Integration of bio-electrochemical cell in membrane bioreactor for membrane cathode fouling reduction through electricity generation

Pseudomonas aeruginosa promoted microbial fuel cells for cytidine acid production wastewater treatment

Microbial fuel cell (MFC) can convert the chemical energy of organic matter in wastewater into electrical energy with high degradation efficiency. In this study, a type of specialized microorganism, Pseudomonas aeruginosa, was screened and added to an MFC to promote the degradation of wastewater generated during the production of cytidine acid while improving the performance of the MFC. The MFC achieved a maximum voltage of 57.7 ± 4.4 mV and a maximum power density of 1.9 ± 0.1 mW/m2; moreover, the degradation efficiencies of chemical oxygen demand (COD), total phosphorus (TP), and phosphate reached 76.3 ± 2.8%, 80.3 ± 3.3%, and 85.3 ± 3.5%, respectively. Gas chromatography-mass spectrometry (GC-MS) and metabolomics analysis revealed that Pseudomonas aeruginosa could effectively degrade organic matter in wastewater. Additionally, the metabolic pathways involved may have been pyrimidine metabolism, arginine and proline metabolism, and taurine and hypotaurine metabolism.

Electro-Conductive Modification of Polyvinylidene Fluoride Membrane for Electrified Wastewater Treatment: Optimization and Antifouling Performance

Electro-conductive membranes coupled with a low-voltage electric field can enhance pollutant removal and mitigate membrane fouling, demonstrating significant potential for electrified wastewater treatment. However, efficient fabrication of conductive membranes poses challenges. An in situ oxidative polymerization approach was applied to prepare PVDF-based conductive membranes (PVDF-CMs) and response surface methodology (RSM) was adopted to optimize modification conditions enhancing membrane performance. The anti-fouling property of the conductive membranes was analyzed using model pollutants. The results indicate that when the concentrations of the pyrrole, BVIMBF4, and FeCl3·6H2O are 0.9 mol/L, 4.8 mmol, and 0.8 mol/L, respectively, the electrical resistance of the PVDF-CM is 93 Ω/sq with the water contact angle of 31°, demonstrating good conductivity and hydrophilicity. Batch membrane filtration experiments coupled with negative voltage indicated that when an external voltage of 2.0 V is applied, membrane fouling rates for the conductive membrane filtering BSA and SA solutions are reduced by 17.7% and 17.2%, respectively, compared to the control (0 V). When an external voltage of 0.5 V is applied, the membrane fouling rate for the conductive membrane filtering HA solution is reduced by 72.6%. This study provides a valuable reference for the efficient preparation of conductive membranes for cost-effective wastewater treatment.

Membrane processes enhanced by various forms of physical energy: A systematic review on mechanisms, implementation, application and energy efficiency

Membrane technologies in water and wastewater treatment have been eagerly pursued over the past decades, yet membrane fouling remains the major bottleneck to overcome. Membrane fouling control methods which couple membrane processes with online in situ application of external physical energy input (EPEI) are getting closer and closer to reality, thanks to recent advances in novel materials and energy deliverance methods. In this review, we summarized recent studies on membrane fouling control techniques that depend on (i) electric field, (ii) acoustic field, (iii) magnetic field, and (iv) photo-irradiation (mostly ultraviolet or visible light). Mechanisms of each energy input were first reported, which defines the applicability of these methods to certain wastewater matrices. Then, means of implementation were discussed to evaluate the compatibility of these fouling control methods with established membrane techniques. After that, preferred applications of each energy input to different foulant types and membrane processes in the experiment reports were summarized, along with a discussion on the trends and knowledge gaps of such fouling control research. Next, specific energy consumption in membrane fouling control and flux enhancement was estimated and compared, based on the experimental results reported in the literature. Lastly, strength and weakness of these methods and future perspectives were presented as open questions.

Performance and mechanism of microbial fuel cell coupled with anaerobic membrane bioreactor system for fouling control

To remove membrane fouling, a bio-electrochemical system that can generate a micro-electric field and micro-current was constructed. After 11 days of operation, the trans-membrane pressure difference of membrane modules in the open- and closed-circuit groups increased by 35.8 kPa and 6.2 kPa, respectively. The concentrations of total polysaccharide and protein in the open-circuit group were 1.8 and 1.1 times higher than those in the closed-circuit group, respectively. In addition, X-ray photoelectron spectroscopy and thermogravimetric analysis showed that inorganic crystals such as calcium carbonate were present on the membrane surface, and the concentration of calcium ion in the control group was 14.7 times that of the experimental group. High-throughput sequencing demonstrated that the enrichment of some electroactive bacteria and other microorganisms has a positive effect on the control of membrane fouling. Therefore, this system can effectively alleviate membrane fouling of a bioreactor, by targeting the membrane foulants.

