Development of a novel anaerobic membrane bioreactor simultaneously integrating microfiltration and forward osmosis membranes for low-strength wastewater treatment

Improved permeability in ceramsite@powdered activated carbon (PAC)-MnOx coupled gravity-driven ceramic membrane (GDCM) for manganese and ammonia nitrogen removal with intermittent short-term vertical aeration

In our work, a gravity-driven ceramic membrane bioreactor (GDCMBR) was developed to remove Mn2+ and NH3-N simultaneously through the birnessite water purification layer in-situ construction on the ceramic membrane due to chemical pre-oxidation (powdered activated carbon (PAC)-MnOx). Considering the trade-off of biofouling and water production, the daily intermittent short-term vertical aeration mode was involving to balance this contradiction with the excellent water purification and improved membrane permeability. And the GDCMBR permeability of operation flux was improved for 5-7 LHM with intermittent short-term vertical aeration. Furthermore, only ∼7 % irreversible membrane resistance (Rir) also confirmed the improved membrane permeability with intermittent short-term vertical aeration. And some manganese oxidizing bacteria (MnOB) and ammonia oxidizing bacteria (AOB) species at genus level were identified during long-term operation with the contact circulating flowing raw water, resulting in the better Mn2+ and NH3-N removal efficiency. Additionally, the nano-flower-like birnessite water purification layer was verified in ceramsite@PAC-MnOx coupled GDCMBR, which evolute into a porous flake-like structure with the increasing intermittent short-term aeration duration. Therefore, the sustainable and effective intermittent short-term aeration mode in ceramsite@PAC-MnOx coupled GDCMBR could improve the membrane permeability with the satisfactory groundwater purification efficiency, as well as providing an energy-efficient strategy for membrane technologies applications in water supply safety.

Integrating anaerobic acidification with two-stage forward osmosis concentration for simultaneously recovering organic matter, nitrogen and phosphorus 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 (NH4+-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 NH4+-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 NH4+-N and TP recovery rate of 94.53 % and 98.59 %, respectively. Correspondingly, the VFAs, NH4+-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).

Impact of Integration of FO Membranes into a Granular Biomass AnMBR for Water Reuse

The granular sludge based anaerobic membrane bioreactor (G-AnMBR) has gained emphasis in the last decade by combining AnMBR advantages (high quality permeate and biogas production towards energy positive treatment) and benefits of granular biomass (boosted biological activity and reduced membrane fouling). With the aim to further reduce energy costs, produce higher quality effluent for water reuse applications and improve system efficiency, a forward osmosis (FO) system was integrated into a 17 L G-AnMBR pilot. Plate and frame microfiltration modules were step by step replaced by submerged FO ones, synthetic wastewater was used as feed (chemical oxygen demand (COD) content 500 mg/L), with hydraulic retention time of 10 h and operated at 25 °C. The system was fed with granular biomass and after the acclimation period, operated neither with gas sparging nor relaxation at around 5 L.m^-2.h^-1 permeation flux during at least 10 days for each tested configuration. Process stability, impact of salinity on biomass, the produced water quality and organic matter removal efficiency were assessed and compared for the system working with 100% microfiltration (MF), 70% MF/30% FO, 50% MF/50% FO and 10% MF/90% FO, respectively. Increasing the FO share in the reactor led to salinity increase and to enhanced fouling propensity probably due to salinity shock on the active biomass, releasing extracellular polymeric substances (EPS) in the mixed liquor. However, above 90% COD degradation was observed for all configurations with a remaining COD content below 50 mg/L and below the detection limit for MF and FO permeates, respectively. FO membranes also proved to be less prone to fouling in comparison with MF ones. Complete salt mass balance demonstrated that major salinity increase in the reactor was due to reverse salt passage from the draw solution but also that salts from the feed solution could migrate to the draw solution. While FO membranes allow for full rejection and very high permeate purity, operation of G-AnMBR with FO membranes only is not recommended since MF presence acts as a purge and allows for reactor salinity stabilization.

