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

The exploitation of bio-electrochemical system and microplastics removal: Possibilities and perspectives

Microplastic (MP) pollution has caused severe concern due to its harmful effect on human beings and ecosystems. Existing MP removal methods face many obstacles, such as high cost, high energy consumption, low efficiency, release of toxic chemicals, etc. Thus, it is crucial to find appropriate and sustainable methods to replace common MP removal approaches. Bio-electrochemical system (BES) is a sustainable clean energy technology that has been successfully applied to wastewater treatment, seawater desalination, metal removal, energy production, biosensors, etc. However, research reports on BES technology to eliminate MP pollution are limited. This paper reviews the mechanism, hazards, and common treatment methods of MP removal and discusses the application of BES systems to improve MP removal efficiency and sustainability. Firstly, the characteristics and limitations of common MP removal techniques are systematically summarized. Then, the potential application of BES technology in MP removal is explored. Furthermore, the feasibility and stability of the potential BES MP removal application are critically evalauted while recommendations for further research are proposed.

Sorting Out the Latest Advances in Separators and Pilot-Scale Microbial Electrochemical Systems for Wastewater Treatment: Concomitant Development, Practical Application, and Future Perspective

To date, dozens of pilot-scale microbial fuel cell (MFC) devices have been successfully developed worldwide for treating various types of wastewater. The availability and configurations of separators are determining factors for the economic feasibility, efficiency, sustainability, and operability of these devices. Thus, the concomitant advances between the separators and pilot-scale MFC configurations deserve further clarification. The analysis of separator configurations has shown that their evolution proceeds as follows: from ion-selective to ion-non-selective, from nonpermeable to permeable, and from abiotic to biotic. Meanwhile, their cost is decreasing and their availability is increasing. Notably, the novel MFCs configured with biotic separators are superior to those configured with abiotic separators in terms of wastewater treatment efficiency and capital cost. Herein, a highly comprehensive review of pilot-scale MFCs (>100 L) has been conducted, and we conclude that the intensive stack of the liquid cathode configuration is more advantageous when wastewater treatment is the highest priority. The use of permeable biotic separators ensures hydrodynamic continuity within the MFCs and simplifies reactor configuration and operation. In addition, a systemic comparison is conducted between pilot-scale MFC devices and conventional decentralized wastewater treatment processes. MFCs showed comparable cost, higher efficiency, long-term stability, and significant superiority in carbon emission reduction. The development of separators has greatly contributed to the availability and usability of MFCs, which will play an important role in various wastewater treatment scenarios in the future.

The promotion of the polycyclic aromatic hydrocarbons degradation mechanism by humic acid as electron mediator in a sediment microbial electrochemical system

To enhance the removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) in sediments and to elucidate the mechanisms by which microbial electrochemical action aids in the degradation of PAHs, humic acid was used as an electron mediator in the microbial electrochemical system in this study. The results revealed that the addition of humic acids led to increases in the removal efficiencies of naphthalene, phenanthrene, and pyrene by 45.91%, 97.83%, and 85.56%, respectively, in areas remote from the anode, when compared to the control group. The investigation into the microbial community structure and functional attributes showed that the presence of humic acid did not significantly modify the microbial community composition or its functional expression at the anode. However, an examination of humic acid transformations demonstrated that humic acid extended the electron transfer range in sediment via the redox reactions of quinone and semiquinone groups, thereby facilitating the PAHs degradation within the sediment.

Effective and Economical 3D Carbon Sponge with Carbon Nanoparticles as Floating Air Cathode for Sustainable Electricity Production in Microbial Fuel Cells

The effective and economical 3D floating air cathodes were fabricated by a simple dipping-drying method with carbon black (CB), ethanol, and PTFE solution. Pristine Type I polyurethane sponge (5 pores/mm) and Pristine Type II polyurethane sponge (3 pores/mm) were used as the support. The deposition of CB on the Pristine Type I and Pristine Type II materials was detected by scanning electron microscopy and Fourier transform infrared spectroscopy. The carbon loss rate test exhibited good CB adhesive stability on both floating air cathodes. Besides, Type I/CB floating air cathode displayed 3.7 times higher tensile strength, 10.58 times higher elongation at break, and 3.3 times lower cost than carbon felt. The electricity production ability of carbon cloth (CC) anode with carbon felt, Type I/CB, and Type II/CB cathode MFCs (CC-CF-MFC, CC-I-MFC, and CC-II-MFC) was evaluated. After 130 days, the CC-I-MFC showed a maximum power density (PD) of 92.58 mW/m3, which was 4.6 times higher than the CC-CF-MFC. Compared with Type II/CB, Type I/CB cathode improved the maximum power density by 160% due to the smaller pores, rougher surface, and higher surface wettability. Further, CC-I-MFC exhibited the best overall oxidation-reduction performance and chemical oxygen demand removal efficiency. Consequently, Type I/CB floating air cathode opens a new opportunity for scaling up simple, inexpensive, and high-performance MFCs for energy production.

Effects of municipal waste compost on microbial biodiversity and energy production in terrestrial microbial fuel cells

Microbial Fuel Cells (MFCs) transform organic matter into electricity through microbial electrochemical reactions catalysed on anodic and cathodic half-cells. Terrestrial MFCs (TMFCs) are a bioelectrochemical system for bioelectricity production as well as soil remediation. In TMFCs, the soil is the ion-exchange electrolyte, whereas a biofilm on the anode oxidises organic matter through electroactive bacteria. Little is known of the overall microbial community composition in a TMFC, which impedes complete exploitation of the potential to generate energy in different soil types. In this context, an experiment was performed to reveal the prokaryotic community structure in single chamber TMFCs with soil in the presence and absence of a municipal waste compost (3% w/v). The microbial community was assessed on the anode and cathode and in bulk soil at the end of the experiment (54 days). Moreover, TMFC electrical performance (voltage and power) was also evaluated over the experimental period, varying the external resistance to improve performance. Compost stimulated soil microbial activity, in line with a general increase in voltage and power. Significant differences were observed in the microbial communities between initial soil conditions and TMFCs, and between the anode, cathode and bulk soil in the presence of the compost. Several electroactive genera (Bacillus, Fulvivirga, Burkholdeira and Geobacter) were found at the anode in the presence of compost. Overall, the use of municipal waste compost significantly increased the performance of the MFCs in terms of electrical power and voltage generated, not least thanks to the selective pressure towards electroactive bacteria on the anode.

