable increase in the membrane surface hydrophobicity as indicated by contact angle measurement, hydrophobicity of silica colloidal fouled membrane remained almost the same. Furthermore, a mechanistic correlation amongst cleaning efficiency, characteristics of the model foulants, and the cleaning reagents could be established. Chemical cleaning of all organically fouled membranes by a 10mM SDS solution particularly at pH 11 resulted in good flux recovery. However, notable flux decline after SDS cleaning of organically fouled membranes was observed indicating that SDS was effective at breaking the organic foulant—Ca2+ complex but was not able to effectively dissolve and completely remove these organic foulants. Although a lower permeate flux recovery was obtained with a caustic solution (pH 11) in the absence of SDS, the permeate flux after cleaning was stable. In contrast, the chemical cleaning solutions used in this study showed low effectiveness against colloidal fouling. It is also interesting to note that membrane fouling and chemical cleaning could permanently alter the hydrophobicity of the membrane surface. [Copyright &y& Elsevier]

Abstract: For the sludge volume reduction, gravity thickening and mechanical thickening processes have been mainly applied. However, these processes usually cause several problems such as large footprint, low thickening efficiency, etc. To solve these problems, a sludge reduction system using submerged membrane in a reactor with excess sludge from a biological nutrient removal (BNR) system was investigated. Both lab and pilot scale experiments for sludge reduction were carried out. The hydraulic retention time (HRT) was in a range of 4.5–6.7days during the experimental period. A flat-sheet membrane with a mean pore size of 0.08µm was used and operated at a flux range of 7–20L/m2·h. During the experimental period, concentrations of BOD and SS were maintained less than 8mg/L, 3mg/L, respectively, which indicated the high quality of treated wastewater. While extracellular polymeric substances (EPS) were lowest at a coagulant concentration of 15ppm, soluble microbial product (SMP) concentrations did not have any correlation with coagulant concentrations. The critical flux was observed in a range of 18–24L/m2·h. These results suggested that the sludge reduction system using membrane bioreactor (MBR) could be applied as one of suitable processes to overcome problems of conventional processes such as gravity and mechanical thickening. [Copyright &y& Elsevier]

Abstract: On principle of polymer blend phase separation, PVDF/PVA hollow fiber membranes were prepared using phase inversion method. The membrane morphology and performance varied with the blending ratio. The PVDF/PVA blends showed incompatibility by the results of dynamic mechanical analysis (DMA) and infrared attenuated total reflection (FTIR-ATR) sampling technique. Based on bursting pressure and tensile strengths results, we suggest that the mechanical properties of PVDF/PVA blend membranes are worse than that of PVDF membrane. PVA can improve the hydrophilicity of PVDF/PVA hollow fiber membranes, which could be illuminated by the decrease in contact angle, the increase in equilibrium water content (EWC) and the variety in dynamic moisture regain. The pure water flux increases while the rejection ratio decreases with PVA content increasing. Moreover, PVA can improve the anti-fouling property of PVDF/PVA hollow fiber membranes, which could be illuminated by the result of increase coefficient of resistance. [Copyright &y& Elsevier]

Abstract: An important aspect of urban water systems is the interactions that take place between different components of the system (e.g. foul water from leaky sewers entering into a drinking water distribution network). It is widely recognised that it is important to consider these interactions in order to maintain effective, efficient and safe water and sanitation services. Hence, an integrated approach to urban water management (IUWM) is necessary. This paper begins by presenting a case study in India that highlights the important interactions that takes place between different components of the urban water system. The case study highlights the need to recognise these interactions in order to provide safe and sustainable urban water services. The paper then presents ongoing research on development of integrated urban water modelling tool that allows an integrated approach to urban water services. By applying an IUWMapproach it is possible to satisfy the water and sanitation needs of a community at the lowest cost to society whilst minimising environmental and social impacts. [Copyright &y& Elsevier]

