Submerged or sidestream? The influence of module configuration on fouling and salinity in osmotic membrane bioreactors

Advancements in membrane technology for efficient POME treatment: A comprehensive review and future perspectives

The treatment of POME related contamination is complicated due to its high organic contents and complex composition. Membrane technology is a prominent method for removing POME contaminants on account of its efficiency in removing suspended particles, organic substances, and contaminants from wastewater, leading to the production of high-quality treated effluent. It is crucial to achieve efficient POME treatment with minimum fouling through membrane advancement to ensure the sustainability for large-scale applications. This article comprehensively analyses the latest advancements in membrane technology for the treatment of POME. A wide range of membrane types including forward osmosis, microfiltration, ultrafiltration, nanofiltration, reverse osmosis, membrane bioreactor, photocatalytic membrane reactor, and their combinations is discussed in terms of the innovative design, treatment efficiencies and antifouling properties. The strategies for antifouling membranes such as self-healing and self-cleaning membranes are discussed. In addition to discussing the obstacles that impede the broad implementation of novel membrane technologies in POME treatment, the article concludes by delineating potential avenues for future research and policy considerations. The understanding and insights are expected to enhance the application of membrane-based methods in order to treat POME more efficiently; this will be instrumental in the reduction of environmental pollution.

Developments of electrospinning technology in membrane bioreactor: A review

The necessity for effective wastewater treatment and purification has grown as a result of the increasing pollution issues brought on by industrial and municipal wastewater. Membrane bioreactor (MBR) technology stands out when compared to other treatment methods because of its high efficiency, environmental friendliness, small footprint, and ease of maintenance. However, the development and application of membrane bioreactors has been severely constrained by the higher cost and shorter service life of these devices brought on by membrane biofouling issues resulting from contaminants and bacteria in the water. The nanoscale size of the electrospinning products provides unique microstructure, and the technology facilitates the production of structurally different membranes, or the modification and functionalization of membranes, which makes it possible to solve the membrane fouling problem. Therefore, many current studies have attempted to use electrospinning in MBRs to address membrane fouling and ultimately improve treatment efficacy. Meanwhile, in addition to solving the problem of membrane fouling, the fabrication technology of electrospinning also shows great advantages in constructing thin porous fiber membrane materials with controllable surface wettability and layered structure, which is helpful for the performance enhancement of MBR and expanding innovation. This paper systematically reviews the application and research progress of electrospinning in MBRs. Firstly, the current status of the application of electrospinning technology in various MBRs is introduced, and the relevant measures to solve the membrane fouling based on electrospinning technology are analyzed. Subsequently, some new types of MBRs and new application areas developed with the help of electrospinning technology are introduced. Finally, the limitations and challenges of merging the two technologies are presented, and pertinent recommendations are provided for future research on the use of electrospinning technology in membrane bioreactors.

Critical review on salt tolerance improvement and salt accumulation inhibition strategies of osmotic membrane bioreactors

The osmotic membrane bioreactor (OMBR) is a novel wastewater treatment and resource recovery technology combining forward osmosis (FO) and membrane bioreactor. It has attracted attention for its low energy consumption and high contaminant removal performance. However, in the long-term operation, OMBR faces the problem of salt accumulation due to high salt rejection and reverse salt flux, which affects microbial activity and contaminants removal efficiency. This review analyzed the feasibility of screening salt-tolerant microorganisms and determining salinity thresholds to improve the salt tolerance of OMBR. Combined with recent research, the inhibition strategies for salt accumulation were reviewed, including the draw solution, FO membrane, operating conditions and coupling with other systems. It is hoped to provide a theoretical basis and practical guidance for the further development of OMBR. Finally, future research directions were prospected. This review provides new insights for achieving stable operation of OMBR and promotes its wide application.