Electrochemical process for petroleum refinery wastewater treatment to produce power and hydrogen using microbial electrolysis cell

This research aims to assess the microbial electrolysis cell (MEC) fed with petroleum refinery wastewater (PRW) to produce power density and bio-electrochemical hydrogen. The MEC produces a maximum bio-electricity of 21.4 mA and a power density of 1200123.90 W/m2 with a loading of chemical oxygen demand (COD) of 17000 mg/L. Due to catalyzed oxidation of complex compounds in PRW with a maintained microbial biofilm growth was observed after 90 d of operation of MEC. Results showed that the oxidation of organic substances in PRW enhanced the size in the growth of microbial film which further increased the generation of electrons leading to current density of 5890 mA/m2. The COD removal efficiency of MEC was found to be 89.9%. The bio-electricity and hydrogen production of the MEC was estimated to be 24.5 mA and 19.2 L respectively when loaded with PRW having a COD of 17500 mg/L after 130 d. Present experiments demonstrate the efficiency of MEC technology efficiency in treating petroleum wastewater with the help of microbial biofilm.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.

Use of biogenic silver nanoparticles on the cathode to improve bioelectricity production in microbial fuel cells

To date, research on microbial fuel cells (MFCs) has. focused on the production of cost-effective, high-performance electrodes and catalysts. The present study focuses on the synthesis of silver nanoparticles (AgNPs) by Pseudomonas sp. and evaluates their role as an oxygen reduction reaction (ORR) catalyst in an MFC. Biogenic AgNPs were synthesized from Pseudomonas aeruginosa via facile hydrothermal synthesis. The physiochemical characterization of the biogenic AgNPs was conducted via scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-visible spectrum analysis. SEM micrographs showed a spherical cluster of AgNPs of 20-100 nm in size. The oxygen reduction reaction (ORR) ability of the biogenic AgNPs was studied using cyclic voltammetry (CV). The oxygen reduction peaks were observed at 0.43 V, 0.42 V, 0.410 V, and 0.39 V. Different concentrations of biogenic AgNPs (0.25-1.0 mg/cm2) were used as ORR catalysts at the cathode in the MFC. A steady increase in the power production was observed with increasing concentrations of biogenic AgNPs. Biogenic AgNPs loaded with 1.0 mg/cm2 exhibited the highest power density (PDmax) of 4.70 W/m3, which was approximately 26.30% higher than the PDmax of the sample loaded with 0.25 mg/cm2. The highest COD removal and Coulombic efficiency (CE) were also observed in biogenic AgNPs loaded with 1.0 mg/cm2 (83.8% and 11.7%, respectively). However, the opposite trend was observed in the internal resistance of the MFC. The lowest internal resistance was observed in a 1.0 mg/cm2 loading (87 Ω), which is attributed to the high oxygen reduction kinetics at the surface of the cathode by the biogenic AgNPs. The results of this study conclude that biogenic AgNPs are a cost-effective, high-performance ORR catalyst in MFCs.

Generation of green electricity from sludge using photo-stimulated bacterial consortium as a sustainable technology

Microbial fuel cell (MFC) is a bio-electrical energy generator that uses respiring microbes to transform organic matter present in sludge into electrical energy. The primary goal of this work was to introduce a new approach to the green electricity generation technology. In this context a total of 6 bacterial isolates were recovered from sludge samples collected from El-Sheikh Zayed water purification plant, Egypt, and screened for their electrogenic potential. The most promising isolates were identified according to 16S rRNA sequencing as Escherichia coli and Enterobacter cloacae, promising results were achieved on using them in consortium at optimized values of pH (7.5), temperature (30°C) and substrate (glucose/pyruvate 1%). Low level red laser (λ = 632.8nm, 8mW) was utilized to promote the electrogenic efficiency of the bacterial consortium, maximum growth was attained at 210 sec exposure interval. In an application of adding standard inoculum (107 cfu/mL) of the photo-stimulated bacterial consortium to sludge based MFC a significant increase in the output potential difference values were recorded, the electricity generation was maintained by regular supply of external substrate. These results demonstrate the future development of the dual role of MFCs in renewable energy production and sludge recycling.

Power generation from wastewater using microbial fuel cells: A review

As the world grapples with an imminent energy crisis brought on by the depletion of nonrenewable resources, such as petroleum, the necessity for alternative and eco-friendly power sources becomes increasingly apparent. In this regard harnessing knowledge gained from natural microorganisms to produce electricity using economical substrates is a promising solution through microbial fuel cells (MFCs). Microbial fuel cells leverage microbes' catabolic abilities to break down organic matter and release electrons that are subsequently transported across an external circuit for electricity generation. This article delves into the fundamental components involved in MFC construction and explores crucial factors that impact their performance including substrate oxidation, electron transfer, and internal resistance. Additionally, it offers a comprehensive analysis of existing microbial fuel cell designs while highlighting their respective strengths and weaknesses. Finally, the article showcases cost-effective MFC models based on thorough studies conducted worldwide while illuminating potential practical applications of this renewable energy technology.

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.

Embracing the future of circular bio-enabled economy: unveiling the prospects of microbial fuel cells in achieving true sustainable energy

Sustainable development and energy security, highlighted by the United Nations Sustainable Development Goals (SDGs), necessitate the use of renewable and sustainable energy sources. However, upon careful evaluation of literature, we have discovered that many existing and emerging renewable energy systems (RESs) prioritize renewability over true sustainability. These systems not only suffer from performance inconsistencies and lack of scalability but also fall short in fully embodying the principles of sustainability and circular economy. To address this gap, we propose considering microbial fuel cells (MFCs) as a viable alternative and integral part of the renewable energy ecosystem. MFCs harness the omnipresence, abundance, and cost-effectiveness of their essential components, making them a promising candidate. Through our comprehensive analysis, we shed light on the limitations and advancements of this technology, which underscore the remarkable potential of MFCs to revolutionize our perception of clean, sustainable energy.

