Decolourisation of Acid orange 7 in a microbial fuel cell with a laccase-based biocathode: Influence of mitigating pH changes in the cathode chamber

Bibliometric analysis and systematic review of electrochemical methods for environmental remediation

Electrochemical methods are increasingly favored for remediating polluted environments due to their environmental compatibility and reagent-saving features. However, a comprehensive understanding of recent progress, mechanisms, and trends in these methods is currently lacking. Web of Science (WoS) databases were utilized for searching the primary data to understand the knowledge structure and research trends of publications on electrochemical methods and to unveil certain hotspots and future trends of electrochemical methods research. The original data were sampled from 9080 publications in those databases with the search deadline of June 1st, 2022. CiteSpace and VOSviewer software facilitated data visualization and analysis of document quantities, source journals, institutions, authors, and keywords. We discussed principles, influencing factors, and progress related to seven major electrochemical methods. Notably, publications on this subject have experienced significant growth since 2007. The most frequently-investigated areas in electrochemical methods included novel materials development, heavy metal remediation, organic pollutant degradation, and removal mechanism identification. "Advanced oxidation process" and "Nanocomposite" are currently trending topics. The major remediation mechanisms are adsorption, oxidation, and reduction. The efficiency of electrochemical systems is influenced by material properties, system configuration, electron transfer efficiency, and power density. Electro-Fenton exhibits significant advantages in achieving synergistic effects of anodic oxidation and electro-adsorption among the seven techniques. Future research should prioritize the improvement of electron transfer efficiency, the optimization of electrode materials, the exploration of emerging technology coupling, and the reduction in system operation and maintenance costs.

The Role of Fungal Fuel Cells in Energy Production and the Removal of Pollutants from Wastewater

Pure water, i.e., a sign of life, continuously circulates and is contaminated by different discharges. This emerging environmental problem has been attracting the attention of scientists searching for methods for the treatment of wastewater contaminated by multiple recalcitrant compounds. Various physical and chemical methods are used to degrade contaminants from water bodies. Traditional methods have certain limitations and complexities for bioenergy production, which motivates the search for new ways of sustainable bioenergy production and wastewater treatment. Biological strategies have opened new avenues to the treatment of wastewater using oxidoreductase enzymes for the degradation of pollutants. Fungal-based fuel cells (FFCs), with their catalysts, have gained considerable attention among scientists worldwide. They are a new, ecofriendly, and alternative approach to nonchemical methods due to easy handling. FFCs are efficiently used in wastewater treatment and the production of electricity for power generation. This article also highlights the construction of fungal catalytic cells and the enzymatic performance of different fungal species in energy production and the treatment of wastewater.

Microbial fuel cell: A green eco-friendly agent for tannery wastewater treatment and simultaneous bioelectricity/power generation

This review paper emphasised on the origin of hexavalent chromium toxicity in tannery wastewater and its remediation using novel Microbial Fuel Cell (MFC) technology, including electroactive bacteria, which are known as exoelectrogens, to simultaneously treat wastewater and its action in the production of bioenergy and the mechanism of Cr⁶⁺ reduction. Also, there are various parameters like electrode, pH, mode of operation, time of operation, and type of exchange membrane used for promising results shown in enhancing MFC production and remediation of Cr⁶⁺. Destructive anthropological activities, such as leather making and electroplating industries are key sources of hexavalent chromium contamination in aquatic repositories. When Cr⁶⁺ enters the food chain and enters the human body, it has the potential to cause cancer. MFC is a green innovation that generates energy economically through the reduction of toxic Cr⁶⁺ to less toxic Cr³⁺. The organic substrates utilized at the anode of MFC act as electrons (e^-) donors. This review also highlighted the utilization of cheap substrates to make MFCs more economically suitable and the energy production at minimum cost.

Laccase-functionalized magnetic framework composite enabled chlorophenols degradation, a potential remediation for fungicides residues in leather

Abstract

Chlorophenols, used as the fungicides in leather, are strictly limited in leather products. In this work, a metal–organic framework material, zeolitic metal azolate framework-7 (MAF-7), was first used to encapsulate laccase (Lac) to prepare MAF-7/Lac bio-composites with 98.5% immobilization yield. Afterward, Lac/MNP@MOM was formed by introducing the magnetic nanoparticles (MNPs) into the Lac@MOM. MAF-7 with better hydrophilicity and stronger pH buffering ability, exhibits good compatibility with laccase, which can reserve the activity of laccase after immobilization. Moreover, the porous structure of MAF-7 is favorable for the sufficient contact between laccase and substrates. Lac/MNP@MOM exhibited excellent activity when exposed to high temperature, extreme pH, and organic solvents, which also simplified complex recovery steps. Furthermore, the degradation rate of 2,4-dichlorophenol (2,4-DCP) could reach as high as 97% within 24 h by immobilized laccase, and after nine consecutive cycles of operation, enzyme activity could remain over 80%, which gives it the potential for practical applications.