Clean-In-Place (CIP) wastewater management using nanofiltration (NF)-forward osmosis (FO)-direct contact membrane distillation (DCMD): Effects of draw salt

A substantial amount of water is being used during Clean-in-Place (CIP) operation, and is transformed into wastewater that can cause eutrophication to the nearby ecosystem. The present study proposed the Nanofiltration (NF) - Forward Osmosis (FO) - Direct Contact Membrane Distillation (DCMD) to recover the cleaning agents and reclaim freshwater from the model CIP wastewater. NF steps were suggested as prefiltration steps to remove organic compounds from the CIP wastewater. NF steps reduced the lactose and protein contents by 100 % and 95.6 %, respectively. The permeates from NF steps were further managed by the integrated FO-DCMD system. Several draw salts such as NaCl, KCl, MgCl2, and CaCl2 were compared to investigate the influence on FO and DCMD performance. It was found that monovalent salts (NaCl and KCl) outperformed the divalent salts (MgCl2 and CaCl2) in terms of water flux for both FO and DCMD. This can be attributed to the lower viscosity and higher mass transfer coefficient. In addition, the replenishment costs of each salt were evaluated since salts loss occurred during FO and DCMD operation. The cost evaluation revealed that NaCl is most the cheapest salts per reclaimed water. All of this observation indicates that NaCl is preferred in terms of water flux and replenishment cost. The NF permeate kept concentrated using the integrated FO-DCMD or single FO with 2 M of NaCl. Compared to a single FO that showed a consistent decline in draw solution concentration, FO-DCMD could maintain the concentration of the draw solution. Despite the constant concentration, flux decline of FO was observed due to fouling formation caused by the high-temperature operation. However, the FO-DCMD could accomplish the recovery of pure water. Finally, the cleaning agents recovered by the NF-FO-DCMD showed the cleaning efficacy comparable to the fresh NaOH. These results suggest the potential of the proposed system to manage the CIP wastewater.

A Review on Opportunities and Limitations of Membrane Bioreactor Configuration in Biofuel Production

Biofuels are a clean and renewable source of energy that has gained more attention in recent years; however, high energy input and processing cost during the production and recovery process restricted its progress. Membrane technology offers a range of energy-saving separation for product recovery and purification in biorefining along with biofuel production processes. Membrane separation techniques in combination with different biological processes increase cell concentration in the bioreactor, reduce product inhibition, decrease chemical consumption, reduce energy requirements, and further increase product concentration and productivity. Certain membrane bioreactors have evolved with the ability to deal with different biological production and separation processes to make them cost-effective, but there are certain limitations. The present review describes the advantages and limitations of membrane bioreactors to produce different biofuels with the ability to simplify upstream and downstream processes in terms of sustainability and economics.

Comparative analysis of membrane fouling mechanisms induced by operation modes of membrane bioreactors with aerobic granular sludge

This experimental work investigated fouling characteristics induced by two different configurations of membrane bioreactor (MBR), which are submerged MBR and sidestream MBR with aerobic granular sludge. Submerged membrane bioreactor with granular sludge (Sub-MGSBR) ran the longest operation time 61 days with a steady overall TMP increase rate; Sidestream membrane bioreactor with granular sludge (SS-MGSBR) performed only 39 days, which exhibited Sub-MGSBR had more efficiently retarding membrane fouling. In both membrane bioreactors with flocculent sludge (MFSBRs) as a control, membrane foulants were compact, and cake resistance was the dominant fouling factor. In MGSBRs, however, pore blocking resistance turned out the key fouling factor. Especially in Sub-MGSBR, it went beyond 75%, and there was the most conglomeration of microorganisms of foulants with the highest porosity. Extracellular polymeric substances (EPS) content of foulants proved membrane fouling was hardly just for granules accumulation into cake but microorganisms' growth in MGSBRs.