Examining current trends and future outlook of bio-electrochemical systems (BES) for nutrient conversion and recovery: an overview

Nutrient-rich waste streams from domestic and industrial sources and the increasing application of synthetic fertilizers have resulted in a huge-scale influx of reactive nitrogen and phosphorus in the environment. The higher concentrations of these pollutants induce eutrophication and foster degradation of aquatic biodiversity. Besides, phosphorus being non-renewable resource is under the risk of rapid depletion. Hence, recovery and reuse of the phosphorus and nitrogen are necessary. Over the years, nutrient recovery, low-carbon energy, and sustainable bioremediation of wastewater have received significant interest. The conventional wastewater treatment technologies have higher energy demand and nutrient removal entails a major cost in the treatment process. For these issues, bio-electrochemical system (BES) has been considered as sustainable and environment friendly wastewater treatment technologies that utilize the energy contained in the wastewater so as to recovery nutrients and purify wastewater. Therefore, this article comprehensively focuses and critically analyzes the potential sources of nutrients, working mechanism of BES, and different nutrient recovery strategies to unlock the upscaling opportunities. Also, economic analysis was done to understand the technical feasibility and potential market value of recovered nutrients. Hence, this review article will be useful in establishing waste management policies and framework along with development of advanced configurations with major emphasis on nutrient recovery rather than removal from the waste stream.

Anode amendment with kaolin and activated carbon increases electricity generation in a microbial fuel cell

The bacterial anode is a key factor for microbial fuel cell (MFC) performance. This study examined the potential of kaolin (fine clay) to enhance bacteria and conductive particle attachment to the anode. The bio-electroactivity of MFCs based on a carbon-cloth anode modified by immobilization with kaolin, activated carbon, and Geobacter sulfurreducens (kaolin-AC), with only kaolin (kaolin), and a bare carbon-cloth (control) anodes were examined. When the MFCs were fed with wastewater, the MFCs based on the kaolin-AC, kaolin, and bare anodes produced a maximum voltage of 0.6 V, 0.4 V, and 0.25 V, respectively. The maximum power density obtained by the MFC based on the kaolin-AC anode was 1112 mW‧m^-2 at a current density of 3.33 A‧m^-2, 12% and 56% higher than the kaolin and the bare anodes, respectively. The highest Coulombic efficiency was obtained by the kaolin-AC anode (16%). The relative microbial diversity showed that Geobacter displayed the highest relative distribution of 64% in the biofilm of the kaolin-AC anode. This result proved the advantage of preserving the bacterial anode exoelectrogens using kaolin. To our knowledge, this is the first study evaluating kaolin as a natural adhesive for immobilizing exoelectrogenic bacteria to anode material in MFCs.

Biodegradation of petroleum wastewater for the production of bioelectricity using activated sludge biomass

Objective

This research is based on the treatment of petroleum wastewater (PWW) with pretreated activated sludge for the production of electricity and removal of chemical oxygen demand (COD) using microbial fuel cell (MFC).

Methods

The application of the MFC system which uses activated sludge biomass (ASB) as a substrate resulted in the reduction of COD by 89.5% of the original value. It generated electricity equivalent to 8.18 mA/m2 which can be reused again. This would solve the majority of environmental crises which we are facing today.

Results

This study discusses the application of ASB to enhance the degradation of PWW for the production of a power density of 1012.95 mW/m2 when a voltage of 0.75 V (voltage) is applied at 30:70% of ASB when MFC is operated in a continuous mode. Microbial biomass growth was catalyzed using activated sludge biomass. The growth of microbes was observed by scanning through an electron microscope. Through oxidation in the MFC system, bioelectricity is generated which is used in the cathode chamber. Furthermore, the MFC operated using ASB in a ratio of 35 with the current density, which decreased to 494.76 mW/m2 at 10% ASB.

Application

Our experiments demonstrate that the efficiency of the MFC system can generate bioelectricity and treat petroleum wastewater by using activated sludge biomass.

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.

Exploring the Oxidative Effects of the Microbial Electro-Fenton Process on the Depolymerization of Lignin Extracted from Rice Straw in a Bio-Electrochemical System Coupled with Wastewater Treatment

Lignin is a potential renewable feedstock to produce value-added compounds, but the overwhelming bulk of it is either burned for energy or discarded as waste. This paper addressed two critical issues: waste-to-value generation and management by demonstrating the in situ depolymerization of lignin extracted from waste rice straw utilizing the microbial electro-Fenton process in a microbial peroxide-producing cell (MPPC), a type of bio-electrochemical cell, for value addition while synchronously treating wastewater. The MPPC electrochemical voltage yields of 0.171 ± 0.05-0.497 ± 0.2 V produced 9 ± 0.43-34 ± 0.11 mM of H₂O₂, which was utilized to depolymerize lignin at various concentrations. Interestingly, a direct correlation was observed between lignin depolymerization and H₂O₂ concentration, while Fourier-transform infrared spectroscopy data revealed a constant disruption of the lignin structure accurately in the wavenumber region of 1000-1750 cm^-1 irrespective of the H₂O₂ concentration. Carboxylic acid derivatives, benzopyran, hexanoic acid, and other valuable compounds were detected in the LC QTOF MS data from the depolymerized lignin mixture. Remarkably, SEM analysis demonstrated morphological changes in depolymerized lignin induced by the oxidative effects of hydroxyl radicals. Biochemical oxygen demand and chemical oxygen demand removal was 60 ± 3-85 ± 1% in anodic wastewater treatment. This research provides a sustainable and efficient technique for lignin valorization and wastewater treatment.

Profile and actual transmissibility of Carbapenem resistance genes: Intracellular and extracellular DNA in hospital wastewater

The current worldwide spread of carbapenem resistance genes (CRGs) has posed a major public health threat, which continues to grow in severity. Hospital wastewaters (HWWs) are major reservoirs for antibiotic resistance genes, while resistomes in HWWs are still poorly characterized when it comes to CRGs. We comprehensively characterized the profile and actual transmissibility of extracellular CRGs (eCRGs) and intracellular CRGs (iCRGs) in HWWs for the first time. In this study, CRGs showed similar relative abundance in treated and untreated HWWs. Meanwhile, HWWs treatments led to the enrichment of bla_IMP-8, probably attributed to the promotion of Novosphingobium and Prosthecobacter after treatment. To evaluate the transmission potential of CRGs, extracellular and intracellular carbapenem-resistant plasmids were captured from HWWs by transformation and conjugation, respectively. We found an interesting phenomenon regarding the transmission characteristics of CRGs: bla_KPC-carrying plasmids could only be captured by transformation, while bla_NDM-carrying plasmids were captured by conjugation. Further experiments showed that HWW treatments increased the conjugation ability of bla_NDM. In conclusion, our study demonstrated that HWWs are significant reservoirs of CRGs and various CRGs exhibit different modes of transmission in HWWs. CRGs cannot be removed by membrane bioreactor and chlorine disinfection. An urgent need is to develop more efficient wastewater treatments to limit CRG dissemination.