Improving biological removal of pharmaceutical active compounds and estrogenic activity in a mesophilic anaerobic osmotic membrane bioreactor treating municipal sewage

The contamination of water sources by pharmaceutically active compounds (PhACs) and their effect on aquatic communities and human health have become an environmental concern worldwide. Membrane bioreactors (MBRs) are an alternative to improve biological removal of recalcitrant organic compounds from municipal sewage. Their efficiency can be increased by using high retention membranes such as forward osmosis (FO) and membrane distillation (MD). Thus, this research aimed to evaluate the performance of an anaerobic osmotic MBR coupled with MD (OMBR-MD) in the treatment of municipal sewage containing PhACs and estrogenic activity. A submerged hybrid FO-MD module was integrated into the bioreactor. PhACs removal was higher than 96% due to biological degradation, biosorption and membrane retention. Biological removal of the PhACs was affected by the salinity build-up in the bioreactor, with reduction in biodegradation after 32 d. However, salinity increment had little or no effect on biosorption removal. The anaerobic OMBR-MD removed >99.9% of estrogenic activity, resulting in a distillate with 0.14 ng L^-1 E2-eq, after 22 d, and 0.04 ng L^-1 E2-eq, after 32 d. OMBR-MD treatment promoted reduction in environmental and human health risks from high to low, except for ketoprofen, which led to medium acute environmental and human health risks. Carcinogenic risks were reduced from unacceptable to negligible, regarding estrogenic activity. Thus, the hybrid anaerobic OMBR-MD demonstrated strong performance in reducing risks, even when human health is considered.

Engineering pressure retarded osmosis membrane bioreactor (PRO-MBR) for simultaneous water and energy recovery from municipal wastewater

Osmotic membrane bioreactors (OMBR) have gained increasing interest in wastewater treatment and reclamation due to their high product water quality and fouling resistance. However, high energy consumption (mostly by draw solution recovery) restricted the wider application of OMBR. Herein, we propose a novel pressure retarded osmosis membrane bioreactor (PRO-MBR) for improving the economic feasibility. In comparison with conventional FO-MBR, PRO-MBR exhibited similar excellent contaminants removal performance and comparable water flux. More importantly, a considerable amount of energy can be recovered by PRO-MBR (4.1 kWh/100 m²·d), as a result of which, 10.02% of the specific energy consumption (SEC) for water recovery was reduced as compared with FO-MBR (from 1.42 kWh/m³ to 1.28 kWh/m³). Membrane orientation largely determined the performance of PRO-MBR, higher power density was achieved in AL-DS orientation (peak value of 3.4 W/m²) than that in AL-FS orientation (peak value of 1.4 W/m²). However, PRO-MBR suffered more severe and complex membrane fouling when operated in AL-DS orientation, because the porous support layer was facing sludge mixed liquor. Further investigation revealed fouling was mostly reversible for PRO-MBR, it exhibited similar flux recoverability (92.4%) to that in FO-MBR (95.1%) after osmotic backwash. Nevertheless, flux decline due to membrane fouling is still a restricting factor to power generation of PRO-MBR, its power density was decreased by 38.2% in the first 60 min due to the formation of fouling. Overall, in perspective of technoeconomic feasibility, the PRO-MBR demonstrates better potential than FO-MBR in wastewater treatment and reclamation and deserves more research attention in the future.

A Novel Hybrid Reactor of Pressure-Retarded Osmosis Coupling with Activated Sludge Process for Simultaneously Treating Concentrated Seawater Brine and Wastewater and Recovering Energy

