Impact of electrode configurations on retention time and domestic wastewater treatment efficiency using microbial fuel cells

Sustainable power production from petrochemical industrial effluent using dual chambered microbial fuel cell

Dual chambered microbial fuel cell (DMFC) is an advanced and effective treatment technology in wastewater treatment. The current work has made an effort to treat petrochemical industrial wastewater (PWW) as a DMFC substrate for power generation and organic substance removal. Investigating the impact of organic load (OL) on organic reduction and electricity generation is the main objective of this study. At the OL of 1.5 g COD/L, the highest total chemical oxygen demand (TCOD) removal efficiency of 88%, soluble oxygen demand (SCOD) removal efficiency of 80% and total suspended solids (TSS) removal efficiency of 71% were seen, respectively. In the same optimum condition of 1.5 g COD/L, the highest current and power density of about 270 mW/m2 and 376 mA/m2 were also observed. According to the results of this study, using high-strength organic wastewater in DMFC can assist in addressing the issue of the petrochemical industries and minimize the energy demand.

Performance evaluation of three constructed wetland-microbial fuel cell systems: wastewater treatment efficiency and electricity generation potential

Constructed wetlands (CWs) have proven to be effective and environmentally friendly for removing pollutants, while microbial fuel cells (MFCs) offer the potential for electricity generation. Thus, this study evaluated the performance of three CW-MFC systems (zigzag, single-column, and triple-column continuous) for domestic wastewater treatment and electricity generation. Results showed that parallel connection of CW-MFCs significantly improved power generation compared to series connection. Additionally, using three copper wires to connect carbon fiber felt electrodes demonstrated superior pollutant capture capabilities compared to a single copper wire. During the 14-day testing period, the single-column system achieved the highest power density of 5.55 mW m-2, followed closely by the triple-column continuous system at 4.77 mW m-2. In contrast, the zigzag system exhibited a lower power density of 2.49 mW m-2. Interestingly, the implementation of facultative anaerobic conditions in the anode, along with the application of a plastic bag cover, facilitated the maintenance of anaerobic conditions in both the single-column and triple-column continuous systems. This resulted in increased power density and reduced internal resistance. In contrast, the zigzag system, with its larger surface area, aeration, and circulation, exhibited higher internal resistance and lower current dissipation. Despite its inferior electricity generation performance, the zigzag system demonstrated higher efficiency removal of chemical oxygen demand (COD), nitrate (NO3-), and phosphate (PO43-) than the single-column system. This can be attributed to the extended contact time, resulting in enhanced pollutant removal. Overall, the multi-column continuous system shows promise as a viable approach for simultaneous domestic wastewater treatment and electricity production, offering potential benefits for sustainable wastewater management.

Microbial fuel cell: Interplay of energy production, wastewater treatment, toxicity assessment with hydraulic retention time

Microbial fuel cell (MFC) operation under similar conditions to conventional methods will support the use of this technology in large-scale wastewater treatment. The operation of scaled-up air-cathode MFC (2 L) fed with synthetic wastewater (similar to domestic) in a continuous flow was evaluated using three different hydraulic retention times (HRT), 12, 8, and 4 h. We found that electricity generation and wastewater treatment could be enhanced under an HRT of 12 h. Additionally, the longer HRT led to greater coulombic efficiency (5.44%) than MFC operating under 8 h and 4 h, 2.23 and 1.12%, respectively. However, due to the anaerobic condition, the MFC was unable to remove nutrients. Furthermore, an acute toxicity test with Lactuca sativa revealed that MFC could reduce wastewater toxicity. These outcomes demonstrated that scaled-up MFC could be operated as a primary effluent treatment and transform a wastewater treatment plant (WWTP) into a renewable energy producer.

Structure evolution of air cathodes and their application in electrochemical sensor development and wastewater treatment

Cathode structure and material are the most important factors to determine the performance and cost of single chamber air-cathode microbial fuel cell (MFC), which is the most promising type of MFC technology. Since the first air cathode was invented in 2004, five major structures (1-layer, 2-layer, 3-layer, 4-layer and separator-support) have been invented and modified to fit new material, improve power performance and lower MFC cost. This paper reviewed the structure evolution of air cathodes in past 18 years. The benefits and drawbacks of these structures, in terms of power generation, material cost, fabrication procedure and modification process are analyzed. The practical application cases (e.g., sensor development and wastewater treatment) employed with different cathode structures were also summarized and analyzed. Based on practical performance and long-term cost analysis, the 2-layer cathode demonstrated much greater potential over other structures. Compared with traditional activated-sludge technology, the cost of an MFC-based system is becoming competitive when employing with 2-layer structure. This review not only provides a detailed development history of air cathode but also reveals the advantages/disadvantages of air cathode with different structures, which will promote the research and application of air-cathode MFC technology.

Enhanced power generation, organics removal and water desalination in a microbial desalination cell (MDC) with flow electrodes

This study introduced a flow electrode microbial desalination cell (FE-MDC), which used activated carbon (AC) particles and carbon nanotubes (CNTs) as the electrode to promote electron harvesting. The recovered electricity energy (0.371 KWh/m³) and columbic efficiency (66.7 %) of the FE-MDC were over 2 times higher than those of the conventional MDC without the flow electrode. Consequently, the salt and COD removal efficiencies were enhanced to 77.8 % and 91.2 %, respectively. Electrochemical analysis implied that the charge transfer resistance of the system was reduced by the flow electrode. Electron accumulation and charging-discharging experiments proved that the flow electrode could accumulate electrons and transfer the electrons to the fixed anode. Bacterial community analysis indicated that the bacterial activity was improved by the flow electrode. The content of the exoelectrogen Pseudomonas increased from 5.0 % to 14.7 %, and Hydrogenophaga improved from 1.4 % to 5.9 %. Finally, a continuous operation mode of the FE-MDC was established, and the flow electrode slurry was returned to the anodic chamber for recirculated utilization. The voltage output, COD removal, and salt removal during the operation mode reached 610 mV, 78.8 %, and 76.1 %, respectively. This study proved that the flow electrode is a promising way to promote the practical application of MDC technology.

