Repeated oxidative degradation of methyl orange through bio-electro-Fenton in bioelectrochemical system (BES)

Performance evaluation of Iron-doped carbon cloth cathodes in bio-electrochemical system for dye degradation

Bio electro-Fenton (BEF) is an advanced bio-electrochemical system that utilizes the synergistic effect of microbial activity and electrochemical reactions to degrade organic pollutants in wastewater. This study investigates the degradation of Chrysoidine Y dye using iron-doped, binder-free carbon cloth cathodes in a BEF system. The cathodes exhibited significant electrochemical enhancements, including increased electrochemical active surface area, improved electrical conductivity, and efficient Fe3+/Fe2+ redox cycling. Under optimal conditions (1000 mg/L substrate concentration, pH 3, 750 Ω applied resistance and 20 ppm dye concentration), the BEF system achieved 73.14 % dye removal and 58.69 % total organic carbon (TOC) reduction within 10 h. Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed the breakdown of chrysoidine Y into non-toxic intermediates. Toxicity tests using chick pea germination showed no adverse effects (Germination Index>80 %) in the treated effluent. Whole genome sequencing of the anodic biofilm identified electrogenic bacteria responsible for electron generation to drive the fenton reaction. These findings highlight the potential of iron-doped cathodes in BEF systems for sustainable and efficient treatment of dye-contaminated wastewater, ensuring effective pollutant removal and environmental safety.

Bio-electro-fenton system assisted with metal-organic framework for degradation of bis-phenol S in wastewater as an emerging contaminant

The bio-electro-fenton (BEF) system is a novel technology that can be utilized to degrade both emerging and persistent pollutants while producing clean, green, and sustainable energy. Various catalysts that have a high active surface area are employed in these systems to enhance the oxygen reduction reaction (ORR) efficiency. In this study, the Nickel/Cobalt metal-organic framework (Ni/Co BTC-MOF) as heterogeneous catalyst was synthesized and deposited by the cathodic electrochemical deposition method on the carbon felt (CF) and graphite plate (GP) electrodes. The results of FT-IR, Field Emission Scanning Electron Microscopy (FE-SEM), X-ray Diffraction (XRD), and Energy Dispersive X-ray spectroscopy (EDS) analysis proved that the synthesis of Ni/Co-BTC MOF successfully carried out. The performance and positive effect of the modified electrodes in ORR were investigated and compared in electrical energy generation. Finally, bio-electro-degradation of bisphenol-S (BPS) as one of the endocrine-disrupting compounds (EDCs) was studied by the optimal modified electrode. According to the results of electrochemical experiments, the highest maximum power density is equal to 133.6 mW/m2, which is related to Ni/Co-BTC@CF, and the highest production voltage is related to Ni/Co-BTC@CF, Ni/Co-BTC@GP, CF, and GP, respectively. The removal efficiency levels of bisphenol S in this system at different concentrations of 1.0, 5.0, and 10.0 mg/l after 24 h were 98.0%, 84.0%, and 41.0%, respectively. Based on the obtained results, the improved BEF system with Ni/Co-BTC@CF catalyst can be a suitable technology to achieve more electricity flow and at the same time have a positive effect on the decomposition of bisphenol S pollutant.

A critical review of approaches to enhance the performance of bio-electro-Fenton and photo-bio-electro-Fenton systems

The development of sustainable advanced energy conversion technologies and efficient pollutant treatment processes is a viable solution to the two global crises of the lack of non-renewable energy resources and environmental harm. In recent years, the interaction of biological and chemical oxidation units to utilize biomass has been extensively studied. Among these systems, bio-electro-Fenton (BEF) and photo-bio-electro-Fenton (PBEF) systems have shown prospects for application due to making rational and practical conversion and use of energy. This review compared and analyzed the electron transfer mechanisms in BEF and PBEF systems, and systematically summarized the techniques for enhancing system performance based on the generation, transfer, and utilization of electrons, including increasing the anode electron recovery efficiency, enhancing the generation of reactive oxygen species, and optimizing operational modes. This review compared the effects of different methods on the electron flow process and fully evaluated the benefits and drawbacks. This review may provide straightforward suggestions and methods to enhance the performance of BEF and PBEF systems and inspire the reader to explore the generation and utilization of sustainable energy more deeply.