As an attractive way to deal with fresh water shortage, membrane-based desalination technologies are receiving increased interest. However, concentrated seawater brine, in needing further treatment, remains a main obstacle for desalination via membrane technology. Here, a hybrid technology integrating pressure-retarded osmosis with activated sludge process (PRO-MBR) was applied for simultaneously treating concentrated seawater brine and municipal wastewater. Performance of the PRO-MBR, including water flux, power density, contaminants removal, and membrane fouling was evaluated and compared at two different membrane orientations (i.e., active layer facing feed solution (AL-FS) mode and active layer facing draw solution (AL-DS) mode). During the PRO-MBR process, the municipal wastewater was completely treated regardless of the membrane orientation, which means that there was no concentrated sewage needing further treatment, owing to the biodegradation of microorganisms in the bioreactor. In the meantime, the concentrated brine of seawater desalination was diluted into the salinity level of seawater, which met the standard of seawater discharge. Owing to the high rejection of forward osmosis (FO) membrane, the removal efficiency of total organic carbon (TOC), total phosphorus (TP), ammonia nitrogen (NH4+-N), and total nitrogen (TN) was higher than 90% at both modes in the PRO-MBR. In addition, the PRO-MBR can simultaneously recover the existing osmotic energy between the municipal wastewater and the seawater brine at both modes. Compared with the AL-DS mode, the AL-FS mode took a shorter time and achieved a bigger power density to reach the same terminal point of the PRO-MBR owing to a better water flux performance. Furthermore, the membrane fouling was much more severe in the AL-DS mode. In conclusion, the current study demonstrated that the PRO-MBR at the AL-FS mode can be a promising and sustainable brine concentrate and municipal wastewater treatment technology for its simultaneous energy and water recovery.

A green, hybrid cleaning strategy for the mitigation of biofouling deposition in the elevated salinity forward osmosis membrane bioreactor (FOMBR) operation

Forward osmosis membrane bioreactors (FOMBRs) are currently gaining attention from the wastewater treatment industry, for their potential to produce high effluent quality and a relatively better flux stability against fouling. However, only using physical cleaning methods is not sufficient to recover the water flux performance satisfactorily under a long-term operation. This study comprehensively investigated the efficiency of a hybrid, environmentally-friendly cleaning strategy involving a combination of physical and free nitrous acid (FNA) cleanings under a long-term FOMBR operation. During 92 days of FOMBR operation, physical cleaning recovered the water flux by 85%, whilst FNA cleaning contributed to an additional 5% of the recovery. In addition, FNA cleaning also offered a retardation of fouling deposition by maintaining the water flux 18-30% more than that obtained by only the physical cleaning. A possible mechanism for FNA's role as the cleaning reagent was proposed for the first time in this study based on the water flux performance and membrane autopsy analysis. The results showed FNA cleaning broke down the residual fouling layer, preferencing protein-based substances. A lower ratio of protein to polysaccharides of the residual fouling layer contributed to a more negatively charged membrane surface (- 42.34 ± 0.30 mV) compared to the virgin one (- 17.54 ± 0.81 mV). This resulted in a stronger electrostatic repulsion between the foulants and the membrane surface, and thus slowed down the biofouling deposition process. This study suggested FNA solution has the great potential not only to recover the membrane performance, also as a strategy to slow down fouling deposition.

Bio-membrane integrated systems for nitrogen recovery from wastewater in circular bioeconomy

Wastewater contains a significant amount of recoverable nitrogen. Hence, the recovery of nitrogen from wastewater can provide an option for generating some revenue by applying the captured nitrogen to producing bio-products, in order to minimize dangerous or environmental pollution consequences. The circular bio-economy can achieve greater environmental and economic sustainability through game-changing technological developments that will improve municipal wastewater management, where simultaneous nitrogen and energy recovery are required. Over the last decade, substantial efforts were undertaken concerning the recovery of nitrogen from wastewater. For example, bio-membrane integrated system (BMIS) which integrates biological process and membrane technology, has attracted considerable attention for recovering nitrogen from wastewater. In this review, current research on nitrogen recovery using the BMIS are compiled whilst the technologies are compared regarding their energy requirement, efficiencies, advantages and disadvantages. Moreover, the bio-products achieved in the nitrogen recovery system processes are summarized in this paper, and the directions for future research are suggested. Future research should consider the quality of recovered nitrogenous products, long-term performance of BMIS and economic feasibility of large-scale reactors. Nitrogen recovery should be addressed under the framework of a circular bio-economy.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

A novel forward osmosis reactor assisted with microfiltration for deep thickening waste activated sludge: performance and implication