Scalable architecture of low-cost household microbial fuel cell for domestic wastewater treatment and simultaneous energy recovery

Researchers are still trying to achieve desirable results while treating actual wastewater at the field size when scaling up a microbial fuel cell (MFC). This pilot-scale project aimed to create a decentralised system for treating domestic wastewater and concurrent energy generation that may be used as a model for the decentralisation process. In this investigation, a cylindrical-shaped earthen membrane was utilized. The arrangement was deployed on-site at a residence for the treatment of domestic wastewater as well as simultaneous generation of power. From August until November 2021, the 36 L pilot-scale setup was operational for a period of 92 days. The setup's performance was affected by seasonal temperature variations during the operation period. The system's performance was measured in terms of COD, nitrate, and NH₃-N removal, with the highest results being 93.52 %, 84.93 %, and 74.78 %, respectively. The pilot-scale setup achieved the highest current of 43.7 mA, and the output voltage of the setup was boosted to 4.1 V using a power management system. The sustainable operation of pilot household MFC showed a positive indication for field application with a low-cost solution.

Pilot scale microbial fuel cells using air cathodes for producing electricity while treating wastewater

Microbial fuel cells (MFCs) can generate electrical energy from the oxidation of the organic matter, but they must be demonstrated at large scales, treat real wastewaters, and show the required performance needed at a site to provide a path forward for this technology. Previous pilot-scale studies of MFC technology have relied on systems with aerated catholytes, which limited energy recovery due to the energy consumed by pumping air into the catholyte. In the present study, we developed, deployed, and tested an 850 L (1400 L total liquid volume) air-cathode MFC treating domestic-type wastewater at a centralized wastewater treatment facility. The wastewater was processed over a hydraulic retention time (HRT) of 12 h through a sequence of 17 brush anode modules (11 m² total projected anode area) and 16 cathode modules, each constructed using two air-cathodes (0.6 m² each, total cathode area of 20 m²) with the air side facing each other to allow passive air flow. The MFC effluent was further treated in a biofilter (BF) to decrease the organic matter content. The field test was conducted for over six months to fully characterize the electrochemical and wastewater treatment performance. Wastewater quality as well as electrical energy production were routinely monitored. The power produced over six months by the MFC averaged 0.46 ± 0.35 W (0.043 W m^-2 normalized to the cross-sectional area of an anode) at a current of 1.54 ± 0.90 A with a coulombic efficiency of 9%. Approximately 49 ± 15 % of the chemical oxygen demand (COD) was removed in the MFC alone as well as a large amount of the biochemical oxygen demand (BOD₅) (70%) and total suspended solid (TSS) (48%). In the combined MFC/BF process, up to 91 ± 6 % of the COD and 91 % of the BOD₅ were removed as well as certain bacteria (E. coli, 98.9%; fecal coliforms, 99.1%). The average effluent concentration of nitrate was 1.6 ± 2.4 mg L^-1, nitrite was 0.17 ± 0.24 mg L^-1 and ammonia was 0.4 ± 1.0 mg L^-1. The pilot scale reactor presented here is the largest air-cathode MFC ever tested, generating electrical power while treating wastewater.

Fundamental understanding of microbial fuel cell technology: Recent development and challenges

The research on microbial fuel cells (MFCs) is rising tremendously but its commercialization is restricted by several microbiological, material, and economic constraints. Hence, a systematic assessment of the research articles published previously focusing on potential upcoming directions in this field is necessary. A detailed multi-perspective analysis of various techniques for enhancing the efficiency of MFC in terms of electric power production is presented in this paper. A brief discussion on the central aspects of different issues are preceded by an extensive analysis of the strategies that can be introduced to optimize power generation and reduce energy losses. Various applications of MFCs in a broad spectrum ranging from biomedical to underwater monitoring rather than electricity production and wastewater treatment are also presented followed by relevant possible case studies. Mathematical modeling is used to understand the concepts that cannot be understood experimentally. These methods relate electrode geometries to microbiological reactions occurring inside the MFC chamber, which explains the system's behavior and can be improved. Finally, directions for future research in the field of MFCs have been suggested. This article can be beneficial for engineers and researchers concerned about the challenges faced in the application of MFC.

Enhancement of methane production from waste activated sludge using hybrid microbial electrolysis cells-anaerobic digestion (MEC-AD) process - A review

Hybrid microbial electrolysis cells-anaerobic digestion (MEC-AD) was proved to increase methane productivity and methane yield of waste activated sludge (WAS) by establishing direct interspecies electron transfer method and enriching functional microorganisms. This review first summarized the pretreatment methods of WAS for MEC-AD and then reviewed the reactor configurations, operation parameters, and the economic benefit of MEC-AD. Furthermore, the enhancement mechanisms of MEC-AD were reviewed based on the analysis of thermodynamics and microbial community. It was found that the decrease of hydrogen partial pressure due to the hydrogenotrophic methanogens enriched in cathodic biofilm and direct interspecies electron transfer between exoelectrogens and anode were the core mechanisms for improving acidogenesis, acetogenesis, and methanogenesis. Finally, the potentially technological issues that need to be addressed to increase energy efficiency in large-scale MEC-AD processes were discussed.

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.