Degradation of tetracycline under a wide pH range in a heterogeneous photo bio-electro-fenton system using FeMn-LDH/g-C3N4 cathode: Performance and mechanism

The widespread use of antibiotics and the inefficiency of traditional degradation treatments pose threats to the environment and human health. Previous studies have reported the potential of bio-electro-Fenton (BEF) processes for antibiotic removal. However, some drawbacks, such as a strict pH range of 2-3 and iron sludge generation, limit their large-scale application. Thus, to overcome the narrow pH range of traditional BEF processes, a photo-BEF (PBEF) system was established using a novel FeMn-layered double hydroxide (LDH)/graphitic carbon nitride (g-C3N4) (FM/CN) composite cathode. The performance of the PBEF system was investigated by degrading tetracycline (TC) under low-power LED lamp irradiation. The results indicated that the pH range of the PBEF system could be expanded to 3-11 using an FM/CN cathode, which exhibited a TC removal efficiency of 63.0%-75.9%. The highest TC removal efficiency was achieved at pH 7. The efficient mineralization of TC by the PBEF system can be high, up to 67.6%. In addition, the TC removal mechanism was discussed in terms of reactive oxygen species, TC degradation intermediate analyses, and density functional theory (DFT) calculations. Strong oxidative hydroxyl radicals (·OH) were the dominant reactive oxidizing species in the PBEF system, followed by ·O2- and h+. Three pathways of TC degradation were proposed based on the analysis of intermediates, and the reactive sites attacked by electrophilic reagents were explored using DFT modeling. In addition, the overall toxicity of TC degradation intermediates effectively decreased in the PBEF system. This work offers deep insights into the TC removal mechanisms and performance of the PBEF system over a wide pH range of 3-11.

Elimination of pharmaceuticals from wastewater using microbial fuel cell-based bio-electro-Fenton process

This study highlights the potential of the microbial fuel cell (MFC)-based bio-electro-Fenton (BEF) process as an efficient and highly adaptable strategy for wastewater treatment. The research aims to optimize the pH of the cathodic chamber (3-7) and catalyst doses (Fe) (0-18.56%) on the graphite felt (GF) cathode, and examine the effect of operating parameters on chemical oxygen demand (COD) removal, mineralization efficiency, pharmaceuticals (ampicillin, diclofenac, and paracetamol) removal, and power generation. The study found that lower pH and higher catalyst dosage on the GF led to better performance of the MFC-BEF system. Under neutral pH, mineralization efficiency, paracetamol removal, and ampicillin removal were enhanced by 1.1 times, and power density improved by 1.25 times as catalyst dosage increased from 0 to 18.56%. Additionally, employing full factorial design (FFD) statistical optimization, the study identifies the optimized conditions for maximum COD removal, mineralization efficiency, and power generation, which are determined to be a pH of 3.82 and a catalyst dose of 18.56%.

Effective degradation of tetracycline via recyclable cellulose nanofibrils/polyvinyl alcohol/Fe3O4 hybrid hydrogel as a photo-Fenton catalyst

In this work, the method of in-situ co-precipitation was used to prepare PVA/CNF/Fe₃O₄ hybrid hydrogel, and the relationship between its structure and performance was explored. The Fe₃O₄NPs prepared by this method were dispersed on the carrier PVA/CNF hydrogel and were easy to recover. The catalytic degradation of tetracycline was investigated using PVA/CNF/Fe₃O₄ hybrid hydrogel as photo-Fenton catalysts. The results showed that light and hydrogel carriers were pivotal factors in promoting Fe²⁺ and Fe³⁺ cycling and that the PVA/CNF/Fe₃O₄ hybrid hydrogel as catalysts were able to activate H₂O₂ to generate a large amount of oxygen radical •OH, resulting in efficient removal of tetracycline. The tetracycline degradation followed a proposed first-order kinetic model and achieved a removal rate of about 98% in 120 min at an optimum pH of 3, H₂O₂ 100 mM, catalyst 0.3 g/L, and a temperature of 25 °C.

