Efficient gas phase VOC removal and electricity generation in an integrated bio-photo-electro-catalytic reactor with bio-anode and TiO2 photo-electro-catalytic air cathode

A new attempt to remove toluene using nickel-iron bimetallic particle electrode reactor

A new attempt of removing toluene waste gas using a three-dimensional electrode reaction device with nickel-iron bimetallic particle electrode is presented in this paper. The particle electrode was prepared by a simple liquid phase reduction method. Through bimetal modification, the particle electrode mass transfer rate is increased to 1.29 times, and the degradation efficiency of the reactor is increased by nearly 40%, which makes it possible to remove toluene waste gas by other electrochemical methods in addition to plasma method. The removal efficiency of the particle electrode can be stabilized at more than 80% after 5 cycles (50 h). At the same time, the relationship between independent working parameters and dependent variables is analyzed using the central composite design, and the operating parameters are optimized. Based on this study, the removal mechanism and possible degradation pathway of toluene were investigated. This study provides a supplement to the possibility and theoretical basis of new technology application for electrocatalytic oxidation removal of VOCs.

Research status of volatile organic compound (VOC) removal technology and prospect of new strategies: a review

As an important component of air pollution, the efficient removal of volatile organic compounds (VOCs) is one of the most important challenges in the world. VOCs are harmful to the environment and human health. This review systematically introduced the main VOC control technologies and research hotspots in recent years, and expanded the description of electrocatalytic oxidation technology and bimetallic catalytic removal technology. Based on a three-dimensional electrode reactor, the theoretical design of a VOC removal control technology using bimetallic three-dimensional particle electrode electrocatalytic oxidation was proposed for the first time. The future research focus of this method was analyzed, and the importance of in-depth exploration of the catalytic performance of particle electrodes and the system reaction mechanism was emphasized. This review provides a new idea for using clean and efficient methods to remove VOCs.

Effect of CuO/ZnO/FTO electrode properties on the performance of a photo-microbial fuel cell sensor for the detection of heavy metals

The development of sustainable, low-cost and responsive technology for heavy metals detection in wastewater is crucial. In this study, by combining CuO/ZnO photocathode with microbial anode, a novel photo-microbial fuel cell (PMFC) sensor was developed. The self-powered PMFC was performed under light and dark condition for heavy metals detection. Compared with MFC sensor, PMFC sensor showed a wider detection range (0.1-4 mg L^-1 of Cd²⁺ and 10-80 mg L^-1 of Cu²⁺). The improved performance in sensing limit and sensitivity was mainly attributed to the intimate P-N heterojunctions formed in CuO/ZnO, which accelerated the electron transport between the photocathode and the microbial anode. Besides, the toxicity of five heavy metals tested in PMFC was shown as Cd²⁺>Cr⁶⁺>Zn²⁺>Hg²⁺>Cu²⁺. This study has taken advantage of the characteristics of PMFC and facilitated its application in heavy metals detection, which provides a new approach for the development of biosensors.

Performance of a packed-bed anode bio-electrochemical reactor for power generation and for removal of gaseous acetone

The packed anode bioelectrochemical system (Pa-BES) developed in this study is a type of BES that introduces waste gas into a cathode and then into an anode, thereby providing the cathode with sufficient oxygen and reducing the amount of oxygen to the anode to promote the output of electricity. When the empty-bed residence time was 45 s and the liquid flowrate was 35 mL/s, the system achieved optimal performance. Under these conditions, removal efficiency, mineralization efficiency, voltage output, and power density were 93.86%, 93.37%, 296.3 mV, and 321.12 mW/m³, respectively. The acetone in the waste gas was almost completely converted into carbon dioxide, indicating that Pa-BES can effectively remove acetone and has the potential to be used in practical situations. A cyclic voltammetry analysis revealed that the packings exhibited clear redox peaks, indicating that the Pa-BES has outstanding biodegradation and power generation abilities. Through microbial community dynamics, numerous organics degraders, electrochemically active bacteria, nitrifying and denitrifying bacteria were found, and the spatial distribution of these microbes were identified. Among them, Xanthobacter, Bryobacter, Mycobacteriums and Terrimonawas were able to decompose acetone or other organic substances, with Xanthobacter dominating. Bacterium_OLB10 and Ferruginibacter are the electrochemically active bacteria in Pa-BES, while Ferruginibacter is the most abundant in the main anode, which is responsible for electron collection and transfer.