Graphical abstract

A techno-economic approach for eliminating dye pollutants from industrial effluent employing microalgae through microbial fuel cells: Barriers and perspectives

Microbial fuel cells are biochemical factories which besides recycling wastewater are electricity generators, if their low power density can be scaled up. This also adds up to work on many factors responsible to increase the cost of running a microbial fuel cell. As a result, the first step is to use environment friendly dead organic algae biomass or even living algae cells in a microbial fuel cell, also referred to as microalgal microbial fuel cells. This can be a techno-economic aspect not only for treating textile wastewater but also an economical way of obtaining value added products and bioelectricity from microalgae. Besides treating wastewater, microalgae in its either form plays an essential role in treating dyes present in wastewater which essentially include azo dyes rich in synthetic ions and heavy metals. Microalgae require these metals as part of their metabolism and hence consume them throughout the integration process in a microbial fuel cell. In this review a detail plan is laid to discuss the treatment of industrial effluents (rich in toxic dyes) employing microbial fuel cells. Efforts have been made by researchers to treat dyes using microbial fuel cell alone or in combination with catalysts, nanomaterials and microalgae have also been included. This review therefore discusses impact of microbial fuel cells in treating wastewater rich in textile dyes its limitations and future aspects.

Alterations in microbial community during the remediation of a black-odorous stream by acclimated composite microorganisms

Microbial application is an efficient, economical, and ecofriendly method for remediating black-odorous rivers. In this study, the field treatment effect and microbial community changes were monitored during remediation by the acclimated complex microorganisms of a typical black-odorous stream. After the treatment, the total phosphorus and ammonia contents decreased by 74.0% and 76.3% and the concentrations of dissolved oxygen increased from 1.65 to 4.90 mg/L, indicating the effectiveness of the acclimated composite microorganisms. The proportion of Bacteroidetes decreased significantly by 48.1% and that of Firmicutes increased by 2.23% on average, and the microbial diversity index first increased and then tended to be uniform. Redundancy analysis demonstrated that the pH, dissolved oxygen, and oxidation-reduction potential together determined the composition of the microbial communities (p < 0.05). These findings showed that the acclimated composite microorganisms can effectively remediate the black odor.

Microbial fuel cells a state-of-the-art technology for wastewater treatment and bioelectricity generation

Wastewater treatment and electricity generation have been the major concerns for the last few years. The scarcity of fossil fuels has led to the development of unconventional energy resources that are pollution-free. Microbial fuel cell (MFC) is an environmental and eco-friendly technology that harvests energy through the oxidation of organic substrates and transform into the electric current with the aid of microorganisms as catalysts. This review presents power output and colour removal values by designing various configurations of MFCs and highlights the importance of materials for the fabrication of anode and cathode electrodes playing vital roles in the formation of biofilm and redox reactions taking place in both chambers. The electron transfer mechanism from microbes towards the electrode surface and the generation of electric current are also highlighted. The effect of various parameters affecting the cell performance such as type and amount of substrate, pH and temperature maintained within the chambers have also been discussed. Although this technology presents many advantages, it still needs to be used in combination with other processes to enhance power output.

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

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

Innovative constructed wetland coupled with microbial fuel cell for enhancing diazo dye degradation with simultaneous electricity generation

A novel earthen separator-based dual-chambered unplanted core of constructed wetland coupled with microbial fuel cell was developed for studying the microbe-material interaction and their effect on treatment performance and electricity generation. The constructed wetland integrated microbial fuel cell was evaluated for the degradation of high molecular weight diazo Congo red dye as a model pollutant. The system exhibited 89.99 ± 0.04% of dye decolorization and 95.80 ± 0.71% of chemical oxygen demand removal efficiency from an initial concentration of 50 ± 10 mg/L and 750 ± 50 mg/L, respectively. Ultraviolet-Visible spectrophotometric and gas chromatography-mass spectrometric analysis revealed naphthalene and phenol as mineralized products. The developed system achieved high power density and current density generation of 235.94 mW/m³ and 1176.4 mA/m³, respectively. Results manifested that dual-chambered constructed wetland coupled with microbial fuel cell has a high capability of dye decolorization and toxicity abatement with appreciable simultaneous bioelectricity generation owing to the significantly low internal resistance of 100 Ω.