Bacterial community structure of electrogenic biofilm developed on modified graphite anode in microbial fuel cell

Formation of electrogenic microbial biofilm on the electrode is critical for harvesting electrical power from wastewater in microbial biofuel cells (MFCs). Although the knowledge of bacterial community structures in the biofilm is vital for the rational design of MFC electrodes, an in-depth study on the subject is still awaiting. Herein, we attempt to address this issue by creating electrogenic biofilm on modified graphite anodes assembled in an air-cathode MFC. The modification was performed with reduced graphene oxide (rGO), polyaniline (PANI), and carbon nanotube (CNTs) separately. To accelerate the growth of the biofilm, soybean-potato composite (plant) powder was blended with these conductive materials during the fabrication of the anodes. The MFC fabricated with PANI-based anode delivered the current density of 324.2 mA cm-2, followed by CNTs (248.75 mA cm-2), rGO (193 mA cm-2), and blank (without coating) (151 mA cm-2) graphite electrodes. Likewise, the PANI-based anode supported a robust biofilm growth containing maximum bacterial cell densities with diverse shapes and sizes of the cells and broad metabolic functionality. The alpha diversity of the biofilm developed over the anode coated with PANI was the loftiest operational taxonomic unit (2058 OUT) and Shannon index (7.56), as disclosed from the high-throughput 16S rRNA sequence analysis. Further, within these taxonomic units, exoelectrogenic phyla comprising Proteobacteria, Firmicutes, and Bacteroidetes were maximum with their corresponding level (%) 45.5, 36.2, and 9.8. The relative abundance of Gammaproteobacteria, Clostridia, and Bacilli at the class level, while Pseudomonas, Clostridium, Enterococcus, and Bifidobacterium at the genus level were comparatively higher in the PANI-based anode.

Application of a membrane-less air cathode microbial fuel cell to treat municipal waste composting leachate

The adverse effects of high strength wastewaters on the microbial activities have created a challenge to biological treatments. Microbial fuel cell has been considered as a promising process because the electrical potential generation can stimulate microorganisms and overcome the inhibitory effect. However, several issues (e.g., scalability, high costs and maintenance) have prevented the process from the industrial applications. Elimination of the proton exchange membrane has been suggested as a remedy to the mentioned problems. In this work, a membrane-less microbial fuel cell was modified by putting the cathode within a thin sand layer (instead of the proton exchange membrane) to treat a high strength wastewater sample. The influences of the feed organic load and time of treatment in the modified system were studied in batch and continuous operations. It was revealed that the batch operation efficiency was higher for the lower feed loadings as a 5-day batch treatment removed 66 ± 4% of the 15,000 ± 500 mg/L initial chemical oxygen demand while the continuous process efficiency with 9-day hydraulic residence time was slightly more than 50%. However, the efficiency of the continuous operation for treatment of higher initial loading values was better than the batch mode with the removal efficiency of 41 ± 2% versus 12 ± 2% for a more concentrated leachate feed (45,000 ± 1000 mg/L). Finally, it was disclosed that the modified membrane-less MFC employed in this work can be effective in treatment of high strength wastewaters in larger scales with lower costs.

General aspects and novel PEMss in microbial fuel cell technology: A review

The current scenario of energy production is mostly shifted towards sustainable renewable energy sources. Other than the energy production from natural resources such as sun, wind and water, microbial fuel cell system (MFC) has earned attraction in recent times. These microbial fuel cell systems are bioelectrochemical cell that possesses a unique ability to generate power as well as treats wastewater simultaneously. In this paper, an overview of the microbial fuel cell system and the effect of significant components on the performance of microbial fuel cell systems are reviewed. Firstly, the importance of the MFC system in power generation, its components, the working principle and various configurations of the MFC were briefly introduced. Biofilm plays a major role in the MFC system. Thus the importance of bio film, bio film formation and characterization techniques are summarised. Further, the review mainly addresses the mechanism of conventional and novel membrane materials on the performance of the MFC system. In addition, special emphasis on ceramic-based materials in the MFC system is presented. Finally, recent applications of the MFC systems are discussed.

Gd-Co nanosheet arrays coated on N-doped carbon spheres as cathode catalyst in photosynthetic microalgae microbial fuel cells

Biocompatible, durable and high catalytic cathode is crucial for the performance of photosynthetic microalgae microbial fuel cell (PMMFC). In this study, gadolinium-cobalt (Gd-Co) nanosheet arrays were coated on N-doped carbon spheres (N-CSs) that were supported using nickel foam (NF), to form a unique 3D hierarchical architecture of Gd-Co@N-CSs/NF cathode material. The morphology and structure of Gd-Co@N-CSs/NF was investigated by physicochemical characterization. The electricity generation and stability of NF, N-CSs/NF, Co@N-CSs/NF and Gd-Co@N-CSs/NF were evaluated using a dual-chamber PMMFC system with Chlorella vulgaris (C. vulgaris) in the cathode chamber. Results showed that doption of Gd to the cathode material resulted in Gd-Co@N-CSs/NF exhibiting superior catalytic activity for the oxygen reduction reaction (ORR), with an ORR peak potential of 0.78 V (vs. RHE). The electron transfer number (n) of Gd-Co@N-CSs/NF was 3.906, indicating ORR was mainly realized via 4e^- transfer pathway. Gd-Co@N-CSs/NF achieved a maximum power density of 115.9 mW m^-2 and an open circuit voltage of 614.8 mV, higher than the other three cathode materials. Gd-Co@N-CSs/NF exhibited excellent stability during 360 h of the PMMFC process, only dropping 5.8 % of maximum voltage. The cell density of C. vulgaris (3.7 × 10¹⁰ cells L^-1) in Gd-Co@N-CSs/NF system was significantly higher than those of NF, N-CSs/NF and Co@N-CSs/NF. This study shows that Gd-Co@N-CSs/NF is a promising cathode material and may be highly beneficial for the enhancement of PMMFC systems.