Photocatalytic Microbial Fuel Cells and Performance Applications: A Review

In recent years, photocatalytic microbial fuel cells have gradually become a hot research topic in pollutant treatment, using either in situ or indirectly the oxidation of organic pollutants by catalytic materials under light and the biodegradation and mineralization of various components in wastewater by microorganisms, or through the generation of electricity by the microbial fuel cell (MFC) system to promote the photogeneration and separation of electrons and holes by the catalytic materials of the photocatalytic cell (PC) system. This study aims to provide new ideas for the development of environmentally friendly wastewater treatment technologies by investigating the use of photocatalytic cells for the efficient degradation and resource utilization of target pollutants. This study aims to raise awareness of the use of photocatalytic microbial fuel cells for pollutant degradation by providing an overview of the practical status of photocatalytic microbial fuel cells. This is achieved by reviewing the key cathode development, production capacity, and progress in the degradation of pollutants in photocatalytic microbial fuel cells. The issues facing future developments are also discussed in terms of how photocatalytic microbial fuel cells work and how they degrade pollutants. This study shows that photocatalytic microbial fuel cells are beneficial for achieving renewable energy (bioenergy, photovoltaic, etc.) capacity and dealing with environmental pollution and that this is a novel technology that deserves to be promoted to achieve the current dual carbon targets.

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.

Ameliorating Cu2+ reduction in microbial fuel cell with Z-scheme BiFeO3 decorated on flower-like ZnO composite photocathode

BiFeO₃ nanoparticle decorated on flower-like ZnO (BiFeO₃/ZnO) was fabricated through a facile hydrothermal-reflux combined method. This material was utilized as a composite photocathode for the first time in microbial fuel cell (MFC) to reduce the copper ion (Cu²⁺) and power generation concomitantly. The resultant BiFeO₃/ZnO-based MFC displayed distinct photoelectrocatalytic activities when different weight percentages (wt%) BiFeO₃ were used. The 3 wt% BiFeO₃/ZnO MFC achieved the maximum power density of 1.301 W m^-2 in the catholyte contained 200 mg L^-1 of Cu²⁺ and the power density was greatly higher than those pure ZnO and pure BiFeO₃ photocathodes. Meanwhile, the MFC exhibited 90.7% removal of Cu²⁺ within 6 h under sunlight exposure at catholyte pH 4. The addition of BiFeO₃ nanoparticles not only manifested outstanding capability in harvesting visible light, but also facilitated the formation of Z-scheme BiFeO₃/ZnO heterojunction structure to induce the charge carrier transfer along with enhanced redox abilities for the cathodic reduction. The pronounced electrical output and Cu²⁺ reduction efficiencies can be realized through the synergistic cooperation between the bioanode and BiFeO₃/ZnO photocathode in the MFC. Furthermore, the developed BiFeO₃/ZnO composite presented a good stability and reusability of photoelectrocatalytic activity up to five cyclic runs.

A vertically configured photocatalytic-microbial fuel cell for electricity generation and gaseous toluene degradation

A vertically configured photocatalytic-microbial fuel cell (photo-MFC) is developed by combining a nanodiamond-decorated ZnO (ZnO/ND) photocathode with a bioanode. The system can effectively couple the light energy with bioenergy to enhance the degradation of volatile organic compounds (VOCs) and boost electricity output. Results show that the composite system exhibits increased performance for toluene removal (60.65%), higher than those of individual parts (ZnO/ND-photocatalysis: 37.16%, MFC: 17.81%). Furthermore, its electrochemical performance is dramatically increased. The peak power density of 120 mW/m² and the current density of 1.07 A/m² are generated under light illumination, which are about 1.57-fold and 1.37-fold higher than that under dark (76 mW/m², 0.78 A/m²), respectively. Microbial community analysis demonstrates Proteobacteria and Firmicute are dominant phyla, implying they play important roles on accelerating the extracellular-electron transfer and toluene degradation. In addition, the underlying mechanism for toluene degradation in the photo-MFC system is preliminary explored. Our results suggest that the photo-MFC has great potential for simultaneous treatment of VOCs with energy recovery.