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

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

Electrochemical impedance spectroscopy (EIS) reveals the role of microbial fuel cell-ceramic membrane bioreactor (MFC-CMBR): Electricity utilization and membrane fouling

Ceramic membrane has become a major concern due to creasing cost and competitive efficiency. Microbial fuel cell-ceramic membrane bioreactor (MFC-CMBR) is considered alternative technology for larger-scale industrial application because of its advantages of convenient detecting and control of membrane fouling. However, MFC-CMBR are highly susceptible to membrane fouling and harsh operating requirements in these wastewaters of different compositions. This research critically discusses that electrochemical response in different types of MFC-CMBRs and control of electricity utilization on ceramic membrane fouling. The experimental results indicated that the application of sludge acclimated in coupling system with higher external resistance could ensure that lower costs (electricity utilization and membrane cleaning) provided enough membrane fouling control. The improved performance of MFC-CMBR-1 could be attributed to its enhanced nitrification/denitrification activity and capacity of electrons migration between electrode and sludge mixture. The coupling system alleviated membrane fouling and impedance increasing by improving the characteristics of sludge (increased particle size, decreased adsorption adhesion free energy), EPS (decreased hydrophobicity, molecular weight distribution regulation). And filtration tests showed that roughness and contact angle for the MFC-CMBR tend for better development compared to CMBR, dependent on the changes in the chemical surface groups as a result of electric distribution ratio. In addition, correlation analysis and filtration experiments showed that the extracellular polymer substances (EPS) enhanced the charge transfer resistance (R_ct), and the protein substance in EPS was the main fouling substance when external resistance was close to the internal resistance of MFC. In summary, the low internal resistance of ceramic membrane lead to obvious better fouling control and electricity utilization than organic membrane, and the paper provides insight into the MFC-CMBR systems for a wide range of detecting membrane fouling and applications of membrane fouling mitigation.

Review on microbial fuel cells applications, developments and costs

The microbial fuel cell (MFC) technology has attracted significant attention in the last years due to its potential to recover energy in a wastewater treatment. The idea of using an MFC in industry is very attractive as the organic wastes can be converted into energy, reducing the waste disposal costs and the energy needs while increasing the company profit. However, taking aside these promising prospects, the attempts to apply MFCs in large-scale have not been succeeded so far since their lower performance and high costs remains challenging. This review intends to present the main applications of the MFC systems and its developments, particularly the advances on configuration and operating conditions. The diagnostic techniques used to evaluate the MFC performance as well as the different modeling approaches are described. Towards the introduction of the MFC in the market, a cost analysis is also included. The development of low-cost materials and more efficient systems, with high higher power outputs and durability, are crucial towards the application of MFCs in industrial/large scale. This work is a helpful tool for discovering new operation and design regimes.

Effect of applied voltage on membrane fouling in the amplifying anaerobic electrochemical membrane bioreactor for long-term operation

A novel and amplifying anaerobic electrochemical membrane bioreactor (AnEMBR, R2) was constructed and operated for a long time (204 days) with synthetic glucose solution having an average chemical oxygen demand (COD) of 315 mg L⁻¹, at different applied voltages and room temperatures. More than twice sodium bicarbonate was added for maintaining a pH of around 6.7 in the supernatant of the reactor R2, close to that of a control reactor called anaerobic membrane bioreactor (AnMBR, R1), after 138 days. And the transmembrane pressure (TMP) for the R2 system was only 0.534 bar at the end of operation and 0.615 bar for the R1 system. Although the electrostatic repulsion force contributed to pushing away the pollutants (proteins, polysaccharose and inorganic salt deposits, and so on), more microorganisms adsorbed and accumulated on the membrane surface after the whole operation, which might result in a rapid increase in membrane filtration resistance in the long-term operation. There were much more exoelectrogenic bacteria, mainly Betaproteobacteria, Deltaproteobacteria and Grammaproteobacteria, on the cathode and the dominant methanogen Methanothrix content on the cathode was three times higher than the AnMBR. The study provides an important theoretical foundation for the application of AnEMBR technology in the treatment of low organic strength wastewater.

A novel and amplifying anaerobic electrochemical membrane bioreactor was constructed and operated for a long time (204 days) with synthetic glucose solution having an average chemical oxygen demand (COD) of 315 mg L⁻¹, at different applied voltages and room temperatures.

Fouling behaviors are different at various negative potentials in electrochemical anaerobic membrane bioreactors with conductive ceramic membranes

Membrane fouling remains a critical challenge to the practical application of anaerobic membrane bioreactor (AnMBR). To address this challenge, a conductive ceramic membrane was prepared for fouling control in AnMBR. By using the conductive membranes, the anti-fouling performances were enhanced about 3 times at potentials below -1.0 V vs Ag/AgCl compared to the conventional AnMBR. The particle size distributions and the electric field calculations suggest that such an enhancement was mainly attributed to the increased particle sizes of foulants in the supernatant and the electric field forces. Moreover, the scanning electron microscope and confocal laser scanning microscope results show that the conductive membrane at -1.0 V could increase the porosity of the gel layer on the surface, whereas the conductive membrane at -2.0 V could inhibit the activity of adhering bacteria. Surprisingly, membrane fouling of electrically-assisted AnMBR (AnEMBR) at -0.5 V was increased, which was attributed to a dense biofilm-like structure formation. Such a result is contrary to the conventional cognition that negative potential could mitigate the membrane fouling. Overall, this work supplements the understanding of the anti-fouling effects of the electric field in AnEMBR, and provides supplementary information for the engineering application of AnEMBR.