Valorization of wastewater: A paradigm shift towards circular bioeconomy and sustainability

Limitation in the availability of natural resources like water is the main drive for focussing on resource recovery from wastewater. Rapid urbanization with increased consumption of natural resources has severely affected its management and security. The application of biotechnological processes offers a feasible approach to concentrating and transforming wastewater for resource recovery and a step towards a circular economy. Wastewater generally contains high organic materials, nutrients, metals and chemicals, which have economic value. Hence, its management can be a valuable resource through the implementation of a paradigm transformation for value-added product recovery. This review focuses on the circular economy of "close loop" process by wastewater reuse and energy recovery identifying the emerging technologies for recovering resources across the wastewater treatment phase. Conventional wastewater treatment technologies have been discussed along with the advanced treatment technologies such as algal treatment, anammox technology, microbial fuel cells (MFC). Apart from recovering energy in the form of biogas and biohydrogen, second and third-generation biofuels as well as biohythane and electricity generation have been deliberated. Other options for resource recovery are single-cell protein (SCP), biopolymers as well as recovery of metals and nutrients. The paper also highlights the applications of treated wastewater in agriculture, aquaponics, fisheries and algal cultivation. The concept of Partitions-release-recover (PRR) has been discussed for a better understanding of the filtration treatment coupled with anaerobic digestion. The review provides a critical evaluation on the importance of adopting a circular economy and their role in achieving sustainable development goals (SDGs). Thus, it is imperative that such initiatives towards resource recovery from wastewater through integration of concepts can aid in providing wastewater treatment system with resource efficiency.

Use of Pineapple Waste as Fuel in Microbial Fuel Cell for the Generation of Bioelectricity

The excessive use of fossil sources for the generation of electrical energy and the increase in different organic wastes have caused great damage to the environment; these problems have promoted new ways of generating electricity in an eco-friendly manner using organic waste. In this sense, this research uses single-chamber microbial fuel cells with zinc and copper as electrodes and pineapple waste as fuel (substrate). Current and voltage peaks of 4.95667 ± 0.54775 mA and 0.99 ± 0.03 V were generated on days 16 and 20, respectively, with the substrate operating at an acid pH of 5.21 ± 0.18 and an electrical conductivity of 145.16 ± 9.86 mS/cm at two degrees Brix. Thus, it was also found that the internal resistance of the cells was 865.845 ± 4.726 Ω, and a maximum power density of 513.99 ± 6.54 mW/m² was generated at a current density of 6.123 A/m², and the final FTIR spectrum showed a clear decrease in the initial transmittance peaks. Finally, from the biofilm formed on the anodic electrode, it was possible to molecularly identify the yeast Wickerhamomyces anomalus with 99.82% accuracy. In this way, this research provides a method that companies exporting and importing this fruit may use to generate electrical energy from its waste.

Prospective review on bioelectrochemical systems for wastewater treatment: Achievements, hindrances and role in sustainable environment

Bioelectrochemical systems (BESs) are a relatively new arena for producing bioelectricity, desalinating sea water, and treating industrial effluents by removing organic matter. Microbial electrochemical technologies (METs) are promising for obtaining value-added products during simultaneous remediation of pollutants from wastewater. The search for more affordable desalination technology has led to the development of microbial desalination cells (MDCs). MDC combines the operation of microbial fuel cells (MFC) with electrodialysis for water desalination and energy generation. It has received notable interest of researchers in desalination and wastewater treatment because of low energy requirement and eco-friendly nature. Firstly, this article provides a brief overview of MDC technology. Secondly, factors affecting functioning of MDC and its applications have been accentuated. Additionally, challenges and future outlook on the development of this technology have been delineated. State-of-the-art information provided in this review would expand the scope of interdisciplinary and translational research.

Ordered porous nitrogen-doped carbon with atomically dispersed FeN4 for efficient oxygen reduction reaction in microbial fuel cell

It is necessary to develop cost-effective platinum group materials (PGM)-free cathode catalysts for the oxygen reduction reaction (ORR) to replace the state-of-the-art noble metal for the commercialization of microbial fuel cells (MFCs). Fe-N-C catalysts are one of the promising candidates for commercial Pt/C. Herein, a new cost-effective and highly stable Fe-N-C catalyst was designed and successfully prepared via a facile process. The catalyst was prepared through one single thermal conversion from Fe-doped ZIF-8 (zeolitic imidazolate framework), a metal-organic framework (MOF) containing well-defined FeN₄ coordination. The mesopores in the unique structure of MOF promoted efficient mass transfer, while those arising from the pyrolysis of the MOF produced more active sites. Unlike previous preparation methods, post-treatments were avoided here. As a result, the Fe-N-C cathode had a high ORR activity with a half-wave potential (E_1/2) of 0.85 V in a 0.1 M KOH aqueous solution. The classic MFC with this cathodic catalyst provided a maximum power density of up to 1508 mW m^-2.

Hydrolyzed polyacrylamide biotransformation during the formation of anode biofilm in microbial fuel cell biosystem: Bioelectricity, metabolites and functional microorganisms

The anode biofilm serves as the core dominating the performance of microbial fuel cell (MFC) biosystem. This research provides new insights into hydrolyzed polyacrylamide (HPAM) biotransformation during the formation of anode biofilm. The current density, coulombic efficiency, voltage, power density, volatile fatty acid (VFA) production and total nitrogen (TN) removal enhanced with the thickening of biofilm (1-6 cm), and the maximums achieved 146 mA·m^-2, 47.3%, 8.76 V, 1.28 W·m^-2, 184 mg·L^-1 and 84.6%, respectively. HPAM concentration descended from 508 mg·L^-1 to 83.3 mg·L^-1 after 60 days. HPAM was metabolized into VFAs, N₂, NO₂^--N and NO₃^--N, thereby releasing electrons. Laccase and tyrosine/tryptophan protein induced HPAM metabolism and bioelectricity production. The microbial functions involving HPAM biotransformation and bioelectricity generation were clarified. The alternative resource recovery, techno-economic comparison and development direction of MFC biosystem were discussed to achieve the synchronization of HPAM-containing wastewater treatment and bioelectricity generation based on MFC biosystem.

An integrated decision making approach for selecting a sustainable waste water treatment technology

Growing global energy demand and the depletion of fossil fuels have highlighted the need for alternate and environmentally benign energy sources. The volume of untreated waste water being disposed of straight into fresh water is becoming a major concern. An integrated treatment method can address the problems of bio-energy generation and wastewater management as both processes can use wastewater as a substrate. Linear diophantine fuzzy sets help handle the uncertainty and difficulties that arise while deciding on an effective treatment technique. The use of control parameters makes these fuzzy sets unique and superior to other existing fuzzy sets. A modified strategy incorporating the Pivot pairwise relative criteria importance assessment and Interactive multi-criteria decision making methodologies is proposed for the linear diophantine fuzzy environment. The applicability and effectiveness of the developed model are established by choosing an appropriate wastewater treatment technology in the context of linear diophantine fuzzy sets. In addition, sensitivity analysis is used in this study to determine the stability of the developed framework. Further, comparison analysis is also addressed to assess the validity of the acquired results.

