Simultaneous enhancement of power generation and chlorophenol degradation in nonmodified microbial fuel cells using an electroactive biofilm carbon felt anode

Optimized feeding schemes of heterotrophic anodic denitrification coupled with cathodic phosphate recovery from wastewater using a microbial fuel cell

Enhanced water quality standards and increasing resource scarcity have prompted extensive research into low-cost nitrogen removal and phosphate recovery from wastewater. Microbial fuel cells (MFCs) offer a viable solution by simultaneously removing nitrogen, recovering phosphorus, and generating electrical energy. This study employed MFCs to achieve simultaneous nitrogen removal and phosphorus recovery, investigating the impact of different feeding schemes. The experimental results indicated that replacing the entire anode chamber solution and recycling the anode effluent to the cathode chamber effectively prevented the accumulation of nitrifying bacteria while achieving the highest pollutant removal performance. Under closed circuit conditions, the system consistently maintained low nitrite concentrations, achieving an average nitrate removal efficiency of 68.09 ± 1.86 % and phosphate recovery efficiency of 83.46 ± 5.30 %. Furthermore, this feeding scheme facilitated microbial growth and reproduction while also improving operational convenience. The study utilized metagenomics and other technologies to comprehensively analyze the system's operation mechanism and reasons for its excellent performance.

Bidirectional effects of melanoidins derived from thermal Maillard reaction on polyhydroxyalkanoates synthesis by mixed culture: Transient and long-term responses

The synthesis of polyhydroxyalkanoates (PHA) by mixed microbial culture (MMC) using thermal hydrolyzed sludge is a promising strategy. However, the thermal hydrolysis by-product melanoidins may disturb PHA synthesis. In this study, transient-cycle experiments revealed bidirectional effects of melanoidins on PHA production: low concentrations (≤400 mg/L) promoted, high concentrations (≥800 mg/L) inhibited. Low melanoidins induced hormesis response and improved electron transfer, with energy metabolism increasing by 45 % and 15 % at 200 and 400 mg/L compared with no melanoidins. Reversely, high melanoidins caused cytotoxicity, with cell death ratio 4.5 times higher at 2000 mg/L than blank. In long-term operation, the promoting effect of low melanoidins diminished or turned inhibitory, possibly due to more PHA degraded. The melanoidins-tolerant genera such as Hydrogenophaga and Pannonibacter might alter MMC enrichment and PHA-producing capacity. These findings highlight the concentration-dependent effects of melanoidins on PHA synthesis, offering an insight into optimizing sludge-to-PHA recycling.

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.

Evolution of interspecific interactions underlying the nonlinear relationship between active biomass and pollutant degradation capacity in bioelectrochemical systems

This study proposes a switching operating mode that alternates between microbial fuel cell (MFC) and microbial electrolysis cell (MEC) to restore the biofilm activity and organic pollutant degradation capacity in bioelectrochemical systems (BESs) during prolonged operation. After the model switching, the toluene degradation kinetics in BESs equipped with graphite sheet (GS) and polyaniline@carbon nanotubes (PANI@CNTs) bioanodes were elevated by 2.10 and 3.14 times, respectively. Nevertheless, the amount of active biomass in the GS and PANI@CNTs bioanodes only increased by 1.04 and 1.05 times, with the PANI@CNTs bioanode consistently outperforming in hierarchical biofilm activity and redox properties. Additionally, the distribution of functional genes across the dominant genera revealed their roles in extracellular electron transfer and the four steps of toluene degradation (primary oxidation, ring-opening, intermediate oxidation, and tricarboxylic acid cycle). Furthermore, the cooperation of substrate exchange among Pseudomonas, Alicycliphilus, and Acidovorax in the MFC mode evolved to interactions among Acidovorax, Alicycliphilus, and Geobacter in the MEC mode, which attributed to the nonlinear relationship between active biomass and pollutant degradation capacity. These results provide insights into the operating mode and interspecific interactions of BESs, with implications for practical applications.

