Microbial fuel cells as pollutant treatment units: Research updates

Enhancing tetracycline removal: Performance and mechanisms of interspecies electron transfer in microbial consortia

With the widespread application of antibiotics in aquaculture, antibiotic contamination of manure has become a serious concern. Interspecies electron transfer between microorganisms plays a crucial role in antibiotic biodegradation. This study investigated the impact and mechanism of electron transfer on tetracycline degradation in microbial electrochemical systems. The results demonstrated that at an initial tetracycline concentration of 5 mg/L, the closed-circuit (CC) group achieved a removal rate exceeding 91.98 % within 4 d, which was 2.71 times higher than that of the open-circuit (OC) group. The electron transfer capacity of the CC group was also significantly greater than that of the OC group. Microbial community analysis identified Serratia, Petrimonas, Pseudochrobactrum, and Sphingobacterium as the key potential tetracycline-degrading genera. Additionally, catalase activity in the CC group was significantly enhanced, reaching up to four times that observed in the OC group. Molecular docking further confirmed the strong affinity between catalase and tetracycline, suggesting that catalase plays a significant role in tetracycline degradation. This study offers both theoretical insights and technical support for enhancing the microbial treatment efficiency of organic pollutants.

Mechanisms and mitigation control of clogging in constructed wetlands: Insight into the enhancement of the bioelectrochemical systems

Constructed wetlands (CWs), a cost-effective and eco-friendly wastewater treatment technology, are extensively applied in various types of wastewater treatment. There is a series of strong impacts on CWs performance by the accumulation of clogging matters which attribute to physical, chemical, and biological processes after the long-term operation. This paper summarizes the mechanism of clogging formation, which can be classified into physical, chemical, and biological clogging. Moreover, it analyzes the typical measures for preventing and controlling clogging in CWs. The integration of bioelectrochemical systems (BES), including microbial fuel cells (MFCs) and microbial electrolysis cells (MECs) into CWs is proposed as a safe and efficient way to alleviate substrate clogging on-site, owing to the fact that BES can easily automate the control or adjustment of its internal electric field form. The mechanism of clogging control by CW-BES is comprehensively described and analyzed. With the help of BES, the clogging substances obtained optimized occurrence form, reduced hydrophobicity and advantageous spatial distribution. Besides, the microbial community achieved promoted structure, accelerated rates of electron transfer and more diverse metabolic pathway. Compared to traditional methods for evaluating the clogging of CWs, the MFC sensor offers the advantages of being fast, enabling in-site detection, and being non-destructive. Future research should be focused on the theoretical underpinnings for putting CW-BES into practical use. Additional, efforts should be made to ensure the stable, long-term operation of CWs.

Electroactive biofilm communities in microbial fuel cells for the synergistic treatment of wastewater and bioelectricity generation

Increasing industrialization and urbanization have contributed to a significant rise in wastewater discharge and exerted extensive pressure on the existing natural energy resources. Microbial fuel cell (MFC) is a sustainable technology that utilizes wastewater for electricity generation. MFC comprises a bioelectrochemical system employing electroactive biofilms of several aerobic and anaerobic bacteria, such as Geobacter sulfurreducens, Shewanella oneidensis, Pseudomonas aeruginosa, and Ochrobacterum pseudiintermedium. Since the electroactive biofilms constitute a vital part of the MFC, it is crucial to understand the biofilm-mediated pollutant metabolism and electron transfer mechanisms. Engineering electroactive biofilm communities for improved biofilm formation and extracellular polymeric substances (EPS) secretion can positively impact the bioelectrochemical system and improve fuel cell performance. This review article summarizes the role of electroactive bacterial communities in MFC for wastewater treatment and bioelectricity generation. A significant focus has been laid on understanding the composition, structure, and function of electroactive biofilms in MFC. Various electron transport mechanisms, including direct electron transfer (DET), indirect electron transfer (IET), and long-distance electron transfer (LDET), have been discussed. A detailed summary of the optimization of process parameters and genetic engineering strategies for improving the performance of MFC has been provided. Lastly, the applications of MFC for wastewater treatment, bioelectricity generation, and biosensor development have been reviewed.

The effect of ammonia concentration on the treatment of bio electrochemical leachate using MFCs technology

Microbial fuel cells (MFCs) have garnered attention in bio-electrochemical leachate treatment systems. The most common forms of inorganic ammonia nitrogen are ammonium (NH 4 + ) and free ammonia. Anaerobic digestion can be inhibited in both direct (changes in environmental conditions, such as fluctuations in temperature or pH, can indirectly hinder microbial activity and the efficiency of the digestion process) and indirect (inadequate nutrient levels, or other conditions that indirectly compromise the microbial community's ability to carry out anaerobic digestion effectively) ways by both kinds. The performance of a double-chamber MFC system-composed of an anodic chamber, a cathode chamber with fixed biofilm carriers (carbon felt material), and a Nafion 117 exchange membrane is examined in this work to determine the impact of ammonium nitrogen (NH 4 - N ) inhibition. MFCs may hold up to 100 mL of fluid. Therefore, the bacteria involved were analysed using 16S rRNA. At room temperature, with a concentration of 800 mg L-1 of ammonium nitrogen and 13,225 mg L-1 of chemical oxygen demand (COD), the study produced a considerable power density of 234 mWm-3. It was found thatNH 4 - N concentrations above 800 mg L-1 have an inhibitory influence on power output and treatment effectiveness. Multiple routes removed the most nitrogen (NH 4 + -N: 87.11 ± 0.7%, NO2 -N: 93.17 ± 0.2% and TN: 75.24 ± 0.3%). Results from sequencing indicate that the anode is home to a rich microbial community, with anammox (6%), denitrifying (6.4%), and electrogenic bacteria (18.2%) making up the bulk of the population. Microbial fuel cells can efficiently and cost-effectively execute anammox, a green nitrogen removal process, in landfill leachate.