High-retention membrane bioreactors for sugarcane vinasse treatment: Opportunities for environmental impact reduction and wastewater valorization

Ethanol production has increased over the years, and Brazil ranking second in the world using sugarcane as the main raw material. However, 10-15 L of vinasse are generated per liter of ethanol produced. Besides large volumes, this wastewater has high polluting potential due to its low pH and high concentrations of organic matter and nutrients. Given the high biodegradability of the organic matter, the treatment of this effluent by anaerobic digestion and membrane separation processes results in the generation of high value-added byproducts such as volatile fatty acids (VFAs), biohydrogen and biogas. Membrane bioreactors have been widely evaluated due to the high efficiency achieved in vinasse treatment. In recent years, high retention membrane bioreactors, in which high retention membranes (nanofiltration, reverse osmosis, forward osmosis and membrane distillation) are combined with biological processes, have gained increasing attention. This paper presents a critical review focused on high retention membrane bioreactors and the challenges associated with the proposed configurations. For nanofiltration membrane bioreactor (NF-MBR), the main drawback is the higher fouling propensity due to the hydraulic driving force. Nonetheless, the development of membranes with high permeability and anti-fouling properties is uprising. Regarding osmotic membrane bioreactor (OMBR), special attention is needed for the selection of a proper draw solution, which desirably should be low cost, have high osmolality, reduce reverse salt flux, and can be easily reconcentrated. Membrane distillation bioreactor (MDBR) also exhibit some shortcomings, with emphasis on energy demand, that can be solved with the use of low-grade and residual heat, or renewable energies. Among the configurations, MDBR seems to be more advantageous for sugarcane vinasse treatment due to the lower energy consumption provided by the use of waste heat from the effluent, and due to the VFAs recovery, which has high added value.

Evaluation of a Hybrid Moving Bed Biofilm Membrane Bioreactor and a Direct Contact Membrane Distillation System for Purification of Industrial Wastewater

Integrated wastewater treatment processes are accepted as the best option for sustainable and unrestricted onsite water reuse. In this study, moving bed biofilm reactor (MBBR), membrane bioreactor (MBR), and direct contact membrane distillation (DCMD) treatment steps were integrated successively to obtain the combined advantages of these processes for industrial wastewater treatment. The MBBR step acts as the first step in the biological treatment and also mitigates foulant load on the MBR. Similarly, MBR acts as the second step in the biological treatment and serves as a pretreatment prior to the DCMD step. The latter acts as a final treatment to produce high-quality water. A laboratory scale integrated MBBR/MBR/DCMD experimental system was used for assessing the treatment efficiency of primary treated (PTIWW) and secondary treated (STIWW) industrial wastewater in terms of permeate water flux, effluent quality, and membrane fouling. The removal efficiency of total dissolved solids (TDS) and effluent permeate flux of the three-step process (MBBR/MBR/DCMD) were better than the two-step (MBR/DCMD) process. In the three-step process, the average removal efficiency of TDS was 99.85% and 98.16% when treating STIWW and PTIWW, respectively. While in the case of the two-step process, the average removal efficiency of TDS was 93.83% when treating STIWW. Similar trends were observed for effluent permeate flux values which were found, in the case of the three-step process, 62.6% higher than the two-step process, when treating STIWW in both cases. Moreover, the comparison of the quality of the effluents obtained with the analysed configurations with that obtained by Jeddah Industrial Wastewater Treatment Plant proved the higher performance of the proposed membrane processes.

The Influence of Forward Osmosis Module Configuration on Nutrients Removal and Microalgae Harvesting in Osmotic Photobioreactor