Waste activated sludge (WAS) treatment has gained growing interests for its increasingly capacity and high process cost. Sludge thickening is generally the first process of the WAS treatment. However, traditional sludge thickening approach was restrained by large footprint, low thickening efficiency, and tendency of releasing phosphorus. Here, we reported a novel microfiltration (MF) membrane assisting forward osmosis (FO) process (MF-FO) for sludge thickening. The MF-FO reactor achieved a sludge thickening of the mixed liquor suspended solids (MLSS) concentration from approximately 7 to 50 g/L after 10-day operation. More importantly, the effluent quality after FO filtration was superior with total organic carbon (TOC), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N) and total phosphorus (TP) of 1.94 ± 0.46, 0.02 ± 0.07, 4.55 ± 1.59 and 0.24 ± 0.26 mg/L, respectively. Additionally, the integration of MF membrane successfully controlled the salinity of the MF-FO reactor in a low range of 1.6-3.1 mS/cm, which mitigated the flux decline of FO membrane and thus prolonged the operating time. In this case, the flux decline of FO membrane in the MF-FO reactor was mainly due to the membrane fouling. Furthermore, the fouling layer on the FO membrane surface was a gel layer mainly composed of biofoulants and organic foulants when the MLSS concentration was less than 30 g/L, while it turned to a cake layer when the MLSS concentration exceeded 30 g/L. Results reported here demonstrated that the MF-FO reactor is a promising WAS thickening technology for its excellent thickening performance and high effluent quality of FO membrane.

Effect of Initial Water Flux on the Performance of Anaerobic Membrane Bioreactor: Constant Flux Mode versus Varying Flux Mode

Anaerobic membrane bioreactors (AnMBRs) have aroused growing interest in wastewater treatment and energy recovery. However, serious membrane fouling remains a critical hindrance to AnMBRs. Here, a novel membrane fouling mitigation via optimizing initial water flux is proposed, and its feasibility was evaluated by comparing the membrane performance in AnMBRs between constant flux and varying flux modes. Results indicated that, compared with the constant flux mode, varying flux mode significantly prolonged the membrane operating time by mitigating membrane fouling. Through the analyses of fouled membranes under two operating modes, the mechanism of membrane fouling mitigation was revealed as follows: A low water flux was applied in stage 1 which slowed down the interaction between foulants and membrane surface, especially reduced the deposition of proteins on the membrane surface and formed a thin and loose fouling layer. Correspondingly, the interaction between foulants was weakened in the following stage 2 with a high water flux and, subsequently, the foulants absorbed on the membrane surface was further reduced. In addition, flux operating mode had no impact on the contaminant removal in an AnMBR. This study provides a new way of improving membrane performance in AnMBRs via a varying flux operating mode.

Ammonium ultra-selective membranes for wastewater treatment and nutrient enrichment: Interplay of surface charge and hydrophilicity on fouling propensity and ammonium rejection

Membrane fouling and ammonium transmembrane diffusion simultaneously pose great challenges in membrane-based pre-concentration of domestic wastewater for efficient subsequent resources recovery (i.e., energy and nutrients). Herein, amine-functionalized osmotic membranes were fabricated by optimizing the grafting pathway of polyamidoamine (PAMAM) dendrimer to mitigate fouling and ammonium transmembrane diffusion. Compared to the control membrane, the PAMAM-grafted membranes with abundant primary amine groups possessed substantially increased hydrophilicity and positive charges (i.e., protonated primary amines) and thus exhibited superior anti-fouling capability and ammonium selectivity. With further increasing the PAMAM grafting ratio, the membrane exhibited a steady enhancement in ammonium selectivity and eventually achieved an ultra-high ammonium rejection of 99.4%. Nevertheless, the anti-fouling capability of such ammonium ultra-selective membrane was weakened due to the suppression of the adverse impact of excessive positive charges over the beneficial effect of increased surface hydrophilicity. This in turn leads to a drop of ammonium rejection below 90% during domestic wastewater concentration. This study demonstrates that the membrane with a moderate primary amine loading could achieve the highest anti-fouling capability with only less than 10% flux decline and meanwhile maintain an excellent ammonium rejection above 94% during raw domestic wastewater concentration. This work provides theoretical guidance for fabricating simultaneously enhanced anti-fouling and ammonia-rejecting membranes.