Self-Enhanced Decomplexation of Cu-Organic Complexes and Cu Recovery from Wastewaters Using an Electrochemical Membrane Filtration System

Heavy metals in industrial wastewaters are typically present as stable metal-organic complexes with their cost-effective treatment remaining a significant challenge. Herein, a self-enhanced decomplexation scenario is developed using an electrochemical membrane filtration (EMF) system for efficient decomplexation and Cu recovery. Using Cu-EDTA as a model pollutant, the EMF system achieved 81.5% decomplexation of the Cu-EDTA complex and 72.4% recovery of Cu at a cell voltage of 3 V. The ^•OH produced at the anode first attacked Cu-EDTA to produce intermediate Cu-organic complexes that reacted catalytically with the H₂O₂ generated from the reduction of dissolved oxygen at the cathode to initiate chainlike self-enhanced decomplexation in the EMF system. The decomplexed Cu products were further reduced or precipitated at the cathodic membrane surface thereby achieving efficient Cu recovery. By scavenging H₂O₂ (excluding self-enhanced decomplexation), the rate of decomplexation decreased from 8.8 × 10^-1 to 4.1 × 10^-1 h^-1, confirming the important role of self-enhanced decomplexation in this system. The energy efficiency of this system is 93.5 g kWh^-1 for Cu-EDTA decomplexation and 15.0 g kWh^-1 for Cu recovery, which is much higher than that reported in the previous literature (i.e., 7.5 g kWh^-1 for decomplexation and 1.2 g kWh^-1 for recovery). Our results highlight the potential of using EMF for the cost-effective treatment of industrial wastewaters containing heavy metals.

Boosting oxygen reduction and permeability properties of doped iron-porphyrin membrane cathode in microbial fuel cells

To achieve a membrane cathode with excellent performance, iron-porphyrin (Fe(por)) was doped to boost the catalytic and permeability properties in microbial fuel cell (MFC). The membrane cathode with the optimal 0.05 g of Fe(por) (denoted as Fe(por)-0.05) had the highest current density of 10.3 A m^-2 and the lowest charge transfer resistance of 12.6 ± 0.3 Ω. The ring-disk electrode (RDE) results further proved that the oxygen reduction reaction (ORR) occurred on the Fe(por)-0.05 through a direct four-electron transfer pathway. Moreover, the membrane cathode performed better permeability properties under electric filed and the Fe(por)-0.05 + E (E was electric field) obtained the lowest flux attenuation ratio of 14.1 ± 0.2%, which was related to its superior hydrophilicity and strong electrostatic repulsion force. Iron-porphyrin can simultaneously enhance the ORR activity and permeability of membrane cathode, providing a new direction for the practical application in MFCs.

In-situ membrane fouling control by electrooxidation and microbial community in membrane electro-bioreactor treating aquaculture seawater

Ammonia and nitrite in aquaculture recirculating seawater need to be strictly controlled to avoid deleterious effects on aquatic organisms. However, traditional biological approach can hardly meet the standard due to the short hydraulic retention time (HRT) and nitrite accumulation. A Membrane Electro-Bioreactor (MEBR) was developed for ammonia removal enhancement and in-situ electrochemical membrane fouling mitigation. The fouling mechanism was first found to proceed via the standard filtration model. The flux decrease was mainly caused by an internal pore clogging phenomenon. Membrane fouling resistance was enhanced by increasing anode potential from 0 to 1.4 V vs. SCE (Saturated Calomel Electrode). The ammonia removal rate in the MEBR was above 95% (HRT: 2 h, after day-13) and membrane fouling was mitigated that operation duration was extended by 71.4%. Higher total proportion of Proteobacteria, Bacteroidetes, Planctomycetes and Actinobacteria was obtained in the MEBR, suggesting higher nitrification and nitrogen removal potentials.

The growth process of the cake layer and membrane fouling alleviation mechanism in a MBR assisted with the self-generated electric field

The electric field assisted membrane bioreactor (MBR) is an effective technique to alleviate membrane fouling. In this study, the spontaneous electric field was introduced into the MBR to observe the growth process of cake layer on the membrane surface. The external resistance for spontaneous electric field MBR (S-50) and S-500 were 50 Ω and 500 Ω respectively. During the experiments, S-50 maintained the highest electric field intensity of 11.83 mV/cm. The reduction of extracellular polymeric substances (EPS) content in activated sludge, transmembrane pressure (TMP) growth rate reached 52.8% and 51.7% respectively. After 28 days operation, S-50 obtained the minimum contaminant specific biovolume (23.316 μm³/μm²), which was 68.2% lower than that of it in Control-MBR. The metal oxide or metal hydroxide were distributed in the cake layer. EPS played a significant role in the formation and growth of the cake layer. Based on the results obtained in this study, the growth of the biofouling layer on the membrane surface could be divided into three stages. EPS first deposited on the membrane surface, and then microorganisms embedded in the cake layer to form clusters. After that, EPS and total cells further increased and led to a faster biovolume growth rate. Subsequently, the biovolume growth rate decreased in the cake layer. The spontaneous electric field delayed the deposition of EPS on the membrane surface. The produced H₂O₂ and •OH were beneficial to the degradation of organics, causing the smaller contaminant biovolume on the membrane surface. This work aims to provide a theoretical basis for the practical application of the electric field to control membrane fouling.