A new photoelectrochemical cell coupled with the Fenton reaction to remove pollutant and generate electricity under the drive of waste heat

The water and energy crises are becoming increasingly serious with rapid population and economic development. It is urgent to develop new wastewater treatment technologies with high efficiency and low energy consumption. Herein, a solar-salinity nexus cell (called PRC) integrated by a photocatalytic fuel cell and reverse electrodialysis was combined with the Fenton reaction. The PRC-Fenton process can extract electrons from organic wastewater driven by salinity gradient energy for power generation and wastewater remediation in two chambers. The Fenton cathode MOF(2Fe/Co)-GO/GF with good electrocatalytic and photocatalytic activity was developed and optimized in a three-electrode system. GO doping obviously enhanced the catalytic activity and stability of the Fenton cathode. The pollutant (ampicillin, AMP) was simultaneously removed in both anode and cathode chambers of the PRC-Fenton system. AMP removal by the MOF(2Fe/Co)-GO/GF cathode remained above 95% in a wide range of pH values (3.0-7.0). The output current of the PRC-Fenton process was 1.7-2.4 mA. Compared to similar systems, PRC-Fenton is suitable for treating toxic and refractory organic pollutants with green energy in two chambers and generating electricity.

Waste-derived iron catalyzed bio-electro-Fenton process for the cathodic degradation of surfactants

The application of waste-derived iron for reuse in wastewater treatment is an effective way of utilizing waste and attaining sustainability in the overall process. In the present investigation, bio-electro-Fenton process was initiated for the cathodic degradation of surfactants using waste-iron catalyzed MFC (WFe-MFC). The waste-iron was derived from spent tonner ink using calcination at 600 °C. Three surfactants namely, sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide, and Triton x-100 were selected as target pollutants. The effect of experimental factors like application of catalyst, contact time, external resistance, and anodic substrate concentration on the SDS degradation was investigated. At a neutral pH, the cathodic surfactants removal efficiency in WFe-MFC was above 85% in a contact time of 180 min with the initial surfactant concentration of ∼20 mg L-1 and external resistance of 100 Ω. The long-term operation using secondary treated real wastewater with unchanged cathode proved that the catalyst was still active to produce effluent SDS concentration of less than 1 mg L-1 in 4 h of contact time after 16 cycles. In a way, the present investigation suggests a potential application for spent tonner ink in the form of Fenton catalyst for wastewater treatment via bio-electro-Fenton MFC.

Recent progress in treatment of dyes wastewater using microbial-electro-Fenton technology

Globally, textile dyeing and manufacturing are one of the largest industrial units releasing huge amount of wastewater (WW) with refractory compounds such as dyes and pigments. Currently, wastewater treatment has been viewed as an industrial opportunity for rejuvenating fresh water resources and it is highly required in water stressed countries. This comprehensive review highlights an overall concept and in-depth knowledge on integrated, cost-effective cross-disciplinary solutions for domestic and industrial (textile dyes) WW and for harnessing renewable energy. This basic concept entails parallel or sequential modes of treating two chemically different WW i.e., domestic and industrial in the same system. In this case, contemporary advancement in MFC/MEC (METs) based systems towards Microbial-Electro-Fenton Technology (MEFT) revealed a substantial emerging scope and opportunity. Principally the said technology is based upon previously established anaerobic digestion and electro-chemical (photo/UV/Fenton) processes in the disciplines of microbial biotechnology and electro-chemistry. It holds an added advantage to all previously establish technologies in terms of treatment and energy efficiency, minimal toxicity and sludge waste, and environmental sustainable. This review typically described different dyes and their ultimate fate in environment and recently developed hierarchy of MEFS. It revealed detail mechanisms and degradation rate of dyes typically in cathodic Fenton system under batch and continuous modes of different MEF reactors. Moreover, it described cost-effectiveness of the said technology in terms of energy budget (production and consumption), and the limitations related to reactor fabrication cost and design for future upgradation to large scale application.

Microbial fuel cell coupled Fenton oxidation for the cathodic degradation of emerging contaminants from wastewater: Applications and challenges

Urbanization and industrialization have resulted in the escalation of the occurrence of emerging contaminants (EC) in the wastewater and ultimately to the receiving water bodies due to their bio-refractory nature. The presence of ECs in the water bodies adversely affects all three domains of life, viz. bacteria, archaea and eukaryotes, and eventually the ecosystem. Fenton oxidation is one of the most suitable method that is capable of degrading a variety of ECs by employing a strong oxidizing agent in the form of •OH. The coupling of Fenton oxidation with microbial fuel cell (MFC) offers benefits, such as low-cost, minimal requirement of external energy, and in-situ generation of oxidizing agents. The resulting system, termed as bio-electro-Fenton MFC (BEF-MFC), is capable of degrading the ECs in the cathodic chamber, while harvesting bioelectricity and simultaneously removing oxidizable organic matter from wastewater in the anodic chamber. This review discusses the applications of BEF-MFC for the treatment of dyes, pharmaceuticals, pesticides, and real complex wastewaters. Additionally, the effect of operating conditions on the performance of BEF-MFC are elaborated and emphasis is also given on possible future direction of research that can be adopted in BEF-MFC in the purview of up-scaling.