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.

Performance Analysis for the Anaerobic Membrane Bioreactor Combined with the Forward Osmosis Membrane Bioreactor: Process Conditions Optimization, Wastewater Treatment and Sludge Characteristics

The anaerobic membrane bioreactors (AnMBR) were operated at 35 °C (H-AnMBR) and 25 °C (L-AnMBR) for long-term wastewater treatment. Two aerobic forward osmosis membrane bioreactors (FOMBRs) were utilized to treat the effluents of H-AnMBR and L-AnMBR, respectively. During the 180 days of operation, it is worth noting that the combined system was feasible, and the pollutant removal efficiency was higher. Though the permeate chemical oxygen demand (COD) of H-AnMBR (18.94 mg/L) was obviously lower than that of L-AnMBR (51.09 mg/L), the permeate CODs of the FOMBRs were almost the same with the average concentrations of 7.57 and 7.58 mg/L for the H-FOMBR and L-FOMBR, respectively. It was interesting that for both the AnMBRs, the permeate total nitrogen (TN) concentration was higher than that in bulk phase. However, the TN concentrations in the effluent remained stable with the values of 20.12 and 15.22 mg/L in the H-FOMBR and L-FOMBR effluents, respectively. For the two systems, the characteristics of activated sludge flocs were different for H-AnMBR-FOMBR sludge and L-AnMBR-FOMBR sludge. The viscosity of L-AnMBR-activated sludge (2.09 Pa·s) was higher compared to that of H-AnMBR (1.31 Pa·s), while the viscosity of activated sludge in L-FOMBR (1.44 Pa·s) was a little lower than that in H-FOMBR (1.48 Pa·s). The capillary water absorption time of L-AnMBR-activated sludge (69.6 s) was higher compared to that of H-AnMBR (49.5 s), while the capillary water absorption time of activated sludge in L-FOMBR (14.6 s) was little lower than that in H-FOMBR (15.6 s). The particle size of H-AnMBR-activated sludge (119.62 nm) was larger than that of L-AnMBR-activated sludge (84.92 nm), but the particle size of H-FOMBR-activated sludge (143.81 nm) was significantly smaller than that of L-FOMBR-activated sludge (293.38 nm). The observations of flocs indicated that the flocs of activated sludge in H-AnMBR were relatively loose, while the flocs of L-AnMBR were relatively tight. The fine sludge floc was less present in the L-FOMBR than in the H-FOMBR. Therefore, in the process of sewage treatment, the influent of each unit in the AnMBR-FOMBR system should have suitable organic content to maintain the particle sizes of sludge flocs.

Forward Osmosis as Concentration Process: Review of Opportunities and Challenges

In the past few years, osmotic membrane systems, such as forward osmosis (FO), have gained popularity as "soft" concentration processes. FO has unique properties by combining high rejection rate and low fouling propensity and can be operated without significant pressure or temperature gradient, and therefore can be considered as a potential candidate for a broad range of concentration applications where current technologies still suffer from critical limitations. This review extensively compiles and critically assesses recent considerations of FO as a concentration process for applications, including food and beverages, organics value added compounds, water reuse and nutrients recovery, treatment of waste streams and brine management. Specific requirements for the concentration process regarding the evaluation of concentration factor, modules and design and process operation, draw selection and fouling aspects are also described. Encouraging potential is demonstrated to concentrate streams more than 20-fold with high rejection rate of most compounds and preservation of added value products. For applications dealing with highly concentrated or complex streams, FO still features lower propensity to fouling compared to other membranes technologies along with good versatility and robustness. However, further assessments on lab and pilot scales are expected to better define the achievable concentration factor, rejection and effective concentration of valuable compounds and to clearly demonstrate process limitations (such as fouling or clogging) when reaching high concentration rate. Another important consideration is the draw solution selection and its recovery that should be in line with application needs (i.e., food compatible draw for food and beverage applications, high osmotic pressure for brine management, etc.) and be economically competitive.