Current advances in microbial fuel cell technology toward removal of organic contaminants - A review

At present, water pollution and demand for clean energy are most pressing global issues. On a daily basis, huge quantity of organic wastes gets released into the water ecosystems, causing health related problems. The need-of-the-hour is to utilize proficient and cheaper techniques for complete removal of harmful organic contaminants from water. In this regard, microbial fuel cell (MFC) has emerged as a promising technique, which can produce useful electrical energy from organic wastes and decontaminate polluted water. Herein, we have systematically reviewed recently published results, observations and progress made on the applications of MFCs in degradation of organic contaminants, including organic synthetic dyes, agro pollutants, health care contaminants and other organics (such as phenols and their derivatives, polyhydrocarbons and caffeine). MFC-based hybrid technologies, including MFC-constructed wetland, MFC-photocatalysis, MFC-catalysis, MFC-Fenton process, etc., developed to obtain high removal efficiency and bioelectricity production simultaneously have been discussed. Further, this review assessed the influence of factors, such as nature of electrode catalysts, organic pollutants, electrolyte, microbes and operational conditions, on the performance of pristine and hybrid MFC reactors in terms of pollutant removal efficiency and power generation simultaneously. Moreover, the limitations and future research directions of MFCs for wastewater treatment have been discussed. Finally, a conclusive summary of the findings has been outlined.

Fungal-mediated electrochemical system: Prospects, applications and challenges

Microbial fuel cells (MFCs) that generate bioelectricity from biodegradable waste have received considerable attention from biologists. Fungi play a significant role as both anodic and cathodic catalysts in MFCs. Saccharomyces cerevisiae is a fungus with an ability to transfer electrons through mediators such as methylene blue (MB), neutral red (NR) or even without a mediator. This unique role of fungal cells in exocellular electron transfer (EET) and their interactions with electrodes hold a lot of promise in areas such as wastewater treatment where yeast cell-based MFCs can be used. The present article highlights the physico-chemical factors affecting the performance of fungal-mediated MFCs in terms of power output and degradation of organic pollutants, along with the challenges associated with fungal MFCs. In addition, to this comparative assessment of fungal-mediated bio-electrochemical systems, their development, possible applications and potential challenges are also discussed.

Potential Use of Papaya Waste as a Fuel for Bioelectricity Generation

Papaya (Carica papaya) waste cause significant commercial and environmental damage, mainly due to the economic losses and foul odours they emit when decomposing. Therefore, this work provides an innovative way to generate electricity for the benefit of society and companies dedicated to the import and export of this fruit. Microbial fuel cells are a technology that allows electricity generation. These cells were produced with low-cost materials using zinc and copper electrodes; while a 150 mL polymethylmethacrylate tube was used as a substrate collection chamber (papaya waste). Maximum values of 0.736 ± 0.204 V and 5.57 ± 0.45 mA were generated, while pH values increased from 3.848 to 8.227 ± 0.35 and Brix decreased slowly from the first day. The maximum power density value was 878.38 mW/cm2 at a current density of 7.245 A/cm2 at a maximum voltage of 1072.77 mV. The bacteria were identified with an identity percentage of 99.32% for Achromobacter xylosoxidans species, 99.93% for Acinetobacter bereziniae, and 100.00% for Stenotrophomonas maltophilia. This research gives a new way for the use of papaya waste for bioelectricity generation.

Degradation of 2,4-dichlorophenol contaminated soil by ultrasound-enhanced laccase

In this paper, ultrasound was used to enhance the degradation effect of laccase for 2,4-dichlorophenol (2,4-DCP) in soil. The degradation effect and mechanism of the ultrasound-enhanced laccase were investigated. From the results, the degradation rate of 2,4-DCP can reach as high as 51.7% under the following conditions: reaction period was 21 h, pH = 5.5, ultrasound power was 240 W, duty cycle was 50%, and moisture content was 50%. Using the ultrasound-enhanced laccase, the degradation rate of 2,4-DCP was significantly higher than that using only laccase or only ultrasound. In addition, when ultrasound was used, the optimum pH for the degradation of 2,4-DCP using laccase was increased, making the degradation technology more practical. The analysis results from high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) revealed the degradation pathway of 2,4-DCP in soil: first, 2,4-DCP gradually became phenol through dechlorination, then the small molecular organic matter was generated from the hydroxyl radical or laccase reaction.