A novel fragmented anode biofilm microbial fuel cell (FAB-MFC) integrated system for domestic wastewater treatment and bioelectricity generation

BACKGROUND

The critical MFC design challenge is to increase anode surface area. A novel FAB-MFC integrated system was developed and evaluated for domestic wastewater treatment. It was operated in fed-batch flow mode at 1-3 days of HRT with 755 mg/L CODIN and 0.76 kg-COD/m3/day. The study includes anaerobic-MFC and aerobic-MFC integrated systems. Microbial electrode jacket dish (MEJ-dish) with hybrid dimension (HD) was invented, first time to authors' knowledge, to boost anode biofilm growth. The treatment system with MEJ+ (FAB) and MEJ- (MFC) anode are called FAB-MFC and MFC, respectively.

RESULTS

Fragmented variable anode biofilm thickness was observed in FAB than MFC. The FAB-MFC (FAB+) simple technique increases the anode biofilm thickness by ~ 5 times MFC. Due to HD the anode biofilm was fragmented in FAB+ system than MFC. At the end of each treatment cycle, voltage drops. All FAB+ integrated systems reduced voltage drop relative to MFC. FAB reduces voltage drops better than MFC in anaerobic-MFC from 6 to 20 mV and aerobic-MFC from 35-47 mV at 1 kΩ external load. The highest power density was achieved by FAB in anaerobic-MFC (FAB = 104 mW/m2, MFC = 98 mW/m2) and aerobic-MFC integrated system (FAB = 59 mW/m2, MFC = 42 mW/m2).

CONCLUSIONS

The ∆COD and CE between FAB and MFC could not be concluded because both setups were inserted in the same reactor. The integrated system COD removal (78-97%) was higher than the solitary MFC treatment (68-78%). This study findings support the FAB+ integrated system could be applied for real applications and improve performance. However, it might depend on influent COD, the microbial nature, and ∆COD in FAB+ and MFC, which requires further study.

A review of the operating parameters on the microbial fuel cell for wastewater treatment and electricity generation

Environmental and economic considerations suggest a more efficient and comprehensive use of biomass for bioenergy production. One of the most attractive technologies is the microbial fuel cell using the catabolic activity of microorganisms to generate electricity from organic matter. The microbial fuel cell (MFC) has operational benefits and higher performance than current technologies for producing energy from organic materials because it converts electricity from the substrate directly (at ambient temperature). However, MFCs are still not suitable for high energy demand due to practical limitations. The overall performance of an MFC depends on the electrode material, the reactor design, the operating parameters, substrates, and microorganisms. Furthermore, the optimization of the parameters will lead to the commercial development of this technology in the near future. The simultaneous effect of the parameters on each other (intensifier or attenuator) has also been investigated. The investigated parameters in this study include temperature, pH, flow rate and hydraulic retention time, mode, external resistance, and initial concentration.

Electrochemical Ammonia Recovery from Anaerobic Centrate Using a Nickel-Functionalized Activated Carbon Membrane Electrode

Ammonia (NH₃) recovery from used water (previously wastewater) is highly desirable to depart from fossil fuel-dependent NH₃ production and curb nitrogen emission to the environment. Electrochemical NH₃ recovery is promising since it can simply convert aqueous NH₄⁺ to gaseous NH₃ using cathodic reactions (OH^- generation). However, the use of a separated electrode and membrane imposes high resistances to the cathodic reaction and NH₃ transfer. This study examined an activated carbon (AC)-based membrane electrode functionalized with nickel to electrochemically recover NH₃ from synthetic anaerobic centrate. The membrane electrode was fabricated using nickel-adsorbed AC powder and a polyvinylidene fluoride (PVDF) binder, and the PVDF membrane layer was formed at the electrode surface by phase inversion. The NH₃-N recovery flux of 50.3 ± 0.4 gNH₃-N/m²/d was produced at 17.1 A/m² with a recovery solution at pH 7, and NH₃-N fluxes and energy consumptions were improved as the recovery solution became acidic (62.2 ± 2.1 gNH₃-N/m²/d with 16.0 ± 1.6 kWh/kgNH₃-N at pH 2). Increasing PVDF loadings did not impact the electrochemical performances of the Ni/AC-PVDF electrode, but slightly lower (7%) NH₃-N fluxes were obtained with higher PVDF loadings. Ni dissolution (3.7-6.0% loss) was affected by the recovery solution pH, but it did not impact the performances over the cycles.

Enhanced methane production in an up-flow microbial electrolysis assisted reactors: Hydrodynamics characteristics and electron balance under different spatial distributions of bioelectrodes

Compared with common anaerobic digestion, microbial electrolysis has been proven feasibly to accelerate biodegradation and methanogenesis with the advantages of effective electron flow regulation. However, its actual application and scale-up required a full understanding and further investigation on electrode size and distribution. For making full use of the space of the integrated reactor and improve methane recovery, an effective interior configuration was significant. In this work, three types of reactors with different cathode spatial distributions, that is, different cathode space ratios (ratio of cathode surface area to reaction region volume), were studied to form a good flow pattern for obtaining high methane production. Tracer experiments and numerical simulation were employed simultaneously for understanding the hydrodynamics characters of the interior flow field. The results showed that by increasing the cathode space ratio to 1.33 cm²/cm³ and 2 cm²/cm³, respectively, better flow patterns with the residence time of 1.336 times and 1.363 times of theoretical hydraulic retention time could be obtained. The stacked structure of nickel meshes was beneficial to prolong the contact time of contaminant and improve the mass transfer. Increasing the cathode space ratio could also enhance the electrochemical performance. Considering the organic removal, methane recovery, electrons generation, and material consumption, the recommended cathode space ratio was 1.33 cm²/cm³. With this structure, COD removal efficiency reached 93.2 ± 1.9% and 94.1 ± 1.5%, methane production rate reached 332.0 and 334.8 mL CH₄/L reactor/day, and methane yield was 171.3 and 246.4 mL CH₄/g COD under the HRT of 24 h and 36 h, respectively.

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.

