In-situ integration of microbial fuel cell with hollow-fiber membrane bioreactor for wastewater treatment and membrane fouling mitigation

Sludge bound-EPS solubilization enhance CH4 bioconversion and membrane fouling mitigation in electrochemical anaerobic membrane bioreactor: Insights from continuous operation and interpretable machine learning algorithms

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days' operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/Lreactor/d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/Lreactor/d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPSPS and S-EPSPN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR.

Elucidating the roles of Cr(VI)-Cu(II) Co-pollution in the stress of aniline degradation stress: Insights into metabolic pathways and functional genes

In order to examine the impact of Cu(II)-Cr(VI) co-pollution in printing and dyeing wastewater on the aniline biodegradation system (ABS), loading experiments were conducted on ABS at varying concentrations of Cu(II)-Cr(VI). The synergistic stress imposed by Cu(II)-Cr(VI) accelerated the deterioration of the systems, with only the C2-3 (2 mg/L Cr(VI)-3 mg/L Cu(II)) sustaining stable operation for 42 days. However, its nitrogen removal performance remained significantly impaired, resulting in a total nitrogen (TN) removal rate below 40%. High-throughput sequencing analysis revealed a stronger correlation between Cr(VI) and microbial diversity compared to Cu(II). Metagenomic sequencing results demonstrated that Cu(II) emerged as the dominant factor influencing the distribution of dominant bacteria in C2-3, as well as its contribution to contaminant degradation. The complex co-pollution systems hindered aniline degradation and nitrogen metabolism through the combined bio-toxicity of heavy metals and aniline, thereby disrupting the transport chain within the systems matrix.

Evolution of aniline degradation and nitrogen removal performance in electro-enhanced sequence batch reactor under salinity stress: Sludge characteristics and microbial diversity

To explore the influence mechanism of different concentrations of salinity on the electro-enhanced aniline biodegradation system, a control group and experimental groups (0%-NaCl, 0.5%-NaCl, 1.5%-NaCl, 2.5%-NaCl, 3.5%-NaCl) were established. The experimental results showed that the electric field strengthened the denitrification performance, while salinity had little effect on the degradation efficiency of aniline and chemical oxygen demand (COD). The removal rate of TN reached 79.6% and 74.9% in 0.5%-NaCl and 1.5%-NaCl, respectively, which were superior than 0%-NaCl. As salinity increased, the nitrogen removal effect was negatively affected. Microbial diversity analysis indicated that the microbial community structure was uniform in the control group, 0%-NaCl, and 0.5%-NaCl, with the dominant genus OLB8 ensuring the nitrogen removal performance. In contrast, in the 2.5%-NaCl and 3.5%-NaCl experimental groups, the organic degrading bacteria were still active, while nitrifiers and denitrifiers were severely damaged. In conclusion, this study suggested that low concentrations of salinity can improve the decontamination performance of the electro-enhanced aniline biodegradation system, while high concentrations of salinity could lead to the collapse of the decontamination mechanism.

Research progress of electrically-enhanced membrane bioreactor (EMBR) in pollutants removal and membrane fouling alleviation

Membrane bioreactor (MBR), as a biological unit for wastewater treatment, has been proven to have the advantages of simple structure and high pollutant removal rate. However, membrane fouling limits its wide application, and it is crucial to adopt effective membrane fouling control methods. As a new type of membrane fouling control technology, electrically-enhanced MBR (EMBR) has attracted more interest recently. It uses the driving force of electric field to make pollutants flocculate or move away from the membrane surface to achieve the purpose of inhibiting membrane fouling. This paper expounds the configuration of EMBR in recent years, including the location of membrane components, the way of electric field application and the selection of electrode and membrane materials, and provides the latest development information in various aspects. The enhanced effect of electric field on the removal of comprehensive and refractory pollutants is outlined in detail. And from the perspective of sludge properties (EPS, SMP, sludge particle size, zeta potential and microbial activity), the influence of electric field on sludge characteristics and the relationship between the changes of sludge properties in EMBR and membrane fouling are discussed. Moreover, the electrochemical mechanisms of electric field alleviating membrane fouling are elucidated from electrophoresis, electrostatic repulsion, electroflocculation, electroosmosis, and electrochemical oxidation, and the regeneration and stability of EMBR are assessed. The existing challenges and future research directions are also proposed. This review could provide theoretical guidance and further studies for subsequent topic, and promoting the wide engineering applications of EMBR.