Abstract: Recent efforts aimed at minimizing membrane fouling have emphasized an increasing demand for on-line monitoring in an effort to accurately predict membrane performance. To this end, an in situ bacterial monitoring system was developed that is integrated within the membrane. Because the target is bacterial monitoring, organic matter fouling must be controlled to avoid interference/masking of bacterial sensing as well as to prevent permeability loses. Combining bacterial monitoring with a membrane designed for fouling control is a novel and unique concept. [Copyright &y& Elsevier]

Abstract: Biofouling potential on NF membranes was investigated in terms of bacterial by-products (BBP) characterizations (e.g., effective diffusivity, zeta potential, and toxicity) and their transport phenomenon. Here, BBP were defined as organic matters derived from microorganisms, such as cell debris, soluble microbial product, and extracellular polymeric substances. The BBP solution extracted fromthe Flavobacteriumlutescens was used in this study. The mean diffusivity value of BBP determined from the classical FFF theory was 3.5 × 10−6 cm2/s, and zeta potential determined from electrophoresis method was shown to be slightly negative. The values of LC50 and IC50 of BBP determined from acute toxicity test were 111.6 and 12.4 mg/L, respectively. With these characterization results, convection–diffusion–electrophoretic migration (CDE) model and Sherwood relationship were employed to investigate the mass transfer of BBP away from the membrane surface during nanofiltration. The results showed that the BBP concentration in concentration polarization (CP) layer increased as permeate flux increased due to enhanced convection as well as for the positively charged NF membrane because of reduced electrostatic repulsion. Therefore, it is concluded that the BBP transport in CP layer is strongly dependent on membrane surface charge and permeate flux. The mass transfer coefficients (k) of BBP during nanofiltration were determined based on the combined film-thermodynamic model by varying shear rate and channel height. The k values increased with either increasing shear rate or decreasing channel height. With the k values determined, empirical constants in Sherwood relationship were effectively estimated using a non-linear parameter estimation method. [Copyright &y& Elsevier]

Abstract: Fouled RO membranes from a real water treatment plant were analyzed biochemically to investigate the role of quorum sensing in controlling the rate and the extent of biofilm formation on the membrane surface. The results showed that 60% of bacterial species found on the fouled membrane surface contribute to biofilm formation through the active intraspecies as well as interspecies communication. It was confirmed that N-acylated homoserine lactones (AHL) produced from microorganisms involved in the quorum sensing transferred bacterial signal. In addition, flow field-flow fractionation (Fl-FFF) analyses demonstrated that most microorganisms contributing to biofilm formation through quorum sensing exhibited favorable adsorption on the membrane surfaces. The skewness values of these microorganisms were noticeably greater than those of organic macromolecules (i.e., natural organic matter) and particles. The study suggests that biochemical control of interfering quorum sensing could be an effective alternative to control biofilm formation and, thus, the reduction in biofouling of RO membranes. [Copyright &y& Elsevier]

Abstract: Special emphasis has recently laid on the biofouling on RO membrane surface for desalination process to provide a better insight into the microbial community composing of biofilms. However, it appears that conventional RFLP tool, which is used to quantify and identify bacterial population, is inefficient for this study purpose, as it requires intensive time and labor. To meet the requirement of on-site application and a shorter analysis time, detection of microbial community by multiple hybridization using fluorescent Quantum dot (QD)–DNA probes are suggested since the excitation of multi-QD probes is possible with a single excitation light source. In our study, streptavidin-coated QDs 525, 585 and 655 were used to detect three different target bacteria in a single experiment, and each QD streptavidin was conjugated to specific oligonucleotides DNA of each bacteria. The hybridization between mixed target DNA of Mycobacterium sp., Rhodobacter sp. and Bacillus sp. and each complementary QD–DNA probe occurred in a separation-dependent solution phase. In comparison with the conventional RFLP method, it appeared that the application of QD–DNA probe was quick and promising, as it provides the information of mixed bacteria in a single test. [Copyright &y& Elsevier]