Synergistically enhanced oxygen reduction reaction and oxytetracycline mineralization by FeCoO/GO modified cathode in microbial fuel cell

The widespread application of antibiotics have aroused serious pollution over the world. Microbial fuel cell (MFC) air cathode was able to simultaneously recover electricity and perform advanced oxidation of pollutions through electro-Fenton (EF). This study synthesized an iron‑cobalt oxide and graphene composite (FeCoO/GO), which possessed high electrochemical activity and ORR catalytic performance. The uniform decoration of FeCoO/GO in MFC air cathode distinctly increased the electricity generation (4.5 times higher than carbon felt) and oxytetracycline (OTC) degradation and detoxification (1.33 times higher). FeCoO/GO boosted the H₂O₂ generation from ORR (1.14 times higher than CF) and mineralization efficiency of OTC (2.63 times higher than CF). UPLC-QTOF-MS verified that OTC was degraded and mineralized through decarboxylation, demethylation, and carbon ring cleavage by the oxidation of ·OH. The enhanced degradation of OTC was not only benefited from the increased ORR catalytic performance, but also the excellent H₂O₂ catalytic activity by Fe and Co for ·OH generation. This study demonstrated an effective strategy by decorating FeCoO/GO in MFC air cathode for the synergistically enhanced ORR and OTC degradation and detoxification, giving promising guidance for the deep removal of antibiotic pollutants in the environment.

A review on bio-electro-Fenton systems as environmentally friendly methods for degradation of environmental organic pollutants in wastewater

Bio-electro-Fenton (BEF) systems have been potentially studied as a promising technology to achieve environmental organic pollutants degradation and bioelectricity generation. The BEF systems are interesting and constantly expanding fields of science and technology. These emerging technologies, coupled with anodic microbial metabolisms and electrochemical Fenton's reactions, are considered suitable alternatives. Recently, great attention has been paid to BEFs due to special features such as hydrogen peroxide generation, energy saving, high efficiency and energy production, that these features make BEFs outstanding compared with the existing technologies. Despite the advantages of this technology, there are still problems to consider including low production of current density, chemical requirement for pH adjustment, iron sludge formation due to the addition of iron catalysts and costly materials used. This review has described the general features of BEF system, and introduced some operational parameters affecting the performance of BEF system. In addition, the results of published researches about the degradation of persistent organic pollutants and real wastewaters treatment in BEF system are presented. Some challenges and possible future prospects such as suitable methods for improving current generation, selection of electrode materials, and methods for reducing iron residues and application over a wide pH range are also given. Thus, the present review mainly revealed that BEF system is an environmental friendly technology for integrated wastewater treatment and clean energy production.

A novel bio-electro-Fenton process for eliminating sodium dodecyl sulphate from wastewater using dual chamber microbial fuel cell

The frequent occurrence of surfactants in urban wastewaters represents a multifaceted environmental concern. In this investigation, bio-electro-Fenton-microbial fuel cell (BEF-MFC) was developed for the degradation of sodium dodecyl sulphate (SDS) from wastewater. The synthesised cathode catalyst (powdered activated carbon and iron oxide) facilitated the Fenton reaction in the cathodic chamber of the MFC, concurrently generating a maximum power density of 105.67 mW m-2. The overall performance of the BEF-MFC for SDS removal and power generation excelled the control MFC (C-MFC) having carbon black coated cathode under similar operating conditions. Although, the rate of SDS degradation was favourable in acidic pH, under neutral pH, 70.8 ± 6.4% of SDS degradation was achieved in 120 min in BEF-MFC. A comparison of environmental impacts of BEF-MFC with up-flow MFC and electrochemical oxidation using life cycle assessment tool suggests that BEF-MFC can be one of the promising technologies for the tertiary treatment of wastewater.