Coupling azo dye degradation and biodiesel production by manganese-dependent peroxidase producing oleaginous yeasts isolated from wood-feeding termite gut symbionts

BACKGROUND

Textile industry represents one prevalent activity worldwide, generating large amounts of highly contaminated and rich in azo dyes wastewater, with severe effects on natural ecosystems and public health. However, an effective and environmentally friendly treatment method has not yet been implemented, while concurrently, the increasing demand of modern societies for adequate and sustainable energy supply still remains a global challenge. Under this scope, the purpose of the present study was to isolate promising species of yeasts inhabiting wood-feeding termite guts, for combined azo dyes and textile wastewater bioremediation, along with biodiesel production.

RESULTS

Thirty-eight yeast strains were isolated, molecularly identified and subsequently tested for desired enzymatic activity, lipid accumulation, and tolerance to lignin-derived metabolites. The most promising species were then used for construction of a novel yeast consortium, which was further evaluated for azo dyes degradation, under various culture conditions, dye levels, as well as upon the addition of heavy metals, different carbon and nitrogen sources, and lastly agro-waste as an inexpensive and environmentally friendly substrate alternative. The novel yeast consortium, NYC-1, which was constructed included the manganese-dependent peroxidase producing oleaginous strains Meyerozyma caribbica, Meyerozyma guilliermondii, Debaryomyces hansenii, and Vanrija humicola, and showed efficient azo dyes decolorization, which was further enhanced depending on the incubation conditions. Furthermore, enzymatic activity, fatty acid profile and biodiesel properties were thoroughly investigated. Lastly, a dye degradation pathway coupled to biodiesel production was proposed, including the formation of phenol-based products, instead of toxic aromatic amines.

CONCLUSION

In total, this study might be the first to explore the application of MnP and lipid-accumulating yeasts for coupling dye degradation and biodiesel production.

Laccase Immobilization Strategies for Application as a Cathode Catalyst in Microbial Fuel Cells for Azo Dye Decolourization

Enzymatic biocathodes have the potential to replace platinum as an expensive catalyst for the oxygen reduction reaction in microbial fuel cells (MFCs). However, enzymes are fragile and prone to loss of activity with time. This could be circumvented by using suitable immobilization techniques to maintain the activity and increase longevity of the enzyme. In the present study, laccase from Trametes versicolor was immobilized using three different approaches, i.e., crosslinking with electropolymerized polyaniline (PANI), entrapment in copper alginate beads (Cu-Alg), and encapsulation in Nafion micelles (Nafion), in the absence of redox mediators. These laccase systems were employed in cathode chambers of MFCs for decolourization of Acid orange 7 (AO7) dye. The biocatalyst in the anode chamber was Shewanella oneidensis MR-1 in each case. The enzyme in the immobilized states was compared with freely suspended enzyme with respect to dye decolourization at the cathode, enzyme activity retention, power production, and reusability. PANI laccase showed the highest stability and activity, producing a power density of 38 ± 1.7 mW m⁻² compared to 25.6 ± 2.1 mW m⁻² for Nafion laccase, 14.7 ± 1.04 mW m⁻² for Cu-Alg laccase, and 28 ± 0.98 mW m⁻² for the freely suspended enzyme. There was 81% enzyme activity retained after 1 cycle (5 days) for PANI laccase compared to 69% for Nafion and 61.5% activity for Cu-alginate laccase and 23.8% activity retention for the freely suspended laccase compared to initial activity. The dye decolourization was highest for freely suspended enzyme with over 85% decolourization whereas for PANI it was 75.6%, Nafion 73%, and 81% Cu-alginate systems, respectively. All the immobilized laccase systems were reusable for two more cycles. The current study explores the potential of laccase immobilized biocathode for dye decolourization in a microbial fuel cell.