Linking proteomic function and structure to electroactive biofilms development across electrode orientations

The functionality of electroactive biofilms (EABs) is profoundly influenced by the proteomic dynamics within microbial communities, particularly through the participation of proteins in electron transfer. This study explored the impact of electrode surface orientation, measured by varying oblique angles, on the performance of EABs in bioelectrochemical systems (BES). Utilizing quantitative proteomics, results indicated that a slightly oblique angle (45°) optimized the spatial arrangement of microbial cells, enhancing electron transport efficiency compared to other angles tested. Specifically, the 45° orientation resulted in a 2.36-fold increase in the abundance of c-type cytochromes compared to the 90°. Additionally, Geobacter, showed a relative abundance of 83.25 % at 45°, correlating with a peak current density of 1.87 ± 0.04 A/m2. These microbial and proteomic adaptations highlighted the intricate balance between microbial behavior and the physical environment, which could be tuned to optimize operations. The findings provided new insights into the design and enhancement of BES.

Utilization of microbial fuel cells as a dual approach for landfill leachate treatment and power production: a review

Landfill leachate, which is a complicated organic sewage water, presents substantial dangers to human health and the environment if not properly handled. Electrochemical technology has arisen as a promising strategy for effectively mitigating contaminants in landfill leachate. In this comprehensive review, we explore various theoretical and practical aspects of methods for treating landfill leachate. This exploration includes examining their performance, mechanisms, applications, associated challenges, existing issues, and potential strategies for enhancement, particularly in terms of cost-effectiveness. In addition, this critique provides a comparative investigation between these treatment approaches and the utilization of diverse kinds of microbial fuel cells (MFCs) in terms of their effectiveness in treating landfill leachate and generating power. The examination of these technologies also extends to their use in diverse global contexts, providing insights into operational parameters and regional variations. This extensive assessment serves the primary goal of assisting researchers in understanding the optimal methods for treating landfill leachate and comparing them to different types of MFCs. It offers a valuable resource for the large-scale design and implementation of processes that ensure both the safe treatment of landfill leachate and the generation of electricity. The review not only provides an overview of the current state of landfill leachate treatment but also identifies key challenges and sets the stage for future research directions, ultimately contributing to more sustainable and effective solutions in the management of this critical environmental issue.

Scaling up of dual-chamber microbial electrochemical systems - An appraisal using systems design approach

Impetus to minimise the energy and carbon footprints of evolving wastewater resource recovery facilities has promoted the development of microbial electrochemical systems (MES) as an emerging energy-neutral and sustainable platform technology. Using separators in dual-chamber MES to isolate anodic and cathodic environments creates endless opportunities for its myriad applications. Nevertheless, the high internal resistance and the complex interdependencies among various system factors have challenged its scale-up. This critical review employed a systems approach to examine the complex interdependencies and practical issues surrounding the implementation and scalability of dual-chamber MES, where the anodic and cathodic reactions are mutually appraised to improve the overall system efficiency. The robustness and stability of anodic biofilms in large-volume MES is dependent on its inoculum source, antecedent history and enrichment strategies. The composition and anode-respiring activity of these biofilms are modulated by the anolyte composition, while their performance demands a delicate balance between the electrode size, macrostructure and the availability of substrates, buffers and nutrients when using real wastewater as anolyte. Additionally, the catholyte governed the reduction environment and associated energy consumption of MES with scalable electrocatalysts needed to enhance the sluggish reaction kinetics for energy-efficient resource recovery. A comprehensive assessment of the dual-chamber reactor configuration revealed that the tubular, spiral-wound, or plug-in modular MES configurations are suitable for pilot-scale, where it could be designed more effectively using efficient electrode macrostructure, suitable membranes and bespoke strategies for continuous operation to maximise their performance. It is anticipated that the critical and analytical understanding gained through this review will support the continuous development and scaling-up of dual-chamber MES for prospective energy-neutral treatment of wastewater and simultaneous circular management of highly relevant environmental resources.

Optimizing total ammonia-nitrogen concentration for enhanced microbial fuel cell performance in landfill leachate treatment: a bibliometric analysis and future directions

Untreated landfill leachate can harm the environment and human health due to its organic debris, heavy metals, and nitrogen molecules like ammonia. Microbial fuel cells (MFCs) have emerged as a promising technology for treating landfill leachate and generating energy. However, high concentrations of total ammonia-nitrogen (TAN), which includes both ammonia and the ammonium ion, can impede MFC performance. Therefore, maintaining an adequate TAN concentration is crucial, as both excess and insufficient levels can reduce power generation. To evaluate the worldwide research on MFCs using landfill leachate as a substrate, bibliometric analysis was conducted to assess publication output, author-country co-authorship, and author keyword co-occurrence. Scopus and Web of Science retrieved 98 journal articles on this topic during 2011-2022; 18 were specifically evaluated and analysed for MFC ammonia inhibition. The results showed that research on MFC using landfill leachate as a substrate began in 2011, and the number of related papers has consistently increased every 2 years, totaling 4060 references. China, India, and the USA accounted for approximately 60% of all global publications, while the remaining 40% was contributed by 70 other countries/territories. Chongqing University emerged as one of the top contributors among this subject's ten most productive universities. Most studies found that maintaining TAN concentrations in the 400-800 mg L-1 in MFC operation produced good power density, pollution elimination, and microbial acclimatization. However, the database has few articles on MFC and landfill leachate; MFC ammonia inhibition remains the main factor impacting system performance. This bibliographic analysis provides excellent references and future research directions, highlighting the current limitations of MFC research in this area.