A novel reduced graphene oxide/polypyrrole conductive ceramic membrane enhanced electric field membrane bioreactor: Mariculture wastewater treatment performance and membrane fouling mitigation

A novel electric field membrane bioreactor (EMBR) for mariculture wastewater treatment utilizing reduced graphene oxide/polypyrrole ceramic membrane (rGO/PPy CM) was constructed and compared with MBRs using CM support and rGO/PPy CM. EMBR (rGO/PPy) obtained the highest pollutant removal rates (84.99% for TOC, 85.98% for NH₄⁺-N), the lowest average membrane fouling rate (2.42 kPa/d) and pollutant adhesion performance by characterization. Meanwhile, the specific fluxes of characteristic foulants in EMBR were enhanced, and the total resistances were reduced by 8.12% to 62.46%. The underlying mechanisms included reduced attraction energy and improved electrostatic repulsion between contaminants in EMBR and membrane by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, DLVO model and force analysis. Therefore, this study complemented the understanding of antifouling effect and mechanism in EMBR by interaction energy and force analysis of characteristic pollutants. These findings also provided new insights into the application of EMBR for mariculture wastewater treatment.

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.

Isolation of a heterotrophic nitrification-aerobic denitrification strain and identification of its potential electricity generation ability in microbial fuel cells

To construct a simultaneous nitrification and denitrification-microbial fuel cell (SND-MFC) reactor for stable electricity generation, a heterotrophic nitrification-aerobic denitrification strain was isolated and purified from aerobic activated sludge from a sewage treatment plant. The strain with an optimal nitrogen removal performance, which was identified as Pseudomonas, was inoculated into the SND-MFC as a single strain. Different electrode materials and electrode distances (EDs) were investigated. The results showed that a maximum ammonium removal rate of 92.31% and a maximum power density of 134.28 mW/m³ were obtained by the SND-MFC using graphene film as the electrodes material. Decreasing the ED did not significantly improved the power generation performance of the pure strain SND-MFC at the initial stage. When the electrode distance of the SND-MFC was 4 cm, the best generation efficiency was achieved with a maximum power density of 151.84 mW/m³.

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.

Investigation and evaluation of membrane fouling in a microbial fuel cell-membrane bioreactor systems (MFC-MBR)

Two membrane bioreactors with and without adding an electric circuit (named as MFC-MBR and C-MBR, respectively) were established to investigate the effects of micro-electric field on membrane fouling. With the aeration rate of 1.5 L/min, the synergistic effect of aeration and micro-electric field was the best in reducing membrane fouling and COD in treatment of a simulated phenol wastewater. Compared with C-MBR, the running time of MFC-MBR was extended for 16 days. Scanning electron microscope (SEM) and energy-dispersive X-ray detector (SEM-EDX) demonstrated that less foulants were attached to the membrane and the attachment was loosend in MFC-MBR. The decreased absolute value of zeta potential indicated repulsion among the negatively-charged sludge particles was reduced and flocculation of the sludge was improved, which alleviated the membrane fouling. The soluble microbial products (SMP) and loosely-bound extracellular polymeric substances (LB-EPS) were also decreased in MFC-MBR. It was found that migration and neutralization of the negatively-charged particles, and degradation of microorganisms contributed to the alleviation of membrane fouling. Moreover, the decreases of carbohydrates in LB-EPS led to higher protein/carbohydrates (PN/PS) ratio, which was a key parameter for alleviating membrane fouling. Meanwhile, the increase of tightly bound extracellular polymeric substances (TB-EPS) could also slow down membrane fouling. Because TB-EPS can be used as a binder to strengthen the flocculation of sludge particles.

Two-stage microbial fuel cell (MFC) and membrane bioreactor (MBR) system for enhancing wastewater treatment and resource recovery based on MFC as a biosensor

Lack of process control between the two stages of a combined microbial fuel cell-membrane bioreactor (MFC-MBR) system limits its application in wastewater treatment due to membrane fouling and high energy consumption. In this study, a two-stage MFC-MBR integrated system was established to investigate the impact of incorporating process control on petroleum refinery wastewater treatment. The results showed that chemical oxygen demand (COD) removal exhibits a linear relationship with the MFC voltage output (R² = 0.9821); therefore, the MFC was used as a biosensor to control the combined system. The removal efficiencies of COD, ammonium nitrogen (NH₄⁺-N), and total nitrogen (TN) were 96.3%, 92.4%, and 86.6%, respectively, in the MFC-MBR biosensor, whereas those in the control system were 74.7%, 71.2%, and 64.7% respectively. Furthermore，using the biosensor control system yielded a 50% reduction in the transmembrane pressure (1.01 kPa day^-1) and decreased membrane fouling in wastewater treatment. The maximum energy recovery of the biosensor system (0.00258 kWh m^-3) was five times higher than that of the control system, as determined by calculating the mass balance of the system. Thus, this study indicates that using the MFC as a biosensor for process control in an MFC-MBR system can improve overall system performance.