The effect of ammonia concentration on the treatment of bio electrochemical leachate using MFCs technology

Microbial fuel cells (MFCs) have garnered attention in bio-electrochemical leachate treatment systems. The most common forms of inorganic ammonia nitrogen are ammonium (NH 4 + ) and free ammonia. Anaerobic digestion can be inhibited in both direct (changes in environmental conditions, such as fluctuations in temperature or pH, can indirectly hinder microbial activity and the efficiency of the digestion process) and indirect (inadequate nutrient levels, or other conditions that indirectly compromise the microbial community's ability to carry out anaerobic digestion effectively) ways by both kinds. The performance of a double-chamber MFC system-composed of an anodic chamber, a cathode chamber with fixed biofilm carriers (carbon felt material), and a Nafion 117 exchange membrane is examined in this work to determine the impact of ammonium nitrogen (NH 4 - N ) inhibition. MFCs may hold up to 100 mL of fluid. Therefore, the bacteria involved were analysed using 16S rRNA. At room temperature, with a concentration of 800 mg L-1 of ammonium nitrogen and 13,225 mg L-1 of chemical oxygen demand (COD), the study produced a considerable power density of 234 mWm-3. It was found thatNH 4 - N concentrations above 800 mg L-1 have an inhibitory influence on power output and treatment effectiveness. Multiple routes removed the most nitrogen (NH 4 + -N: 87.11 ± 0.7%, NO2 -N: 93.17 ± 0.2% and TN: 75.24 ± 0.3%). Results from sequencing indicate that the anode is home to a rich microbial community, with anammox (6%), denitrifying (6.4%), and electrogenic bacteria (18.2%) making up the bulk of the population. Microbial fuel cells can efficiently and cost-effectively execute anammox, a green nitrogen removal process, in landfill leachate.

Deciphering the differentiated performance on electricity generation and COD degradation by Rhodopseudomonas-dominated bioanode in light or dark

Anoxygenic phototrophic bacteria is a promising catalyst for constructing bioanode, but the mixed culture with non-photosynthetic bacteria is inevitable in an open environment application. In this study, a Rhodopseudomonas-dominated mixed culture with other electrogenic bacteria was investigated for deciphering the differentiated performance on electricity generation in light or dark conditions. The kinetic study showed that reaction rate of OM degradation was 9 times higher than that under dark condition, demonstrating that OM degradation was enhanced by photosynthesis. However, CE under light condition was lower. It indicated that part of OM was used to provide hydrogen donors for the fixation of CO2 or hydrogen production in photosynthesis, decreasing the OM used for electron transfer. In addition, higher COD concentration was not conducive to electricity generation. EIS analysis demonstrated that higher OM concentration would increase Rct to hinder the transfer of electrons from bacteria to the electrode. Indirect and direct electron transfer were revealed by CV analysis for light and dark biofilm, respectively, and nanowires were also observed by SEM graphs, further revealing the differentiate performance. Microbial community analysis demonstrated Rhodopseudomonas was dominated in light and decreased in dark, but Geobacter increased apparently from light to dark, resulting in different power generation performance. The findings revealed the differentiated performance on electricity generation and pollutant removal by mixed culture of phototrophic bacteria in light or dark, which will improve the power generation from photo-microbial fuel cells.

Utilization of microbial fuel cells as a dual approach for landfill leachate treatment and power production: a review