Impacts of hydraulic retention time on a continuous flow mode dual-chamber microbial fuel cell for recovering nutrients from municipal wastewater

Nutrients recovery has become a meaningful solution to address shortage in the fertilizer production which is the key issue of nations' food security. The concept of municipal wastewater is based on its ability to be a major potential source for recovered nutrients because of its vast quantity and nutrient-rich base. Microbial fuel cell (MFC) has emerged as a sustainable technology, which is able to recover nutrients and simultaneously generate electricity. In this study a two-chambered MFC was constructed, and operated in a continuous flow mode employing artificial municipal wastewater as a substrate. The effects of hydraulic retention time (HRT) on the recovery of nutrients by MFC were studied. The COD removal rates were insignificantly influenced by varying HRT from 0.35 to 0.69 d, that were over 92%. Furthermore, the recovery rate of nutrients was insignificantly affected while increasing the HRT, which fluctuates from 80% to 90%. In contrast, the maximum power generation declined when HRT increased and the lowest one was 510.3 mV at the HRT of 0.35 d. These results demonstrate that the lab-scale double chamber MFC using municipal wastewater as the substrate can provide a highly effective removal strategy for organic matter, nutrients recovery and electricity output when operating at a specific HRT.

A review on the contribution of electron flow in electroactive wetlands: Electricity generation and enhanced wastewater treatment

In less than a decade, bioelectrochemical systems/microbial fuel cell integrated constructed wetlands (electroactive wetlands) have gained a considerable amount of attention due to enhanced wastewater treatment and electricity generation. The enhancement in treatment has majorly emanated from the electron transfer or flow, particularly in anaerobic regions. However, the chemistry associated with electron transfer is complex to understand in electroactive wetlands. The electroactive wetlands accommodate diverse microbial community in which each microbe set their own potential to further participate in electron transfer. The conductive materials/electrodes in electroactive wetlands also contain some potential, due to which, several conflicts occur between microbes and electrode, and results in inadequate electron transfer or involvement of some other reaction mechanisms. Still, there is a considerable research gap in understanding of electron transfer between electrode-anode and cathode in electroactive wetlands. Additionally, the interaction of microbes with the electrodes and understanding of mass transfer is also essential to further understand the electron recovery. This review mainly deals with the electron transfer mechanism and its role in pollutant removal and electricity generation in electroactive wetlands.

Outlook on the Role of Microbial Fuel Cells in Remediation of Environmental Pollutants with Electricity Generation

A wide variety of pollutants are discharged into water bodies like lakes, rivers, canal, etc. due to the growing world population, industrial development, depletion of water resources, improper disposal of agricultural and native wastes. Water pollution is becoming a severe problem for the whole world from small villages to big cities. The toxic metals and organic dyes pollutants are considered as significant contaminants that cause severe hazards to human beings and aquatic life. The microbial fuel cell (MFC) is the most promising, eco-friendly, and emerging technique. In this technique, microorganisms play an important role in bioremediation of water pollutants simultaneously generating an electric current. In this review, a new approach based on microbial fuel cells for bioremediation of organic dyes and toxic metals has been summarized. This technique offers an alternative with great potential in the field of wastewater treatment. Finally, their applications are discussed to explore the research gaps for future research direction. From a literature survey of more than 170 recent papers, it is evident that MFCs have demonstrated outstanding removal capabilities for various pollutants.

Improved Simultaneous Decolorization and Power Generation in a Microbial Fuel Cell with the Sponge Anode Modified by Polyaniline and Chitosan

In recent years, microbial fuel cell (MFC) has been regarded as a promising technology for dye wastewater treatment. Compared with traditional anaerobic reactors, MFC has better decolorization effect while producing electricity simultaneously. In this paper, a double-chamber MFC with the sponge anode modified by polyaniline and chitosan-NCNTs was employed for simultaneous azo dye decolorization and bioelectricity generation. The influence of dye concentration, co-substrate concentration, and operating temperature on the performance of MFC with the modified anodes were studied. The results showed that a high decolorization efficiency (98.41%) and maximum power density (2816.67 mW m^-3) of MFC equipped with modified bioanodes were achieved due to the biocompatibility and bioelectrocatalysis of modified material. And the biomass on the modified anode's surface was increased by 1.47 times. Additionally, microbial community analysis revealed that the modification of polyaniline and chitosan-NCNTs improved the selective enrichment of specific communities and the main microorganism was the electroactive and decolorizing bacteria Enterobacter (62.84%). Therefore, the composite anode is capable of fully utilizing the synergistic role of various materials, leading to superior performance of dye decolorization in MFCs. This work provided a strategy for the research on the recovery of biomass energy and decolorization in wastewater treatment. Graphical Abstract.

Novel trickling microbial fuel cells for electricity generation from wastewater

There are two main challenges associated with the scale-up of air-cathode microbial fuel cells (MFCs): performance reduction and cathode leakage/flooding. In this study, a novel 13.4 L reactor that contains 4 tubular MFCs was designed and operated in a trickling mode for 65 days under different conditions. The trickling water flow through the horizontally aligned MFCs alleviated the hydraulic pressure applied to the air-cathodes. With a total cathode working area of over 1700 cm², this reactor generated power densities up to 1 W/m² with coulombic efficiencies over 50% using acetate. Using a brewery waste stream as carbon source, an average power density of 0.27 W/m² was generated with ∼60% COD removal at hydraulic retention time of 1.6 h. The decent performance of this reactor compared with other air-cathode MFCs at the similar scale and the alleviated hydraulic pressure on air-cathodes demonstrate the great potential of this design and operation for future MFC optimization and scaling up.

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.