From Waste to Watts: Updates on Key Applications of Microbial Fuel Cells in Wastewater Treatment and Energy Production

Due to fossil fuel depletion and the rapid growth of industry, it is critical to develop environmentally friendly and long-term alternative energy technologies. Microbial fuel cells (MFCs) are a powerful platform for extracting energy from various sources and converting it to electricity. As no intermediate steps are required to harness the electricity from the organic substrate’s stored chemical energy, MFC technology offers a sustainable alternative source of energy production. The generation of electricity from the organic substances contained in waste using MFC technology could provide a cost-effective solution to the issue of environmental pollution and energy shortages in the near future. Thus, technical advancements in bioelectricity production from wastewater are becoming commercially viable. Due to practical limitations, and although promising prospects have been reported in recent investigations, MFCs are incapable of upscaling and of high-energy production. In this review paper, intensive research has been conducted on MFCs’ applications in the treatment of wastewater. Several types of waste have been extensively studied, including municipal or domestic waste, industrial waste, brewery wastewater, and urine waste. Furthermore, the applications of MFCs in the removal of nutrients (nitrogen and sulphates) and precious metals from wastewater were also intensively reviewed. As a result, the efficacy of various MFCs in achieving sustainable power generation from wastewater has been critically addressed in this study.

Study of membrane fouling mechanism during the phenol degradation in microbial fuel cell and membrane bioreactor coupling system

This study evaluated the feasibility of phenol degradation in microbial fuel cell (MFC) and membrane bioreactor (MBR) coupling system, and explored the mechanism of MBR membrane fouling. Four aspects were researched in open and closed circuit conditions: the degradation capacity of the coupling system, the increase of trans-membrane pressure (TMP), and the adhesion of phenol degradation products and microorganisms on the membrane. The results showed that the degradation of phenol and COD in the closed circuit coupling system was higher than that in the open circuit. The micro-electric field can inhibit the growth of TMP and keep dodecamethylcyclohexasiloxane away from the membrane, meanwhile can also reduce the abundance and species diversity of microorganisms. Nevertheless, the micro-electric field could not completely eliminate the membrane fouling due to the fact that the phenol degradation product of ethanethiol, microorganisms of Proteobacteria and Actinobacteria were more favorable on the membrane.

Study on Start-Up Membraneless Anaerobic Baffled Reactor Coupled with Microbial Fuel Cell for Dye Wastewater Treatment

In this study, the antitoxicity performance of the traditional anaerobic baffled reactor (ABR) and the newly constructed membraneless anaerobic baffled reactor coupled with microbial fuel cell (ABR-MFC) was compared for the treatment of simulated printing and dyeing wastewater under the same hydraulic residence time. The sludge performances of ABR-MFC and ABR were evaluated on the dye removal rate, extracellular polymer (EPS) content, sludge particle size, methane yield, and the surface morphology of granular sludge. It was found that the maximum power density of the ABR-MFC reactor reached 1226.43 mW/m³, indicating that the coupled system has a good power generation capacity. The concentration of the EPS in the ABR-MFC reactor was about 3 times that in the ABR, which could be the result of the larger average particle size of sludge in the ABR-MFC reactor than in the ABR. The dye removal rate of the ABR-MFC reactor (91.71%) was higher than that of the ABR (1.49%). The methane production and microbial species in the ABR-MFC system were higher than those in the ABR. Overall, the MFC embedded in the ABR can effectively increase the resistance of the reactor, promote the formation of granular sludge, and improve the performance of the reactor for wastewater treatment.

Alternating current-enhanced carbon nanotubes hollow fiber membranes for membrane fouling control in novel membrane bioreactors

A novel electro-assisted membrane bioreactor (EMBR) was built up with alternating current (AC) voltage applying on carbon nanotubes hollow fiber membranes (CNTs-HFMs) as the basic separation unit (AC-EMBR). Herein, a combination effect of electrostatic repulsion, electrochemical oxidation and translational motion behaviors was used to mitigate membrane fouling with +1.0 V for 1 min and -1.2 V for 1 min repeatedly applying on CNTs-HFMs. During the 73-day operation, the CNTs-HFMs in AC-EMBR exhibited a superior antifouling capability with a lower average fouling rate of 0.017 bar/d comparing to control groups, which were 0.021 bar/d in EMBR with CNTs-HFMs as cathode (C-EMBR), 0.025 bar/d in EMBR with CNTs-HFMs as anode (A-EMBR) and 0.029 bar/d in MBR without voltage, respectively. The AC potential led pollutants to loosely attach on membranes, which reduced irreversible fouling as well as reduced unrecoverable fouling levels. Bound extracellular polymeric substances (EPS) concentration in biomass of AC-EMBR was lower than those in the other reactors, which also contributed to suppressing membrane fouling. Meanwhile, an excellent effluent quality was obtained in AC-EMBR with COD removal rate higher than 96% and effluent NH₄⁺-N concentration lower than 2 mg/L. Microbial community diversity has been promoted by AC electric field according to the microbial community analysis. The results of this study suggested the effectiveness of utilizing AC for membrane fouling mitigation and wastewater treatment in MBR systems.

