Using single-chamber microbial fuel cells as renewable power sources of electro-Fenton reactors for organic pollutant treatment

Electrocatalysis coupled heterogeneous electro-Fenton like treatment of coal gasification wastewater using tourmaline as catalyst: process parameters and response surface

Coal gasification technology is essential for realizing clean and efficient conversion of coal, as well as for reducing carbon emissions. However, coal gasification technology is accompanied by a large amount of coal gasification wastewater that is biodegradable. In this work, tourmaline was applied as a catalyst in electro-Fenton like process for treating coal gasification wastewater. The optimal applied parameters of coal gasification wastewater were investigated as follows: current density of 90 mA cm-2, tourmaline dosage of 8 g L-1, electrode gap of 1 cm, and temperature at 25 °C; the COD removal ratio reached 91.24% after 240-min treatment. In addition, the current density and tourmaline dosage were further optimized by response surface method. The result was about current density with 82.4 mA cm-2 and catalyst with 7.57 g L-1; the predicted COD removal efficiency was 86.91%. Under the optimal parameters the actual COD removal efficiency was 88.25% a little high than the predicted value. To explore the reusability of tourmaline as Fenton reaction catalyst, five cycles of experiments were carried out. The result demonstrated that tourmaline could be used as catalyst for treating coal gasification wastewater by electro-Fenton like process.

Methane emission reduction oriented extracellular electron transfer and bioremediation of sediment microbial fuel cell: A review

Sediment is the internal and external source of water environment pollution, so sediment remediation is the premise of water body purification. Sediment microbial fuel cell (SMFC) can remove the organic pollutants in sediment by electroactive microorganisms, compete with methanogens for electrons, and realize resource recycling, methane emission inhibiting and energy recovering. Due to these characteristics, SMFC have attracted wide attention for sediment remediation. In this paper, we comprehensively summarized the recent advances of SMFC in the following areas: (1) The advantages and disadvantages of current applied sediment remediation technologies; (2) The basic principles and influencing factors of SMFC; (3) The application of SMFC for pollutant removal, phosphorus transformation and remote monitoring and power supply; (4) Enhancement strategies for SMFC in sediments remediation such as SMFC coupled with constructed wetland, aquatic plant and iron-based reaction. Finally, we have summarized the drawback of SMFC and discuss the future development directions of applying SMFC for sediment bioremediation.

Disclosing the mutual influence of photocatalytic fuel cell and photoelectro-Fenton process in the fabrication of a sustainable hybrid system for efficient Amaranth dye removal and simultaneous electricity production

Photocatalytic fuel cell (PFC) was employed to provide renewable power sources to photoelectro-Fenton (PEF) process to fabricate a double-chambered hybrid system for the treatment of azo dye, Amaranth. The PFC-PEF hybrid system was interconnected by a circuit attached to the electrodes in PFC and PEF. Circuit connection is the principal channel for the electron transfer and mobility between PFC and PEF. Thus, different circuit connections were evaluated in the hybrid system for their influences on the Amaranth dye degradation. The PFC-PEF system under the complete circuit connection condition attained the highest decolourization efficiency of Amaranth (PFC: 98.85%; PEF: 95.69%), which indicated that the complete circuit connection was crucial for in-situ formation of reactive species in dye degradation. Besides, the pivotal role of ultraviolet (UV) light irradiation in the PFC-PEF system for both dye degradation and electricity generation was revealed through various UV light-illuminating conditions applied for PFC and PEF. A remarkable influence of UV light irradiation on the production of hydrogen peroxide and generation and regeneration of Fe²⁺ in PEF was demonstrated. This study provided a comprehensive mechanistic insight into the dye degradation and electricity generation by the PFC-PEF system.

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.

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.

Improving Wastewater Treatment by Triboelectric-Photo/Electric Coupling Effect

The ability to meet higher effluent quality requirements and the reduction of energy consumption are the biggest challenges in wastewater treatment worldwide. A large proportion of the energy generated during wastewater treatment processes is neglected and lost in traditional wastewater treatment plants. As a type of energy harvesting system, triboelectric nanogenerators (TENGs) can extensively harvest the microscale energies generated from wastewater treatment procedures and auxiliary devices. This harvested energy can be utilized to improve the removal efficiency of pollutants through photo/electric catalysis, which has considerable potential application value in wastewater treatment plants. This paper gives an overall review of the generated potential energies (e.g., water wave energy, wind energy, and acoustic energy) that can be harvested at various stages of the wastewater treatment process and introduces the application of TENG devices for the collection of these neglected energies during wastewater treatment. Furthermore, the mechanisms and catalytic performances of TENGs coupled with photo/electric catalysis (e.g., electrocatalysis, photoelectric catalysis) are discussed to realize higher pollutant removal efficiencies and lower energy consumption. Then, a thorough, detailed investigation of TENG devices, electrode materials, and their coupled applications is summarized. Finally, the intimate coupling of self-powered photoelectric catalysis and biodegradation is proposed to further improve removal efficiencies in wastewater treatment. This concept is conducive to improving knowledge about the underlying mechanisms and extending applications of TENGs in wastewater treatment to better solve the problems of energy demand in the future.