Performance and inorganic fouling of a submergible 255 L prototype microbial fuel cell module during continuous long-term operation with real municipal wastewater under practical conditions

A submergible 255 L prototype MFC module was operated under practical conditions with municipal wastewater having a large share in industrial discharges for 98 days to investigate the performance of two of the largest, ever investigated multi-panel stainless steel/activated carbon air cathodes (85 × 85 cm). At a flow rate of 144 L/d, power density of 78 mW/m²_Cat (317 mW/m³) and COD, TSS and TN removal of 41 ± 16 %, 36 ± 16 % and 18 ± 14 %, respectively, were reached. Observed Coulombic efficiency and substrate-specific energy recovery were 29.5 ± 14 % and 0.184 ± 0.125 kWh_el/kg_COD,deg, respectively. High salt content of wastewater (TDS = 2.8 g/L) led to severe inorganic fouling causing a drastic decline in power output and energy recovery of more than 90 % in the course of experiments. Mechanical cleaning of the cathodes restored only 22 % (17 mW/m²_Cat) of the power output and did not improve nutrient removal or energy recovery.

Exoelectrogenic Anaerobic Granular Sludge for Simultaneous Electricity Generation and Wastewater Treatment

A thick and electroactive biofilm is the key to the successful development of microbial electrochemical systems and technologies (METs). In this study, intact anaerobic granular sludge (AGS), which is a spherical and dense microbial association, was successfully demonstrated as a novel and efficient biocatalyst in METs such as microbial fuel cells. Three different strategies were explored to shift the microbial composition of AGS from methanogenic to exoelectrogenic microbes, including varying the external resistance and organic loading and manipulating the anode potential. Among all the strategies, only with positive anode potential, AGS was successfully shifted from methanogenic to exoelectrogenic conditions, as indicated by the significantly high current response (10.32 A/m²) and 100% removal of organic carbon from wastewater. Moreover, the AGS bioanode showed no significant decrease in current generation and organic removal at pH 5, indicating good tolerance of AGS to acidic conditions. Finally, 16S rRNA sequencing revealed the enrichment of exoelectrogens and inhibition of methanogens in the microbial community of AGS after anode potential control. This study provides a proof of concept for extracting electrical energy from organic wastes by exoelectrogenic AGS along with simultaneous wastewater treatment and meanwhile opens up a new paradigm to create an efficient and cost-effective exoelectrogenic biocatalyst for boosting the industrial application of METs.

Surfactant addition to enhance bioavailability of bilge water in single chamber microbial fuel cells (MFCs)

Effective remediation of bilge water, a shipboard oily liquid waste, is important for both commercial and military vessels due to the domestic and international regulations. In this study, bilge water was used as a substrate for exoelectrogenic bacteria and biodegradation of bilge water and concurrent electricity generation were investigated using Pseudomonas putida ATCC 49128 in single chamber microbial fuel cells (MFCs). To enhance bioavailability of the bilge water, two types of surfactants were added (100 ppm) into the oily wastewater containing 0.1% standard bilge mix (SBM) and their impacts on electricity production were evaluated under various conditions. Anionic surfactant (sodium dodecyl sulfate, SDS) addition increased soluble chemical oxygen demand (SCOD) by forming micelle, producing maximum power density of 225.3 ± 3.2 mW m^-2. However, the MFC with nonionic surfactant (Triton X-100) produced only 2.3 ± 0.1 mW m^-2 due to no enhancement on biodegradable SCOD. A high NaCl concentration (100-500 mM) adversely affected power production due to decrease in available SCOD caused by emulsion coalescence. This is a first study to use surfactants to enhance bioavailability of non-biodegradable oily wastewater in a single chamber MFC.

Tungsten oxide as electrocatalyst for improved power generation and wastewater treatment in microbial fuel cell

Microbial fuel cell (MFC) is a device that oxidizes the organic matter present in wastewater and simultaneously generates electricity from it. For practical applications, the power production of MFCs needs to be enhanced and the use of novel anode and cathode catalyst can certainly help in this regard. Such a novel catalyst, WO₃, was explored as both anode and cathode catalyst in this study. Performance of MFCs was enhanced when WO₃ was used as an electrocatalyst. The maximum power density of MFC was increased by five times when WO₃ was used as anode catalyst and by four times when it was used as cathode catalyst as compared to control MFC using electrode without any catalyst. Almost six times increment in maximum power production of MFC was observed when WO₃ was used as catalyst on both the electrodes. Electrochemical analysis of WO₃ also proved that it could enhance the current density of the modified electrode owing to its electrochemical catalytic properties. Furthermore, chemical oxygen demand (COD) removal of MFC having WO₃ coated electrodes was also observed to be higher, thus suggesting an overall enhancement in the performance of MFC by the use of WO₃ as an electrocatalyst.

Evaluating a multi-panel air cathode through electrochemical and biotic tests

To scale up microbial fuel cells (MFCs), larger cathodes need to be developed that can use air directly, rather than dissolved oxygen, and have good electrochemical performance. A new type of cathode design was examined here that uses a "window-pane" approach with fifteen smaller cathodes welded to a single conductive metal sheet to maintain good electrical conductivity across the cathode with an increase in total area. Abiotic electrochemical tests were conducted to evaluate the impact of the cathode size (exposed areas of 7 cm², 33 cm², and 6200 cm²) on performance for all cathodes having the same active catalyst material. Increasing the size of the exposed area of the electrodes to the electrolyte from 7 cm² to 33 cm² (a single cathode panel) decreased the cathode potential by 5%, and a further increase in size to 6200 cm² using the multi-panel cathode reduced the electrode potential by 55% (at 0.6 A m^-2), in a 50 mM phosphate buffer solution (PBS). In 85 L MFC tests with the largest cathode using wastewater as a fuel, the maximum power density based on polarization data was 0.083 ± 0.006 W m^-2 using 22 brush anodes to fully cover the cathode, and 0.061 ± 0.003 W m^-2 with 8 brush anodes (40% of cathode projected area) compared to 0.304 ± 0.009 W m^-2 obtained in the 28 mL MFC. Recovering power from large MFCs will therefore be challenging, but several approaches identified in this study can be pursued to maintain performance when increasing the size of the electrodes.