Catalytic Membrane Reactors: The Industrial Applications Perspective

Catalytic membrane reactors have been widely used in different production industries around the world. Applying a catalytic membrane reactor (CMR) reduces waste generation from a cleaner process perspective and reduces energy consumption in line with the process intensification strategy. A CMR combines a chemical or biochemical reaction with a membrane separation process in a single unit by improving the performance of the process in terms of conversion and selectivity. The core of the CMR is the membrane which can be polymeric or inorganic depending on the operating conditions of the catalytic process. Besides, the membrane can be inert or catalytically active. The number of studies devoted to applying CMR with higher membrane area per unit volume in multi-phase reactions remains very limited for both catalytic polymeric and inorganic membranes. The various bio-based catalytic membrane system is also used in a different commercial application. The opportunities and advantages offered by applying catalytic membrane reactors to multi-phase systems need to be further explored. In this review, the preparation and the application of inorganic membrane reactors in the different catalytic processes as water gas shift (WGS), Fisher Tropsch synthesis (FTS), selective CO oxidation (CO SeLox), and so on, have been discussed.

An overview of microbial fuel cell usage in wastewater treatment, resource recovery and energy production

Wastewater treatment is a high-cost and energy-intensive process not only due to large amounts of pollutants but also for the large volumes of water to be treated, which are mainly generated by human activities and different industries. In this regard, biological wastewater treatments have become substitutes to the current technologies, owing to the improved treatment efficiency and added value. Microbial fuel cells (MFCs) as one of the promising biological treatments have arisen as a viable solution for chemical oxygen demand (COD) removal and electricity generation simultaneously. Therefore, in this article, the effects of various operating conditions on the COD removal and power production from MFCs are thoroughly discussed. In addition, the advantages and weaknesses of current MFCs technologies used for different types of wastewater are summarized. Finally, the technical barriers facing by MFCs operation and the economic feasibility of using MFCs for wastewater treatment are provided.

Sweet Drinks as Fuels for an Alkaline Fuel Cell with Nonprecious Catalysts

Sugar has the potential to create enough energy to power mobile electronics. Various sugar-powered fuel cells have been reported, however, most of them used pure glucose as substrate and enzymes/noble metals as catalysts. In this work, an alkaline fuel cell with cheap catalysts were constructed, and different sweet drinks were used as fuels for power generation. The influence of different substrates on the electrochemical performance was characterized under the controlled conditions. Our experimental results showed that the fuel cell fueled with carbonated soft drinks had the best performance under the conditions of 99.95 g/L chemical oxygen demand and 3M KOH. The power densities of the fuel cell fueled with different substrates decreased in the order of Pepsi (33.41 W/m2) > Sprite (28.38 W/m2) > apple juice (20.63 W/m2) > Coca (16.31 W/m2) > pear juice (15.31 W/m2) > orange juice (12.75 W/m2), which was consistent with linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) analysis. This is the first report on alkaline fuel cell (AFC) performance using different sweet drinks as substrate. These values are more than 10 times higher than those of reported microbial fuel cells. Our findings demonstrated that sweet drinks fueled alkaline fuel cells can be a promising energy source for low-power electronics.

Evaluation of the fouling potential of sludge in a membrane bioreactor integrated with microbial fuel cell

This study focused on the fouling characteristics evaluation of the sludge in a membrane bioreactor integrated with microbial fuel cell (MFC-MBR) to reveal the mechanisms of membrane fouling mitigation. The filtration of soluble microbial products (SMPs) in MFC-MBR showed lower flux decline rate than those in the control system (C-MBR). Based on the extended Derjaguin-Landau-Verwey-Overbeek analysis, decreases in free energies of adhesion between the SMPs and clean membrane or SMP-fouled membrane were observed in MFC-MBR. When approaching the clean membrane or SMP-fouled membrane, the SMPs in MFC-MBR had to overcome a higher energy barrier compared to those in C-MBR, indicating the inhibition of adsorption of SMPs on the membrane surface in MFC-MBR. Additionally, sludge flocs in MFC-MBR exhibited lower hydrophobicity and were less negative surface charged in comparison to those in the C-MBR. In MFC-MBR, the sludge flocs approaching the clean membrane, SMP-fouled membrane and cake layer all experienced higher energy barriers and lower secondary energy minimums compared to those in C-MBR, exhibiting the lower potential of cake layer formation. These results confirmed that decreases of the fouling potentials of SMPs and sludge flocs were essential for the membrane fouling mitigation in the MFC-MBR.