Landfill leachate, which is a complicated organic sewage water, presents substantial dangers to human health and the environment if not properly handled. Electrochemical technology has arisen as a promising strategy for effectively mitigating contaminants in landfill leachate. In this comprehensive review, we explore various theoretical and practical aspects of methods for treating landfill leachate. This exploration includes examining their performance, mechanisms, applications, associated challenges, existing issues, and potential strategies for enhancement, particularly in terms of cost-effectiveness. In addition, this critique provides a comparative investigation between these treatment approaches and the utilization of diverse kinds of microbial fuel cells (MFCs) in terms of their effectiveness in treating landfill leachate and generating power. The examination of these technologies also extends to their use in diverse global contexts, providing insights into operational parameters and regional variations. This extensive assessment serves the primary goal of assisting researchers in understanding the optimal methods for treating landfill leachate and comparing them to different types of MFCs. It offers a valuable resource for the large-scale design and implementation of processes that ensure both the safe treatment of landfill leachate and the generation of electricity. The review not only provides an overview of the current state of landfill leachate treatment but also identifies key challenges and sets the stage for future research directions, ultimately contributing to more sustainable and effective solutions in the management of this critical environmental issue.

Treatment of phenolic wastewater by anaerobic fluidized bed microbial fuel cell using carbon brush as anode: microbial community analysis and m-cresol degradation mechanism

Anaerobic fluidized bed microbial fuel cell (AFB-MFC) is a technology that combines fluidized bed reactor and microbial fuel cell to treat organic wastewater and generate electricity. The performance and the mechanism of treating m-cresol wastewater in AFB-MFC using carbon brush as biofilm anode were studied. After 48 h of operation, the m-cresol removal efficiency of AFB-MFC, MAR-AFB (fluidized bed bioreactor with acclimated anaerobic sludge), MAR-FB (ordinary fluidized bed reactor with only macroporous adsorptive resin) and AST (traditional anaerobic sludge treatment) were 95.29 ± 0.67%, 85.78 ± 1.81%, 71.24 ± 1.86% and 70.41 ± 0.32% respectively. The maximum output voltage and the maximum power density of AFB-MFC using carbon brush as biofilm anode were 679.7 mV and 166.6 mW/m2 respectively. The results of high-throughput sequencing analysis indicated the relative abundance of dominant electroactive bacteria, such as Trichococcus, Geobacter, and Pseudomonas, on the anode carbon brushes was higher than that of AST, and also identified such superior m-cresol-degrading bacteria as Bdellovibrio, Thermomonas, Hydrogenophaga, etc. Based on the determination of m-cresol metabolites detected by Gas Chromatography-Mass Spectrometry (GC-MS), the possible biodegradation pathway of m-cresol under anaerobic and aerobic conditions in AFB-MFC was speculated. The results showed that m-cresol was decomposed into formic acid-acetic anhydride and 3-methylpropionic acid under the action of electrochemistry, which is a simple degradation pathway without peripheral metabolism in AFB-MFC.

Nano-hydroxyapatite/carbon nanotube: An excellent anode modifying material for improving the power output and diclofenac sodium removal of microbial fuel cells

Anode material and surface properties have a crucial impact on the performance of MFCs. Designing and fabricating various modified carbon-based anodes with functional materials is an effective strategy to improve anode performance in MFCs. Anode materials with excellent bioaffinity can promote bacterial attachment, growth, and extracellular electron transfer. In this study, positively charged nano hydroxyapatite (nHA) with remarkable biocompatibility combined with carbon nanotubes (CNTs) with unique structure and high conductivity were used as anode modifying material. The nHA/CNTs modified carbon brush (CB) exhibited improved bacteria adsorption capacity, electrochemical activity and reticular porous structure, thus providing abundant sites and biocompatible microenvironment for the attachment and growth of functional microbial and accelerating extracellular electron transfer. Consequently, the nHA/CNTs/CB-MFCs achieved the maximum power density of 4.50 ± 0.23 mW m-2, which was 1.93 times higher than that of the CB-MFCs. Furthermore, diclofenac sodium (DS), which is a widely used anti-inflammatory drug and is also a persistent toxic organic pollutant constituting a serious threat to public health, was used as the model organic pollutant. After 322 days of long-term operation, enhanced diclofenac sodium removal efficiency and simultaneous bioelectricity generation were realized in nHA/CNTs/CB-MFCs, benefiting from the mature biofilm and the diverse functional microorganisms revealed by microbial community analysis. The nHA/CNTs/CB anode with outstanding bioaffinity, electrochemical activity and porous structure presents great potential for the fabrication of high-performance anodes in MFCs.