Microalgae have attracted great interest recently due to their potential for nutrients removal from wastewater, renewable biodiesel production and bioactive compounds extraction. However, one major challenge in microalgal bioremediation and the algal biofuel process is the high energy cost of separating microalgae from water. Our previous studies demonstrated that forward osmosis (FO) is a promising technology for microalgae harvesting and dewatering due to its low energy consumption and easy fouling control. In the present study, two FO module configurations (side-stream and submerged) were integrated with microalgae (C. vulgaris) photobioreactor (PBR) in order to evaluate the system performance, including nutrients removal, algae harvesting efficiency and membrane fouling. After 7 days of operation, both systems showed effective nutrients removal. A total of 92.9%, 100% and 98.7% of PO₄-P, NH₃-N and TN were removed in the PBR integrated with the submerged FO module, and 82%, 96% and 94.8% of PO₄-P, NH₃-N and TN were removed in the PBR integrated with the side-stream FO module. The better nutrients removal efficiency is attributed to the greater algae biomass in the submerged FO-PBR where in situ biomass dewatering was conducted. The side-stream FO module showed more severe permeate flux loss and biomass loss (less dewatering efficiency) due to algae deposition onto the membrane. This is likely caused by the higher initial water flux associated with the side-stream FO configuration, resulting in more foulants being transported to the membrane surface. However, the side-stream FO module showed better fouling mitigation by simple hydraulic flushing than the submerged FO module, which is not convenient for conducting cleaning without interrupting the PBR operation. Taken together, our results suggest that side-stream FO configuration may provide a viable way to integrate with PBR for a microalgae-based treatment. The present work provides novel insights into the efficient operation of a FO-PBR for more sustainable wastewater treatment and effective microalgae harvesting.

Modeling and assessment of the transfer effectiveness in integrated bioreactor with membrane separation

Integrating a reaction process with membrane separation allows for effective product removal, favorable shifting of the reaction equilibrium, overcoming eventual inhibitory or toxic effects of the products and has the advantage of being energy and space saving. It has found a range of applications in innovative biotechnologies, generating value-added products (exopolysaccharides, antioxidants, carboxylic acids) with high potential for separation/ concentration of thermosensitive bioactive compounds, preserving their biological activity and reducing the amount of solvents and the energy for solvent recovery. Evaluating the effectiveness of such integrated systems is based on fluid dynamics and mass transfer knowledge of flowing matter close to the membrane surface – shear deformation rates and shear stress at the membrane interface, mass transfer coefficients. A Computational Fluid Dynamics (CFD)-based approach for assessing the effectiveness of integrated stirred tank bioreactor with submerged membrane module is compiled. It is related to the hydrodynamic optimization of the selected reactor configuration in two-phase flow, as well as to the concentration profiles and analysis of the reactor conditions in terms of reaction kinetics and mass transfer.

Modeling and Life Cycle Assessment of a Membrane Bioreactor–Membrane Distillation Wastewater Treatment System for Potable Reuse

Wastewater treatment for indirect potable reuse (IPR) is a possible approach to address water scarcity. In this study, a novel membrane bioreactor–membrane distillation (MBR-MD) system was evaluated to determine the environmental impacts of treatment compared to an existing IPR facility (“Baseline”). Physical and empirical models were used to obtain operational data for both systems and inform a life cycle inventory. Life cycle assessment (LCA) was used to compare the environmental impacts of each system. Results showed an average 53.7% reduction in environmental impacts for the MBR-MD system when waste heat is used to operate MD; however, without waste heat, the environmental impacts of MBR-MD are significantly higher, with average impacts ranging from 218% to 1400% greater than the Baseline, depending on the proportion of waste heat used. The results of this study demonstrate the effectiveness of the novel MBR-MD system for IPR and the reduced environmental impacts when waste heat is available to power MD.

A breakthrough dynamic-osmotic membrane bioreactor/nanofiltration hybrid system for real municipal wastewater treatment and reuse

This study designed a Dynamic-Osmotic membrane bioreactor/nanofiltration (OsMBR/NF) system for municipal wastewater treatment and reuse. Results indicated that a continuously rotating FO module with 60 RPM in Dynamic-OsMBR system could enhance shear stress and reduce cake layer of foulants, leading to higher flux (50%) compared to Traditional-OsMBR during a 40-operation day. A negligible specific reverse salt flux (0.059 G/L) and a water flux of 2.86 LMH were recorded when a mixture of 0.1 M EDTA-2Na/0.1 M Na₂CO₃/0.9 mM Triton114 functioned as draw solution (DS). It was found that the Dynamic-OsMBR/NF hybrid system could effectively remove pollutants (∼98% COD, ∼99% PO₄^3-P, ∼93% NH₄⁺-N, > 99% suspended solids) from wastewater. In short, this developed system can be considered a breakthrough technology as it successfully minimizes membrane fouling by shear force, and achieves high water quality for reuse by two membrane- barriers.