Treatment of mixed dairy and dye wastewater in anode of microbial fuel cell with simultaneous electricity generation

Microbial fuel cell (MFC) is a green technology that converts the stored chemical energy of organic matter to electricity; therefore, it can be used for wastewater purification and energy production simultaneously. In this study, three kinds of dairy products, including milk, cheese water, and yogurt water, were mixed with Acid orange 7 (AO7) as the model wastewater and used as the anolyte of an MFC. The capability of the system in energy production and dye removal was also investigated. The FESEM images were used to investigate the biofilms attachment to the anodes. Moreover, the polarization curves, electrochemical impedance spectroscopy, cyclic voltammetry (CV), voltage-time profiles, and coulombic efficiency were used to evaluate the electrochemical activity of the MFCs. Based on the CV results, the biofilm formation significantly improved the electrochemical activity of the electrodes. Maximum power density, voltage, and coulombic efficiency were obtained as 44.05 mW.m^-2, 332.4 mV, and 1.76%, respectively, for cheese water + AO7 anolyte, but the milk + AO7 MFC produced a stable voltage for a long time and its performance was similar to the cheese water + AO7 anolyte. Maximum COD removal and decolorization efficiencies were obtained equal to 84.57 and 92.18% for yogurt water + AO7 and cheese water + AO7 anolytes, respectively.

Inducing laccase activity in white rot fungi using copper ions and improving the efficiency of azo dye treatment with electricity generation using microbial fuel cells

This work presents a white rot fungus-microbial fuel cell (WRF-MFC) that uses WRF that is grown at its cathode. Adding Cu²⁺ to the fungi-containing solid medium stimulated WRF-secreting laccase, which catalyzed the redox reaction in the MFC and thereby promoting the generation of electricity. Adding 12.5 mg L^-1 Cu²⁺ to a G. lucidum-containing medium provided the greatest laccase stimulation and increased the laccase activity by a factor of 1.6. Adding 12.5 mg L^-1 Cu²⁺ to the WRF chamber of WRF-MFC increased its decolorization of Acid Orange 7 (AO-7) and increased its power density to 223 mW m^-2, which was 1.77 times that of an MFC without WRF. The enhancement of decolorization and electricity generation improved the performance of the WRF-MFC, indicating that a laccase-catalyzed cathode has great potential effectiveness in microbial fuel cells.

KDM3A and KDM4C Regulate Mesenchymal Stromal Cell Senescence and Bone Aging via Condensin-mediated Heterochromatin Reorganization

Epigenomic changes and stem cell deterioration are two hallmarks of aging. Accumulating evidence suggest that senescence of mesenchymal stromal cells (MSCs) perpetuates aging or age-related diseases. Here we report that two H3K9 demethylases, KDM3A and KDM4C, regulate heterochromatin reorganization via transcriptionally activating condensin components NCAPD2 and NCAPG2 during MSC senescence. Suppression of KDM3A or KDM4C by either genetic or biochemical approach leads to robust DNA damage response and aggravates cellular senescence, whereas overexpression of KDM3A/KDM4C or NCAPD2 promotes heterochromatin reorganization and blunts DNA damage response. Moreover, MSCs derived from Kdm3a−/− mice exhibit defective chromosome organization and exacerbated DNA damage response, which are associated with accelerated bone aging. Consistently, analysis of human bone marrow MSCs and transcriptome database reveals inverse correlation of KDM3A/KDM4C and/or NCAPD2/NCAPG2 with aging. Taken together, the present finding unveils that H3K9 demethylases function as a surveillance mechanism to restrain DNA damage accumulation in stem cells during aging.

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KDM3A and KDM4C restrain DNA damage response during MSC senescence

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KDM3A and KDM4C promote heterochromatin reorganization via induction of condensin

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Loss of Kdm3a exacerbates MSC senescence and bone aging in mice

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Chronological aging of human MSCs is associated with reduced expression of KDM3A and KDM4C

The Role of Natural Laccase Redox Mediators in Simultaneous Dye Decolorization and Power Production in Microbial Fuel Cells

Redox mediators could be used to improve the efficiency of microbial fuel cells (MFCs) by enhancing electron transfer rates and decreasing charge transfer resistance at electrodes. However, many artificial redox mediators are expensive and/or toxic. In this study, laccase enzyme was employed as a biocathode of MFCs in the presence of two natural redox mediators (syringaldehyde (Syr) and acetosyringone (As)), and for comparison, a commonly-used artificial mediator 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) was used to investigate their influence on azo dye decolorization and power production. The redox properties of the mediator-laccase systems were studied by cyclic voltammetry. The presence of ABTS and As increased power density from 54.7 ± 3.5 mW m−2 (control) to 77.2 ± 4.2 mW m−2 and 62.5 ± 3.7 mW m−2 respectively. The power decreased to 23.2 ± 2.1 mW m−2 for laccase with Syr. The cathodic decolorization of Acid orange 7 (AO7) by laccase indicated a 12–16% increase in decolorization efficiency with addition of mediators; and the Laccase-Acetosyringone system was the fastest, with 94% of original dye (100 mgL−1) decolorized within 24 h. Electrochemical analysis to determine the redox properties of the mediators revealed that syringaldehyde did not produce any redox peaks, inferring that it was oxidized by laccase to other products, making it unavailable as a mediator, while acetosyringone and ABTS revealed two redox couples demonstrating the redox mediator properties of these compounds. Thus, acetosyringone served as an efficient natural redox mediator for laccase, aiding in increasing the rate of dye decolorization and power production in MFCs. Taken together, the results suggest that natural laccase redox mediators could have the potential to improve dye decolorization and power density in microbial fuel cells.