Self-generated electric field to suppress sludge production and fouling development in a membrane bioreactor for wastewater treatment

Compared with conventional sludge reduction techniques, electric field assisted membrane bioreactor (MBR) is a cost-effective technology with low power consumption. In this study, spontaneous electric field without extra power supply was introduced into the MBR for wastewater treatment to complete the in situ sludge reduction and membrane fouling mitigation. A novel spontaneous electric field membrane bioreactor (SEF-MBR) equipped with Cu-nanowires (Cu-NWs) conductive microfiltration membrane as cathode was established by using baffles to form anaerobic and aerobic tanks. SEF-MBR 1 with external resistance of 500 Ω maintained a highest electric field intensity of 1.25 mV/cm. Compared with Control-MBR, the reduction of mixed liquor suspended solids (MLSS) growth rate, extracellular polymeric substances (EPS) growth rate, total cell number and water content of SEF-MBR 1 reached 50.0%, 43.0%, 37.1% and 6.4%, respectively. After 43 days operation, SEF-MBR 1 obtained the minimum MLSS concentration and sludge volume, which were 29.9% and 83.8% lower than that of it in Control-MBR. The total biovolume of the contaminants (i.e., EPS and cells) on the membrane surface of SEF-MBR 1 was 68.8% lower than that of Control-MBR. SEF-MBR 1 exhibited a better performance with a lower membrane fouling rate (0.58 kPa/d) than Control-MBR (1.09 kPa/d). Economic analysis showed that a total of 148.1 kWh/m³ of electric energy was saved in the SEF-MBR 1. This technology reduced the sludge production in the sewage biological treatment process, which realized the sludge reduction had a positive impact on the membrane fouling mitigation.

Enhanced Scenedesmus sp. growth in response to gibberellin secretion by symbiotic bacteria

Microalgae usually co-exist with bacteria, which may influence the microalgal growth, in aquatic environment. In this study, thirteen strains that can promote microalgal growth were isolated from Scenedesmus sp. LX1 culture. Additional results showed that these strains could secrete gibberellin (GA), which is a phytohormones, promoting the growth and metabolism of the Scenedesmus sp. LX1. Low concentration (0.1 mg L^-1) of GA can increase the microalgae biomass by 51% after 4 days. GA could enhance the photosynthetic activity by increasing the photosynthetic pigment content, such as culture after 2 h with low GA concentration (0.1 mg L^-1), chlorophyll a and β-carotene increased from 0.59 μg per 10⁶ cells to 0.72 μg per 10⁶ cells and from 0.20 μg per 10⁶ cells to 0.38 μg per 10⁶ cells, respectively. In addition, GA could also stimulate the dehydrogenase activity, ATP accumulation, and carbonic anhydrase activity to increase the metabolic activity of the microalgae. Interestingly, the microalgae can selectively enhance the bacterial GA secretion in turn, indicating that there was a specific feedback regulation mechanism between the microalgae and the bacteria. The results of this study show a new mechanism of symbiotic-bacteria that enhances microalgal growth. It's a great significance to understand the microalgal growth and water bloom in aquatic environment.

Abatement of the membrane biofouling: Performance of an in-situ integrated bioelectrochemical-ultrafiltration system

The practical applications of membrane-based water treatment techniques are constrained by the problem of membrane fouling. Various studies have revealed that interactions between extracellular polymeric substances (EPS) and the membrane surface determine the extent of irreversible fouling. Herein, we describe a novel bioelectrochemical system (BES) integrated with an ultrafiltration (UF) membrane in order to provide an enhanced antifouling property. It was found that the integrated BES membrane system had a superior performance compared to a conventional (control) UF system, as manifested by a much lower development of transmembrane pressure. The BES significantly reduced microbial viability in the membrane tank and the imposed electrode potential contributed to the degradation of biopolymers, which favored the alleviation of membrane fouling. Notably, the electron transfer between the acclimated microorganisms and the conductive membrane in the BES integrated system exhibited an increasing trend with the operation time, indicating a gradual increase in microbial electrical activity. Correspondingly, the accumulation of extracellular polymeric substances (EPS) on the membrane surface of the BES integrated system showed a substantial decrease compared to the control system, which could be attributed to a series of synergistic effects induced by the BES integration. The differences in the microbial diversity between the control and the BES integrated system revealed the microbial selectivity of the poised potential. Specifically, microbial strains with relatively high EPS production, like the genus of Zoogloea and Methyloversatilis, were reduced significantly in the BES integrated system, while the expression of the electroactive bacteria was promoted, which facilitated extracellular electron transfer (EET) and therefore the bioelectrochemical reactions. Overall, this study has presented a feasible and promising new approach for membrane fouling mitigation during the process of water treatment.