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 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.

Proton exchange membrane and bio-Fenton micro fuel cells for energy harvesting, gas leakage detection, and dye degradation

The present work focuses on the non-conventional design and operation of micro fuel cells. Two different kinds of fuel cells, Proton Exchange Membrane (PEM) and Biological Fenton (BF) based fuel cells, are fabricated to harvest energy. For the PEM fuel cell, H2 and O2 are generated by Mg/HCl reaction and Fenton's reaction respectively, and are subsequently fed into two terminals of the PEM fuel cell. For the BF fuel cell, the reaction product of hemoglobin (Hb) with hydrogen peroxide (H2O2) is used as a source of chemical fuel to generate electrical energy within the fuel cell. An array of PEM microscale fuel cells is fabricated to scale up the reaction which can be used for MEMS/NEMS applications. Furthermore, the application of this adhesive and flexible PEM fuel cell as a hydrogen leakage sensor is demonstrated. In the BF fuel cell, an electronic imbalance across a carbon tape is generated owing to the formation of reactive hydroxyl radicals and concurrent electrons in the system. The generation of a highly oxidizing hydroxyl radical is also utilized to degrade Methylene Blue (MB) dye along with energy harvesting. This multi-purpose fuel cell can be synergistically used in industrial applications of waste treatment as well as energy production.

Fenton/Fenton-like processes with in-situ production of hydrogen peroxide/hydroxyl radical for degradation of emerging contaminants: Advances and prospects

Fenton processes based on the reaction between Fe²⁺ and H₂O₂ to produce hydroxyl radicals, have been widely studied and applied for the degradation of toxic organic contaminants in wastewater due to its high efficiency, mild condition and simple operation. However, H₂O₂ is usually added by bulk feeding, which suffers from the potential risks during the storage and transportation of H₂O₂ as well as its low utilization efficiency. Therefore, Fenton/Fenton-like processes with in-situ production of H₂O₂ have received increasing attention, in which H₂O₂ was in-situ produced through O₂ activation, then decomposed into hydroxyl radicals by Fenton catalysts. In this review, the in situ production of H₂O₂ for Fenton oxidation was introduced, the strategies for activation of O₂ to generate H₂O₂ were summarized, including chemical reduction, electro-catalysis and photo-catalysis, the influencing factors and the mechanisms of the in situ production and utilization of H₂O₂ in various Fenton/Fenton-like processes were analyzed and discussed, and the applications of these processes for the degradation of toxic organic contaminants were summarized. This review will deepen the understanding of the tacit cooperation between the in situ production and utilization of H₂O₂ in Fenton process, and provide the further insight into this promising process for degradation of emerging contaminants in industrial wastewater.

A comprehensive review on emerging constructed wetland coupled microbial fuel cell technology: Potential applications and challenges

Constructed wetlands (CWs) integrated with bioelectrochemical systems (BESs) are being intensively researched with the names like constructed wetland-microbial fuel cell (CW-MFC), electro-wetlands, electroactive wetlands, and microbial electrochemical technologies-based constructed wetland since the last decade. The implantation of BES in CW facilitates the tuning of redox activities and electron flow balance in aerobic and anaerobic zones in the CW bed matrix, thereby alleviating the limitation associated with electron acceptor availability and increasing its operational controllability. The benefits of CW-MFC include high treatment efficiency, electricity generation, and recalcitrant pollutant abatement. This article presents CW-MFC technology's journey since its emergence to date, encompassing the research done so far, including the basic principle and functioning, bio-electrocatalysts as its machinery, influential factors for microbial interactions, and operational parameters controlling different processes. A few key challenges and potential applications are also discussed for the CW-MFC systems.