Optimized production, purification and molecular characterization of fungal laccase through Alternaria alternata

Objective

Industrial effluents and agriculture biomass are main environmental hazards which are facing by developing country like Pakistan. Along with various other industrial applications, laccases are also involved in the oxidation of various industrial hazardous compounds to detoxify them. This study was designed to produce and purify laccase from ascomyceteous fungi, i.e. Alternaria alternata through solid stat fermentation.

Materials and methods

Abundantly available Sarkanda grass “Saccharum spontaneum” was used as agro-waste substrate for laccase production from fungus A. alternata. Previously only white rot fungi are familiar for laccase production and almost no work has been done on laccase production by A. alternata. In this research work, different physical and chemical parameters were optimized for maximum laccase production through solid state fermentation (SSF).

Results

Enzyme was purified and its molecular weight was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Maximum laccase activity (21.87±0.0115 unit/mL) was detected on 7th day of incubation having pH 5 of the medium at 35°C. None of the added metal ions increased laccase production. Galactose and “yeast extract” used as optimum carbon and nitrogen source for highest laccase production.

Conclusion

A monomeric protein (laccase) having approximately 51 kDa molecular weight obtained after SDS-PAGE.

Fungi-Based Microbial Fuel Cells

Fungi are among the microorganisms able to generate electricity as a result of their metabolic processes. Throughout the last several years, a large number of papers on various microorganisms for current production in microbial fuel cells (MFCs) have been published; however, fungi still lack sufficient evaluation in this regard. In this review, we focus on fungi, paying special attention to their potential applicability to MFCs. Fungi used as anodic or cathodic catalysts, in different reactor configurations, with or without the addition of an exogenous mediator, are described. Contrary to bacteria, in which the mechanism of electron transfer is pretty well known, the mechanism of electron transfer in fungi-based MFCs has not been studied intensively. Thus, here we describe the main findings, which can be used as the starting point for future investigations. We show that fungi have the potential to act as electrogens or cathode catalysts, but MFCs based on bacteria–fungus interactions are especially interesting. The review presents the current state-of-the-art in the field of MFC systems exploiting fungi.

Bio-energy generation in an affordable, single-chamber microbial fuel cell integrated with adsorption hybrid system: effects of temperature and comparison study

A microbial fuel cell (MFC) integrated with adsorption system (MFC-AHS) is tested under various operating temperatures with palm oil mill effluent as the substrate. The optimum operating temperature for such system is found to be at ∼35°C with current, power density, internal resistance (R_in), Coulombic efficiency (CE) and maximum chemical oxygen demand (COD) removal of 2.51 ± 0.2 mA, 74 ± 6 mW m^-3, 25.4 Ω, 10.65 ± 0.5% and 93.57 ± 1.2%, respectively. Maximum current density increases linearly with temperature at a rate of 0.1772 mA m^-2 °C^-1, whereas maximum power density was in a polynomial function. The temperature coefficient (Q₁₀) is found to be 1.20 between 15°C and 35°C. Present studies have demonstrated better CE performance when compared to other MFC-AHSs. Generally, MFC-AHS has demonstrated higher COD removals when compared to standalone MFC regardless of operating temperatures.

ABBREVIATIONS

ACFF: activated carbon fiber felt; APHA: American Public Health Association; CE: Coulombic efficiency; COD: chemical oxygen demand; ECG: electrocardiogram; GAC: granular activated carbon; GFB: graphite fiber brush; MFC: microbial fuel cell; MFC-AHS: microbial fuel cell integrated with adsorption hybrid system; MFC-GG: microbial fuel cell integrated with graphite granules; POME: palm oil mill effluent; PTFE: polytetrafluoroethylene; SEM: scanning electron microscope.