A novel bio-electro-Fenton system with dual application for the catalytic degradation of tetracycline antibiotic in wastewater and bioelectricity generation

In this new insight, the potential application of the eco-friendly Bio-Electro-Fenton (BEF) system was surveyed with the aim of simultaneous degradation of tetracycline and in situ generation of renewable bioenergy without the need for an external electricity source. To shed light on this issue, catalytic degradation of tetracycline was directly accrued via in situ generated hydroxyl free radicals from Fenton's reaction in the cathode chamber. Simultaneously, the in situ electricity generation as renewable bioenergy was carried out through microbial activities. The effects of operating parameters, such as electrical circuit conditions (in the absence and presence of external resistor load), substrate concentration (1000, 2000, 5000, and 10 000 mg L⁻¹), catholyte pH (3, 5, and 7), and FeSO₄ concentration (2, 5, and 10 mg L⁻¹) were investigated in detail. The obtained results indicated that the tetracycline degradation was up to 99.04 ± 0.91% after 24 h under the optimal conditions (short-circuit, pH 3, FeSO₄ concentration of 5 mg L⁻¹, and substrate concentration of 2000 mg L⁻¹). Also, the maximum removal efficiency of anodic COD (85.71 ± 1.81%) was achieved by increasing the substrate concentration up to 2000 mg L⁻¹. However, the removal efficiencies decreased to 78.29 ± 2.68% with increasing substrate concentration up to 10 000 mg L⁻¹. Meanwhile, the obtained maximum voltage, current density, and power density were 322 mV, 1195 mA m⁻², and 141.60 mW m⁻², respectively, at the substrate concentration of 10 000 mg L⁻¹. Present results suggested that the BEF system could be employed as an energy-saving and promising technology for antibiotic-containing wastewater treatment and simultaneous sustainable bioelectricity generation.

In this new insight, the potential application of the Bio-Electro-Fenton system was surveyed with the aim of simultaneous degradation of tetracycline and in situ generation of renewable bioenergy without the need for an external electricity source.

A novel core-shell Fe@Co nanoparticles uniformly modified graphite felt cathode (Fe@Co/GF) for efficient bio-electro-Fenton degradation of phenolic compounds

In this study, a core-shell Fe@Co nanoparticles uniformly modified graphite felt (Fe@Co/GF) was fabricated as the cathode by one-pot self-assembly strategy for the degradation of vanillic acid (VA), syringic acid (SA), and 4-hydroxybenzoic acid (HBA) in the Bio-Electro-Fenton (BEF) system. The Fe@Co/GF cathode showed dual advantages with excellent electrochemical performance and catalytic reactivity not only due to the high electron transfer efficiency but also the synergistic redox cycles between Fe and Co species, both of which significantly enhanced the in situ generation of H₂O₂ and hydroxyl radicals (OH) to 152.40 μmol/L and 138.48 μmol/L, respectively. In this case, the degradation rates of VA, SA, and HBA reached 100, 94.32, and 100%, respectively, within 22 h. Representatively, VA was degraded and ultimately mineralized via demethylation, decarboxylation and ring-opening reactions. This work provided a promising approach for eliminating typical recalcitrant organic pollutants generated by the pre-treatment of lignocellulose resources.

Performance of electro-Fenton process coupling with microbial fuel cell for simultaneous removal of herbicide mesotrione

The aim of this work was to investigate the performance of electro-Fenton process coupling with microbial fuel cell for removal of herbicide mesotrione. After a six months acclimation, the anodic biofilm exhibited stable degradation ability to herbicide mesotrione, and the bioelectricity generated by the anodic biofilm could be utilized to in-situ generate H₂O₂ in cathode. Under the optimized conditions, the mesotrione removal rates reached 0.83 mg L^-1h^-1 for anodic microbial degradation and 1.39 mg L^-1h^-1 for cathodic Fenton oxidation, respectively. The bacteria possessing functions of compounds degradation (e.g. Petrimonas, Desulfovibrio, and Mycobacterium) and electrons transfer (e.g. Petrimonas, Cloacibacillus, and Azospirillum) were selectively enriched in anodic biofilm. Therefore, with the advantages of pollutant removal by simultaneous microbial degradation and Fenton oxidation, the MFC-Fenton offer a promising and sustainable approach for wastewater treatment and refractory contaminants elimination.