Microbial Fuel Cell Construction Features and Application for Sustainable Wastewater Treatment

A microbial fuel cell (MFC) is a system that can generate electricity by harnessing microorganisms' metabolic activity. MFCs can be used in wastewater treatment plants since they can convert the organic matter in wastewater into electricity while also removing pollutants. The microorganisms in the anode electrode oxidize the organic matter, breaking down pollutants and generating electrons that flow through an electrical circuit to the cathode compartment. This process also generates clean water as a byproduct, which can be reused or released back into the environment. MFCs offer a more energy-efficient alternative to traditional wastewater treatment plants, as they can generate electricity from the organic matter in wastewater, offsetting the energy needs of the treatment plants. The energy requirements of conventional wastewater treatment plants can add to the overall cost of the treatment process and contribute to greenhouse gas emissions. MFCs in wastewater treatment plants can increase sustainability in wastewater treatment processes by increasing energy efficiency and reducing operational cost and greenhouse gas emissions. However, the build-up to the commercial-scale still needs a lot of study, as MFC research is still in its early stages. This study thoroughly describes the principles underlying MFCs, including their fundamental structure and types, construction materials and membrane, working mechanism, and significant process elements influencing their effectiveness in the workplace. The application of this technology in sustainable wastewater treatment, as well as the challenges involved in its widespread adoption, are discussed in this study.

Lignocellulose reconstituted shape-controllable self-supporting carbonaceous capacitance-anodes with high electron transfer rates for high-performance microbial electrochemical system

Natural biomass is a promising candidate for manufacturing an efficient anode in the microbial electrochemical system (MES) for its abundance and low cost. However, the structure and performance of the electrode highly depend on the biomass species. A simple and sustainable method for creating a self-supporting electrode is proposed by freeze-drying and carbonizing a blend of cellulose, lignin, and hemicellulose. This strategy leads to a cork-like structure and improved mechanical strength of the lignocellulose carbon. A power density of 4780 ± 260 mW m^-2 (CLX-800) was achieved, which was the highest record for unmodified lignocellulose-based anodes in the microbial fuel cells. The morphological as lamellar multilayer and rich in hydrophilic functional groups could facilitate the formation of thick electroactive biofilms and enrich Geobacter with the highest abundance of 92.3%. The CLX material is expected to be the ideal electrode for high performance and functionally controllability.

Putting the electro-bugs to work: A systematic review of 22 years of advances in bio-electrochemical systems and the parameters governing their performance

Wastewater treatment using bioelectrochemical systems (BESs) can be considered as a technology finding application in versatile areas such as for renewable energy production and simultaneous reducing environmental problems, biosensors, and bioelectrosynthesis. This review paper reports and critically discusses the challenges, and advances in bio-electrochemical studies in the 21st century. To sum and critically analyze the strides of the last 20+ years on the topic, this study first provides a comprehensive analysis on the structure, performance, and application of BESs, which include Microbial Fuel Cells (MFCs), Microbial Electrolysis Cells (MECs) and Microbial Desalination Cells (MDCs). We focus on the effect of various parameters, such as electroactive microbial community structure, electrode material, configuration of bioreactors, anode unit volume, membrane type, initial COD, co-substrates and the nature of the input wastewater in treatment process and the amount of energy and fuel production, with the purpose of showcasing the modes of operation as a guide for future studies. The results of this review show that the BES have great potential in reducing environmental pollution, purifying saltwater, and producing energy and fuel. At a larger scale, it aspires to facilitate the path of achieving sustainable development and practical application of BES in real-world scenarios.

Ammonia/ammonium removal/recovery from wastewaters using bioelectrochemical systems (BES): A review

This review updates the current research efforts on using BES to recover NH₃/NH₄⁺, highlighting the novel configurations and introducing the working principles and the applications of microbial fuel cell (MFC), microbial electrolysis cell (MEC), microbial desalination cell (MDC), and microbial electrosynthesis cell (MESC) for NH₃/NH₄⁺ removal/recovery. However, commonly studied BES processes for NH₃/NH₄⁺ removal/recovery are energy intensive with external aeration needed for NH₃ stripping being the largest energy input. In such a process bipolar membranes used for yielding a local alkaline pool recovering NH₃ is not cost-effective. This gives a chance to microbial electrosynthesis which turned out to be a potential alternative option to approach circular bioeconomy. Furtherly, the reactor volume and NH₃/NH₄⁺ removal/recovery efficiency has a weakly positive correlation, indicating that there might be other factors controlling the reactor performance that are yet to be investigated.

A Review of Recent Advances in Microbial Fuel Cells: Preparation, Operation, and Application

The microbial fuel cell has been considered a promising alternative to traditional fossil energy. It has great potential in energy production, waste management, and biomass valorization. However, it has several technical issues, such as low power generation efficiency and operational stability. These issues limit the scale-up and commercialization of MFC systems. This review presents the latest progress in microbial community selection and genetic engineering techniques for enhancing microbial electricity production. The summary of substrate selection covers defined substrates and some inexpensive complex substrates, such as wastewater and lignocellulosic biomass materials. In addition, it also includes electrode modification, electron transfer mediator selection, and optimization of operating conditions. The applications of MFC systems introduced in this review involve wastewater treatment, production of value-added products, and biosensors. This review focuses on the crucial process of microbial fuel cells from preparation to application and provides an outlook for their future development.

Improvement of zero waste sustainable recovery using microbial energy generation systems: A comprehensive review

Microbial energy generation systems, i.e., bioelectrochemical systems (BESs) are promising sustainable technologies that have been used in different fields of application such as biofuel production, biosensor, nutrient recovery, wastewater treatment, and heavy metals removal. However, BESs face great challenges such as large-scale application in real time, low power performance, and suitable materials for their configuration. This review paper aimed to discuss the use of BES systems such as conventional microbial fuel cells (MFCs), as well as plant microbial fuel cell (P-MFC), sediment microbial fuel cell (S-MFC), constructed wetland microbial fuel cell (CW-MFC), osmotic microbial fuel cell (OsMFC), photo-bioelectrochemical fuel cell (PBFC), and MFC-Fenton systems in the zero waste sustainable recovery process. Firstly, the configuration and electrode materials used in BESs as the main sources to improve the performance of these technologies are discussed. Additionally, zero waste recovery process from solid and wastewater feedstock, i.e., energy recovery: electricity generation (from 12 to 26,680 mW m^-2) and fuel generation, i.e., H₂ (170 ± 2.7 L^-1 L^-1 d^-1) and CH₄ (107.6 ± 3.2 mL^-1 g^-1), nutrient recovery of 100% (PO₄³-P), and 13-99% (NH₄⁺-N), heavy metal removal/recovery: water recovery, nitrate (100%), sulfate (53-99%), and sulfide recovery/removal (99%), antibiotic, dye removal, and other product recovery are critically analyzed in this review paper. Finally, the perspective and challenges, and future outlook are highlighted. There is no doubt that BES technologies are an economical option for the simultaneous zero waste elimination and energy recovery. However, more research is required to carry out the large-scale application of BES, as well as their commercialization.