Water and nutrient recovery by a novel moving sponge - Anaerobic osmotic membrane bioreactor - Membrane distillation (AnOMBR-MD) closed-loop system

For the first time, a novel sponge-based moving bed-anaerobic osmosis membrane bioreactor/membrane distillation (AnOMBR/MD) system using mixed Na₃PO₄/EDTA-2Na as the draw solution was employed to treat wastewater for enhanced water flux and reduced membrane fouling. Results indicated that the moving sponge-AnOMBR/MD system obtained a stable water flux of 4.01 L/m² h and less membrane fouling for a period lasting 45 days. Continuous moving sponge around the FO module is the main mechanism for minimizing membrane fouling during the 45-day AnOMBR operation. The proposed system's nutrient removal was almost 100%, thus showing the superiority of simultaneous FO and MD membranes. Nutrient recovery from the MF permeate was best when solution pH was controlled to 9.5, whereby 17.4% (wt/wt) of phosphorus was contained in precipitated components. Moreover, diluted draw solute following AnOMBR was effectively regenerated using the MD process with water flux above 2.48 L/m² h and salt rejection > 99.99%.

Bioelectrochemically-assisted nitrogen removal in osmotic membrane bioreactor

Nitrogen removal in osmosis membrane bioreactor (OMBR) is important to its applications but remains a challenge. In this study, a bioelectrochemically-assisted (BEA) operation was integrated into the feed side of OMBRs to enhance nitrogen removal, and sodium acetate was served as a draw solute and supplementary carbon source for the growth of denitrifying bacteria due to reversed-solute. The effects of operation mode and influent ammonium (NH₄ ⁺) concentration were systematically examined. Compared to a conventional OMBR, the integrated BEA-OMBR achieved higher total nitrogen removal efficiency of 98.13%, and chemical oxygen demand removal efficiency of 95.83% with the influent NH₄ ⁺-N concentration of 39 mg L^-1. The sequencing analyses revealed that ammonia-oxidizing bacteria (0-0.04%), nitrite-oxidizing bacteria (0-0.16%), and denitrifying bacteria (1.98-8.65%) were in abundance of the microbial community in the feed/anode side of integrated BEA-OMBR, and thus BEA operation increased the diversity of the microbial community in OMBR. Future research will focus on improving nitrogen removal from a high ammonium strength wastewater by looping anolyte effluent to the cathode. These findings have demonstrated that BEA operation can be an effective approach to improve nitrogen removal in OMBRs toward sustainable wastewater treatment.

Unlocking the application potential of forward osmosis through integrated/hybrid process

Study of forward osmosis (FO) has been increasing steadily over recent years with applications mainly focusing on desalination and wastewater treatment processes. The working mechanism of FO lies in the natural movement of water between two streams with different osmotic pressure, which makes it useful in concentrating or diluting solutions. FO has rarely been operated as a stand-alone process. Instead, FO processes often appear in a hybrid or integrated form where FO is combined with other treatment technologies to achieve better overall process performance and cost savings. This article aims to provide a comprehensive review on the need for hybridization/integration for FO membrane processes, with emphasis given to process enhancement, draw solution regeneration, and pretreatment for FO fouling mitigation. In general, integrated/hybrid FO processes can reduce the membrane fouling propensity; prepare the solution suitable for subsequent value-added uses and production of renewable energy; lower the costs associated with energy consumption; enhance the quality of treated water; and enable the continuous operation of FO through the regeneration of draw solution. The future potential of FO lies in the success of how it can be hybridized or integrated with other technologies to minimize its own shortcomings, while enhancing the overall performance.