Integrated mathematical model to simulate the performance of a membrane bioreactor

Membrane bioreactor technology includes the integration of biological wastewater treatment and physical separation by membrane filtration. When analyzing the system performance, efficiency of biological processes, physical separation and membrane fouling must be taken into consideration. Over the years, mathematical modelling of wastewater treatment has evolved and is being used extensively to optimize the performance of treatment systems. A Number of attempts have been made towards the development of mathematical models for membrane bioreactors and most of these models have not considered the effect of soluble microbial products on membrane fouling. Also the effect of periodic membrane cleaning was neglected. In this study, an integrated mathematical model was developed for the membrane bioreactor. A biological model based on activated sludge processes (extended with biopolymer kinetics) and a physical model with cake layer kinetics and membrane fouling have been combined. In order to overcome the drawbacks of previous attempts of modelling, the influence of soluble microbial products and extracellular polymeric substances are considered in the model integration. Further, the physical processes of the sludge removal and membrane cleaning which have strong influence on membrane fouling are considered in the model. "AQUASIM", a computer program for the identification and simulation of aquatic systems, was used for solving the processes. Calibrated and validated model enables the prediction of the system performance and membrane fouling under different operating conditions.

Occurrence and Fate of Emerging Pollutants in Water Environment and Options for Their Removal

Emerging pollutants (EPs) are chemicals known to cause major impacts on the terrestrial, aquatic life and human health as a result of their chronic and acute toxicity. Although lots of studies on EPs behavior in the aquatic environment are currently available in literature, an urgent requirement exists to complete toxicological studies and develop and implement efficient and ecological methods for their removal. This paper raises some relevant problems related to water environment pollution with EPs, the risks they can generate for aquatic life and humans and opportunities to reduce the effects of pollution by EPs removal. Categories of emerging chemicals of concern in the environment, their sources, fate and impacts, with some examples are discussed. Organic UV filters are shortly presented as a relative new EPs category, with a focus on the need to develop extensive experimental studies on their environmental occurrence, fate and removal. Furthermore, sources for the aquatic environment resulting from discharging EPs directly into rivers from wastewater treatment plants are examined. The incidence of environmental and human health risks related to EPs is also considered. The removal of EPs from the environment as a solution to risk mitigation is addressed, with emphasis on several non-conventional processes involving biological removal of EPs. The paper provides a critical look at the current challenges posed by the presence of emerging pollutants in the aquatic environment, with critical comments and recommendations for further research to reduce the impact of EPs on water and human health and improve the performance of developed methods for their removal.

A comprehensive review of nutrient-energy-water-solute recovery by hybrid osmotic membrane bioreactors

Hybrid osmotic membrane bioreactor (OMBR) takes advantage of the cooperation of varying biological or desalination processes and can achieve NEWS (nutrient-energy-water-solute) recovery from wastewater. However, a lack of universal parameters hinders our understanding. Herein, system configurations and new parameters are systematically investigated to help better evaluate recovery performance. High-quality water can be produced in reverse osmosis/membrane distillation-based OMBRs, but high operation cost limits their application. Although bioelectrochemical system (BES)/electrodialysis-based OMBRs can effectively achieve solute recovery, operation parameters should be optimized. Nutrients can be recovered from various wastewater by porous membrane-based OMBRs, but additional processes increase operation cost. Electricity recovery can be achieved in BES-based OMBRs, but energy balances are negative. Although anaerobic OMBRs are energy-efficient, salinity accumulation limits methane productions. Additional efforts must be made to alleviate membrane fouling, control salinity accumulation, optimize recovery efficiency, and reduce operation cost. This review will accelerate hybrid OMBR development for real-world applications.