Defined and unknown roles of conductive nanoparticles for the enhancement of microbial current generation: A review

The ability of various bacteria to make use of solid substrates through extracellular electron transfer (EET) or extracellular electron uptake (EEU) has enabled the development of valuable biotechnologies such as microbial fuel cells (MFCs) and microbial electrosynthesis (MES). It is common practice to use metallic and semiconductive nanoparticles (NPs) for microbial current enhancement. However, the effect of NPs is highly variable between systems, and there is no clear guideline for effectively increasing the current generation. In the present review, the proposed mechanisms for enhancing current production in MFCs and MES are summarized, and the critical factors for NPs to enhance microbial current generation are discussed. Implications for microbially induced iron corrosion, where iron sulfide NPs are proposed to enhance the rate of EEU, photochemically driven MES, and several future research directions to further enhance microbial current generation, are also discussed.

Novel study on microbial fuel cells via a comprehensive bibliometric and dynamic approach

Microbial fuel cells (MFCs) are eco-friendly and useful bioelectrical devices that harness the natural metabolisms of microbes to produce electrical power directly from organic materials. In this study, a bibliometric analysis is conducted to evaluate MFC research from 2001 to 2018 on the basis of the Science Citation Index Expanded database. Overall, MFC research has experienced a dramatic increase over last 18 years, with an exponential growth in the accumulated number of publications. Most publications are closely related to the industrialization and commoditization of MFCs, along with environmental issues, which are currently the biggest global challenges in MFC studies. A small proportion (4.34%) of the scientific journals published more than half (54.34%) of the total articles in the MFC field. Articles from the top 10 countries/regions accounted for the majority (83.16%) of the total articles, clearly indicating that advanced MFC technologies are currently dominated by these countries/regions. Moreover, an increasing number of MFC researchers are considering two-chamber and three-chamber MFC reactions. In particular, they are focusing on environmental technology instead of merely improving the efficiency of electricity generation. Materials research in the MFC field is still a popular area worldwide, and many researchers have focused on novel and eco-friendly cathode and anode developments. Meanwhile, only a few MFC studies are concerned with biological research.

Sustainable strategy on microbial fuel cell to treat the wastewater for the production of green energy

Microbial fuel cell (MFC) is one of the promising alternative energy systems where the catalytic conversion of chemical energy into electrical energy takes places with the help of microorganisms. The basic configuration of MFC consists of three major components such as electrodes (anode and cathode), catalyst (microorganism) and proton transport/exchange membrane (PEM). MFC classified into four types based on the substrate utilized for the catalytic energy conversion process such as Liquid-phase MFC, Solid-phase MFC, Plant-MFC and Algae-MFC. The core performance of MFC is organic substrate oxidation and electron transfer. Microorganisms and electrodes are the key factors that decide the efficiency of MFC system for electricity generation. Microorganism catalysis degradation of organic matters and assist the electron transfer to anode surface, the conductivity of anode material decides the rate of electron transport to cathode through external circuit where electrons are reduced with hydrogen and form water with oxygen. Not limited to electricity generation, MFC also has diverse applications in different sectors including wastewater treatment, biofuel (biohydrogen) production and used as biosensor for detection of biological oxygen demand (BOD) of wastewater and different contaminants concentration in water. This review explains different types of MFC systems and their core performance towards energy conversion and waste management. Also provides an insight on different factors that significantly affect the MFC performance and different aspects of application of MFC systems in various sectors. The challenges of MFC system design, operations and implementation in pilot scale level and the direction for future research are also described in the present review.

Impact of light on microalgal photosynthetic microbial fuel cells and removal of pollutants by nanoadsorbent biopolymers: Updates, challenges and innovations

Photosynthetic microbial fuel cells (PMFCs) with microalgae have huge potential for treating wastewater while simultaneously converting light energy into electrical energy. The efficiency of such cells directly depends on algal growth, which depends on light intensity. Higher light intensity results in increased potential as well as enhancement in generation of biomass rich in biopolymers. Such biopolymers are produced either by microbes at anode and algae at cathode or vice versa. The biopolymers recovered from these biological sources can be added in wastewater alone or in combination with nanomaterials to act as nanoadsorbents. These nanoadsorbents further increase the efficiency of PMFC by removing the pollutants like metals and dyes. In this review firstly the effect of different light intensities on the growth of microalgae, importance of diatoms in a PMFC and their impact on PMFCs efficiencies have been narrated. Secondly recovery of biopolymers from different biological sources and their role in removal of metals, dyes along with their impact on circular bioeconomy have been discussed. Thereafter bottlenecks and future perspectives in this field of research have been narrated.

Integrating anaerobic digestion with bioelectrochemical system for performance enhancement: A mini review

Strategies for enhancing performance of anaerobic digestion (AD) process has been widely studied. The bioelectrochemical system (BES), including microbial fuel cell, microbial electrolysis cell (MEC), microbial desalination cell, and microbial electrosynthesis, had been proposed to integrate with AD for performance enhancement. This mini-review summarizes the current researches that integrated AD with BES to enhance the performance of the former. The working principles of BES were introduced. The integrated configurations of AD-BES as well as the associated applications were summarized. The statistics analysis for AD-MEC performances reported in literature were then performed to confirm the effects of reactor size and applied voltage on the methane productivity and enhancement. The challenges and prospects of the integrated AD-BES were delineated, and the potential scenarios of applying integrated AD-BES in field were discussed.