Feasibility of isolated novel facultative quorum quenching consortiums for fouling control in an AnMBR

Anaerobic membrane bioreactor (AnMBR) technology is being recognized as an appealing strategy for wastewater treatment, however, severity of membrane fouling inhibits its widespread implementations. This study engineered novel facultative quorum quenching consortiums (FQQs) coping with membrane fouling in AnMBRs with preliminary analysis for their quorum quenching (QQ) performances. Herein, Acyl-homoserine lactones (AHLs)-based quorum sensing (QS) in a lab-scale AnMBR initially revealed that N-Hexanoyl-dl-homoserine lactone (C6-HSL), N-Octanoyl-dl-homoserine lactone (C8-HSL) and N-Decanoyl-dl-homoserine lactone (C10-HSL) were the dominant AHLs in AnMBRs in this study. Three FQQs, namely, FQQ-C6, FQQ-C8 and FQQ-C10, were harvested after anaerobic screening of aerobic QQ consortiums (AeQQs) which were isolated by enrichment culture, aiming to degrade C6-HSL, C8-HSL and C10-HSL, respectively. Growth of FQQ-C6 and FQQ-C10 using AHLs as carbon source under anaerobic condition was significantly faster than those using acetate, congruously suggesting that their QQ performance will not be compromised in AnMBRs. All FQQs degraded a wide range of AHLs pinpointing their extensive QQ ability. FQQ-C6, FQQ-C8 and FQQ-C10 remarkably alleviated extracellular polymeric substances (EPS) production in a lab-scale AnMBR by 72.46%, 35.89% and 65.88%, respectively, and FQQ-C6 retarded membrane fouling of the AnMBR by 2 times. Bioinformatics analysis indicated that there was a major shift in dominant species from AeQQs to FQQs where Comamonas sp., Klebsiella sp., Stenotrophomonas sp. and Ochrobactrum sp. survived after anaerobic screening and were the majority in FQQs. High growth rate utilizing AHLs under anaerobic condition and enormous EPS retardation efficiency in FQQ-C6 and FQQ-C10 could be attributed to Comamonas sp.. These findings demonstrated that FQQs could be leveraged for QQ under anaerobic systems. We believe that this was the first work proposing a bacterial pool of facultative QQ candidates holding biotechnological promises for membrane fouling control in AnMBRs.

A Review on Microbial Electrocatalysis Systems Coupled with Membrane Bioreactor to Improve Wastewater Treatment

Microbial electrocatalysis is an electro reaction that uses microorganisms as a biocatalyst, mainly including microbial electrolytic cells (MEC) and microbial fuel cells (MFC), which has been used for wastewater treatment. However, the low processing efficiency is the main drawback for its practical application and the additional energy input of MEC system results in high costs. Recently, MFC/MEC coupled with other treatment processes, especially membrane bioreactors (MBR), has been used for high efficiency and low-cost wastewater treatment. In these systems, the wastewater treatment efficiency can be improved after two units are operated and the membrane fouling of MBR can also be alleviated by the electric energy that was generated in the MFC. In addition, the power output of MFC can also reduce the energy consumption of microbial electrocatalysis systems. This review summarizes the recent studies about microbial electrocatalysis systems coupled with MBR, describing the combination types and microorganism distribution, the advantages and limitations of the systems, and also addresses several suggestions for the future development and practical applications.

A spontaneous electric field membrane bioreactor with the innovative Cu-nanowires conductive microfiltration membrane for membrane fouling mitigation and pollutant removal

In this study, a spontaneous electric field membrane bioreactor (SEF-MBR), equipped with the innovative Cu-nanowires conductive microfiltration membrane, was developed to achieve membrane fouling mitigation and high-quality effluent. The membrane fouling was significantly mitigated due to the presence of spontaneous electric field that the intensity of the spontaneous electric field in the established SEF-MBR was up to 0.073 V/cm. After over 2-month operation, the membrane flux of SEF-MBR was 2.1 times that of the control reactor. The thickness of fouling layer on the Cu-nanowires conductive membrane surface was about 80 μm, which was far thinner than that on the surface of commercial polyvinylidene fluoride (PVDF) membrane. Meanwhile, it was featured with the lower microbe density and extracellular polymeric substance (EPS) content. The effluent quality of SEF-MBR met the first-class discharge standards, and the removal rates were 94.5% for chemical oxygen demand (COD), 99.8% for NH 4 + - N , 78.5% for total nitrogen (TN), and 86.6% for total phosphorus (TP). The established system with the innovative Cu-nanowires conductive membrane showed a promising prospect for using the spontaneous electric field to mitigate membrane fouling and achieve high-quality effluent without extra power consumption. PRACTITIONER POINTS: The innovative Cu-NWs conductive microfiltration membrane was prepared. The spontaneous electric field in the novel SEF-MBR mitigated membrane fouling. The fouling layer of the novel SEF-MBR was thinner with lower microbe and EPS content. The effluent quality of the novel SEF-MBR met the first-class discharge standard.

Anaerobic membrane bioreactors for wastewater treatment: Novel configurations, fouling control and energy considerations

Water shortage, public health and environmental protection are key motives to treat wastewater. The widespread adoption of wastewater as a resource depends upon development of an energy-efficient technology. Anaerobic membrane bioreactor (AnMBR) technology has gained increasing popularity due to their ability to offset the disadvantages of conventional treatment technologies. However there are several hurdles, yet to climb over, for wider spread and scale-up of the technology. This paper reviews fundamental aspects of anaerobic digestion of wastewater, and identifies the challenges and opportunities to the further development of AnMBRs. Membrane fouling and its implications are discussed, and strategies to control membrane fouling are proposed. Novel AnMBR configurations are discussed as an integrated approach to overcome technology limitations. Energy demand and recovery in AnMBRs is analyzed. Finally key issues that require urgent attention to facilitate global penetration of AnMBR technology are highlighted.