A review on self-sustainable microbial electrolysis cells for electro-biohydrogen production via coupling with carbon-neutral renewable energy technologies

Microbial electrolysis cell (MEC) technology is a promising bioelectrochemical hydrogen production technology that utilizes anodic bio-catalytic oxidation and cathodic reduction processes. MECs require a lower external energy input than water electrolysis; however, as they also require the application of external power sources, this inevitably renders MEC systems a less sustainable option. This issue is the main obstacle hindering the practical application of MECs. Therefore, this review aims to introduce a self-sustainable MEC technology by combining conventional MECs with advanced carbon-neutral technologies, such as solar-, microbial-, osmotic-, and thermoelectric-powers (and their combinations). Moreover, new approaches to overcome the thermodynamic barriers and attain self-sustaining MECs are discussed in detail, thereby providing a working principle, current challenges, and future perspective in the field. This review provides comprehensive insights into reliable hydrogen production as well as the latest trends towards self-sustainable MECs for practical application.

TiO2 anchored on MoS2 nanosheets based on molybdenite exfoliation as an efficient cathode for enhanced Cr (VI) reduction in microbial fuel cell

MoS₂ nanosheet-decorated TiO₂ nanocomposites were prepared via facile liquid-phase exfoliation of natural molybdenite combined with in situ hydrolysis route. These materials were used as a photocathode for the first time in microbial fuel cell (MFC) to reduce hexavalent chromium (Cr (VI)). Results showed the maximum power density of 1 wt% MoS₂/TiO₂-based MFC was 3.7 and 1.9 times higher than that of blank graphite and TiO₂-based MFC, respectively. This MFC achieved 99.57% removal of Cr (VI) with a concentration of 20 mg L^-1 within 8 h under visible light illumination at pH 2 and high degradation rate of 2.49 g m^-3 h^-1. The introduction of MoS₂ nanosheets as a cocatalyst can expand the absorption of visible light, thereby leading to increased electronic participation in Cr (VI) reduction. Moreover, the appropriate amounts of MoS₂ nanosheets also contribute to electrons migration and additional active site. The enhanced power output and Cr (VI) reduction efficiency of MFC can be attributed to the synergistic coupling between bioanode and MoS₂/TiO₂ photocathode. On the basis of its facile and scalable synthetic strategy as well as its stable and outstanding photoelectrocatalytic performance for MFC, this MoS₂/TiO₂ nanocomposite showed potential in the efficient treatment of wastewater.

A novel UV-assisted PEC-MFC system with CeO2/TiO2/ACF catalytic cathode for gas phase VOCs treatment

Emissions of volatile organic compounds (VOCs) air pollutants could worsen air quality and adversely affect human health, thus developing more efficient low-temperature VOCs removal techniques is desired. A novel continuous system integrating UV-assisted photo-electrochemical catalysis with microbial fuel cell (UV-assisted PEC-MFC) has been established for promoting removal of gaseous ethyl acetate or toluene and generating electricity simultaneously. In this system, CeO₂/TiO₂/ACF catalytic cathode is prepared and used for combination with bio-anode for accelerating cathodic reaction. This UV-assisted PEC-MFC system exhibits an excellent elimination capacity (EC) of ethyl acetate (∼0.39 g/m³, EC: ∼2.52 g/m³/h) or toluene (∼0.29 g/m³, EC: 1.89 g/m³/h) under close-circuit condition. Furthermore, an outstanding elimination capacity (EC: 28.04 g/m³/h) for high concentration toluene (∼4.10 g/m³) removal is obtained after toluene gas passes sequentially through the catalytic cathode then the bio-anode. This way of PEC degradation and biodegradation, avoids inhibition of exoelectrogens activity from toxicity of high concentration toluene. Simultaneously, the cell voltage of UV-assisted PEC-MFC system is stable at 0.11 V (vs. SCE) and 1.452×10^-4 kWh is generated from treatment of toluene gas stream in 6 h duration time. The possible mechanism of VOCs removal in this novel system has been proposed and discussed. This study provides new technical basis for treating gaseous pollutants via integrating photo-electrochemical catalysis with electricity generating microbial fuel cell for energy conversion.