Prospects in bioelectrochemical technologies for wastewater treatment

Bioelectrochemical technologies are emerging as innovative solutions for waste treatment, offering flexible platforms for both oxidation and reduction reaction processes. A great variety of applications have been developed by utilizing the energy produced in bioelectrochemical systems, such as direct electric power generation, chemical production or water desalination. This manuscript provides a literature review on the prospects in bioelectrochemical technologies for wastewater treatment, including organic, nutrients and metals removal, production of chemical compounds and desalination. The challenges and perspectives for scale-up were discussed. A technological strategy to improve the process monitoring and control based on big data platforms is also presented. To translate the viability of wastewater treatment based on bioelectrochemical technologies into commercial application, it is necessary to exploit interdisciplinary areas by combining the water/wastewater sector, energy and data analytics technologies.

Deriving electricity from dye processing wastewater using single chamber microbial fuel cell with carbon brush anode and platinum nano coated air cathode

Single chamber air cathode microbial fuel cell (MFC) is a promising and sustainable technology to generate electricity. In the present study, the potential of air cathode MFC treating dye processing wastewater was investigated at various organic loads with interest focused on power densities, organic removal and coulombic efficiencies. The highest power density of about 515 mW/m² (6.03 W/m³) with 56% of coulombic efficiency was procured at 1.0 (g COD/L) organic load. The high potency of TCOD (total chemical oxygen demand), SCOD (soluble chemical oxygen demand) and TSS (Total Suspended Solids) removal of about 85%, 73% and 68% respectively was achieved at the organic load of 1.0 (g COD/L). The bacterial strains in anode region at the initial stage of MFC operation were reported to be responsible for potential organic removal. The bacterial strains in air cathode MFC were identified as Paenibacillus sp. strain JRA1 (MH27077), Pseudomonas sp. strain JRA2 (MH27078), Ochrobactrum sp. strain JRA3 (MH27079), Sphingobacterium sp. strain JRA4 (MH27080), Stenotrophomonas sp. strain JRA5 (MH27081), Bacillus sp. strain JRA6 (MH27082) and Clostridium sp. strain JRA7 (MH27083) using phylogenetic analysis. After 60 days of air cathode MFC operation, the bacterial community in biofilm samples was dominated by Bacillus, Ochrobactrum and Pseudomonas (20-22%). The biofilm sample collected from the carbon brush consisted of Bacillus (33%), Ochrobactrum (30%), Pseudomonas (28%), Clostridium (6%) and Stenotrophomonas (3%). The present study revealed the treatment efficiency of dye processing wastewater along with power generation in single chambered air cathode MFC.

Effects of azo dye on simultaneous biological removal of azo dye and nutrients in wastewater

The potential disrupting effects of Azo dye on wastewater nutrients removal deserved more analysis. In this study, 15 days exposure experiments were conducted with alizarin yellow R (AYR) as a model dye to determine whether the dye caused adverse effects on biological removal of both the dye and nutrients in acclimated anaerobic-aerobic-anoxic sequencing batch reactors. The results showed that the AYR removal efficiency was, respectively, 85.7% and 66.8% at AYR concentrations of 50 and 200 mg l^-1, while higher AYR inlet (400 mg l^-1) might inactivate sludge. Lower removal of AYR at 200 mg l^-1 of AYR was due to the insufficient support of electron donors in the anaerobic process. However, the decolorized by-products p-phenylenediamine and 5-aminosalicylic were completely decomposed in the following aerobic stage at both 50 and 200 mg l^-1 of AYR concentrations. Compared with the absence of AYR, the presence of 200 mg l^-1 of AYR decreased the total nitrogen removal efficiency from 82.4 to 41.1%, and chemical oxygen demand (COD) removal efficiency initially decreased to 68.1% and then returned to around 83.4% in the long-term exposure time. It was also found that the inhibition of AYR, nitrogen and COD removal induced by a higher concentration of AYR was due to the increased intracellular reactive oxygen species production, which caused the rise of oxidation-reduction potential value and decreased ammonia monooxygenase and nitrite oxidoreductase activities.

Factors Affecting the Effectiveness of Bioelectrochemical System Applications: Data Synthesis and Meta-Analysis

Microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) are promising bioelectrochemical systems (BESs) for simultaneous wastewater treatment and energy/resource recovery. Unlike conventional fuel cells that are based on stable chemical reactions, these BESs are sensitive to environmental and operating conditions, such as temperature, pH, external resistance, etc. Substrate type, electrode material, and reactor configuration are also important factors affecting power generation in MFCs and hydrogen production in MECs. In order to discuss the influence of these above factors on the performance of MFCs and MECs, this study analyzes published data via data synthesis and meta-analysis. The results revealed that domestic wastewater would be more suitable for treatment using MFCs or MECs, due to their lower toxicity for anode biofilms compared to swine wastewater and landfill leachate. The optimal temperature was 25–35 °C, optimal pH was 6–7, and optimal external resistance was 100–1000 Ω. Although systems using carbon cloth as the electrodes demonstrated better performance (due to carbon cloth’s large surface area for microbial growth), the high prices of this material and other existing carbonaceous materials make it inappropriate for practical applications. To scale up and commercialize MFCs and MECs in the future, enhanced system performance and stability are needed, and could be possibly achieved with improved system designs.