A novel UASB-MFC dual sensors system for wastewater treatment: On-line sensor recovery and electrode cleaning in the long-term operation

In this research, the UASB-MFC dual sensors system was established and treatment the brewery wastewater. The COD removal rate attain about 90% and the NH₄⁺-N concentration less than 15 mg/L, MFCs has a voltage range of 0.34-0.42 V. Meanwhile, as the biosensor for coupling system, MFCs can be used to make simultaneous monitor COD and TVFA. The potential distribution can in-situ accelerate the reattachment of micro-organisms, which shorten the recovery time to 55% of the original. The long-term performance of MFCs were tested by electrochemical methods and found that the degradation of biosensors was mainly caused by the precipitation of Ca²⁺ and Mg²⁺ on the cathode surface and affected by concentration. More importantly, cleaning the electrode by an self-enhanced method without external assistance ECS (Electrodes Connection Switching) can improve the MFCs performance to 83.2 %-84.6%. Dual sensors system in UASB gives a novel possibility for UASB-MFC sensor self-sustaining in a long-term.

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.

A Review on the Mechanism, Impacts and Control Methods of Membrane Fouling in MBR System

Compared with the traditional activated sludge process, a membrane bioreactor (MBR) has many advantages, such as good effluent quality, small floor space, low residual sludge yield and easy automatic control. It has a promising prospect in wastewater treatment and reuse. However, membrane fouling is the biggest obstacle to the wide application of MBR. This paper aims at summarizing the new research progress of membrane fouling mechanism, control, prediction and detection in the MBR systems. Classification, mechanism, influencing factors and control of membrane fouling, membrane life prediction and online monitoring of membrane fouling are discussed. The research trends of relevant research areas in MBR membrane fouling are prospected.

Optimization of nutrient removal of novel electrochemically active carriers by response surface methodology

In order to improve the nutrient removal capacity of the carriers in the integrated fixed-film activated sludge (IFAS) system, a novel electrochemically active carrier was developed in this study. The nutrient removal performance of the carrier under different operating conditions was deeply investigated based on response surface methodology. The higher concentration of mixed liquor suspended solid (MLSS) and lower dissolved oxygen (DO) value inhibited ammonium (NH₄⁺-N) removal performance of the carrier, while promoted total nitrogen (TN) depletion. Lower influent C/N ratio favored denitrification of the carrier. In addition, it was found that the enhanced removal of NH₄⁺-N and TN in IFAS depended not only on the increase of carrier biomass, but also on the electrochemical activity of the novel carrier. Under the most effective conditions, the novel carrier could improve the TN removal efficiency by 19.7% compared with the activated sludge process.

Long term effects of Pb2+ on the membrane fouling in a hydrolytic-anoxic-oxic-membrane bioreactor treating synthetic electroplating wastewater

Long-term effects of Pb²⁺ on the operating performance and membrane fouling of two hydrolytic-anoxic-oxic-membrane bioreactors treating synthetic electroplating wastewater were investigated. The COD, NH₄⁺-N and TN removal efficiencies decreased by 5.5%, 10.4% and 7.9% with long-term exposure of 2 mg L^-1 Pb²⁺, while serious decreases achieved 25.4%, 35.0% and 26.2% with 6 mg L^-1 Pb²⁺ exposure, respectively. 2 mg L^-1 Pb²⁺ mitigated the cake layer fouling rate by 25.4% but increased the pore blocking rate by 69.1%, which was contributed by the increase of low and moderate molecular weight (MW) components in the soluble and colloidal foulants (SCFs). 6 mg L^-1 Pb²⁺ accelerated the cake layer fouling rate by 101.1%, but mitigated the pore blocking rate by 6.4% due to the increase of high MW SCFs (especially polysaccharides). Thermodynamic analyses showed that Pb²⁺ regulated the concentration and protein/polysaccharide ratio of loosely bound extracellular polymeric substances, thus changing the flocs hydrophobicity and aggregation capacity, leading the cake layer fouling rate variation.

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.

Power generation and microbial community analysis in microbial fuel cells: A promising system to treat organic acid fermentation wastewater

To explore a sustainable and efficient treatment approach for organic acid fermentation wastewater, two microbial fuel cells (MFCs) systems inoculated with wastewater or domesticated microbial community were constructed in this study. Compared with the MFC inoculated with domesticated microbial community, the MFC inoculated with wastewater not only showed higher power density (543.75 mW m^-2) and coulomb efficiency (22.10%), but also exhibited higher removal rates of chemical oxygen demand (75.59%), total nitrogen (76.15%), and ammonia nitrogen (83.23%), meeting the demand of wastewater discharge standard of China. Sequencing analysis revealed that the MFC inoculated with wastewater were richer in microbial community, and some bacteria such as Saprospiraceae and Caldilineaceae were beneficial for its good performance. In contrast, the microbial community of the MFC inoculated with domesticated microbial community was relatively simple. These results indicated that MFCs may be a sustainable method for organic acid fermentation wastewater treatment without any preprocessing.