Anaerobic membrane bioreactors for treatment of emerging contaminants: A review

Emerging contaminants (ECs) are synthetic organic chemicals that released into the environment, which pose a serious threat to the ecosystem and human health. Due to the high costs of physicochemical methods and the possibility of secondary pollution, and conventional biological treatment techniques are not efficient to remove ECs. Thus, there is a need to develop novel technologies to treat ECs. Anaerobic digestion (AD) is reported to degrade most ECs. Anaerobic membrane bioreactor (AnMBR) is an upgraded AD technology that has high system stability and microbial community abundance. The biogas production and EC biodegradation efficiency in the AnMBR system are markedly higher than those in the traditional AD system. In recent years, AnMBR is widely used to remove environmental ECs. This review analyzes the feasibility and challenges of AnMBR in the treatment of ECs and provides useful insights for improving the performance and efficiency of AnMBR to treat ECs.

Fouling and performance of outer selective hollow fiber membrane in osmotic membrane bioreactor: Cross flow and air scouring effects

This study assessed impacts of cross-flow velocity (CFV) and air scouring on the performance and membrane fouling mitigation of a side-stream module containing outer-selective hollow fiber thin film composite forward osmosis membrane in osmosis membrane bioreactor (OMBR) system for urban wastewater treatment. CFV of draw solution was optimized, followed by the impact assessment of three CFVs on feed solution (FS) stream and periodic injection of air scouring into the side-stream module. Overall, the OMBR system exhibited high and stable performance with initial water flux of approximately 15 LMH, high removal efficiencies of bulk organic matter and nutrients. While FS's CFVs insignificantly affected the performance and membrane fouling, regular air scouring showed substantial impact with better performance and high efficiency in mitigating membrane fouling. These results indicated that periodic air scouring can be applied into the side-stream membrane module for efficient fouling mitigation without interruption the operation of the OMBR system.

Recent Progresses of Forward Osmosis Membranes Formulation and Design for Wastewater Treatment

Production of potable water or reclaimed water with higher quality are in demand to address water scarcity issues as well as to meet the expectation of stringent water quality standards. Forward osmosis (FO) provides a highly promising platform for energy-efficient membrane-based separation technology. This emerging technology has been recognized as a potential and cost-competitive alternative for many conventional wastewater treatment technologies. Motivated by its advantages over existing wastewater treatment technologies, the interest of applying FO technology for wastewater treatment has increased significantly in recent years. This article focuses on the recent developments and innovations in FO for wastewater treatment. An overview of the potential of FO in various wastewater treatment application will be first presented. The contemporary strategies used in membrane designs and fabrications as well as the efforts made to address membrane fouling are comprehensively reviewed. Finally, the challenges and future outlook of FO for wastewater treatment are highlighted.

Innovative upflow anaerobic sludge osmotic membrane bioreactor for wastewater treatment

A novel upflow anaerobic sludge-forward osmotic membrane bioreactor was developed for simultaneous wastewater treatment, membrane fouling reduction, and nutrient recovery. An upflow anaerobic sludge blanket (UASB) reactor was incorporated into the system, suspending the anaerobic sludge at the bottom of the reactor. A forward osmosis membrane replaced the traditional three-phase separator of the UASB technology. The removals of chemical oxygen demand, PO₄^3-, and NH₄⁺ were all more than 95% with low membrane fouling in this system. Halotolerant Fusibacter, which can ferment organics to acetate, was increased rapidly from 0.1% to 5% in this saline environment. Acetoclastic Methanosaeta was the most dominant prokaryotes and responsible for majority of methane production. Reduction of membrane fouling in this system was verified by the fluorescence excitation-emission matrix spectrophotometry. Furthermore, phosphorus recovery and salinity build-up mitigation were achieved using periodic microfiltration to recover 57-105 mg/L phosphorus from pH 9 to 12.