Application of Microbial Fuel Cell (MFC) for Pharmaceutical Wastewater Treatment: An Overview and Future Perspectives

Pharmaceutical wastewater (PWW) is rapidly growing into one of the world’s most serious environmental and public health issues. Existing wastewater treatment systems carry numerous loopholes in supplying the ever-increasing need for potable water resulting from rises in population, urbanization, and industrial growth, and the volume of wastewater produced is growing each day. At present, conventional treatment methods, such as coagulation, sedimentation, oxidation, membrane filtration, flocculation, etc., are used to treat PWW. In contrast to these, the application of microbial fuel cells (MFCs) for decontaminating PWW can be a promising technology to replace these methods. MFC technologies have become a trending research topic in recent times. MFCs have also garnered the interest of researchers worldwide as a promising environmental remediation technique. This review extensively discusses the flaws in standalone conventional processes and the integration of MFCs to enhance electricity production and contaminant removal rates, especially with respect to PWW. This article also summarizes the studies reported on various antibiotics and wastes from pharmaceutical industries treated by MFCs, and their efficiencies. Furthermore, the review explains why further research is needed to establish the actual efficiency of MFCs to achieve sustainable, environmentally friendly, and cost-effective wastewater treatment. A brief on technoeconomic impacts has also been made to provide a glimpse of the way these technologies might replace present-day conventional methods.

Contribution of configurations, electrode and membrane materials, electron transfer mechanisms, and cost of components on the current and future development of microbial fuel cells

Microbial fuel cells (MFCs) are a technology that can be applied to both the wastewater treatment and bioenergy generation. This work discusses the contribution of improvements regarding the configurations, electrode materials, membrane materials, electron transfer mechanisms, and materials cost on the current and future development of MFCs. Analysis of the most recent scientific publications on the field denotes that dual-chamber MFCs configuration offers the greatest potential due to the excellent ability to be adapted to different operating environments. Carbon-based materials show the best performance, biocompatibility of carbon-brush anode favors the formation of the biofilm in a mixed consortium and in wastewater as a substrate resembles the conditions of real scenarios. Carbon-cloth cathode modified with nanotechnology favors the conductive properties of the electrode. Ceramic clay membranes emerge as an interesting low-cost membrane with a proton conductivity of 0.0817 S cm^-1, close to that obtained with the Nafion membrane. The use of nanotechnology in the electrodes also enhances electron transfer in MFCs. It increases the active sites at the anode and improves the interface with microorganisms. At the cathode, it favors its catalytic properties and the oxygen reduction reaction. These features together favor MFCs performance through energy production and substrate degradation with values above 2.0 W m^-2 and 90% respectively. All the recent advances in MFCs are gradually contributing to enable technological alternatives that, in addition to wastewater treatment, generate energy in a sustainable manner. It is important to continue the research efforts worldwide to make MFCs an available and affordable technology for industry and society.

Carbon neutrality of wastewater treatment - A systematic concept beyond the plant boundary

Recently, every industry has been working to achieve carbon neutrality, and the wastewater sector is no exception. However, little research focuses on the carbon accounting of wastewater treatment and the roadmap to carbon neutrality. Here, to systematically perform accounting, we provide a sketch that describes three boundaries of the wastewater system and propose that the carbon neutrality of the wastewater system is far beyond the plant boundary. Moreover, we identify the direct and indirect carbon emissions of wastewater treatment. In addition to direct emissions of CH₄ and N₂O, direct fossil CO₂ emissions from wastewater treatment should be included in accounting to set accurate guidelines. Next, the technologies that assist in achieving carbon-neutral wastewater treatment both within-the-fence of wastewater treatment plants and beyond the plant boundary are summarized. All measurements of energy recovery, resource recovery, and water reuse contribute to reaching this goal. The concepts of energy neutrality and carbon neutrality are identified. Successful wastewater treatment cases in energy self-sufficiency may not achieve carbon neutrality. Meanwhile, resource recovery methods are encouraged, especially to produce carbon-based materials. Ultimately, the trend of preference for the decentralized sewage treatment system is pinpointed, and systematic thinking to set the urban infrastructure layout as a whole is advocated.

Microbial fuel cells for mineralization and decolorization of azo dyes: Recent advances in design and materials

Microbial fuel cells (MFCs) exhibit tremendous potential in the sustainable management of dye wastewater via degrading azo dyes while generating electricity. The past decade has witnessed advances in MFC configurations and materials; however, comprehensive analyses of design and material and its association with dye degradation and electricity generation are required for their industrial application. MFC models with high efficiency of dye decolorization (96-100%) and a wide variation in power generation (29.4-940 mW/m²) have been reported. However, only 28 out of 104 studies analyzed dye mineralization - a prerequisite to obviate dye toxicity. Consequently, the current review aims to provide an in-depth analysis of MFCs potential in dye degradation and mineralization and evaluates materials and designs as crucial factors. Also, structural and operation parameters critical to large-scale applicability and complete mineralization of azo dye were evaluated. Choice of materials, i.e., bacteria, anode, cathode, cathode catalyst, membrane, and substrate and their effects on power density and dye decolorization efficiency presented in review will help in economic feasibility and MFCs scalability to develop a self-sustainable solution for treating azo dye wastewater.

Integration of microbial electrochemical systems and photocatalysis for sustainable treatment of organic recalcitrant wastewaters: Main mechanisms, recent advances, and present prospects

In recent years, microbial electrochemical systems (MESs) have demonstrated to be an environmentally friendly technology for wastewater treatment and simultaneous production of value-added products or energy. However, practical applications of MESs for the treatment of recalcitrant wastewater are limited by their low power output and slow rates of pollutant biodegradation. As a novel technology, hybrid MESs integrating biodegradation and photocatalysis have shown great potential to accelerate the degradation of bio-recalcitrant pollutants and increase the system output. In this review, we summarize recent advances of photo-assisted MESs for enhanced removal of recalcitrant pollutants, and present further discussion about the synergistic effect of biodegradation and photocatalysis. In addition, we analyse in detail different set-up configurations, discuss mechanisms of photo-enhanced extracellular electron transfer, and briefly present ongoing research cases. Finally, we highlight the current limitations and corresponding research gaps, and propose insights for future research.