An approach to the photocatalytic mechanism in the TiO2-nanomaterials microorganism interface for the control of infectious processes

The approach of this timely review considers the current literature that is focused on the interface nanostructure/cell-wall microorganism to understand the annihilation mechanism. Morphological studies use optical and electronic microscopes to determine the physical damage on the cell-wall and the possible cell lysis that confirms the viability and microorganism death. The key parameters of the tailoring the surface of the photoactive nanostructures such as the metal functionalization with bacteriostatic properties, hydrophilicity, textural porosity, morphology and the formation of heterojunction systems, can achieve the effective eradication of the microorganisms under natural conditions, ranging from practical to applications in environment, agriculture, and so on. However, to our knowledge, a comprehensive review of the microorganism/nanomaterial interface approach has rarely been conducted. The final remarks point the ideal photocatalytic way for the effective prevention/eradication of microorganisms, considering the resistance that the microorganism could develop without the appropriate regulatory aspects for human and ecosystem safety.

Automatic microbial electro-Fenton system driven by transpiration for degradation of acid orange 7

Microbial electro-Fenton system (MEFS) shows potential application for degradation of recalcitrant pollutants. In order to simplify the MEFS and adapt to the practical application situations, such as water, soil or sludge remediation, we developed an automatic MEFS (AMEFS) for degradation of a recalcitrant dye, acid orange 7. The AMEFS contained a microchannel-structured carbon decorated with iron oxides as electro-Fenton cathode. The AMEFS could be either two-electrode configuration that the microchannel-structured carbon connected with an additional bioanode by an external circuit, or single-electrode configuration that the microchannel-structured carbon served as both bioanode and cathode. Thanks to the microchannel structure of the carbon cathode, the AMEFS could be auto-driven by a process similar to the transpiration process of natural plants. The two-electrode AMEFS had higher degradation efficiency of acid orange 7 at lower external resistance, and achieved the highest degradation efficiency of 96% at the short-circuit condition. The single-electrode configuration simplified the setup of the AMEFS and possessed comparable performance with that of two-electrode configuration at short-circuit condition. Moreover, it could degrade high concentration acid orange 7 of up to 50 mg L^-1 and achieve a high degradation efficiency of over 93%. The AMEFS could be applied for soil and sludge remediation by direct insertion of the microchannel structured carbon into contaminated body.

Deciphering the mechanism of carbon sources inhibiting recolorization in the removal of refractory dye: Based on an untargeted LC-MS metabolomics approach

In this study, the biological decolorization of reactive black 5 (RB5) by Klebsiella sp. KL-1 in yeast extract (YE) medium was captured the recolorization after exposure to O₂, which induced a 15.82% reduction in decolorization efficiency. Similar result was also observed in YE + lactose medium, but not in YE + glucose/xylose media (groups YE + Glu/Xyl). Through biodegradation studies, several degradation intermediates without quinoid structure were produced in groups YE + Glu/Xyl and differential degradation pathways were deduced in diverse groups. Metabolomics analysis revealed significant variations in up-/down-regulated metabolites using RB5 and different carbon sources. Moreover, the underlying mechanism of recolorization inhibition was proposed. Elevated reducing power associated with variable metabolites (2-hydroxyhexadecanoic acid, 9(R)-HODE cholesteryl ester, linoleamide, oleamide) rendered additional reductive cleavage of C-N bond on naphthalene ring. This study provided a new orientation to inhibit recolorization and deepened the understanding of the molecular mechanism of carbon sources inhibiting recolorization in the removal of refractory dyes.

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

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

Feasibility and applicability of the scaling-up of bio-electro-Fenton system for textile wastewater treatment

Textile wastewater entering natural water bodies could cause serious environment and health issues. Bio-electro-Fenton (BEF) as an efficient and energy saving wastewater treatment technology has recently attracted widespread attention. So far, there is no research available on the scaling-up of BEF process. In this work, an innovative 20 L up-scaled BEF system was constructed for the treatment of methylene blue (MB) containing wastewater. The system was first tested in batch mode. The results showed that the system performance was majorly related to the operating parameters including initial MB concentration, catholyte pH and concentration, cathodic aeration rate, Fe²⁺ dosage, and applied voltage. At the optimal condition, 20 mg L^-1 of MB was efficiently removed following the apparent first order kinetics. The corresponding rate constants for the decolorization and mineralization were 0.68 and 0.20 h^-1, respectively. Furthermore, MB decolorization efficiency of 99% and mineralization efficiency of 74% were observed when the hydraulic retention time was 28 h in continuous mode. This work demonstrates the scaling-up potential of BEF for recalcitrant wastewater treatment.