Membrane bioreactors and electrochemical processes for treatment of wastewaters containing heavy metal ions, organics, micropollutants and dyes: Recent developments

Research and development activities on standalone systems of membrane bioreactors and electrochemical reactors for wastewater treatment have been intensified recently. However, several challenges are still being faced during the operation of these reactors. The current challenges associated with the operation of standalone MBR and electrochemical reactors include: membrane fouling in MBR, set-backs from operational errors and conditions, energy consumption in electrochemical systems, high cost requirement, and the need for simplified models. The advantage of this review is to present the most critical challenges and opportunities. These challenges have necessitated the design of MBR derivatives such as anaerobic MBR (AnMBR), osmotic MBR (OMBR), biofilm MBR (BF-MBR), membrane aerated biofilm reactor (MABR), and magnetically-enhanced systems. Likewise, electrochemical reactors with different configurations such as parallel, cylindrical, rotating impeller-electrode, packed bed, and moving particle configurations have emerged. One of the most effective approaches towards reducing energy consumption and membrane fouling rate is the integration of MBR with low-voltage electrochemical processes in an electrically-enhanced membrane bioreactor (eMBR). Meanwhile, research on eMBR modeling and sludge reuse is limited. Future trends should focus on novel/fresh concepts such as electrically-enhanced AnMBRs, electrically-enhanced OMBRs, and coupled systems with microbial fuel cells to further improve energy efficiency and effluent quality.

A novel aerobic electrochemical membrane bioreactor with CNTs hollow fiber membrane by electrochemical oxidation to improve water quality and mitigate membrane fouling

A novel electro-assisted membrane bioreactor (EMBR) was constructed by integrating conductive carbon nanotubes hollow fiber membranes (CNTs-HFMs) into an aerobic activated sludge system. Herein, the CNTs-HFMs served as anode and filtration core simultaneously. Contrasted with the other two MBRs (PVDF-HFMs and CNTs-HFMs without electro-assistance), the effluent COD and NH₄⁺N were lower than 40 mg/L and 3 mg/L at +1.0 V even HRT as short as 4 h. However, they were mostly over 50 mg/L (COD) and 5 mg/L (NH₄⁺N) under the same conditions in the other two MBRs. The hydraulic cleaning for electro-assisted CNTs-HFMs was carried out only once during 60-day operation, and the permeate flux recovered to 100% of the original status. While four and five times hydraulic cleaning were executed for other two MBRs (PVDF-HFMs and CNTs-HFMs), respectively. Furthermore, merely 50 min continuous electrochemical oxidation was enough to resume flux of the heavily fouled CNTs-HFMs, i.e. flux recovered to 2020.87 L/(bar•m²•h) from 394.68 L/(bar•m²•h) (pure water flux, ∼2200 L/(bar·m²·h)). Simpson and Shannon indexes indicated enhanced microbial community stability in EMBR. Thus, electro-assisted CNTs-HFMs endow EMBR excellent anti-fouling ability and good effluent quality.

Novel Anaerobic Electrochemical Membrane Bioreactor with a CNTs Hollow Fiber Membrane Cathode to Mitigate Membrane Fouling and Enhance Energy Recovery

A novel anaerobic treatment system that combines the impact of applied voltage with membrane filtration over carbon nanotubes hollow fiber membranes (CNTs-HFMs) was developed at low temperature (15-20 °C) to mitigate membrane fouling, treat wastewater, and recover energy (CH₄). Herein, electro-assisted CNTs-HFMs served a dual function as the cathode and membrane filtration. In contrast with other two anaerobic membrane bioreactors (AnMBRs; polyvinylidene fluoride hollow fiber membranes and CNTs-HFMs without electro-assistance), the CNTs-HFMs with electro-assistance (-1.2 V applied voltage) had slower transmembrane pressure (TMP) increasing rates and better TMP recovery with a more than 95% effluent chemical oxygen demand (COD) removal rate during an almost 100-day operation period. This result can be attributed to the presence of an electrostatic repulsion force pushing pollutants (mainly extracellular polymeric substances, EPS) away from the membrane surface, thereby hindering the formation of a gel layer and mitigating membrane pore blocking in the anaerobic electro-assisted membrane bioreactor (AnEMBR). Due to the almost two-times higher Methanomicrobia content and more H₂-utilizing methanogens than the other two AnMBRs, approximately more than 111.12 mL/gVSS d of CH₄ was obtained in the AnEMBR with electro-assistance. This work provides an efficient strategy for mitigating membrane fouling, improving water quality, and enhancing CH₄ yield.

The mechanism of synergistic effect between iron-carbon microelectrolysis and biodegradation for strengthening phenols removal in coal gasification wastewater treatment

A novel iron-carbon microelectrolysis (ICME) inoculated with activated sludge (AS) process was specifically designed to look into the roles of microelectrolysis and biodegradation as well as their synergistic effect on phenols removal in coal gasification wastewater (CGW) treatment. The results indicated that the removal efficiency of COD, phenols and TOC in integrated ICME-AS process reached 87.36 ± 2.98%, 92.62 ± 0.76% and 84.45 ± 0.65%, respectively. Moreover, phenols-degrading bacteria and electrochemical-active bacteria presented better adaptability to phenolic impact. Meanwhile their syntrophic interaction was driven under the simulation of microelectrolysis. Furthermore, electrochemical redox efficiency was significantly improved, and the corresponding maximum power output reached 0.043 ± 0.01 mW/cm². Apparently, the synergistic effect between microelectrolysis and biological action effectively strengthened phenols degradation and electricity generation. The results proved that the integrated ICME-AS process was a promising technology applied for CGW and other refractory industrial wastewater treatments.

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.