Photocathode optimization and microbial community in the solar-illuminated bio-photoelectrochemical system for nitrofurazone degradation

To further enhance the bio-photoelectrochemical system (BPES) performance for nitrofurazone (NFZ) degradation and current output, the g-C₃N₄/CdS photocathode was optimized, and microbial community shift from inoculation to the BPES was analyzed. Results showed that photocathode with g-C₃N₄/CdS (mass ratio of 1:9) loading of 7.5 mg/cm² exhibited the best performance, with NFZ removal of 83.14% (within 4 h) and current of ~9 mA in the BPES. Proteobacteria accounted for the largest proportion: 66.53% (inoculation), 71.89% (microbial electrolysis cell (MEC) anode), 74.67% (BPES anode) and 57.31% (BPES cathode), respectively. In addition, Geobacter was the most dominant genus in MEC and BPES anode and cathode, which occupied 31.64%, 67.73% and 41.34%, respectively. The microbial compositions of BPES anode and cathode were similar, but different from that of MEC anode. Notably, Rhodopseudomonas, a photosynthetic species, was detected in the BPES. Cognition of microbial community in the BPES is important for advancing its development.

Nitrofurazone degradation in the self-biased bio-photoelectrochemical system: g-C3N4/CdS photocathode characterization, degradation performance, mechanism and pathways

In this study, a self-biased bio-photoelectrochemical system (SB-BPES) was constructed using a bioanode and the g-C₃N₄/CdS heterojunction photocathode for nitrofurazone (NFZ) degradation under solar irradiation. The physio-chemical properties and optical performance of photocatalysts were characterized, and photo-electrochemical properties of various photocathodes were analyzed. Results showed that g-C₃N₄/CdS exhibited the broadest visible light absorption range (to 594 nm) and the most efficient e^--h⁺ separation; and its corresponding photocathode showed the highest photocurrent (9.8 μA), and the lowest charge transfer resistance (5.43 ☓ 10³ Ω). In the solar-illuminated SB-BPES with g-C₃N₄/CdS photocathode, about 80% of NFZ removal rate was achieved within 10 h. More importantly, TOC removal of 62.6% was achieved in 24 h, which was 1.8 times of that from the open circuit SB-BPES, and 4.3 folds of that from microbial degradation; also, about 1.5 times of those from SB-BPES with g-C₃N₄ and CdS photocathodes. Besides, reproducible current generations (∼1.0 mA) were produced. These verified that it was a self-sustained system for spontaneously pollutants degradation and electricity generation. Moreover, possible degradation mechanism and pathways were proposed according to the identified intermediates. This study provides inspiration for synchronic improving refractory organics degradation and net energy recovery.

Photocatalytic membrane combined with biodegradation for toluene oxidation

Photocatalytic membrane coupled to biodegradation offers potential for degrading volatile organic compounds (VOCs) in photocatalytic membrane biofilm reactor. An intimately coupled photocatalysis and biodegradation reactor was operated in continuous operation for 500 days to treat simulated waste gas containing toluene. Toluene removal efficiency obtained 99%, with the elimination capacity of 550 g m^-3·h^-1. Membrane photocatalysis coupled to biodegradation was created to improve toluene removal from 11 to 20%. The dominant genera were Lysinibacillus, Hydrogenophaga, Pseudomonas at 30 d, Rudaea, Dongia, Litorilinea at 230 d xyl, Tod, Tcb, Bed, Tmo, Tbu, Tou, Dmp, Cat were functional genes of toluene metabolism, as shown by16S rDNA and metagenomic sequencing. Photocatalysis destroyed part of the toluene into biodegradable intermediates that were immediately mineralized by microorganisms in biofilm, some toluene was directly degraded by toluene degrading bacterial community into carbon dioxide and water. The novel hybrid photocatalytic membrane biofilm reactor is a cost-effective and robust alternative to VOCs treatment.