Enhanced Bio-Electro-Fenton degradation of phenolic compounds based on a novel Fe-Mn/Graphite felt composite cathode

Phenolic compounds are problematic byproducts generated from lignocellulose pretreatment. In this study, the feasibility degradation of syringic acid (SA), vanillic acid (VA), and 4-hydroxybenzoic acid (HBA) by Bio-Electro-Fenton (BEF) system with a novel Fe-Mn/graphite felt (Fe-Mn/GF) composite cathode were investigated. The nano-scale Fe-Mn multivalent composite catalyst with core shell structure distributed more evenly on GF surface to form a catalyst layer with higher oxygen reduction reaction performance. Accordingly, the maximum power density generated with Fe-Mn/GF cathode was 48.1% and 238.9% higher than Fe/GF and GF respectively, which further enhanced the in situ generation of H₂O₂ due to the superiority of nano-scale core shell structure and synergistic effect of Fe and Mn species. The degradation efficiency of the three phenolic compounds in the BEF system could reached 100% after optimization of influencing parameters. Furthermore, a possible SA degradation pathway by BEF process in the present system was proposed based on the detected intermediates. These results demonstrated an efficient approach for the degradation of phenolic compounds derived from lignocellulose hydrolysates.

Effects of hydraulic retention time on the performance and microbial community of an anaerobic baffled reactor-bioelectricity Fenton coupling reactor for treatment of traditional Chinese medicine wastewater

The aim of the present paper was to investigate the effects of hydraulic retention time (HRT) on the performance and microbial community dynamics of an anaerobic baffled reactor-bioelectricity Fenton (ABR-BEF) coupling reactor for treating traditional Chinese medicine (TCM) wastewater. The results show that the average removal of chemical oxygen demand (COD) and NH₃-N at HRTs of 24 h and 18 h were high (>90% and >70%, respectively), but decreased to about 40% and 30% when operating at 12 h HRT. For the electrical production performance, the maximum power density was 196.86 mW/m³ at a HRT of 18 h. Methanomicrobia was the dominant archaea in the coupling reactor and the relative abundance of Methanothrix and Methanolinea increased with decreasing HRT. For the bacteria, the relative abundance of Planctomycetia significantly decreased with a short HRT; however, Anaerolineaceae was always the dominant bacterial taxa, which could guarantee efficient treatment of TCM wastewater.

Performance of a novel ABR-bioelectricity-Fenton coupling reactor for treating traditional Chinese medicine wastewater containing catechol

In this study, a novel anaerobic baffled reactor-bioelectricity-Fenton (ABR-BEF) coupling reactor, combining an ABR, microbial fuel cell (MFC), and Fenton system, was used to treat traditional Chinese medicine (TCM) wastewater containing catechol. The bio-electrochemical degradation of the catechol reached 99.7% after 8 h at dissolved oxygen (DO) concentration of 4 mg/L in the cathodic chamber. The removal rates of chemical oxygen demand (COD) reached 91.7%, when the ratio rate was 1 and the DO concentration was 4 mg/L. Moreover, the maximum open-circuit voltage and power density of the coupling reactor reached 424.9 mV and 77.1 mW/m³, respectively. According to the PICRUSt analysis, carbohydrate metabolism took up the most abundant function of metabolism and the enrichment of membrane transporters may relieve TCM wastewater toxicity. These results suggest that the ABR-BEF coupling reactor could be applied as an efficient approach to treat TCM wastewater.

A bio-electro-Fenton system with a facile anti-biofouling air cathode for efficient degradation of landfill leachate

Bio-electro-Fenton (BEF) system holds great potential for sustainable degradation of refractory organics. Activated carbon (AC) air cathode was modified by co-pyrolyzing of AC with glucose and doping with nano-zero-valent iron (denoted as nZVI@MAC) in order to promote two-electron oxygen reduction reaction (2e^- ORR) for enhanced oxidizing performance. Single chamber microbial fuel cells (SCMFCs) with nZVI@MAC cathode was examined to degrade landfill leachate. It was revealed that nZVI@MAC cathode SCMFC showed higher degradation efficiency towards landfill leachate. Six landfill leachate treatment cycles indicated that nZVI@MAC cathode SCMFC exhibited higher COD removal efficiencies over AC and nZVI@AC and greatly enhanced columbic efficiency compared to AC and nZVI@AC cathode. Anti-biofouling effect was found on nZVI@MAC cathode because of the high Fenton oxidation effects at the vicinity of the cathode. Electrochemical characterizations indicated that MAC cathode had superior 2e^- ORR capability than AC and nZVI@AC cathode, which was further evidenced by higher H₂O₂ production from nZVI@MAC cathode in SCMFC. Graphitic structure of MAC was evidenced by High Resolution Transmission Electron Microscopy, and glucose pyrolysis also resulted in nano carbon spheres on the activated carbon skeletons. Raman spectra indicated more defects were generated on MAC during its co-pyrolyzation with glucose.