Vanadium nitride decorated carbon cloth anode promotes aniline degradation and electricity generation of MFCs by efficiently enriching electroactive bacteria and promoting extracellular electron transfer

To increase the colonization of electroactive bacteria and accelerate the rate of extracellular electron transfer, a simple coated anode of microbial fuel cell was designed. Here, we took advantage of vanadium nitride (VN) particles to modify the carbon cloth (VN@CC). Compared with bare carbon cloth, the designed VN@CC bioanodes exhibited a larger electrochemically active area, better biocompatibility, and smaller charge transfer impedance. The MFC with VN@CC bioanodes achieved the maximum power density of 3.89 W m-2 and chemical oxygen demand removal rate of 84% when 1000 mg L-1 aniline was degraded, which were about 1.88 and 2.8 times that of CC. The morphology of biofilm and 16s rRNA gene sequence analysis proved that the VN@CC bioanodes facilitated the enrichment of electroactive bacteria (99.02%) and increased the ratio of fast electron transfer in the extracellular electron transfer, thus enhancing the MFC performance of aniline degradation and power output. This work disclosed that it was feasible to increase the overall performance of MFC by enhancing the EET efficiency and presented valuable insights for future work.

Mechanistic insights into the response of electroactive biofilms to Cd2+ shock: bacterial viability and electron transfer behavior at the cellular and community levels

Electroactive biofilms (EABs) play a crucial role in environmental bioremediation due to their excellent extracellular electron transfer (EET) capabilities. However, Cd2+ can have toxic effects on the electrochemical performance of EABs, and the comprehensive inhibition mechanism of EABs in response to Cd2+ shock remains elusive. This study indicated that Cd2+ shock significantly reduced biomass and increased oxidative stress in EABs at the cellular level. The bacterial viability of EABs in phase III under 0.5 mM Cd2+ shock (EABCd2+-III0.5) decreased by 16.31% compared to EABCK-III. Moreover, intracellular NADH, c-Cyts, and the abundance of electroactive species were essential indicators to evaluate EET behavior of EABs. In EABCd2+-III0.5, these indicators decreased by 26.32%, 33.40%, and 20.65%, respectively. Structural equation modeling analysis established quantitative correlations between core components and electrochemical activity at cellular and community levels. The correlation analysis revealed that the growth and electron transfer functions of EABs were predictive indicators for their electrochemical performance, with standardized path coefficients of 0.407 and 0.358, respectively. These findings enhance our understanding of EABs' response to Cd2+ shock and provide insights for improving their performance in heavy metal wastewater.

New insights into enhanced biodegradation of 4-bromphenol in a nitrate-reducing system: Process performance and mechanism

Due to the recalcitrant nature of halogenated phenol, conventional anaerobic bioprocess is often limited by low removal efficiency and poor process stability. At the presence of electron acceptors such as nitrate, 4-bromophenol (4-BP) removal efficiency is significantly higher than that in the anaerobic control system, but the mechanism involved is still unclear. Therefore, an up-flow nitrate-reducing bioreactor (NRBR) was designed and consecutively performed for 215 days to explore the synergistic mechanism for BPs biodegradation and nitrate reduction. Complete 4-BP biodegradation could be obtained in NRBR at HRT and 4-BP loading rate of 24 h and 0.29 mol m - 3d - 1, while the TOC removal and nitrate reduction efficiencies were as high as 91.33±2.11% and 98.31±1.33%, respectively. Population evolution analyses revealed that the microorganisms involved in 4-BP debromination and biodegradation (Candidatus Peregrinibacteria, Denitratisoma, Anaerolineaceae and Ignavibacterium) as well as nitrate reduction (Denitratisoma, Anaerolineaceae, Limnobacter and Ignavibacterium) were significantly enriched in NRBR. Major intermediates during 4-BP biodegradation, including 4-bromocatechol, 4‑bromo-6-oxo-hexanoic acid and succinic acid were identified, while a distinct 4-BP biodegradation pathway via hydration, aromatic-ring cleavage, hydrolysis debromination and oxidation was expounded. Metagenomic analysis indicated that oxidation (had, pht4, boh, butA), hydrolysis debromination ((S)-2-haloacid dehalogenase) and bio-mineralization (gabD, sdhA) of 4-BP were largely enhanced in NRBR. Moreover, carbon, nitrogen, energy and amino acid metabolisms were significantly facilitated with the injection of nitrate in order to provide energy and electron, thus enhanced microbial activities and enzymatic reactions in NRBR. The proposed mechanism provides new insights into our mechanistic understanding of halogenated phenol biodegradation and the development of sustainable bioremediation strategies.