Exploring Submerged Forward Osmosis for Water Recovery and Pre-Concentration of Wastewater Before Anaerobic Digestion: A Pilot Scale Study

Applying forward osmosis directly on raw municipal wastewater is of high interest for the simultaneous production of a high quality permeate for water reuse and pre-concentrating wastewater for anaerobic digestion. This pilot scale study investigates, for the first time, the feasibility of concentrating real raw municipal wastewater using a submerged plate and frame forward osmosis module (0.34 m2) to reach 70% water recovery. Membrane performance, fouling behavior, and effective concentration of wastewater compounds were examined. Two different draw solutions (NaCl and MgCl2), operating either with constant draw concentration or in batch with draw dilution over time, were evaluated. Impact of gas sparging on fouling and external concentration polarization was also assessed. Water fluxes up to 15 L m-2 h-1 were obtained with clean water and 35 g NaCl/L as feed and draw solution, respectively. When using real wastewater, submerged forward osmosis proved to be resilient to clogging, demonstrating its suitability for application on municipal or other complex wastewater; operating with 11.7 g NaCl/L constant draw solution, water and reverse salt fluxes up to 5.1 ± 1.0 L m-2 h-1 and 4.8 ± 2.6 g m-2 h-1 were observed, respectively. Positively, total and soluble chemical oxygen demand concentration factors of 2.47 ± 0.15 and 1.86 ± 0.08, respectively, were achieved, making wastewater more suitable for anaerobic treatment.

Characteristics and influencing factors of organic fouling in forward osmosis operation for wastewater applications: A comprehensive review

Wastewater reuse is considered one of the most promising practices for the achievement of sustainable water management on a global scale. In the context of the safe reuse of water, membrane filtration is a competitive technique due to its superior efficiency in several processes. However, membrane fouling by organics is an inevitable challenge that is encountered during the practical application of membrane processes. The resolution of the membrane fouling challenge requires an in-depth understanding of many complex interactions between organic foulants and the membrane. In the last few decades, the forward osmosis (FO) membrane process, which exploits osmosis as a driving force, has emerged as an effective technology for water production with low energy consumption, thus leveraging the water-energy nexus. However, their successful application is severely hampered by membrane fouling, which is caused by such complex fouling mechanisms as cake enhanced osmotic pressure (CEOP), reverse salt diffusion (RSD), internal, and external concentration polarization as well as by the traditional fouling processes encompassing colloids, microbial (biofouling), inorganic, and organic fouling. Of these fouling types, the fouling potential of organic matter in FO has not been given sufficient attention, in particular, when FO is applied to wastewater treatment. This paper aims to provide a comprehensive overview of FO membrane fouling for wastewater applications with a special focus on the identification of the major factors that lead to the unique properties of organic fouling in this filtration process. Based on the critical assessment of organic fouling formation and the governing mechanisms, proposals were advanced for future research aimed at the mitigation of FO membrane fouling to enhance process efficiency in wastewater applications.

Efficient fouling control using outer-selective hollow fiber thin-film composite membranes for osmotic membrane bioreactor applications

This paper investigates the efficiency of fouling mitigation methods using a novel outer selective hollow fiber thin-film composite forward osmosis (OSHF TFC FO) membrane for osmosis membrane bioreactor (OMBR) system treating municipal wastewater. Two home-made membrane modules having similar transport properties were used. Two operation regimes with three different fouling mitigation strategies were utilized to test the easiness of membrane for fouling cleaning. These two membrane modules demonstrated high performance with high initial water flux of 14.4 LMH and 14.1 LMH and slow increase rate of mixed liquor's salinity in the bioreactor using 30 g/L NaCl as draw solution. OMBR system showed high removals of total organic carbon and NH4 + -N (>98%). High fouling cleaning efficiency was achieved using OSHF TFC FO membrane with different fouling control methods. These results showed that this membrane is suitable for OMBR applications due to its high performance and its simplicity for fouling mitigation.