Challenges in the application of microbial fuel cells to wastewater treatment and energy production: A mini review

Wastewater is now considered to be a vital reusable source of water reuse and saving energy. However, current wastewater has multiple limitations such as high energy costs, large quantities of residuals being generated and lacking in potential resources. Recently, great attention has been paid to microbial fuel cells (MFCs) due to their mild operating conditions where a variety of biodegradable substrates can serve as fuel. MFCs can be used in wastewater treatment facilities to break down organic matter, and they have also been analysed for application as a biosensor such as a sensor for biological oxygen which demands monitoring. MFCs represent an innovation technology solution that is simple and rapid. Despite the advantages of this technology, there are still practical barriers to consider including low electricity production, current instability, high internal resistance and costly materials used. Thus, many problems must be overcome and doing this requires a more detailed analysis of energy production, consumption, and application. Currently, real-world applications of MFCs are limited due to their low power density level of only several thousand mW/m². Efforts are being made to improve the performance and reduce the construction and operating costs of MFCs. This paper explores several aspects of MFCs such as anode, cathode and membrane, and in an effort to overcome the practical challenges of this system.

Microbial fuel cell and membrane bioreactor coupling system: recent trends

Membrane bioreactor (MBR) and microbial fuel cell (MFC) are new technologies based on microbial process. MBR takes separation process as the core to achieve the high efficient separation and enrichment the beneficiation of microbes during the biological treatment. MFC is a novel technology based on electrochemical process to realize the mutual conversion between biomass energy and electric energy, in order to solve the problems of serious membrane fouling and low efficiency of denitrification in membrane bioreactor, the low power generation efficiency, and unavailability of bioelectric energy of MFC. In recent years, MFC-MBR coupling system emerged. It can effectively mitigate the membrane fouling and reduce the excess sludge production. Simultaneously, the electricity can be used effectively. The new coupling system has good prospects for development. In this paper, we summarized the research progresses of the two kinds of coupling systems in recent years and analyzed the coupling structure and forms. Based on the above, the future development fields of the MFC-MBR coupling system were prospected.

Dual-Function Electrocatalytic and Macroporous Hollow-Fiber Cathode for Converting Waste Streams to Valuable Resources Using Microbial Electrochemical Systems

Dual-function electrocatalytic and macroporous hollow-fiber cathodes are recently proposed as promising advanced material for maximizing the conversion of waste streams such as wastewater and waste CO₂ to valuable resources (e.g., clean freshwater, energy, value-added chemicals) in microbial electrochemical systems. The first part of this progress report reviews recent developments in this type of cathode architecture for the simultaneous recovery of clean freshwater and energy from wastewater. Critical insights are provided on suitable materials for fabricating these cathodes, as well as addressing some challenges in the fabrication process with proposed strategies to overcome them. The second and complementary part of the progress report highlights how the unique features of this cathode architecture can solve one of the intrinsic bottlenecks (gas-liquid mass transfer limitation) in the application of microbial electrochemical systems for CO₂ reduction to value-added products. Strategies to further improve the availability of CO₂ to microbial catalysts on the cathode are proposed. The importance of understanding microbe-cathode interactions, as well as electron transfer mechanisms at the cathode-cell and cell-cell interface to better design dual-function macroporous hollow-fiber cathodes, is critically discussed with insights on how the choice of material is important in facilitating direct electron transfer versus mediated electron transfer.

Membrane electro-oxidizer: A new hybrid membrane system with electrochemical oxidation for enhanced organics and fouling control

The synergistic combination of membrane filtration with advanced oxidation is of particular interest for next-generation wastewater treatment technologies. A membrane electro-oxidizer (MEO) hybridizing a submerged microfilter and an electrochemical cell was developed and investigated for tertiary treatment of secondary industrial (textile) wastewater effluent. Laboratory- and pilot-scale MEO systems were designed and evaluated for treatment efficiency and membrane fouling control. The MEO achieved substantial removal of color (50-90%), turbidity (>90%), and bacteria (>4 log) as well as chemical oxygen demand (13-31%) and 1,4-dioxane (∼25-53%). Fluorescence-based parallel factor analysis disclosed the degradation of humic-like organics with fluorophores. Size exclusion chromatograms with organic carbon detection confirmed the removal of specific organic molecules with ∼100 Da. While investigating the effects of oxidant quenching agents, reactive chlorine species and hydrogen peroxide were found to be most responsible for the anodic oxidation of secondary effluent organics. The efficacy of membrane fouling mitigation by the MEO was greater when higher electric current densities were applied, but was not dependent on the number of electrochemical cells installed. The MEO is a promising technology for enhanced organics removal with simultaneous fouling control due to its multifunctional active oxidants.

A bio-electrochemical membrane system for more sustainable wastewater treatment with MnO2/PANI modified stainless steel cathode and photosynthetic provision of dissolved oxygen by algae

A competitive sewage treatment technology should meet the standard of water quality requirement and accomplish recovery of potential energy. This study presents such a new system, with coupled membrane bioreactor-microbial fuel cell features, which can not only treat wastewater, but also recovers energy from wastewater by electricity generation, and form a new resource by photosynthesis while providing the dissolved oxygen by algae. Specifically, in the system, the MnO₂/polyaniline is used to modify the stainless steel mesh and to function well as system membrane and cathode, with satisfactory filtration and catalysis performance. The system enables continuous wastewater treatment with stable pollutant removal and electricity generation. Under the membrane flux of 119.4 Lm^-2 h^-1, a maximum power density of 1.2 W m^-3 can be achieved, the algae multiply 6.1 times, and satisfactory wastewater treatment effect is achieved.