Boosting o-xylene removal and power generation in an airlift microbial fuel cell system

Microbial fuel cells (MFCs) are widely acknowledged to be a promising eco-friendly abatement technology of pollutants, and are capable of generating electricity. However, the poor mass transfer and reaction rate in MFCs significantly decrease their treatment capacity for contaminants, especially hydrophobic substances. The present work developed a novel MFC integrated with an airlift (ALR) reactor using a polypyrrole modified anode to promote the bioaccessibility of gaseous o-xylene and attachment of microorganisms. The results indicated that the established ALR-MFC system showed excellent elimination capability, with removal efficiency exceeding 84% even at high o-xylene concentration (1600 mg m^-3). The maximum output voltage of 0.549 V and power density of 13.16 mW m^-2 obtained by the Monod-type model were approximately twice and sixfold higher than that of a conventional MFC, respectively. According to the microbial community analysis, the superior performances of the ALR-MFC in terms of o-xylene removal and power generation were mainly ascribed to the enrichment of degrader (i.e. Shinella) and electrochemical active bacteria (i.e. Proteiniphilum). Moreover, the electricity generation of the ALR-MFC did not decrease at a high O₂ concentration, as O₂ was conducive to o-xylene degradation and electron release. The supplication of an external carbon source such as sodium acetate (NaAc) was conducive to increasing output voltage and coulombic efficiency. The electrochemical analysis revealed that released electrons can be transmitted with the action of NADH dehydrogenase to OmcZ, OmcS, and OmcA outer membrane proteins via a direct or indirect pathway, and ended up transferring to the anode directly.

Electroactive Microorganisms in Advanced Energy Technologies

Large-scale production of green and pollution-free materials is crucial for deploying sustainable clean energy. Currently, the fabrication of traditional energy materials involves complex technological conditions and high costs, which significantly limits their broad application in the industry. Microorganisms involved in energy production have the advantages of inexpensive production and safe process and can minimize the problem of chemical reagents in environmental pollution. This paper reviews the mechanisms of electron transport, redox, metabolism, structure, and composition of electroactive microorganisms in synthesizing energy materials. It then discusses and summarizes the applications of microbial energy materials in electrocatalytic systems, sensors, and power generation devices. Lastly, the research progress and existing challenges for electroactive microorganisms in the energy and environment sectors described herein provide a theoretical basis for exploring the future application of electroactive microorganisms in energy materials.

Natural siderite derivatives activated peroxydisulfate toward oxidation of organic contaminant: A green soil remediation strategy

Natural siderite (FeCO₃), simulated synthetic siderite and nZVI/FeCO₃ composite were used as green and easily available iron-based catalysts in peroxydisulfate activation for remediating 2-chlorophenol as the target contaminant and this technique can effectively degrade organic pollutants in the soil. The key reaction parameters such as catalysts dosage, oxidant concentration and pH, were investigated to evaluate the catalytic performance of different materials in catalytic systems. The buffering property of natural soil conduced satisfactory degradation performance in a wide pH range (3-10). Both the main non-radical of ¹O₂ and free radicals of SO₄^·- and OH^· were evidenced by quenching experiment and electron paramagnetic resonance. The reduction of nZVI on FFC surface not only has the advantage for electronic transfer to promote the circulation of Fe(III) to Fe(II), but also can directly dechlorinate. Furthermore, the intermediates were comprehensively analyzed by GC-MS and a potential removal mechanism of three oxidant system for 2-CP soil degradation was obtained. Briefly, this research provides a new perspective for organic contaminate soil treatment using natural siderite or simulated synthetic siderite as efficient and environmental catalytic material.