Effective phosphate removal for advanced water treatment using low energy, migration electric-field assisted electrocoagulation

A migration electric-field assisted electrocoagulation (MEAEC) system was developed to increase phosphate removal from domestic wastewater, with reduced energy consumption, using a titanium charging (inert) electrode and a sacrificial iron anode. In the MEAEC, an electric field was applied between the inert electrode (titanium) and an air cathode to drive migration of phosphate anions towards the sacrificial anode. Current was then applied between the sacrificial anode (Fe or Al mesh) and the air cathode to drive electrocoagulation of phosphate. A MEAEC with the Fe electrode using primary clarifier effluent achieved 98% phosphate removal, producing water with a total phosphorus of 0.3 mg/L with <6 min total treatment time (five cycles; each 10 s inert electrode charging, and 1 min electrocoagulation), at a constant current density of 1 mA/cm². In the absence of the 10 s charging time, electrocoagulation required 15 min for the same removal. With an aluminum anode and the same phosphorus removal, the MEAEC required 7 cycles (7 min total treatment, 1 min 10 s total charging), while conventional electrocoagulation required 20 min. The energy demand of Fe-MEAEC was only 0.039 kWh/m³ for 98% phosphate removal, which was 35% less than with the Al-MEAEC of 0.06 kWh/m³, and 28% less than that previously obtained using an inert graphite electrode. Analysis of the precipitate showed that a less porous precipitate was obtained with the Al anode than with the Fe anode. The phosphorus in precipitate of Fe-MEAEC was identified as PO₄^3- and HPO₄^2-, while the Fe was present as both Fe²⁺ and Fe³⁺. Only HPO₄^2- and Al³⁺ were identified in the precipitate of the Al-MEAEC. These results indicated that the MEAEC with a titanium inert charging electrode and iron anode could achieve the most efficient phosphate removal with very low energy demands, compared to previous electrochemical approaches.

Efficiently "pumping out" value-added resources from wastewater by bioelectrochemical systems: A review from energy perspectives

Bioelectrochemical systems (BES) can accomplish simultaneous wastewater treatment and resource recovery via interactions between microbes and electrodes. Often deemed as "energy efficient" technologies, BES have not been well evaluated for their energy performance, such as energy production and consumption. In this work, we have conducted a review and analysis of energy balance in BES with parameters like normalized energy recovery, specific energy consumption, and net energy production. Several BES representatives based on their functions were selected for analysis, including direct electricity generation in microbial fuel cells, hydrogen production in microbial electrolysis cells, nitrogen recovery in BES, chemical production in microbial electrosynthesis cells, and desalination in microbial desalination cells. Energy performance was normalized to water volume (kWh m^-3), organic removal (kWh kg COD^-1), nitrogen recovery (kWh kg N^-1), chemical production (kWh kg^-1), or removed salt during desalination (kWh kg^-1). The key operating factors such as pumping system (recirculation/feeding pumps) and external power supply were discussed for their effects on energy performance. This is an in-depth analysis of energy performance of various BES and expected to encourage more thinking, analysis, and presentation of energy data towards appropriate research and development of BES technology for resource recovery from wastewater.

Improving biocathode community multifunctionality by polarity inversion for simultaneous bioelectroreduction processes in domestic wastewater

Bioelectrochemical systems (BESs) have been tentatively applied for wastewater treatment processes, but the complex composition of wastewater could lead to difficulties in establishing functional biofilm or result in performance instability. Few studies have investigated the enrichment of biocathode with domestic wastewater (DW) and the function. A biocathode with multi-pollutant removal capabilities was enriched based on polarity inverted bioanode, which was established with DW. The biocathode function was examined using model pollutants (nitrate, nitrobenzene and Acid Orange 7) supplemented as sole or mixed electron acceptors. When compared to the anaerobic control treatment, the biofilm demonstrated significantly enhanced reduction abilities in the open circuit. For the closed circuit, their removal efficiencies were further enhanced for both the sole and mixed substrates conditions. The bioanodes community structure and diversity markedly changed after operating for 50 d as biocathodes. The biocathode multifunctionality and stability could be related to the maintenance of organic matters fermentative bacteria (mainly belonging to Bacteroidetes, Firmicutes and Synergistetes) and the enrichment of versatile pollutant-reducing bacteria (e.g. Pseudomonas, Thauera and Comamonas from Proteobacteria). Other pollutants, such as perchlorate, sulfate, heavy metals, and halogenated organics, may also work as potential electron acceptors. This study provides a new strategy to improve the biocathode community multifunctionality for simultaneous bioelectroreduction, which can be combined with other wastewater treatment processes in actual application.

Increasing the bio-electrochemical system performance in azo dye wastewater treatment: Reduced electrode spacing for improved hydrodynamics

The electrodes spacing would exert a pronounced effect on bio-electrochemical systems (BESs) performance, especially for the scaling-up of reactors and practical applications. In this study, we traced the effect of electrode spacing on wastewater treatment performances from the aspects of hydrodynamics and electrochemical characteristics. Three series of folded stainless steel mesh (f-SSM) electrodes with electrode spacing of 2, 4 and 8mm were designed for azo dye (acid orange 7 (AO7)) wastewater treatment. Results showed that BES with electrode spacing of 2mm (R_S2) obtained the highest efficiencies of AO7 decolorization (90.9±0.4%) and COD removal (36.8±3.8%) at HRT of 8h, which was 30.7% and 15.2% higher than that in BES with electrode spacing of 8mm (R_S8), respectively. Moreover, the relationship between pollutants removal, internal resistance and hydrodynamics of BESs with different electrode spacing supported the hydrodynamics was significantly influence the pollutants removal performance.