Evidence, Determination, and Implications of Membrane-Independent Limiting Flux in Forward Osmosis Systems

A stepwise method for determining limiting flux and limiting osmotic pressure and a constant osmotic pressure method to validate the limiting flux were developed. First, five of the most commonly used FO membranes were characterized for water permeability ( A), solute permeability ( B), and structural parameter ( S). During both stepwise and constant osmotic pressure fouling experiments, membrane fouling constrained water flux to a singular, common upper limit, the limiting flux, for all membranes despite very different A and A/ B values for the membranes. Conversely, there was not an upper limit to reverse salt flux. It was observed that reverse salt flux increases as S decreases; however, this does not mean that higher S values are desirable. Higher S values (> ∼600 μm) also increase dilutive internal concentration polarization, which is recognized as the major impediment to achieving high FO water flux. For osmotic processes where membrane fouling occurs, membrane transport parameters A and B may not be useful performance indicators, and the goal of improving water flux by developing highly permeable, highly selective membranes may not be realistic. Instead, optimizing fouling mitigation strategies, hydrodynamics at the membrane surface, and membrane module configuration may be more promising alternatives for improving performance.

Treating anaerobic effluents using forward osmosis for combined water purification and biogas production

Forward osmosis (FO) can be used to reclaim nutrients and high-quality water from wastewater streams. This could potentially contribute towards relieving global water scarcity. Here we investigated the feasibility of extracting water from four real and four synthetic anaerobically digested effluents, using FO membranes. The goal of this study was to 1) evaluate FO membrane performance in terms of water flux and nutrient rejection 2) examine the methane yield that can be achieved and 3) analyse FO membrane fouling. Out of the four tested real anaerobically digested effluents, swine manure and potato starch wastewater achieved the highest combined average FO water flux (>3 liter per square meter per hour (LMH) with 0.66 M MgCl₂ as initial draw solution concentration) and methane yield (>300 mL CH₄ per gram of organic waste expressed as volatile solids (VS)). Rejection of total ammonia nitrogen (TAN), total Kjeldahl nitrogen (TKN) and total phosphorous (TP) was high (up to 96.95%, 95.87% and 99.83%, respectively), resulting in low nutrient concentrations in the recovered water. Membrane autopsy revealed presence of organic and biological fouling on the FO membrane. However, no direct correlation between feed properties and methane yield and fouling potential was found, indicating that there is no inherent trade-off between high water flux and high methane production.

Impact of salinity on the population dynamics of microorganisms in a membrane bioreactor treating produced water

Biomass characteristics may change subject to a salinity increase when treating high strength wastewater. In this study, the impact of salinity in a membrane bioreactor (MBR) was investigated for the treatment of produced water (PW). MBR was operated as a pre-treatment prior to nanofiltration (NF) and reverse osmosis (RO). Mixed PW, that was originated from different oil, gas, and oil-gas wells, were subjected to pre-treatment for 146 days including three different operational phases: Low-salinity (~10 mS/cm), gradual increased salinity (10-40 mS/cm) and high salinity (~40 mS/cm). The results of this study showed that microorganisms could adapt using real wastewater and treat PW up to a certain level of the salinity. At high salinity levels of PW, the floc structure started to be disrupted and membrane fouling was accelerated. PCR-DGGE analysis confirmed the changes in microbial communities' composition in relation with high salinity. The results of the final treatment experiments presented that NF and RO treatment produced high-quality effluents that could be suitable for reuse.

Treatment of Palm Oil Mill Effluent Using Membrane Bioreactor: Novel Processes and Their Major Drawbacks

Over the years, different types of alternative technologies have been developed and used for palm oil mill effluent (POME) treatment. Specifically, membrane bioreactor (MBR) has been employed to relegate pollutants contained in POME under different operating conditions, and the technology was found to be promising. The major challenge impeding the wider application of this technology is membrane fouling, which usually attracts high operating energy and running cost. In this regard, novel methods of mitigating membrane fouling through the treatment processes have been developed. Therefore, this review article specifically focuses on the recent treatment processes of POME using MBR, with particular emphasis on innovative processes conditions such as aerobic, anaerobic, and hybrid processing as well as their performance in relation to fouling minimization. Furthermore, the effects of sonication and thermophilic and mesophilic conditions on membrane blockage were critically reviewed. The types of foulants and fouling mechanism as influenced by different operating conditions were also analyzed censoriously.