Abstract: Biofoulants by autopsy of RO membrane and microbiological quality of the intake water were investigated with the samples obtained from existing RO desalination plant. The analysis of organic matters of the biofilm on the membrane surface showed that macromolecular substances such as proteins and carbohydrates were the major composites and contributed to the biofilm formation. Comparison of microbial communities between the RO membrane and seawater intake samples revealed that α-proteobacteria was the most abundant bacterial group both in the membrane surface and the intake water, and the phylum Firmicute and Planctomycetes, which were proposed not to be originated from the seawater intake, appeared as the potential biofoulants target. The final goal of this research project is to develop a rapid and sensitive biosensor system to detect the problematic biofoulants on RO system in seawater desalination process, with the tool of fluorescence nanoparticles. Preliminary result of this study showed that RO biofouling was contributed both by microbial cells and the extra organic substances and these identification and sensing of specific biofoulant targets will be beneficial to process efficiency. [Copyright &y& Elsevier]

Many desalination plants still struggle to control biological fouling in seawater reverse osmosis (SWRO) systems as there are no standard methods to monitor this type of fouling. Strategies to control biofouling in SWRO systems have been proposed such as antifouling coating and lowering biofouling potential in SWRO feedwater through pretreatment processes. Measuring biofouling potential in the pretreatment and SWRO feedwater has gained increased interest due to its direct link to biofouling. Moreover, this approach can be used as an early warning system allowing for taking corrective actions in the pretreatment processes to meet the required SWRO feedwater quality. This article presents the biofouling potential methods/tools developed for seawater, their applications to monitor and assess raw seawater, SWRO pretreatment and SWRO feedwater, and how these methods are employed to control SWRO biofouling membrane systems. The reported removal efficiency of biofouling potential during SWRO pretreatment processes was found to be low to moderate. Threshold values for biofouling limitation were then proposed based on several lab and plant studies. Research on biofouling potential has provided insight into SWRO pretreatment performance optimisation and biofouling control. Future research is anticipated to determine better pretreatment processes and to identify robust threshold values for mitigating biofouling in SWRO membranes. • The use of biofouling potential indicators is a promising approach to control biofouling in SWRO systems. • Few indicators exist to assess biofouling potential during the pretreatment and in SWRO feedwater. • Low to moderate removal of biofouling potential is observed during SWRO pretreatment processes. • Preliminary guidelines for controlling biofouling in SWRO membranes are proposed. [ABSTRACT FROM AUTHOR]

Abstract: The variation of quality and fouling properties of wwtp effluent over time influences the performance of ultrafiltration (UF) plants. This research reports three experiments in which the specific ultrafiltration resistance (SUR) measurement is applied to obtain more insight in quality variation an impact on UF performance. Firstly the overall performance (flux, recovery and trans-membrane pressure) of a UF pilot was compared with the SUR values of the feedwater. Secondly the effect of pre treatment was investigated. At last the relation between the slopes of filtration cycles of a UF installation and SUR measurements of feedwater were compared. The results clearly indicate that the overall performance of the UF pilot depends on the SUR values of the feedwater. The SUR values should be less than 10×1012 m−2 for a stable UF performance. Also the effect of pre treatment depends on the SUR values of raw wwtp effluent. Very low SUR values (∼4×1012 m−2) mean less effect compared to higher SUR values. The relation and correlation between SUR values of feed water and single filtration cycles of UF installations depends on the condition of the membranes in the units. Using fouled membranes the variation of SUR values corresponds to higher TMP variations than using cleaner membranes. [Copyright &y& Elsevier]