The electron transport mechanism of downflow Leersia hexandra Swartz constructed wetland-microbial fuel cell when used to treat Cr(VI) and p-chlorophenol

Constructed wetland-microbial fuel cells are used to treat heavy metal and/or refractory organic wastewater. However, the electron transport mechanism of downflow Leersia hexandra constructed wetland-microbial fuel cells (DLCW-MFCs) is poorly understood when used to treat composite-polluted wastewater containing Cr(VI) and p-chlorophenol (4-CP) (C&P). In this study, metagenomics and in situ electrochemical techniques were used to investigate the electrochemical properties and the electricigens and their dominant gene functions. The DLCW-MFC was used to treat C&P and single-pollutant wastewater containing Cr(VI) (SC) and 4-CP (SP). The results showed that C&P had a higher current response and charge transfer capability and lower solution resistance plus charge transfer resistance. The anode bacteria solution of C&P contained more electron carriers (RF, FMN, FAD, CoQ10, and Cyt c). Metagenomic sequencing indicated that the total relative abundance of the microorganisms associated with electricity production (Desulfovibrio, Pseudomonas, Azospirillum, Nocardia, Microbacterium, Delftia, Geobacter, Acinetobacter, Bacillus, and Clostridium) was the highest in C&P (4.24%). However, Microbacterium was abundant in SP (0.12%), which exerted antagonistic effects on other electricigens. Among the 10 electricigens based on gene annotation, C&P had a higher overall relative abundance of the Unigene gene annotated to the KO pathway and CAZy level B compared with SC and SP, which were 1.31% and 0.582% respectively. Unigene153954 (ccmC), Unigene357497 (coxB), and Unigene1033667 (ubiG) were related to the electron carrier Cyt c, electron transfer, and CoQ biosynthesis, respectively. These were annotated to Desulfovibrio, Delftia, and Pseudomonas, respectively. Unigene161312 (AA1) used phenols and other substrates as electron donors and was annotated to Pseudomonas. Other functional carbohydrate enzyme genes (e.g., GT2, GT4, and GH31) used carbohydrates as donors and were annotated to other electricigens. This study provides a theoretical basis for electron transfer to promote the development of CW-MFCs.

The in-depth revelation of the mechanism by which a downflow Leersia hexandra Swartz constructed wetland-microbial fuel cell synchronously removes Cr(VI) and p-chlorophenol and generates electricity

The composite pollution by Cr(VI) and p-chlorophenol (4-CP) has high toxicity and harms water safety. However, research on the effective removal of Cr(VI) and 4-CP composite-polluted wastewater (C&P) and efficient synchronous electricity generation with reclaimed resources is limited. In this study, a downflow Leersia hexandra constructed wetland-microbial fuel cell (DLCW-MFC) was builded to treat C&P, as well as wastewater singularly polluted by Cr(VI) (SC) and 4-CP (SP), respectively, to reveal the mechanism by which DLCW-MFC treats C&P and synchronously generates electricity. The results demonstrate that the cathode layer had a stronger removal effect on pollutants than the middle layer and anode zone layer. Moreover, SC and SP had stronger pollutant removal effects than C&P. Cr(VI) had more competitive with electrons than 4-CP, and they had a synergistic effect on efficient electricity generation. The L.hexandra in SC and SP had a better growth state and lower Cr enrichment concentration than that in C&P. Cr existed in the DLCW-MFC mainly in the form of Cr(III). Gas chromatography-mass spectrometry was used to investigate the degradation pathway of 4-CP in C&P, and indicated that Phenol, 2,4-bis(1,1-dimethylethyl)- and benzoic acid compounds were the main intermediates formed at the cathode, and further mineralized to form medium-long-chain organic compounds to form CO₂. The microbial community distribution results revealed that Simplicispira, Cloacibacterium, and Rhizobium are associated with Cr(VI) removal and 4-CP degradation, and were found to be rich in the cathode of C&P. The anode of C&P was found to have more Acinetobacter (1.34%) and Spirochaeta (4.83%) than SC and SP, and the total relative abundance of electricigens at the anode of C&P (7.46%) was higher than that at the anodes of SC and SP. This study can provide a theoretical foundation for the DLCW-MFC to treat heavy metal and chlorophenol composite-polluted wastewater and synchronously generate electricity.