Microbial electrochemical systems for hydrogen peroxide synthesis: Critical review of process optimization, prospective environmental applications, and challenges

Hydrogen peroxide (H₂O₂) is an industrial chemical that has been widely adopted for various industrial applications, including water and wastewater treatment. Currently, the majority of H₂O₂ is being produced through the anthraquinone oxidation process, which is disadvantageous due to the requirement of toxic raw materials and high energy input. Recently, microbial electrochemical cells (MXCs), such as microbial fuel cells and microbial electrolysis cells, have demonstrated great potential for effective H₂O₂ production via cathodic oxygen-reduction reaction (ORR). Previous studies have specified key operational parameters for scaling-up of H₂O₂-producing MXCs, where improvements in production rate, conversion efficiency, product concentration and stability are attainable. Moreover, various systems have demonstrated their value proposition in the contaminant removal aspects through direct removal of various environmental pollutants, water disinfection, and many more. This review is intended to highlight promising ways of H₂O₂ production with MXCs and on-site environmental applications of bioelectrochemically-produced H₂O₂.

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.

Hybrid microbial electrolytic/UV system for highly efficient organic pollutants removal

This study for the first time proposed an efficient microbial electrolyte/UV system for Methyl Orange decomposition. With an external applied voltage of 0.2 V and cathode aeration of 20 mL/min, H₂O₂ could be in-situ generated from two-electron reduction of oxygen in cathode, reaching to 8.1 mg/L in 2 hr and continued to increase. The pollutant removal efficiency of approximate 94.7% was achieved at initial neutral pH, with the activation of •OH in the presence of UV illumination. Although the nature of its guiding principles remain on the vista of practical exploration, this proof-of-concept study provides an alternative operation pattern of solar-microbial hybrid technology for future wastewater treatment from a basic but multidisciplinary view.

Persulfate activation by Fe(III) with bioelectricity at acidic and near-neutral pH regimes: Homogeneous versus heterogeneous mechanism

The combination of persulfate (PS) activation by iron ions with electrochemical process (electro/Fe³⁺/PS) is a promising advanced oxidation process. However, almost all these systems were performed in an unbuffered solution and actually under acidic pH condition, with the electricity being frequently supplied by external power. Considering the high buffering capacity of wastewater and energy saving, peroxydisulfate (PDS) activation by Fe(III) species with bioelectricity provided by microbial fuel cell (MFC) for bisphenol A (BPA) oxidation was investigated at fixed near-neutral pH as well as acidic pH. The results indicate that 90.8% of BPA could be removed at pH 2.5. Though the iron existed in the form of precipitate, BPA could still be efficiently removed at pH 6.0. The precipitate formed in the system at pH 6.0 was identified as the amorphous iron oxyhydroxides. Sulfate radicals in the bulk solution and that adsorbed on the precipitate were the dominant reactive species responsible for the oxidation of BPA in the homogeneous and heterogeneous MFC/Fe(III)/PDS processes, respectively. The mechanisms of BPA degradation at both pH values were proposed via EPR and quenching tests as well as XPS analysis. The effects of operating parameters, the mineralization, the mineralization current efficiency and energy consumption were also explored.

An overview on the removal of synthetic dyes from water by electrochemical advanced oxidation processes

Wastewater containing dyes are one of the major threats to our environment. Conventional methods are insufficient for the removal of these persistent organic pollutants. Recently much attention has been received for the oxidative removal of various organic pollutants by electrochemically generated hydroxyl radical. This review article aims to provide the recent trends in the field of various Electrochemical Advanced Oxidation Processes (EAOPs) used for removing dyes from water medium. The characteristics, fundamentals and recent advances in each processes namely anodic oxidation, electro-Fenton, peroxicoagulation, fered Fenton, anodic Fenton, photoelectro-Fenton, sonoelectro-Fenton, bioelectro-Fenton etc. have been examined in detail. These processes have great potential to destroy persistent organic pollutants in aqueous medium and most of the studies reported complete removal of dyes from water. The great capacity of these processes indicates that EAOPs constitute a promising technology for the treatment of the dye contaminated effluents.

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.