Abstract: The paper presents the applicability of a membrane coupled anaerobic baffled reactor (ABR) for low-cost, waterborne sanitation to those communities with limited access to basic sanitation and are inappropriate for on-site, dry sanitation systems. This represents a challenge as anaerobic MBRs must be operated without aeration. Consequently fluxes in anaerobic systems will be considerably lower than in aerobic systems, and fouling characteristics and hence operating requirements will be different to aerobic MBR. To evaluate the interaction between membranes and the conditions, a standardized test cell technique was used. [Copyright &y& Elsevier]

Abstract: After the advent of critical flux concept, studies on constant subcritical flux operation of membrane bioreactors (MBRs) gained interest, presumably, because of preferred least fouling operational strategy; however, such a chosen operational condition has demonstrated the continuous slow and irreversible fouling followed by a sudden rise in transmembrane pressure (TMP). Such peculiar fouling behaviour has been explained to be evolved due to extracellular polymeric substances (EPS) originated through the course of biological processes inherent to MBRs. A subcritical flux fouling model based on the role of two forms of EPS, viz. bound and free, has been presented here. The model, studied for MBR treating municipal wastewater, could successfully predict the time at which a sudden change in the TMP–time profile occurs; the predicted time of 200 h by the model has shown good agreement with the observed time of approximately 190 h. Although the fouling problem is one of the major bottlenecks for the MBR technology to become widely applicable as an efficient municipal wastewater treatment technology, from the operational point of view, prediction of the time after which severe fouling occurs (a sudden jump in the TMP–time profile) during subcritical operation could be an important step. Such a prediction would help in developing an efficient and well regulated cleaning protocol for better management of MBR treatment plant operations. [Copyright &y& Elsevier]

Abstract: Membrane fouling is a principal limitation of wide application of membrane bioreactors (MBR) to wastewater treatment. In this study, to control the membrane fouling the position of a membrane module in a submerged MBR was elevated from bottom to top of the reactor. This could divide the reactor into two different zones: upper and lower. Air was not supplied at the lower zone whereas aeration was given to the upper zone where the membrane filtration was carried out. Biosolids concentration was reduced in the upper zone because the mixed liquor could be settled down to the lower zone. Therefore, membrane fouling could be lessened in the upper zone due to the reduced biosolids concentration. In this study, to verify if this newly designed MBR configuration could mitigate membrane fouling, the effect of the vertical position of the membrane module in a lab-scale MBR on membrane fouling was investigated. Furthermore, a pilot plant (50 m3/d) of the membrane coupled biological nutrients removal (BNR) process was designed based on the above configuration and was run for 5 months. In the lab test, the higher the membrane was located in the bioreactor, the less membrane fouling was observed. With the pilot plant operation, MLSS concentration in the upper part was lessened to 16~33% than that in the lower part of the tank where air was not supplied. It indicates that two different zones were successfully formed. The interval of periodical chemical cleanings with NaOCl was extended from 2 to 4 months, indicating that the membrane fouling was mitigated. DO concentration at the upper part was 5.3 mg/L, whereas DO at the lower part was 0.4 mg/L. Therefore, this may result in better denitrrification efficiency in the anoxic tank because the recycled sludge to the anoxic tank has low DO concentration. Nitrate concentration at the lower part of the MBR was 2.8 mg/L, whereas that at the upper part was 5.8 mg/L, suggesting that partial denitrification of nitrate was carried out in the lower part of the MBR. Moreover, overall TN removal was 75%, which was higher than that of the conventional BNR processes, indicating that denitrification rate in the anoxic tank increased due to the low DO level of the returned sludge. Consequently, this newly designed MBR could make it possible to control membrane fouling and to get a better TN removal. [Copyright &y& Elsevier]