Treatment of greywater by forward osmosis technology: role of the operating temperature

Effects of operating conditions were investigated in terms of water flux, reverse salt flux (RSF) and pollutant rejection in a forward osmosis (FO) membrane system treating synthetic greywater. Changing cross-flow velocity had a slight impact on the performance of the FO membrane. Elevating operating temperature was more effective than increasing draw solution concentration to enhance the water flux. Further observation on the effect of heating mode showed that when the temperature was increased from 20 to 30°C, heating the feed solution (FS) side was better than heating the draw solution (DS) side or heating both sides; further increasing the temperature to 40 and 50°C, heating both the FS and DS achieved much higher water flux compared with only increasing the FS or DS temperature. Under isothermal conditions, a higher water flux and a lower RSF were achieved at 40°C than at other temperatures. Changing either FS or DS temperature had similar influences on water flux and RSF. The FO process revealed high rejection of nitrate (95.7%-100%), ammonia nitrogen (98.8%-100%), total nitrogen (97.4%-99.9%), linear alkylbenzene sulfonate (100%) and Mg (97.5%-100%). A mathematical model that could well simulate the water flux evolution in the present FO system was recommended.

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.

Entrapped-cells-based anaerobic forward osmosis membrane bioreactor treating medium-strength domestic wastewater: Fouling characterization and performance evaluation

A novel entrapped cells-based-anaerobic forward osmosis membrane bioreactor (E-FOMBR) was developed. Its performance and fouling were investigated in comparison with suspended cells-based-anaerobic forward osmosis membrane bioreactor (S-FOMBR). E-FOMBR and S-FOMBR were operated under the same conditions with two widely used draw solutions (NaCl and (NH₄)₂SO₄). The membrane fouling especially irreversible fouling in S-FOMBR was more severe than that in E-FOMBR regardless of the type of draw solution. The permeate flux of E-FOMBR were 1.79 and 1.85 LMH while those of S-FOMBR were 1.49 and 1.14 LMH with NaCl and (NH₄)₂SO₄ as draw solutions, respectively. More deterioration of biological activity (suggested by lower organic removal) due to accumulation of salt was observed in S-FOMBR compared to E-FOMBR. Proteobacteria dominated in both FOMBRs but was more abundant in E-FOMBR than S-FOMBR. The superiority of E-FOMBR over S-FOMBR included higher and stable system performance, higher flux, and longer operation time.

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.

Advanced membrane bioreactors systems: New materials and hybrid process design

Membrane bioreactor (MBR) is deemed as one of the most powerful technologies for efficient municipal and industrial wastewater treatment around the world. However, low microbial activity of activated sludge and serious membrane fouling still remain big challenges in worldwide application of MBR technology. Nowadays, more and more progresses on the research and development of advanced MBR with new materials and hybrid process are just on the way. In this paper, an overview on the perspective of high efficient strains applied into MBR for biological activity enhancement and fouling reduction is provided first. Secondly, as emerging fouling control strategy, design and fabrication of novel anti-fouling composited membranes are comprehensively highlighted. Meanwhile, hybrid MBR systems integrated with some novel dynamic membrane modules and/or with other technologies like advanced oxidation processes (AOPs) are introduced and compared. Finally, the challenges and opportunities of advanced MBRs combined with bioenergy production in wastewater treatment are discussed.

The role of salinity on the changes of the biomass characteristics and on the performance of an OMBR treating tannery wastewater

Tannery wastewaters are difficult to treat biologically due to the high salinity and organic matter concentration. Conventional treatments, like sequential batch reactors (SBR) and membrane bioreactors (MBR), have showed settling problems, in the case of SBR, and ultrafiltration (UF) membrane fouling in the case of MBR, slowing their industrial application. In this work, the treatment of tannery wastewater with an osmotic membrane bioreactor (OMBR) is assessed. Forward osmosis (FO) membranes are characterized by a much lower fouling degree than UF membranes. The permeate passes through the membrane pores (practically only water by the high membrane rejection) from the feed solution to the draw solution, which is also an industrial wastewater (ammonia absorption effluent) in this work. Experiments were carried out at laboratory scale with a FO CTA-NW membrane from Hydration Technology Innovations (HTI). Tannery wastewater was treated by means of an OMBR using as DS an actual industrial wastewater mainly consisting of ammonium sulphate. The monitoring of the biological process was carried out with biological indicators like microbial hydrolytic enzymatic activities, dissolved and total adenosine triphosphate (ATP) in the mixed liquor and microbial population. Results indicated a limiting conductivity in the reactor of 35 mS cm^-1 (on the 43th operation day), from which process was deteriorated. This process performance diminution was associated by a high decrease of the dehydrogenase activity and a sudden increase of the protease and lipase activities. The increase of the bacterial stress index also described appropriately the process performance. Regarding the relative abundance of bacterial phylotypes, 37 phyla were identified in the biomass. Proteobacteria were the most abundant (varying the relative abundance between 50.29% and 34.78%) during the first 34 days of operation. From this day on, Bacteroidetes were detected in a greater extent varying the relative abundance of this phylum between 27.20% and 40.45%.