A microbial electro-fenton cell for removing carbamazepine in wastewater with electricity output

High electrical energy is required for the electro-Fenton process to remove pharmaceuticals and personal care products (PPCPs) in wastewater. The aim of this study was to develop a novel and more cost-effective process, specifically a microbial electro-Fenton cell (MeFC), for treating PPCPs in wastewater. Acetylene black was selected as the catalyst for H₂O₂ electrogeneration and Fe-Mn binary oxide for hydroxyl radical production. In addition to lowering energy needs, the MeFC produced a maximum power density of 112 ± 11 mW/m² with 1 g/L acetate as a representative substrate and 10 mg/L carbamazepine (CBZ) as a typical PPCP. Comparing with electro-Fenton process, the CBZ removal in the MeFC was 38% higher within 24 h operation (90% vs. 62%). Furthermore, the CBZ removal rate in the MeFC was 10-100 times faster than that in other biological treatment processes. Such enhanced degradation of CBZ in the MeFC was attributed to the synergistic reactions between radical oxidation of CBZ and biodegradation of degradative intermediates. The MeFC provides a promising method to remove PPCPs from wastewater coupling with efficient removal of other biodegradable organics.

Hydrogen peroxide generation in microbial fuel cells using graphene-based air-cathodes

Utilization of two-electron oxygen reduction reaction (ORR) in bioelectrochemical systems (BES) is a novel way to generate H₂O₂ from wastewater, and cathode catalyst is a key factor affecting ORR performance. Here, the catalytic performance of plain graphene, oxidized graphene and graphene oxide (GO) in microbial fuel cells (MFCs) and the influence of oxygen-containing functional groups are reported. Oxidized graphene air-cathode had 78% and 131% higher H₂O₂ productions than plain graphene cathode respectively in an abiotic reactor and an MFC. GO showed nearly no H₂O₂ production in the tests. XPS revealed that oxygen atomic fraction of oxidized graphene reached 5.7%, mostly in the form of COC. These results show that oxidized graphene had good catalytic performance for H₂O₂ production, and oxygen-containing functional groups, especially COC could significantly enhance its performance, but overoxidation worked adversely. Meanwhile, using oxidized graphene air-cathode could realize simultaneous wastewater treatment, power output and H₂O₂ generation in MFCs.

Chlorinated phenol treatment and in situ hydrogen peroxide production in a sulfate-reducing bacteria enriched bioelectrochemical system

Wastewaters are increasingly being considered as renewable resources for the sustainable production of electricity, fuels, and chemicals. In recent years, bioelectrochemical treatment has come to light as a prospective technology for the production of energy from wastewaters. In this study, a bioelectrochemical system (BES) enriched with sulfate-reducing bacteria (SRB) in the anodic chamber was proposed and evaluated for the biodegradation of recalcitrant chlorinated phenol, electricity generation (in the microbial fuel cell (MFC)), and production of hydrogen peroxide (H₂O₂) (in the microbial electrolysis cell (MEC)), which is a very strong oxidizing agent and often used for the degradation of complex organics. Maximum power generation of 253.5 mW/m², corresponding to a current density of 712.0 mA/m², was achieved in the presence of a chlorinated phenol pollutant (4-chlorophenol (4-CP) at 100 mg/L (0.78 mM)) and lactate (COD of 500 mg/L). In the anodic chamber, biodegradation of 4-CP was not limited to dechlorination, and further degradation of one of its metabolic products (phenol) was observed. In MEC operation mode, external voltage (0.2, 0.4, or 0.6 V) was added via a power supply, with 0.4 V producing the highest concentration of H₂O₂ (13.3 g/L-m² or 974 μM) in the cathodic chamber after 6 h of operation. Consequently, SRB-based bioelectrochemical technology can be applied for chlorinated pollutant biodegradation in the anodic chamber and either net current or H₂O₂ production in the cathodic chamber by applying an optimum external voltage.