Abstract: Among the different classifications of membrane fouling, organic fouling is perhaps the most poorly understood, with relationships to (organic) colloidal fouling and biofouling. Problematical foulants have been identified as polysaccharides and proteins but these components occur in both abiotic macromolecular and colloidal forms. In low-pressure membranes, there is some degree of hydraulic reversibility during backwashing but this option does not exist for high-pressure membranes; in both cases, the effectiveness of chemical cleaning is potentially constrained by the compatibility of membrane material with cleaning agent. Pretreatment by coagulation can reduce organic fouling while there is little consensus on the attributes of powdered activated carbon pretreatment. In general, the organic fouling behavior of membrane bioreactors (MBRs) is consistence with that of low-pressure membranes. [Copyright &y& Elsevier]

Abstract: This study aims to identify the nature of organic species (soluble or colloidal) governing membrane fouling within the context of a membrane bioreactor (MBR). A knowledge of their nature and origin (excreted during treatment or associated with the influent) can help to better adapt operational conditions and cleaning procedures. In this work, a fractionation step by ultracentrifugation and innovative organic matter characterisation were done in parallel with dead end microfiltration tests. The complementarities of classical parameters and innovative analyses can help depict foulant species physicochemical properties. Results show that the fouling layer is mostly governed by the deposition of soluble compounds whereas the impact of the colloidal fraction (poorly presents in supernatant) is less. HPLC–SEC and fluorescence analyses reveal the important role of proteins-like substances (polypeptides) in membrane bioreactor fouling. [Copyright &y& Elsevier]

Abstract: Membrane bioreactors (MBR) combine conventional wastewater treatment and membrane filtration to create a system that uses very efficient, specialized microbes, produces a high quality effluent, and leaves small footprint. Fouling remains the major drawback of membrane processes, including MBR systems. Recently, one of the more frequent strategies employed to combat fouling and its consequent reduction in production is air sparging, in which injecting gas bubbles to the membrane generates high shear stress and scours cake layers from the membrane surface. This study mainly focused on permeate flux enhancement by air sparging. The results showed that air sparging over several weeks significantly increased permeate flux. In interpreting the findings, the dimensionless fouling and shear stress numbers are utilized. The fouling number is the ratio of the Peclet number for mass transfer and the Sherwood number. It was found that fouling resistance significantly decreased with air injection ratios between 0.4 and 0.5. This paper introduces a new approach: dividing the fouling number by the Reynolds number, which basically corresponds to the ratio of the Schmidt and Sherwood numbers. That dimensionless number, subsequently called the viscous fouling number shows qualitatively the same graph as the fouling number if viscosity remains constant. If viscosity changes during the filtration process, the fouling number and the viscous fouling number diverge from each other. Using the viscous fouling number instead of the fouling number may be especially useful for processes where fluctuations in viscosity are significant, as they are in MBR. [Copyright &y& Elsevier]

Abstract: In this study, the mixed liquor suspended solids (MLSS) concentration, the bound EPS amount in the activated sludge, and the trans-membrane pressure''s effect on the specific cake resistance was investigated and the mathematical relationship among these factors proposed using the unstirred batch cell test. In this research, it is assumed that the mixed liquor suspended solids (MLSS) concentration, the bound EPS amount in the activated sludge, and the trans-membrane pressure affect the specific resistance of the cake. Therefore, to establish empirically the functional relationship between these variables, three different experiments are performed independently. As results, it is concluded that the specific cake resistance value is not changed significantly even though the MLSS increases from 4000 to 10,000 mg/L as far as the bound EPS concentration and the trans-membrane pressure are maintained to be constant. Additionally, relatively low pressure ranging from 0.5 to 2.0 psi has no significant influence on the specific cake resistance value. However, the amount of bound EPS affects the specific cake resistance showing the sigmoid relationship between them. Consequently, the functional relationship among the bound EPS, trans-membrane pressure, MLSS, and specific cake resistance and is established based on the empirical data. [Copyright &y& Elsevier]