Modeling methane production in anaerobic forward osmosis bioreactor using a modified anaerobic digestion model No. 1

Anaerobic membrane bioreactor (AnMBR) using microfiltration (MF) or ultrafiltration (UF) membranes was introduced to enhance poor biomass retention of conventional anaerobic digestion (CAD). Recently, forward osmosis (FO) membrane have been applied to AnMBR, which is called AnFOMBR. FO membrane assures not only high biomass retention but also high removal efficiency for low molecular weight (LMW) matters. Methane production rates in CAD, AnMBR, and AnFOMBR were compared using a modified IWA anaerobic digestion model No. 1 (ADM1) in this work. Accumulation of biomass in AnMBR/AnFOMBR results in enhanced biochemical reaction and gains more methane production. AnFOMBR may experience a significant inhibition by accumulated free ammonia and cations, although concentrated soluble substrates rejected by FO membrane are favorable for more methane production. Rejection rate of inorganic nitrogen is a key parameter to determine the inhibition in methane production of AnFOMBR.

Assessing the integration of forward osmosis and anaerobic digestion for simultaneous wastewater treatment and resource recovery

This study assessed the performance and key challenges associated with the integration of forward osmosis (FO) and anaerobic digestion for wastewater treatment and resource recovery. Using a thin film composite polyamide FO membrane, maximising the pre-concentration factor (i.e. system water recovery) resulted in the enrichment of organics and salinity in wastewater. Biomethane potential evaluation indicated that methane production increased correspondingly with the FO pre-concentration factor due to the organic retention in the feed solution. At 90% water recovery, about 10% more methane was produced when using NaOAc compared with NaCl because of the contribution of biodegradable reverse NaOAc flux. No negative impact on anaerobic digestion was observed when wastewater was pre-concentrated ten-fold (90% water recovery) for both draw solutes. Interestingly, the unit cost of methane production using NaOAc was slightly lower than NaCl due to the lower reverse solute flux of NaOAc, although NaCl is a much cheaper chemical.

Salinity build-up in osmotic membrane bioreactors: Causes, impacts, and potential cures

Osmotic membrane bioreactor (OMBR), which integrates forward osmosis (FO) with biological treatment, has been developed to advance wastewater treatment and reuse. OMBR is superior to conventional MBR, particularly in terms of higher effluent quality, lower membrane fouling propensity, and higher membrane fouling reversibility. Nevertheless, advancement and future deployment of OMBR are hindered by salinity build-up in the bioreactor (e.g., up to 50 mS/cm indicated by the mixed liquor conductivity), due to high salt rejection of the FO membrane and reverse diffusion of the draw solution. This review comprehensively elucidates the relative significance of these two mechanisms towards salinity build-up and its associated effects in OMBR operation. Recently proposed strategies to mitigate salinity build-up in OMBR are evaluated and compared to highlight their potential in practical applications. In addition, the complementarity of system optimization and modification to effectively manage salinity build-up are recommended for sustainable OMBR development.

Permeability recovery of fouled forward osmosis membranes by chemical cleaning during a long-term operation of anaerobic osmotic membrane bioreactors treating low-strength wastewater

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 (H₂O₂) 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 H₂O₂ 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% H₂O₂ 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.

Impacts of inorganic draw solutes on the performance of thin-film composite forward osmosis membrane in a microfiltration assisted anaerobic osmotic membrane bioreactor

A Donnan equilibrium led to a higher NH₄⁺–N concentration and more severe FO biofouling for the draw solutes NaCl and MgCl₂, respectively.