Corrugated stainless-steel mesh as a simple engineerable electrode module in bio-electrochemical system: Hydrodynamics and the effects on decolorization performance

The application of bio-electrochemical system (BESs) is strongly depended on the development of the engineering applicable electrode. Here we described an economical and readily processable electrode module with three-dimensional structure, the corrugated stainless-steel mesh electrode module (c-SMEM). This novel developed electrode module was demonstrated to provide a good hydrodynamic characteristic and significantly enhanced the decolorization performance of the BES when serving for treating azo dye (acid orange 7, AO7) containing wastewater. Compared to the conventional planar electrodes module (p-SMEM), c-SMEM was found to prolong the mean residence time (MRT_θ) of AO7 and change the flow pattern closer to the plug flow. As a result, the maximum enhancement of the volumetric decolorization rate (vDR) can reach to 255%, even when the c-SMEM and p-SMEM have the same electrode surface area. In addition, a techno-economic analysis model was established to elucidated the effects of the decolorization performance and the material cost on the initial capital cost, which revealed the BES with c-SMEM could be economically comparable to or even better than the traditional bio-decolorization technologies. These results suggest c-SMEM holds great potential for engineering application, which may help paving the way of applying BES at large-scale.

Electricity production and benzene removal from groundwater using low-cost mini tubular microbial fuel cells in a monitoring well

A low-cost mini tubular microbial fuel cell (MFC) was developed for treating groundwater that contained benzene in monitoring wells. Experimental results indicate that increasing the length and density, and reducing the size of the char particles in the anode effectively reduced the internal resistance. Additionally, a thinner polyvinyl alcohol (PVA) hydrogel separator and PVA with a higher molecular weight improved electricity generation. The optimal parameters for the MFC were an anode density of 1.22 g cm^-3, a coke of 150 μm, an anode length of 6 cm, a PVA of 105,600 g mol^-1, and a separator thickness of 1 cm. Results of continuous-flow experiments reveal that the increasing the sets of MFCs and connecting them in parallel markedly improved the degradation of benzene. More than 95% of benzene was removed and electricity of 38 mW m^-2 was generated. The MFC ran continuously up to 120 days without maintenance.

Aerobic granular sludge inoculated microbial fuel cells for enhanced epoxy reactive diluent wastewater treatment

Microbial consortiums aggregated on the anode surface of microbial fuel cells (MFCs) are critical factors for electricity generation as well as biodegradation efficiencies of organic compounds. Here in this study, aerobic granular sludge (AGS) was assembled on the surface of the MFC anode to form an AGS-MFC system with superior performance on epoxy reactive diluent (ERD) wastewater treatment. AGS-MFCs successfully shortened the startup time from 13d to 7d compared to the ones inoculated with domestic wastewater. Enhanced toxicity tolerance as well as higher COD removal (77.8% vs. 63.6%) were achieved. The higher ERD wastewater treatment efficiency of AGS-MFC is possibly attributed to the diverse microbial population on MFC biofilm, as well as the synergic degradation of contaminants by both the MFC anode biofilm and AGS granules.

Effect of gradual transition of substrate on performance of flat-panel air-cathode microbial fuel cells to treat domestic wastewater

In order to confirm the effects of the low conductivity and biodegradability of wastewater, flat-panel air-cathode microbial fuel cells (FA-MFCs) were operated by supplying substrates with different volume ratios of domestic wastewater mixed with an artificial medium: the artificial medium only, 25% wastewater, 50% wastewater, 75% wastewater, 100% of wastewater with 500mg-COD/L by adding acetate, and raw domestic wastewater (230mg-COD/L). With the increase of wastewater ratio, the maximum power density and organic removal efficiency decreased from 187 to 60W/m³ and 51.5 to 37.4%, respectively, but the Coulombic efficiency was maintained in the range of 18.0-18.9%. The FA-MFCs could maintain their low internal resistances and overcome the decreasing conductivity. The acetate concentration was more important than the total organics for power production. This study suggests that the FA-MFC configuration has great applicability for practical applications when supplied by domestic wastewater with low conductivity and biodegradability.

Continuous treatment of high strength wastewaters using air-cathode microbial fuel cells

Treatment of low strength wastewaters using microbial fuel cells (MFCs) has been effective at hydraulic retention times (HRTs) similar to aerobic processes, but treatment of high strength wastewaters can require longer HRTs. The use of two air-cathode MFCs hydraulically connected in series was examined to continuously treat high strength swine wastewater (7-8g/L of chemical oxygen demand) at an HRT of 16.7h. The maximum power density of 750±70mW/m² was produced after 12daysof operation. However, power decreased by 85% after 185d of operation due to serious cathode fouling. COD removal was improved by using a lower external resistance, and COD removal rates were substantially higher than those previously reported for a low strength wastewater. However, removal rates were inconsistent with first order kinetics as the calculated rate constant was an order of magnitude lower than rate constant for the low strength wastewater.

The effect of flow modes and electrode combinations on the performance of a multiple module microbial fuel cell installed at wastewater treatment plant

A larger (6.1 L) MFC stack made in a scalable configuration was constructed with four anode modules and three (two-sided) cathode modules, and tested at a wastewater treatment plant for performance in terms of chemical oxygen demand (COD) removal and power generation. Domestic wastewater was fed either in parallel (raw wastewater to each individual anode module) or series (sequentially through the chambers), with the flow direction either alternated every one or two days or kept fixed in a single direction over time. The largest impact on performance was the wastewater COD concentration, which greatly impacted power production, but did not affect the percentage of COD removal. With higher COD concentrations (∼500 mg L^-1) and alternating flow conditions, power generation was primarily limited by the cathode specific area. In alternating flow operation, anode modules connected to two cathodes produced an average maximum power density of 6.0 ± 0.4 W m^-3, which was 1.9 ± 0.2 times that obtained for anodes connected to a single cathode. In fixed flow operation, a large subsequent decrease in COD influent concentration greatly reduced power production independent of reactor operation in parallel or serial flow modes. Anode modules connected to two cathodes did not consistently produce more power than the anodes connected to a single cathode, indicating power production became limited by restricted anode performance at low CODs. Cyclic voltammetry and electrochemical impedance spectroscopy data supported restricted anode performance with low COD. These results demonstrate that maintaining power production of MFC stack requires higher influent and effluent COD concentrations. However, overall performance of the MFC in terms of COD removal was not affected by operational modes.