Abstract: Four nanofiltration and low pressure reverse osmosis membranes were investigated concerning their retention and fouling behavior during filtration of a surface water (River Alb) spiked with four polar micropollutants. Filtration and cleaning experiments were also conducted in deionized water spiked with the model contaminants in order to evaluate the influence of the water matrix on retention. Steric and electrostatic effects were found to be the most important factors influencing retention of the organic substances. In the presented experiments, fouling had little influence on retention. In case of the DI water experiments, treatment of the membranes with NaOH solution considerably lowered the retention of the investigated micropollutants, whereas in the experiments with river water the effect of alkaline treatment on the rejection of the trace organic substances decreased to an insignificant amount already 1 h after membrane cleaning. [Copyright &y& Elsevier]

Abstract: The total effluent load of a paper mill can be significantly decreased by recycling of purified clear filtrate (CF) back to paper-making process. The CF treated with membranes can be reused, for instance, as wire section shower water and in the dilution of chemicals. The main requirements for a membrane in CF treatment are high filtration capacity, high retention of turbidity and low fouling tendency. Previous studies have shown that the regenerated cellulose (RC) ultrafiltration (UF) membrane C30F (current trade name UC030T) is especially suitable for the treatment of paper mill process waters. Every paper-making process is, however, different. Thus, filtration experiments are required in order to find the most optimal membrane for the treatment of a certain process water. In this study the best membrane for the treatment of acidic clear filtrate (ACF) was searched. The performance of the C30F membrane was compared with five UF and three microfiltration (MF) membranes. The results revealed that in addition to the C30F membrane, also some other membranes produced high filtration capacity with ACF (approximately 200L/(m2h bar)). All the tested membranes also retained over 90% of turbidity. The extremely hydrophilic C30F membrane had, however, lower fouling tendency compared to the other tested membranes. Therefore, it was concluded that the C30F membranes were the best possible membrane for the ACF treatment. [Copyright &y& Elsevier]

Silver-containing antibacterial membranes are commonly used to control biofouling during bacteria filtration. Unfortunately, fast and uncontrolled release of silver to water is a challenge since this causes mass accumulation of silver in water resources and insufficient long-term antimicrobial effect. To overcome these disadvantages, we propose to add AgCl-TiO 2 xerogels (0–0.8 wt%) in the polyacrylonitrile membranes. The long-term silver retaining of the membranes was evaluated by measuring the silver release under filtration of deionized water in the absence and the presence of 1 M NaCl up to 5 days. The antibiofouling and the antibacterial efficacies were determined by measuring the changes in antibacterial activity and DI water flux of the membranes at the end of 5 days of E. coli filtration. The 0.2 wt% AgCl-TiO 2 xerogel incorporated polyacrylonitrile membrane demonstrated a constant ~1 μg of silver release/cm2 per filtration cycle after a total filtration of 0.05 L/cm2 with 1 M NaCl solution. Additionally, it showed antibacterial efficacy and ~100% recovery of deionized water flux by simple backwashing with water after having been used in many E. coli filtration cycles. Thus, this membrane could potentially be used up to ~5.8 years for 8000 h a year for the filtration of high salinity water. Silver-containing antibacterial membranes are commonly used to control biofouling during bacteria filtration. Uncontrolled release of silver from the membrane causes massive silver accumulation in water which in turn leads to contamination of water resources and threat to aquatic organisms. Although silver release is strongly influenced by the salinity of water, the release data was collected through filtration of pure DI water or tap water in literature. To overcome the shortcomings of the published studies, we propose to use AgCl-TiO 2 xerogels in membranes due to low solubility of AgCl in water and measure the release by filtering high-salinity water. Unlabelled Image • Polyacrylonitrile membranes incorporated with AgCl-TiO 2 xerogels were developed. • 0.2 wt% AgCl-TiO 2 in the membranes provided a significant antibiofouling property. • The long-term release of silver ions was tested using 1 M NaCl and deionized water. • Sustained silver release was achieved at high NaCl concentrations. • 0.2%AgCl-TiO 2 xerogel could provide membrane ~5.8 years × 8000 h/year lifetime. [ABSTRACT FROM AUTHOR]