Effect of nickel (II) on the performance of anodic electroactive biofilms in bioelectrochemical systems

The impact of nickel (Ni²⁺) on the performance of anodic electroactive biofilms (EABs) in the bioelectrochemical system (BES) was investigated in this study. Although it has been reported that Ni²⁺ influences microorganisms in a number of ways, it is unknown how its presence in the anode of a BES affects extracellular electron transfer (EET) of EABs, microbial viability, and the bacterial community. Results revealed that the addition of Ni²⁺ decreased power output from 673.24 ± 12.40 mW/m² at 0 mg/L to 179.26 ± 9.05 mW/m² at 80 mg/L. The metal and chemical oxygen demand removal efficiencies of the microbial fuel cells (MFCs) declined as Ni²⁺ concentration increased, which could be attributed to decreased microbial viability as revealed by SEM and CLSM. FTIR analysis revealed the involvement of various microbial biofilm functional groups, including hydroxyl, amides, methyl, amine, and carboxyl, in the uptake of Ni²⁺. The presence of Ni²⁺ on the anodic biofilms was confirmed by SEM-EDS and XPS analyses. CV demonstrated that the electron transfer performance of the anodic biofilms was negatively correlated with the various Ni²⁺ concentrations. EIS showed that the internal resistance of the MFCs increased with increasing Ni²⁺ concentration, resulting in a decrease in power output. High-throughput sequencing results revealed a decrease in Geobacter and an increase in Desulfovibrio in response to Ni²⁺ concentrations of 10, 20, 40, and 80 mg/L. Furthermore, the various Ni²⁺ concentrations decreased the expression of EET-related genes. The Ni²⁺-fed MFCs had a higher abundance of the nikR gene than the control group, which was important for Ni²⁺ resistance. This work advances our understanding of Ni²⁺ inhibition on EABs, as well as the concurrent removal of organic matter and Ni²⁺ from wastewater.

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.

Role of bioelectrochemical systems for the remediation of emerging contaminants from wastewater: A review

Bioelectrochemical systems (BESs) are a unique group of wastewater remediating technology that possesses the added advantage of valuable recovery with concomitant wastewater treatment. Moreover, due to the application of robust microbial biocatalysts in BESs, effective removal of emerging contaminants (ECs) can be accomplished in these BESs. Thus, this review emphasizes the recent demonstrations pertaining to the removal of complex organic pollutants of emerging concern present in wastewater through BES. Owing to the recalcitrant nature of these pollutants, they are not effectively removed through conventional wastewater treatment systems and thereby are discharged into the environment without proper treatment. Application of BES in terms of ECs removal and degradation mechanism along with valuables that can be recovered are discussed. Moreover, the factors affecting the performance of BES, like biocatalyst, substrate, salinity, and applied potential are also summarized. In addition, the present review also elucidates the occurrence and toxic nature of ECs as well as future recommendations pertaining to the commercialization of this BES technology for the removal of ECs from wastewater. Therefore, the present review intends to aid the researchers in developing more efficient BESs for the removal of ECs from wastewater.

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

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