Recent advancements in microbial fuel cells: A review on its electron transfer mechanisms, microbial community, types of substrates and design for bio-electrochemical treatment

The development in urbanization, growth in industrialization and deficiency in crude oil wealth has made to focus more for the renewable and also sustainable spotless energy resources. In the past two decades, the concepts of microbial fuel cell have caught more considerations among the scientific societies for the probability of converting, organic waste materials into bio-energy using microorganisms catalyzed anode, and enzymatic/microbial/abiotic/biotic cathode electro-chemical reactions. The added benefit with MFCs technology for waste water treatment is numerous bio-centered processes are available such as sulfate removal, denitrification, nitrification, removal of chemical oxygen demand and biological oxygen demand and heavy metals removal can be performed in the same MFC designed systems. The various factors intricate in MFC concepts in the direction of bioenergy production consists of maximum coulombic efficiency, power density and also the rate of removal of chemical oxygen demand which calculates the efficacy of the MFC unit. Even though the efficacy of MFCs in bioenergy production was initially quietly low, therefore to overcome these issues few modifications are incorporated in design and components of the MFC units, thereby functioning of the MFC unit have improvised the rate of bioenergy production to a substantial level by this means empowering application of MFC technology in numerous sectors including carbon capture, bio-hydrogen production, bioremediation, biosensors, desalination, and wastewater treatment. The present article reviews about the microbial community, types of substrates and information about the several designs of MFCs in an endeavor to get the better of practical difficulties of the MFC technology.

Biodegradation and metabolism of tetrabromobisphenol A in microbial fuel cell: Behaviors, dynamic pathway and the molecular ecological mechanism

Tetrabromobisphenol A (TBBPA) has aroused widespread pollution in industrial wastewater. Microbial fuel cell (MFC) was proved powerful in organics degradation and simultaneous resource recovery during wastewater treatment. However, the TBBPA biotransformation potential, pathway and the related molecular mechanism remain poorly understood. In this study, the enhanced degradation and detoxification performance of TBBPA in MFC anode was confirmed, evidenced by the shorter degradation period (2.3 times shorter) and less generation of bisphenol A. UPLC-QTOF-MS analysis verified TBBPA metabolism went through reductive debromination, hydrolytic debromination, oxidative ring cleavage and o-methylation. Accompanied with those biochemical processes, the metabolites underwent dynamic changes. The distinctly decreased abundance and fewer interactions with other functional genera for the potential reductive dehalogenators (Pseudomonas, etc.) possibly led to the suppressed reductive debromination (5.1%) in the closed bioanode. Otherwise, the more abundant potential function bacteria with more collaborated interrelations, including hydrolytic dehalogenators (Acinetobacter, etc.), aromatics degrading bacteria (Geobacter, Holophaga, etc.) and electroactive bacteria (Geobacter, Desulfovibrio, etc.) made great sense to the enhanced hydrolytic debromination and detoxification of TBBPA. This study revealed that MFC anode was beneficial to TBBPA degradation and provided theoretical support for the decomposition and transformation of micro-pollutants in the municipal sewage treatment coupled with MFC process.

Microbial fuel cells for remediation of environmental pollutants and value addition: Special focus on coupling diatom microbial fuel cells with photocatalytic and photoelectric fuel cells

With the advent of global industrialisation and adaptation of smart life there is rise in anthropogenic pollution especially in water. Remediation of the pollutants (such as metals, and dyes) present in industrial effluents is possible via microbes and algae present in the environment. Microbes are used in a microbial fuel cell (MFC) for remediation of various organic and inorganic pollutants. However, for industrial scale application coupling the MFCs with photocatalytic and photoelectric fuel cell has a potential in improving the output of power. It can also be used for remediation of pollutants more expeditiously, conserving fossil fuels, cleaning environment, hence making the coupled hybrid fuel cell to run economically. Furthermore, such MFC inbuilt with algae in living or powder form give additional value addition products like biofuel, polysaccharides, biopolymers, and polyhydroxy alkanoates etc. This review provides bird's eye view on the removal of environmental pollutants by different biological sources like bacteria and algae. The article is focussed on diatoms as potential algae since they are rich source of crude oil and high value added products in a hybrid photocatalytic MFC. It also covers bottle necks, challenges and future in this field of research.

The influential role of external electrical load in microbial fuel cells and related improvement strategies: A review

The scope of the currentreviewis to discuss and evaluate the role of the external electrical load/resistor (EEL) on the overall behavior and functional properties of microbial fuel cells (MFCs). In this work, a comprehensive analysis is made by considering various levels of MFC architecture, such as electric and energy harvesting efficiency, anode electrode potential shifts, electro-active biofilm formation, cell metabolism and extracellular electron transfer mechanisms, as a function of the EEL and its control strategies. It is outlined that taking the regulation of EEL into account at MFC optimization is highly beneficial, and in order to support this step, in this review, a variety of guidelines are collected and analyzed.

Recent advancement in remediation of synthetic organic antibiotics from environmental matrices: Challenges and perspective

Continuous discharge and persistence of antibiotics in aquatic ecosystem is identified as emerging environment health hazard. Partial degradation and inappropriate disposal induce appearance of diverse antibiotic resistant genes (ARGs) and bacteria, hence their execution is imperative. Conventional methods including waste water treatment plants (WWTPs) are found ineffective for the removal of recalcitrant antibiotics. Therefore, constructive removal of antibiotics from environmental matrices and other alternatives have been discussed. This review summarizes present scenario and removal of micro-pollutants, antibiotics from environment. Various strategies including physicochemical, bioremediation, use of bioreactor, and biocatalysts are recognized as potent antibiotic removal strategies. Microbial Fuel Cells (MFCs) and biochar have emerged as promising biodegradation processes due to low cost, energy efficient and environmental benignity. With higher removal rate (20-50%) combined/ hybrid processes seems to be more efficient for permanent and sustainable elimination of reluctant antibiotics.