Development of a novel proton exchange membrane-free integrated MFC system with electric membrane bioreactor and air contact oxidation bed for efficient and energy-saving wastewater treatment

A novel combined system integrating MFC and electric membrane bioreactor (EMBR) was developed, in which a quartz sand chamber (QSC) was used, replacing expensive proton exchange membrane (PEM). An air contact oxidation bed (ACOB) and embedded trickling filter (TF) with filled volcano rock, was designed to increase dissolved oxygen (DO) in cathodic EMBR to save aeration cost. Membrane fouling in EMBR was successful inhibited/reduced by the generated bioelectricity of the system. The combined system demonstrated superior effluent quality in removing chemical oxygen demand (>97%) and ammonia nitrogen (>93%) during the stable operation, and the phosphorus removal was about 50%. Dominant bacteria (Nitrosomonas sp.; Comamonas sp.; Candidatus Kuenenia) played important roles in the removal of organic matter and ammonia nitrogen. The system has good application prospects in the efficient use of water and the development of sustainable wastewater recycling technology.

Electro-Conductive Membranes for Permeation Enhancement and Fouling Mitigation: A Short Review

The research on electro-conductive membranes has expanded in recent years. These membranes have strong prospective as key components in next generation water treatment plants because they are engineered in order to enhance their performance in terms of separation, flux, fouling potential, and permselectivity. The present review summarizes recent developments in the preparation of electro-conductive membranes and the mechanisms of their response to external electric voltages in order to obtain an improvement in permeation and mitigation in the fouling growth. In particular, this paper deals with the properties of electro-conductive polymers and the preparation of electro-conductive polymer membranes with a focus on responsive membranes based on polyaniline, polypyrrole and carbon nanotubes. Then, some examples of electro-conductive membranes for permeation enhancement and fouling mitigation by electrostatic repulsion, hydrogen peroxide generation and electrochemical oxidation will be presented.

Contaminant Removal from Source Waters Using Cathodic Electrochemical Membrane Filtration: Mechanisms and Implications

Removal of recalcitrant anthropogenic contaminants from water calls for the development of cost-effective treatment technologies. In this work, a novel electrochemical membrane filtration (EMF) process using a conducting microfiltration membrane as the cathode has been developed and the degradation of sulphanilic acid (SA) examined. The electrochemical degradation of SA in flow-by mode followed pseudo-first-order kinetics with the degradation rate enhanced with increase in charging voltage. Hydrogen peroxide as well as oxidants such as HO^• and Fe(IV)O²⁺ were generated electrochemically with HO^• found to be the dominant oxidant responsible for SA degradation. In addition to the anodic splitting of water, HO^• was formed via a heterogeneous Fenton process with surface-bound Fe(II) resulting from aerobic corrosion of the steel mesh. In flow-through mode, the removal rate of SA was 13.0% greater than obtained in flow-by mode, presumably due to the better contact of the contaminant with the oxidants generated in the vicinity of the membrane surface. A variety of oxidized products including hydroquinone, p-benzoquinone, oxamic acid, maleic acid, fumaric acid, acetic acid, formic acid, and oxalic acid were identified and an electrochemical degradation pathway proposed. These findings highlight the potential of the cathodic EMF process as an effective technology for water purification.

A critical review of bioelectrochemical membrane reactor (BECMR) as cutting-edge sustainable wastewater treatment

Reclamation of wastewater along with minimum energy utilization has been the paramount concern today. Tremendous industrialization and corresponding demographic resulted in elevated water and energy demand; however, scarcity of sufficient water and energy resource triggers rigorous research for sustainable water treatment technology. Recent technologies like activated sludge, filtration, adsorption, coagulation, and oxidation have been considered as promising sustainable technologies, but high cost, low efficiency, and efficacy are the major concerns so far. Wastewater is food for billions of bacteria, where some exceptional bacterial species have the ability to transport electrons that are produced during metabolism to outside the cell membrane. Indeed, wastewater can itself be considered as a prominent candidate to resolve the problem of sustainability. Bioelectrochemical membrane reactor is a promising technology, which is an integration of microbial fuel cell (MFC) to membrane bioreactor (MBR). It promises the benefit of harvesting electricity while biologically treating any type of wastewater to the highest extent while passing wastewater through anaerobic, aerobic, and integrated membrane compartments in successive manner. In this review, we provide critical rethinking to take this idea of integration of MFC-MBR and apply them to produce a fully functional prototype of bioelectrochemical membrane reactor that could be used commercially.

Effects of current generation and electrolyte pH on reverse salt flux across thin film composite membrane in osmotic microbial fuel cells

Osmotic microbial fuel cells (OsMFCs) take advantages of synergy between forward osmosis (FO) and microbial fuel cells (MFCs) to accomplish wastewater treatment, current generation, and high-quality water extraction. As an FO based technology, OsMFCs also encounter reverse salt flux (RSF) that is the backward transport of salt ions across the FO membrane into the treated wastewater. This RSF can reduce water flux, contaminate the treated wastewater, and increase the operational expense, and thus must be properly addressed before any possible applications. In this study, we aimed to understand the effects of current generation and electrolyte pH on RSF in an OsMFC. It was found that electricity generation could greatly inhibit RSF, which decreased from 16.3 ± 2.8 to 3.9 ± 0.7 gMH when the total Coulomb production increased from 0 to 311 C. The OsMFC exhibited 45.9 ± 28.4% lower RSF at the catholyte pH of 3 than that at pH 11 when 40 Ω external resistance was connected. The amount of sodium ions transported across the FO membrane was 18.3-40.7% more than that of chloride ions. Ion transport was accomplished via diffusion and electrically-driven migration, and the theoretical analysis showed that the inhibited electrically-driven migration should be responsible for the reduced RSF. These findings are potentially important to control and reduce RSF in OsMFCs or other osmotic-driven processes.