A novel approach for fouling mitigation in anaerobic-anoxic-oxic membrane bioreactor (A2O-MBR) by integrating worm predation

Membrane fouling is one of the biggest challenges in the widespread application of membrane bioreactors. In this study, a combined system of anaerobic-anoxic-oxic membrane bioreactor (A²O-MBR) and worm reactor (WR) was established for fouling control. In A²O-MBR-WR, the membrane filtration cycle was prolonged by 66.7% due to the confluence of microaerobic treatment and worm predation in WR with the interaction between WR and A²O-MBR. Compared with conventional A²O-MBR, membrane rejection of soluble and colloidal foulants (SCF) in the combined system was decreased by 26.0%, which could be attributed to the higher biodegradability of SCF and the higher bacterial activity in A²O-MBR. Although floc size in A²O-MBR was reduced due to sludge disintegration and worm predation in WR, changes of floc surface properties could counteract this negative effect on fouling. Complex effects of sludge flocs on membrane fouling were further analyzed by the interaction energy between sludge flocs and the clean/fouled membrane based on extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The energy barriers indicated that flocs in A²O-MBR-WR were difficult to adhere to the membrane and were more likely to detach. Moreover, high-throughput sequencing analysis revealed that the microbial community of the cake layer in the combined system was more even and had a higher proportion of foulants degradation related bacteria, which was beneficial for fouling mitigation. The combination of A²O-MBR and WR has shown significant advantages in membrane fouling mitigation.

Membrane Fouling Potentials of an Exoelectrogenic Fouling-Causing Bacterium Cultured With Different External Electron Acceptors

Integrated microbial fuel cell (MFC) and membrane bioreactor (MBR) systems are a promising cost-effective and energy-saving technology for wastewater treatment. Membrane fouling is still an important issue of such integrated systems in which aeration (oxygen) is replaced with anode electrodes (anodic respiration). Here, we investigated the effect of culture conditions on the membrane fouling potential of fouling-causing bacteria (FCB). In the present study, Klebsiella quasipneumoniae strain S05, which is an exoelectrogenic FCB isolated from a MBR treating municipal wastewater, was cultured with different external electron acceptors (oxygen, nitrate, and solid-state anode electrode). As results, the fouling potential of S05 was lowest when cultured with anode electrode and highest without any external electron acceptor (p < 0.05, respectively). The composition of soluble microbial products (SMP) and extracellular polymeric substances (EPS) was also dependent on the type of electron acceptor. Protein and biopolymer contents in SMP were highly correlated with the fouling potential (R² = 0.73 and 0.81, respectively). Both the fouling potential and yield of protein and biopolymer production were significantly mitigated by supplying electron acceptors sufficiently regardless of its types. Taken together, the aeration of MBR could be replaced with solid-state anode electrodes without enhancement of membrane fouling, and the anode electrodes must be placed sufficiently to prevent the dead spaces in the integrated reactor.

Microalgae cultivation and nutrients removal from sewage sludge after ozonizing in algal-bacteria system

The feasibility of growing algae in concentrated wastewater generated from sludge ozonation for simultaneous nutrients removal and biomass production was studied. The effects of bacteria addition into microalgae on nutrients removal, biomass yield and settleability, the growth rate of algae and concentrations of extracellular polymeric substances (EPS) and soluble microbial products (SMP) were investigated. The results showed that the growth rate of algae in algal-bacteria system (0.2182) was improved than in algae-only system (0.1852), while both of them are comparable with others reported previously. And the addition of bacteria enhanced COD, NH₄⁺-N, TN and TP removal rate by 23.9 ± 3.3%, 27.7 ± 3.6%, 16.6 ± 1.8% and 14.9 ± 2.2%, respectively. And 32.8 ± 0.7% of the TN and 50.3 ± 1.8% of the TP were recycled from ozonated sludge-supernatant (OSS) being absorbed into algal-bacterial biomass. The algal-bacteria system also demonstrated advantages on biomass settleability and heavy metals removal. Finally, the mechanism involving matter exchange and algal-bacteria system on OSS treatment in this study were discussed through evaluation of nutrients, SMP and EPS contents, nitrogen and phosphorus balance.

Impacts of energy distribution and electric field on membrane fouling control in microbial fuel cell-membrane bioreactor (MFC-MBR) coupling system

To investigate the influence of energy allocation on membrane fouling, three coupling systems at different concentrations of mixed liquid suspended solids (MLSS) and a control system without microbial fuel cell (MFC) were established. The results show that MFC acted negative effect in low-loading stage (0.59 kg-COD·m^-3·d^-1), while high MLSS acted active effect on organics degradation in high-loading stage (2.00 kg-COD·m^-3·d^-1), and electric field could be a positive factor with sufficient energy. Besides, membrane filtration experiments in the electric field with microbial contaminants indicate that soluble microbial products (SMP) and loosely bound extracellular polymeric substances (LB-EPS) had greater tendencies to cause irreversible membrane fouling. SMP and the residual cell liquid (Cell) were more susceptible than extracellular polymeric substances (EPS), demonstrating that the irreversible fouling was reduced mainly due to SMP decrease in the electric field.