Bioanodes containing catalysts from onion waste and Bacillus subtilis for energy generation from pharmaceutical wastewater in a microbial fuel cell

Performance of the FAOW8 + B. subtilis bioanode in an MFC (a 14-day test) using pharmaceutical wastewater (pH = 9.2) as a substrate.

Waste valorization using solid-phase microbial fuel cells (SMFCs): Recent trends and status

This review article discusses the use of solid waste processed in solid-phase microbial fuel cells (SMFCs) as a source of electrical energy. Microbial Fuel Cells (MFCs) are typically operated in the liquid phase because the ion transfer process is efficient in liquid media. Nevertheless, some researchers have considered the potential for MFCs in solid phases (particularly for treating solid waste). This has promise if several important factors are optimized, such as the type and amount of substrate, microorganism community, system configuration, and type and number of electrodes, which increases the amount of electricity generated. The critical factor that affects the SMFC performance is the efficiency of electron and proton transfer through solid media. However, this limitation may be overcome by electrode system enhancements and regular substrate mixing. The integration of SMFCs with other conventional solid waste treatments could be used to produce sustainable green energy. Although SMFCs produce relatively small amounts of energy compared with other waste-to-energy treatments, SMFCs are still promising to achieve zero-emission treatment. Therefore, this article addresses the challenges and fills the gaps in SMFC research and development.

Operation mechanism of constructed wetland-microbial fuel cells for wastewater treatment and electricity generation: A review

Constructed wetland-microbial fuel cells (CWL-MFCs) are eco-friendly and sustainable technology, simultaneously implementing contaminant removal and electricity production. According to intensive research over the last five years, this review on the operation mechanism was conducted for in-depth understanding and application guidance of CWL-MFCs. The electrochemical mechanism based on anodic oxidation and cathodic reduction is the core for improved treatment in CWL-MFCs compared to CWLs. As the dominant bacterial community, the abundance and gene-expression patterns of electro-active bacteria responds to electrode potentials and contaminant loadings, further affecting operational efficiency of CWL-MFCs. Plants benefit COD and N removal by supplying oxygen for aerobic degradation and rhizosphere secretions for microorganisms. Multi-electrode configuration, carbon-based electrodes and rich porous substrates affect transfer resistance and bacterial communities. The possibilities of CWL-MFCs targeting at recalcitrant contaminants like flame retardants and interchain interactions among effect components need systematic research.

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.

Microbial fuel cell system: a promising technology for pollutant removal and environmental remediation

The microbial fuel cell (MFC) system is a promising environmental remediation technology due to its simple compact design, low cost, and renewable energy producing. MFCs can convert chemical energy from waste matters to electrical energy, which provides a sustainable and environmentally friendly solution for pollutant degradations. In this review, we attempt to gather research progress of MFC technology in pollutant removal and environmental remediation. The main configurations and pollutant removal mechanism by MFCs are introduced. The research progress of MFC systems in pollutant removal and environmental remediation, including wastewater treatment, soil remediation, natural water and groundwater remediation, sludge and solid waste treatment, and greenhouse gas emission control, as well as the application of MFCs in environmental monitoring have been reviewed. Subsequently, the application of MFCs in environmental monitoring and the combination of MFCs with other technologies are described. Finally, the current limitations and potential future research has been demonstrated in this review.

Triclosan Removal in Microbial Fuel Cell: The Contribution of Adsorption and Bioelectricity Generation

The occurrence of Triclosan (TCS) in natural aquatic systems has been drawing increasing attention due to its endocrine-disruption effects as well as for the development of antibiotic resistances. Wastewater discharge is the main source of water contamination by TCS. In this study, the removal of TCS in microbial fuel cells (MFCs) was carefully investigated. A 94% removal of TCS was observed with 60 mV electricity generation as well as a slight drop in pH. In addition, we found that adsorption also contributed to the removal of TCS in aqueous solution and 21.73% and 19.92% of the total mass was adsorbed to the inner wall of the reactor and to the electrode, respectively. The results revealed that the attenuation of TCS depends on both biodegradation and physical adsorption in the anode chamber. Thus, the outcomes of our study provide a better understanding of the TCS removal mechanism in MFCs.

Development and Application of Supported Ionic Liquid Membranes in Microbial Fuel Cell Technology: A Concise Overview

Membrane separators are key elements of microbial fuel cells (MFCs), especially of those constructed in a dual-chamber configuration. Until now, membranes made of Nafion have been applied the most widely to set-up MFCs. However, there is a broader agreement in the literature that Nafion is expensive and in many cases, does not meet the actual (mainly mass transfer-specific) requirements demanded by the process and users. Driven by these issues, there has been notable progress in the development of alternative materials for membrane fabrication, among which those relying on the deployment of ionic liquids are emerging. In this review, the background of and recent advances in ionic liquid-containing separators, particularly supported ionic liquid membranes (SILMs), designed for MFC applications are addressed and evaluated. After an assessment of the basic criteria to be fulfilled by membranes in MFCs, experiences with SILMs will be outlined, along with important aspects of transport processes. Finally, a comparison with the literature is presented to elaborate on how MFCs installed with SILM perform relative to similar systems assembled with other, e.g., Nafion, membranes.