Experimental Study of Power Generation and COD Removal Efficiency by Air Cathode Microbial Fuel Cell Using Shewanella baltica 20

Microbial fuel cells (MFCs) are a kind of bioreactor for generating electricity, facilitated by exoelectrogens while treating wastewater. The present article focuses on the performance of an air cathode plexiglass MFC in terms of chemical oxygen demand (COD) removal efficiency and power output by performing two sets of experiments. The proton exchange membrane and electrode materials were Nafion 117 and carbon felts, whereas, for stable biofilm formation on the anode surface, a pure culture of Shewanella baltica 20 was used. Firstly, sterile Luria-Bertani (LB) media containing lactate, ranging from 20 to 100 mM, was continuously fed to an MFC, and a maximum power density of 55 mW/m2 was observed. Similarly, artificial wastewater with COD ranging from 3250 mg/L to 10,272 mg/L was supplied to the MFC in the second set of experiments. In this case, the maximum power density and COD removal efficiency were 12 mW/m2 and 57%, respectively. In both cases, the hydraulic retention time (HRT) was 1.5 h. It was found that electricity generation depends on the characteristics of the wastewater. These initial findings confirm that the design aspects of an MFC, i.e., surface area to volume ratio, and external resistance with respect to the quality of influent need to be optimised to improve the MFC’s performance.

Towards sustainable wastewater treatment: Influence of iron, zinc and aluminum as anode in combination with salt bridge on microbial fuel cell performance

Microbial fuel cell (MFC) is a green technology and does not harm the environment. It can be used for wastewater treatment, hydrogen production and power generation. There are lot of avenues need to be investigated to increase the efficiency of MFC and in order to make it acceptable publicly. Efficiency of MFC depends on many factors. In this study, the influence of anode materials (Fe, Al and Zn), their sizes (12, 16 and 20 cm²) and shapes (square, rectangular and circular) were investigated on MFC efficiency. Dual chamber MFC setup was prepared in which Rhodobacter capsulatus was used as biocatalytic agent. Results revealed that Zn anode gave the highest voltage of 1.57 V with corresponding 0.23 A of current. Size of 20 cm² of anode gave maximum voltage of 1.66 V with corresponding value of 0.08 A current, while anode size of 16 cm² gave maximum current of 0.75 A with corresponding voltage of 1.65 V. Regarding their studied shapes, circular shape of anode gave the highest voltages of 1.70 V. Salt bridge played an important role in internal resistance of the fuel cell. The results were checked by changing the diameter and length of the salt bridge. The best results were noticed with 16 cm² circular Zn anode and Fe as cathode. Salt bridge with 7.5 cm length gave the highest voltage of 1.65 V, while 4 gauge diameter salt bridge gave the highest current of 0.85 A.

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.

Mitigation of tannery effluent with simultaneous generation of bioenergy using dual chambered microbial fuel cell

In this study, a dual chambered microbial fuel cell (MFC) was fabricated for the treatment of tannery wastewater with concurrent production of bio-energy. The tannery effluent acts as an anolyte and a synthetic electrolytic solution as the catholyte. Five electrochemically active bacteria from the biofilm were isolated that showed homology with Klebsiella quasipneumoniae, Klebsiella pneumoniae, Cloacibacterium normanese, Bacillus firmus and Pseudomonas reactans, using 16S rDNA analysis. The physiochemical studies of treated wastewater showcased the 88%, 74% and 94% reduction in COD, BOD and TDS level, respectively. The maximum voltage output and power density obtained using electroactive consortium in MFC was 940 mV and 7371 mW/cm³, respectively. The techno-economic feasibility of the bio-electrochemical system was studied for future bioprospecting. The present study reports a significant power generation with simultaneous effluent treatment up to a maximum of ∼85%, in a sustainable and eco-friendly manner.

Local fruit wastes driven benthic microbial fuel cell: a sustainable approach to toxic metal removal and bioelectricity generation

The present work focused on the utilization of three local wastes, i.e., rambutan (Nephelium lappaceum), langsat (Lansium parasiticum), and mango (Mangifera indica) wastes, as organic substrates in a benthic microbial fuel cell (BMFC) to reduce the cadmium and lead concentrations from synthetic water. Out of the three wastes, the mango waste promoted a maximum current density (87.71 mA/m²) along with 78% and 80% removal efficiencies for Cd²⁺ and Pb²⁺, respectively. The bacterial identification proved that Klebsiella pneumoniae, Enterobacter, and Citrobacter were responsible for metal removal and energy generation. In the present work, the BMFC mechanism, current challenges, and future recommendations are also enclosed.

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.

Microbial Electrolysis Cell as a Diverse Technology: Overview of Prospective Applications, Advancements, and Challenges

Microbial electrolysis cells (MECs) have been explored for various applications, including the removal of industrial pollutants, wastewater treatment chemical synthesis, and biosensing. On the other hand, MEC technology is still in its early stages and faces significant obstacles regarding practical large-scale implementations. MECs are used for energy generation and hydrogen peroxide, methane, hydrogen/biohydrogen production, and pollutant removal. This review aimed to investigate the aforementioned uses in order to better understand the different applications of MECs in the following scenarios: MECs for energy generation and recycling, such as hydrogen, methane, and hydrogen peroxide; contaminant removal, particularly complex organic and inorganic contaminants; and resource recovery. MEC technology was examined in terms of new concepts, configuration optimization, electron transfer pathways in biocathodes, and coupling with other technologies for value-added applications, such as MEC anaerobic digestion, combined MEC–MFC, and others. The goal of the review was to help researchers and engineers understand the most recent developments in MEC technologies and applications.