Oxidation of organic contaminant in a self-driven electro/natural maghemite/peroxydisulfate system: Efficiency and mechanism

Electro-assisted iron-mediated persulfate (PS) activation process has been successfully employed to oxidize organic contaminant. However, a majority of iron-based catalysts used for PS activation was synthesized through complicated or demanding procedures and may have potential risks on environment during the preparation process. Herein, natural maghemite (NM) which is abundant on the earth was employed to activate peroxydisulfate (PDS) in an electrolytic cell. The voltage was provided by microbial fuel cell (MFC) instead of external power as reported in the previous studies, so as to establish a self-driven electro/natural maghemite/PDS system (MFC/NM/PDS) for the oxidation of acid orange 7 (AO7). The results showed that above 90% removal efficiency of AO7 was achieved in a wide range of pH (3.0-9.0) after 100min reaction. Singlet oxygen was identified for the first time during PDS activation and surface bound sulfate radicals served as the dominant active species responsible for AO7 oxidation. The underlying mechanism of AO7 elimination in the MFC/NM/PDS system was elucidated through quenching tests, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) techniques. The variation of TOC and cytotoxicity to Escherichia coli was explored. The intermediate products formed were identified using LC-TOF-MS technique and a possible pathway of AO7 degradation was proposed.

Hydronium jarosite activation of peroxymonosulfate for the oxidation of organic contaminant in an electrochemical reactor driven by microbial fuel cell

Electro-assisted Fenton-like (EAFL) system based on sulfate radicals (SO₄^-) has been extensively explored for the degradation of recalcitrant organic contaminant. Nevertheless, external power supply should be provided uninterruptedly in the EAFL process and thus the high energy consumption is ineluctable. Recently, microbial fuel cell (MFC), a bio-electrochemical system where exoelectricigens are used to catalyze fuels into electricity energy has gained popularity mainly due to its renewability. Herein, a novel heterogeneous EAFL system, hydronium jarosite (HJ) activation of peroxymonosulfate (PMS) in an electrochemical reactor driven by an uncoated single-chamber MFC (MFC/HJ/PMS), was employed to decolorize acid orange 7 (AO7). The results suggest that the MFC/HJ/PMS system can remove AO7 efficiently in a wide pH range (3-9). The concentration of total iron leached could meet European Union discharge standards and hydronium jarosite could be used at least three circles. The results of electron paramagnetic resonance analysis and radical scavenging experiments indicate SO₄^- is the major active species responsible for the AO7 elimination. The work provides an efficient, energy-saving and cost-effective approach to treat organic wastewater and develops the conceivable utilization of hydronium jarosite, precipitates produced in hydrometallurgical process.

Advanced treatment of petrochemical secondary effluent by Fenton: performance and organics removal characteristics

The Fenton process was used to treat petrochemical secondary effluent. The effects of initial pH, H₂O₂, and FeSO₄·7H₂O dosages on chemical oxygen demand (COD) removal, the dissolved organic matter (DOM) removal and the transformation and migration of typical organic matters during the treatment process were investigated. The results showed that the optimum conditions were initial pH of 3.0, H₂O₂ (30%) dosage of 0.4 mL/L, and FeSO₄·7H₂O dosage of 1.0 g/L. The highest COD removal efficiency of 61.9% could be achieved for this condition when the average influent COD was 78.5 mg/L. Most of the DOM in the petrochemical wastewater could be removed effectively by Fenton through direct oxidation and coagulation. For example, for trans-1,2-dichlorocyclopentane, results showed that 56.3% of it could be removed by Fenton oxidation, while 13.3% of it could be absorbed by the in situ generated Fenton chemical sludge. The Fenton process is simple and it is suitable for the advanced treatment of petrochemical secondary effluent.

Electricity generation through degradation of organic matters in medicinal herbs wastewater using bio-electro-Fenton system

In the present study, the potential application of the bio-electro-Fenton (BEF) process for the treatment of medicinal herbs wastewater in a mediator-less microbial fuel cell (MFC) system is investigated. This process is operated in a dual-chamber MFC with anaerobic seed sludge as biocatalyst in an anode chamber under conditions of neutral pH, an aerobic cathode chamber equipped with a Fe@Fe2O3/graphite composite cathode and a Nafion membrane as a separator. The performance of the MFC is determined in three different mixed liquor suspended solids (MLSS) loadings, Nafions (112, 115) and a salt bridge in an air-cathode BEF process, in terms of power generation, chemical oxygen demand (COD) removal efficiency, columbic and energy efficiencies. Under optimal conditions, the batch experiment results show that the cathode chamber of the BEF reactor, equipped with Nafion 112 and inoculated with seed sludge at 3000 mg L(-1) MLSS concentration, produces the maximum power density of 49.76 mW m(-2), 0.56 mg L(-1) and 29 mol L(-1) of H2O2 and Fe(2+), respectively. Under these conditions, the MFC achieves COD removal 78.05% in the anaerobic anode chamber and 84.02% as a result of aerobic processes from the air-cathode BEF chamber, whilst the maximum voltage εcb and εE values are 600 mV, 4.09% and 1.37%, respectively.