A novel single chamber vertical baffle flow biocathode microbial electrochemical system with microbial separator

A 10-liter single chamber vertical baffle flow biocathode microbial electrochemical system (MES) with microbial separator was designed for wastewater treatment. The anode and cathode compartments were incompletely isolated by the microbial separator, which enabled module integration and centralized sludge collection of MES. The effluent COD was <50 mg L^-1 with COD removal of 86 ± 2% and low sludge yield rate of 0.05 ± 0.02 g-sludge g^-1 -COD. The MES performance was mainly restricted by biocathodes and supporting matrixes with higher permeability resulted in better cathode performance. The MES obtained the maximum power density of 67.5 ± 7.8 mW m^-2 with two layers of filter cloth and one layer of polyurethane sponge (S2P1) and supporting matrix with moderate permeability was more suitable in overall power generation and anode stability. The influences on bio-community of both cathodes and separators by the permeability of supporting matrixes were observed.

Reduced graphene oxide and biofilms as cathode catalysts to enhance energy and metal recovery in microbial fuel cell

In this study, reduced graphene oxide (rGO) was developed and employed as cathode catalyst in a membrane-less microbial fuel cell (MFC) to improve energy and metal (copper) recovery in combined with biofilms. Results showed that rGO-based cathode exhibited better characterizations in structure and electron transfer than graphene oxide (GO)-based cathode. The voltage with rGO was about 67% increased, and Cu²⁺ removal efficiency was 43% improved as compared to GO. Cu species on cathode demonstrated the favorable Cu²⁺ reduction to Cu with the catalysis of rGO. Moreover, microbial community analysis indicated that rGO-based cathode exhibited better biocompatibility for functional bacteria that related to electron transfer and Cu²⁺ resistance, such as Geobacter and Pseudomonas, demonstrating the interspecific synergism of microorganisms for efficient energy and copper recovery. It will be of important significance for the heavy metal and energy recovery from low concentrations wastewater by using microbial fuel cell.

Biofouling of membranes in microbial electrochemical technologies: Causes, characterization methods and mitigation strategies

The scope of the review is to discuss the current state of knowledge and lessons learned on biofouling of membrane separators being used for microbial electrochemical technologies (MET). It is illustrated what crucial membrane features have to be considered and how these affect the MET performance, paying particular attention to membrane biofouling. The complexity of the phenomena was demonstrated and thereby, it is shown that membrane qualities related to its surface and inherent material features significantly influence (and can be influenced by) the biofouling process. Applicable methods for assessment of membrane biofouling are highlighted, followed by the detailed literature evaluation. Finally, an outlook on e.g. possible mitigation strategies for membrane biofouling in MET is provided.

Electrochemical performance and microbial community analysis in air cathode microbial fuel cells fuelled with pyroligneous liquor

Microbial fuels cells (MFCs) have been applied for the degradation of pyroligneous liquor (PL) derived from apple tree branches, at different concentrations. The substrate removal, electrochemical properties, and microbial community characteristics were analysed to evaluate the performance of MFCs. Maximum current density (1.94 A/m²), coulombic efficiency (28%), and phenol removal rate (84%) were achieved with MFCs fed with PL at the optimal concentration of 1 g chemical oxygen demand (COD)/L. The polarisation test, cyclic voltammetry, and electrochemical impedance of the electrode redox reaction further explained how the addition of PL could stimulate formation of the electrochemically active biofilm, at the optimal concentration of 1 g COD/L. The microbial community of the anodic biofilm demonstrated that MFCs fed with 1 g COD/L had the highest relative abundance of the typical electrogenic bacteria Geobacter (33%), followed by Sphaerochaeta (6%) and Clostridium (4%). The results revealed that syntrophic interaction of these functional microorganisms contributed significantly to the PL degradation and electrical current generation.

Microbial Electrochemical Technologies for Wastewater Treatment: Principles and Evolution from Microbial Fuel Cells to Bioelectrochemical-Based Constructed Wetlands

Microbial electrochemical technologies (MET) rely on the presence of the metabolic activity of electroactive bacteria for the use of solid-state electrodes for oxidizing different kinds of compound that can lead to the synthesis of chemicals, bioremediation of polluted matrices, the treatment of contaminants of interest, as well as the recovery of energy. Keeping these possibilities in mind, there has been growing interest in the use of electrochemical technologies for wastewater treatment, if possible with simultaneous power generation, since the beginning of the present century. In the last few years, there has been growing interest in exploring the possibility of merging MET with constructed wetlands offering a new option of an intensified wetland system that could maintain a high performance with a lower footprint. Based on that interest, this paper explains the general principles of MET, and the different known extracellular electron transfer mechanisms ruling the interaction between electroactive bacteria and potential solid-state electron acceptors. It also looks at the adoption of those principles for the development of MET set-ups for simultaneous wastewater treatment and power generation, and the challenges that the technology faces. Ultimately, the most recent developments in setups that merge MET with constructed wetlands are presented and discussed.

Shewanella putrefaciens CN32 outer membrane cytochromes MtrC and UndA reduce electron shuttles to produce electricity in microbial fuel cells

The extracellular electron transfer (EET) process of Shewanella species is believed to be indispensable for their anaerobic respiration with an electrode. However, the function of outer membrane c-type cytochromes (OM c-Cyts, the primary components of the EET pathway) is still controversial. In this study, we investigated the effect of two OM c-Cyts (MtrC and UndA) of Shewanella putrefaciens CN32 with respect to electricity production and anodic EET efficiency. Deletion of the mtrC gene severely prolonged the microbial fuel cell (MFC) start-up time and decreased electricity production due to depressed flavin-mediated electron transfer, whereas deletion of the undA gene did not have a significant impact. Strikingly, the depression of EET by the deletion of mtrC could be partially relieved by acclimation, which might be due to an increase in the transmembrane transport of electron shuttles and/or the activation of other redox proteins. These results suggested that MtrC may be the primary reductase of flavins to ensure fast indirect EET, which plays a crucial role in MFC electricity generation.