Graphene-Coated Hollow Fiber Membrane as the Cathode in Anaerobic Electrochemical Membrane Bioreactors--Effect of Configuration and Applied Voltage on Performance and Membrane Fouling

Electrically conductive, graphene-coated, hollow-fiber porous membranes were used as cathodes in anaerobic electrochemical membrane bioreactors (AnEMBRs) operated at different applied voltages (0.7 and 0.9 V) using a new rectangular reactor configuration compared to a previous tubular design (0.7 V). The onset of biofouling was delayed and minimized in rectangular reactors operated at 0.9 V compared to those at 0.7 V due to higher rates of hydrogen production. Maximum transmembrane pressures for the rectangular reactor were only 0.10 bar (0.7 V) or 0.05 bar (0.9 V) after 56 days of operation compared to 0.46 bar (0.7 V) for the tubular reactor after 52 days. The thickness of the membrane biofouling layer was approximately 0.4 μm for rectangular reactors and 4 μm for the tubular reactor. Higher permeate quality (TSS = 0.05 mg/L) was achieved in the rectangular AnEMBR than that in the tubular AnEMBR (TSS = 17 mg/L), likely due to higher current densities that minimized the accumulation of cells in suspension. These results show that the new rectangular reactor design, which had increased rates of hydrogen production, successfully delayed the onset of cathode biofouling and improved reactor performance.

A new design of activated carbon membrane air-cathode for wastewater treatment and energy recovery

A novel design of membrane air-cathode (MAC) with a double activated carbon layer was developed and served as a filtration cathode in a single chambered microbial fuel cell.

Electroconductive and electroresponsive membranes for water treatment

In populated, water-scarce regions, seawater and wastewater are considered as potable water resources that require extensive treatment before being suitable for consumption. The separation of water from salt, organic, and inorganic matter is most commonly done through membrane separation processes. Because of permeate flux and concentration polarization, membranes are prone to fouling, resulting in a decline in membrane performance and increased energy demands. As the physical and chemical properties of commercially available membranes (polymeric and ceramic) are relatively static and insensitive to changes in the environment, there is a need for stimuli-reactive membranes with controlled, tunable surface and transport properties to decrease fouling and control membrane properties such as hydrophilicity and permselectivity. In this review, we first describe the application of electricity-conducting and electricity-responsive membranes (ERMs) for fouling mitigation. We discuss their ability to reduce organic, inorganic, and biological fouling by several mechanisms, including control over the membrane’s surface morphology, electrostatic rejection, piezoelectric vibrations, electrochemical reactions, and local pH changes. Next, we examine the use of ERMs for permselectivity modification, which allows for the optimization of rejection and control over ion transport through the application of electrical potentials and the use of electrostatically charged membrane surfaces. In addition, electrochemical reactions coupled with membrane filtration are examined, including electro-oxidation and electro-Fenton reactions, demonstrating the capability of ERMs to electro-oxidize organic contaminates with high efficiency due to high surface area and reduced mass diffusion limitations. When applicable, ERM applications are compared with commercial membranes in terms of energy consumptions. We conclude with a brief discussion regarding the future directions of ERMs and provide examples of several applications such as pore size and selectivity control, electrowettability, and capacitive deionization. To provide the reader with the current state of knowledge, the review focuses on research published in the last 5 years.

Integrating membrane filtration into bioelectrochemical systems as next generation energy-efficient wastewater treatment technologies for water reclamation: A review

Bioelectrochemical systems (BES) represent an energy-efficient approach for wastewater treatment, but the effluent still requires further treatment for direct discharge or reuse. Integrating membrane filtration in BES can achieve high-quality effluents with additional benefits. Three types of filtration membranes, dynamic membrane, ultrafiltration membrane and forward osmosis membrane that are grouped based on pore size, have been studied for integration in BES. The integration can be accomplished either in an internal or an external configuration. In an internal configuration, membranes can act as a separator between the electrodes, or be immersed in the anode/cathode chamber as a filtration component. The external configuration allows BES and membrane module to be operated independently. Given much progress and interest in the integration of membrane filtration into BES, this paper has reviewed the past studies, described various integration methods, discussed the advantages and limitations of each integration, and presented challenges for future development.

Long-term investigation of a novel electrochemical membrane bioreactor for low-strength municipal wastewater treatment

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

Carbon filtration cathode in microbial fuel cell to enhance wastewater treatment

A homogeneous carbon membrane with multi-functions of microfiltration, electron conduction, and oxygen reduction catalysis was fabricated without using noble metals. The produced carbon membrane has a pore size of 553nm, a resistance of 6.0±0.4Ωcm(2)/cm, and a specific surface area of 32.2m(2)/g. After it was assembled in microbial fuel cell (MFC) as filtration air cathode, a power density of 581.5mW/m(2) and a current density of 1671.4mA/m(2) were achieved, comparable with previous Pt air cathode MFCs. The filtration MFC was continuously operated for 20days and excellent wastewater treatment performance was also achieved with removal efficiencies of TOC (93.6%), NH4(+)-N (97.2%), and total nitrogen (91.6%). In addition, the carbon membrane was much cheaper than traditional microfiltration membrane, suggesting a promising multi-functional material in wastewater treatment field.