Electrochemical decolorization of methyl orange powered by bioelectricity from single-chamber microbial fuel cells

Methyl orange (MO), a typical azo dye, is a well-known recalcitrant pollutant in dye wastewater. An aeration electrochemical system with single-chamber microbial fuel cell (MFC) as renewable power sources is proposed for MO decolorization. The enhanced color removal efficiency up to 90.4% within 360 min is observed with voltage across the aeration electrolytic reactor fixed at 700 mV. The results from gas chromatography-mass spectrometry (GC-MS) analysis indicate the destruction of MO, with generation of low molecular weight compounds such as benzene derivatives. Comparison experiments imply the indirect electrochemical oxidation of MO by generated H2O2 is mainly responsible for MO decolorization in present study. This work offers a cost-effective electrochemical method for enhancing electrochemical degradation of dyes with bioelectricity generated from MFCs.

A comparison of central composite design and Taguchi method for optimizing Fenton process

In the present study, a comparison of central composite design (CCD) and Taguchi method was established for Fenton oxidation. [Dye]_ini, Dye : Fe⁺², H₂O₂ : Fe⁺², and pH were identified control variables while COD and decolorization efficiency were selected responses. L₉ orthogonal array and face-centered CCD were used for the experimental design. Maximum 99% decolorization and 80% COD removal efficiency were obtained under optimum conditions. R squared values of 0.97 and 0.95 for CCD and Taguchi method, respectively, indicate that both models are statistically significant and are in well agreement with each other. Furthermore, Prob > F less than 0.0500 and ANOVA results indicate the good fitting of selected model with experimental results. Nevertheless, possibility of ranking of input variables in terms of percent contribution to the response value has made Taguchi method a suitable approach for scrutinizing the operating parameters. For present case, pH with percent contribution of 87.62% and 66.2% was ranked as the most contributing and significant factor. This finding of Taguchi method was also verified by 3D contour plots of CCD. Therefore, from this comparative study, it is concluded that Taguchi method with 9 experimental runs and simple interaction plots is a suitable alternative to CCD for several chemical engineering applications.

Application of electro-Fenton technology to remediation of polluted effluents by self-sustaining process

The applicability of electro-Fenton technology to remediation of wastewater contaminated by several organic pollutants such as dyes and polycyclic aromatic hydrocarbons has been evaluated using iron-enriched zeolite as heterogeneous catalyst. The electro-Fenton technology is an advanced oxidation process that is efficient for the degradation of organic pollutants, but it suffers from the high operating costs due to the need for power investment. For this reason, in this study microbial fuel cells (MFCs) were designed in order to supply electricity to electro-Fenton processes and to achieve high treatment efficiency at low cost. Initially, the effect of key parameters on the MFC power generation was evaluated. Afterwards, the degradation of Reactive Black 5 dye and phenanthrene was evaluated in an electro-Fenton reactor, containing iron-enriched zeolite as catalyst, using the electricity supplied by the MFC. Near complete dye decolourization and 78% of phenanthrene degradation were reached after 90 min and 30 h, respectively. Furthermore, preliminary reusability tests of the developed catalyst showed high degradation levels for successive cycles. The results permit concluding that the integrated system is adequate to achieve high treatment efficiency with low electrical consumption.

Electrocatalytic degradation of 2,4-dichlorophenol using a Pd/graphene gas-diffusion electrode

The Pd/graphene gas-diffusion cathode exhibits high electrocatalytic dechlorination activity.

Electrosorption driven by microbial fuel cells to remove phenol without external power supply

This work studied the operating parameters (pH, electrolyte concentration, initial phenol concentration, MFCs connection numbers and mode), adsorption isotherms and kinetics of a novel electrosorption driven by microbial fuel cells (MFC-Sorption) to remove phenol without external electric grid energy supply. It proved that high electrolyte concentration and low solution pH promoted the performance of phenol removal. 3 MFCs connections in series achieved a adsorption capacity of 1.76 mmol/g, which was much higher than that in parallel connection (1.46 mmol/g). Well fitted with Langmuir isotherm, the maximum adsorption capacity by MFC-Sorption and electrosorption was observed 48% and 65% higher than that by conventional adsorption. The phenol removal by MFC-Sorption was supposed to be more suitable for a pseudo-second-order kinetics, and with the increase of initial phenol concentration from 20 mg/L to 300 mg/L, the initial adsorption rate increased 26.99-fold. It concluded that the MFC-Sorption system could cost-effectively remove pollutant of phenol.