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.

Critical review of fouling mitigation strategies in membrane bioreactors treating water and wastewater

The current research was an effort to critically review all approaches used for membrane fouling control in the membrane bioreactors treating water and wastewater. The first generation of antifouling methods tried to optimize operational conditions, or used chemical agents to control membrane fouling. Despite their positive impacts on the fouling mitigation, these methods did not provide a sustainable solution for the problem. Moreover, chemical agents may affect microorganisms in bioreactors and has some environmental drawbacks. The improved knowledge of membrane fouling mechanism and effective factors has directed the attention of researchers to novel methods that focus on disrupting fouling mechanism through affecting fouling causing bacteria. Employing nanomaterials, cell entrapment, biologically- and electrically-based methods are the latest efforts. The results of this review indicate that sustainable control of membrane fouling requires employing more than one single approach. Large scale application of fouling mitigation strategies should be the focus of future studies.

Effect of air-exposed biocathode on the performance of a Thauera-dominated membraneless single-chamber microbial fuel cell (SCMFC)

To investigate the effect of air-exposed biocathode (AEB) on the performance of single-chamber microbial fuel cell (SCMFC), wastewater quality, bioelectrochemical characteristics and the electrode biofilms were researched. It was demonstrated that exposing the biocathode to air was beneficial to nitrogen removal and current generation. In Test 1 of 95% AEB, removal rates of ammonia, total nitrogen (TN) and chemical oxygen demand (COD) reached 99.34%±0.11%, 99.34%±0.10% and 90.79%±0.12%, respectively. The nitrogen removal loading rates were 36.38gN/m³/day. Meanwhile, current density and power density obtained at 0.7A/m³ and 104mW/m³ respectively. Further experiments on open-circuit (Test 2) and carbon source (Test 3) indicated that this high performance could be attributed to simultaneous biological nitrification/denitrification and aerobic denitrification, as well as bioelectrochemical denitrification. Results of community analysis demonstrated that both microbial community structures on the surface of the cathode and in the liquid of the chamber were different. The percentage of Thauera, identified as denitrifying bacteria, maintained at a high level of over 50% in water, but decreased gradually in the AEB. Moreover, the genus Nitrosomonas, Alishewanella, Arcobacter and Rheinheimera were significantly enriched in the AEB, which might contribute to both enhancement of nitrogen removal and electricity generation.

A novel bio-electrochemical system with sand/activated carbon separator, Al anode and bio-anode integrated micro-electrolysis/electro-flocculation cost effectively treated high load wastewater with energy recovery

A novel bio-electrochemical system (BES) was developed by integrating micro-electrolysis/electro-flocculation from attaching a sacrificing Al anode to the bio-anode, it effectively treated high load wastewater with energy recovery (maximum power density of 365.1 mW/m³ and a maximum cell voltage of 0.97 V), and achieving high removals of COD (>99.4%), NH₄⁺-N (>98.7%) and TP (>98.6%). The anode chamber contains microbes, activated carbon (AC)/graphite granules and Al anode. It was separated from the cathode chamber containing bifunctional catalytic and filtration membrane cathode (loaded with Fe/Mn/C/F/O catalyst) by a multi-medium chamber (MMC) filled with manganese sand and activated carbon granules, which replaced expensive PEM and reduced cost. An air contact oxidation bed for aeration was still adopted before liquid entering the cathode chamber. micro-electrolysis/electro-flocculation helps in achieving high removal efficiencies and contributes to membrane fouling migration. The increase of activated carbon in the separator MMC increased power generation and reduced system electric resistance.

Treatment of palm oil mill effluent using combination system of microbial fuel cell and anaerobic membrane bioreactor

It was found that the operational temperature and the incorporation of microbial fuel cell (MFC) into anaerobic membrane bioreactor (AnMBR) have significant effect on AnMBRs' filtration performance. This paper addresses two issues (i) effect of temperature on AnMBR; and (ii) effect of MFC on AnMBRs' performance. The highest COD removal efficiency was observed in mesophilic condition (45°C). It was observed that the bioreactors operated at 45°C had the highest filtration resistance compared to others, albeit the excellent performance in removing the organic pollutant. Next, MFC was combined with AnMBR where the MFC acted as a pre-treatment unit prior to AnMBR and it was fed directly with palm oil mill effluent (POME). The supernatant from MFC was further treated by AnMBR. Noticeable improvement in filtration performance was observed in the combined system. Decrease in polysaccharide amount was observed in combined system which in turn suggested that the better filtration performance.

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.