Long-term evaluation of an air-cathode microbial fuel cell with an anion exchange membrane in a 226L wastewater treatment reactor

Although the treatment of municipal wastewater using microbial fuel cells (MFCs) has been extensively studied, scaling the systems up for practical use remains challenging. In this study, a 226 L sewage treatment reactor was equipped with 27 MFC units, and its chemical oxygen demand (COD) removal and electricity production were evaluated. The MFC units were tubular air cores with a diameter of 5 cm and length of 100 cm, which were wrapped with a carbon-based cathode, anion exchange membrane (AEM), and nonwoven graphite fabric. The air-cathode-AEM MFC generated 0.12-0.30 A/m², 0.072-0.51 W/m³, and 1.7-4.6 Wh/m³ in a chemostat reactor with a COD of 140-36 mg/L and hydraulic retention time (HRT) of 9-42 h throughout a year. The decrease in the COD was represented as the first-order rate constant of 0.038. The rate constant was comparable to that of other air-cathode MFCs with cation exchange membranes, indicating the necessity of a posttreatment to meet the discharge standard. It has been estimated that the MFC operation for 24 h before post-aeration can reduce the energy required to meet the discharge standard by 70%, suggesting the potential applicability of MFC in long HRT-treatments such as oxidation ditch. The resistances of the anode, cathode, and AEM were 15, 7.0, and 0.51 mΩ m², respectively, and surface dirt rather than deterioration primarily increased the AEM resistance. A current exceeding 0.2 A/m² significantly increases the anode potential, indicating that the current was limited by low COD. Increasing the anode-specific surface area can improve air-AEM MFCs used for practical applications.

Heterogeneous Advanced Oxidation Processes: Current Approaches for Wastewater Treatment

Nowadays, water pollution is one of the most dangerous environmental problems in the world. The presence of the so-called emerging pollutants in the different water bodies, impossible to eliminate through conventional biological and physical treatments used in wastewater treatment plants due to their persistent and recalcitrant nature, means that pollution continues growing throughout the world. The presence of these emerging pollutants involves serious risks to human and animal health for aquatic and terrestrial organisms. Therefore, in recent years, advanced oxidation processes (AOPs) have been postulated as a viable, innovative and efficient technology for the elimination of these types of compounds from water bodies. The oxidation/reduction reactions triggered in most of these processes require a suitable catalyst. The most recent research focuses on the use and development of different types of heterogeneous catalysts, which are capable of overcoming some of the operational limitations of homogeneous processes such as the generation of metallic sludge, difficult separation of treated water and narrow working pH. This review details the current advances in the field of heterogeneous AOPs, Fenton processes and photocatalysts for the removal of different types of emerging pollutants.

Effect of starch-derived organic acids on the removal of polycyclic aromatic hydrocarbons in an aquaculture-sediment microbial fuel cell

This study constructed sediment microbial fuel cells (SMFCs) for polycyclic aromatic hydrocarbons (PAHs) removal in contaminated aquaculture sediment. Starch, a waste deposited in aquaculture sediment, was employed as the co-substrate for electricity generation and PAHs removal, and the effect of starch-derived organic acids on SMFC performance was assessed. The results indicated that sufficient starch promoted PAHs removal (69.9% for naphthalene, 55.6% for acenaphthene, and 46.8% for pyrene) in dual-chamber SMFC, whereas excessive starch attenuated SMFC performance because the organic acids accumulation reduced anode pH, decreased species diversity, and changed the microbial communities. The electricity generation and PAHs removal were positively correlated (R > 0.96), and both of them were related to Macellibacteroides belonging to Bacteroidetes. However, a larger single-chamber SMFC device did not obtain enhanced PAHs removal owing to the restricted "effective range" of the anode. Hence, more challenges need to be addressed to realize the practical application of SMFC.

Development of an MFC-biosensor for determination of Pb+2: an assessment from computational fluid dynamics and life cycle assessment perspectives

Microbial fuel cell (MFC)-based biosensor sensing has emerged as an innovative approach to in situ and immediate monitoring of substrate concentration. MFC-biosensor uses bioanode as a sensing element. In this study, the performance of MFC-biosensor, operated with Pb⁺², was studied at different hydraulic retention times (HRTs). The HRT ranges were 0.5, 1, and 2 days. The power density generation increased with the decreasing HRT. The highest achievable power density was obtained at HRT of 1 days with the density value of 597 mW/m². The power density produced in the MFC system was stored in the energy storage system. The computational fluid dynamics (CFD) method simulates detailed three-dimensional flow and heat transfer properties in reactors and provides information about potential reactor design. CFD was chosen to simulate the concentration distribution of the substrate in the MFC in different reactor type and different HRTs. It was observed that there was good turbulence in the reactor in a two day HRT and the reactor volume was used effectively. Life cycle assessment (LCA) was performed at 1 day with the highest power density. An LCA was implemented to the production and operation processes of a microbial fuel cell. According to the results, these two processes caused 4.23 × 10^-6 loss of healthy years, extinction of 1.3 × 10^-8 species in a year and loss of $ 0.33 source availability. The emissions to air, water, and soil were also calculated. These results showed that MFC-biosensor provided information on the rate of biodegradation processes.

A critical review on early-warning electrochemical system on microbial fuel cell-based biosensor for on-site water quality monitoring

The microbial fuel cell (MFC) sensor is a very promising self-powered self-sustainable system for early warning water quality detection. These sensors are cost-effective, biodegradable, compact in design, and portable in nature are favorable for real-time in situ water quality monitoring. This review represents the mechanism action behind the toxicity detection, optimization strategies, process parameters, role of biofilm, the role of external resistance, hydrodynamic study, and mathematical modeling for improving the performance of the sensor. Additionally, the techno-economic prospect of this MFC-based sensor and its challenges, limitations are addressed to make it economically more favorable for commercial use. The future direction is also explored based on the sensor's disadvantages and limitations. Comprehensively, this review covered all the possible directions of MFC sensor fabrication, their application, recent advancement, prospects challenges, and their possible solutions.

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.

A comprehensive review on emerging trends in industrial wastewater research

Rapid industrialization is one of the intricate factors that is linked to the depletion of water resources and increased generation of wastewater. Due to various obstructions and impediments, such as ineffective treatment solutions, exorbitant prices, lack of basic amenities, insufficient financial assistance, and technical expertise, sustainable treatment of industrial effluents has become an onerous process in most parts of the world. The majority of current treatment solutions are conventional and outdated, and thus fall short to remove all the contaminants efficiently from the industrial wastewater. Moreover, poorly treated or untreated industrial effluents are indiscriminately dumped into water bodies such as lakes, ponds, and rivers, causing substantial health hazards to humans and animals and serious threats to the aquatic ecosystem. Thus, there is a need for highly efficient, cost-effective, and sustainable technologies for the treatment of industrial wastewater. Employment of microbial technologies such as microbial fuel cells and microalgal technologies, treatment of wastewater can be coupled with the production of bioelectricity and valuable biomass, respectively. Moreover, with nanofiltration and biochar technologies, the efficiency of the overall treatment procedure can be increased to a greater extent. The present review aims to highlight opportunities and challenges associated with some of the emerging trends in industrial wastewater research.