Recent advancements in bioremediation of dye: Current status and challenges

The rampant industrialization and unchecked growth of modern textile production facilities coupled with the lack of proper treatment facilities have proliferated the discharge of effluents enriched with toxic, baleful, and carcinogenic pollutants including dyes, heavy metals, volatile organic compounds, odorants, and other hazardous materials. Therefore, the development of cost-effective and efficient control measures against such pollution is imperative to safeguard ecosystems and natural resources. In this regard, recent advances in biotechnology and microbiology have propelled bioremediation as a prospective alternative to traditional treatment methods. This review was organized to address bioremediation as a practical option for the treatment of dyes by evaluating its performance and typical attributes. It further highlights the current hurdles and future prospects for the abatement of dyes via biotechnology-based remediation techniques.

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.

Biodegradation of polycyclic aromatic hydrocarbons: Using microbial bioelectrochemical systems to overcome an impasse

Polycyclic aromatic hydrocarbons (PAHs) are hardly biodegradable carcinogenic organic compounds. Bioremediation is a commonly used method for treating PAH contaminated environments such as soils, sediment, water bodies and wastewater. However, bioremediation has various drawbacks including the low abundance, diversity and activity of indigenous hydrocarbon degrading bacteria, their slow growth rates and especially a limited bioavailability of PAHs in the aqueous phase. Addition of nutrients, electron acceptors or co-substrates to enhance indigenous microbial activity is costly and added chemicals often diffuse away from the target compound, thus pointing out an impasse for the bioremediation of PAHs. A promising solution is the adoption of bioelectrochemical systems. They guarantee a permanent electron supply and withdrawal for microorganisms, thereby circumventing the traditional shortcomings of bioremediation. These systems combine biological treatment with electrochemical oxidation/reduction by supplying an anode and a cathode that serve as an electron exchange facility for the biocatalyst. Here, recent achievements in polycyclic aromatic hydrocarbon removal using bioelectrochemical systems have been reviewed. This also concerns PAH precursors: total petroleum hydrocarbons and diesel. Removal performances of PAH biodegradation in bioelectrochemical systems are discussed, focussing on configurational parameters such as anode and cathode designs as well as environmental parameters like porosity, salinity, adsorption and conductivity of soil and sediment that affect PAH biodegradation in BESs. The still scarcely available information on microbiological aspects of bioelectrochemical PAH removal is summarised here. This comprehensive review offers a better understanding of the parameters that affect the removal of PAHs within bioelectrochemical systems. In addition, future experimental setups are proposed in order to study syntrophic relationships between PAH degraders and exoelectrogens. This synopsis can help as guide for researchers in their choices for future experimental designs aiming at increasing the power densities and PAH biodegradation rates using microbial bioelectrochemistry.

Microbial community dynamics in a pilot-scale MFC-AA/O system treating domestic sewage

To investigate the effluent concentrations of pollutants, electricity production and microbial community structure, a pilot-scale microbial fuel cell coupled anaerobic-anoxic-oxic system for domestic sewage treatment was constructed, and continuously operated for more than 1 year under natural conditions. The results indicated that the treatment system ran well most of the whole period, but both effluent qualities and electricity production deteriorated at low temperature. The results of MiSeq sequencing showed that the microbial community structures of both anode and cathode biofilms changed extensively during long-term operation and were correlated with changes in effluent qualities. Fifteen genera of electricigens were detected in the anode biofilm, mainly including Clostridium, Paracoccus, Pseudomonas, and Arcobacter. Partial Mantel test results showed that the temperature had significant effects on the microbial community structure. The electricity production was found to have higher relevance to the variation of the anodic community than that of the cathodic community.

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.

Mixed cellulose ester filter as a separator for air-diffusion cathode microbial fuel cells

Separator is important to prevent bio-contamination of the catalyst layer of air-diffusion cathode microbial fuel cells (MFCs). Mixed cellulose ester filter (MCEF) was examined as a separator for an air-cathode MFC in the present study. The MCEF-MFC produced a maximum power density of 780.7 ± 18.7 mW/m², which was comparable to 770.9 ± 35.9 mW/m² of MFC with Nafion membrane (NFM) as a separator. Long-term examination demonstrated a more stable performance of the MCEF-MFC than NFM-MFC. After 25 cycles, the maximum voltage of the MCEF-MFC decreased by only 1.3% from 425.1 ± 4.3 mV (initial 5 cycles) to 419.5 ± 2.3 mV (last 5 cycles). However, it was decreased by 9.1% from 424.8 ± 5.7 to 386 ± 2.5 mV for the NFM-MFC. The coulombic efficiency (CE) of the MCEF-MFC did not change (from 3.11 ± 0.09% to 3.13 ± 0.02%), while it decreased by 9.12% from 3.18 ± 0.04% to 2.89 ± 0.02% for the NFM-MFC. The MCEF separator was with less biofouling than the NFM separator over 60 days' operation, which might be the reason for the more table long-term performance of the MCEF-MFC. The results demonstrated that MCEF was feasible as a separator to set up good-performing and cost-effective air-diffusion cathode MFC.

Treatment of domestic sewage with anoxic/oxic membrane-less microbial fuel cell with intermittent aeration

An anoxic/oxic microbial fuel cell (MFC) reactor was applied to treat domestic sewage with intermittent aeration at cathodic chamber. The MFC yielded maximum power density of 2.05W/m(3) at current density 6.05A/m(3), 91.7±0.3% chemical oxygen demand (COD) and 98.2±0.3% ammonia-nitrogen (NH3-N) removals could be reached with most of the hydrophilic (HPI), hydrophobic acid (HPO-A), transphilic acid (TPI-A) of the former being consumed with minimal residual aromatics and the most of NH3-N being converted to N2. When the circuit was opened, the COD removal was dropped to 81.1±0.6% and NH3-N to 80.4±0.9% with most of the HPI, TPI-A and hydrophobic neutral (HPO-N) fractions of the former being consumed with excess aromatic residue and 60% of the latter being converted to NO2(-)-N or NO3(-)-N in effluent. Bioelectrochemical reactions in the tested MFC enhance COD and NH3-N removals from domestic sewage.