Stimulation of oxygen to bioanode for energy recovery from recalcitrant organic matter aniline in microbial fuel cells (MFCs)

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

Combination of partial nitrification and microbial fuel cell for simultaneous ammonia reduction, organic removal, and energy recovery

The chemical oxygen demand (COD) in municipal wastewater has become an obstacle for anammox in mainstream applications. In this study, the single chamber microbial fuel cell (MFC) was installed as an influent device for a partial nitrification-sequencing batch reactor (PN-SBR) to realize integrating COD removal and partial nitrification. After 80 days of operation, the nitrite accumulation rate reached 93%, while the COD removal efficiency was 56%. The output voltage and the power density of MFC were 66.62 mV and 2.40 W/m3, respectively. The content of EPS, especially polysaccharides in the stable phase, has increased compared with the seed sludge. The most dominant genus in MFC anode biofilm and SBR granular sludge was Thauera, which has organic compounds degradation capacity and could degrade nitrate. This study revealed the microbial interaction between MFC and partial nitrification and provided a new strategy for stable ammonia and nitrite supply for mainstream anammox plants.

Micro-aeration assisted with electrogenic respiration enhanced the microbial catabolism and ammonification of aromatic amines in industrial wastewater

Improvement of refractory nitrogen-containing organics biodegradation is crucial to meet discharged nitrogen standards and guarantee aquatic ecology safety. Although electrostimulation accelerates organic nitrogen pollutants amination, it remains uncertain how to strengthen ammonification of the amination products. This study demonstrated that ammonification was remarkably facilitated under micro-aerobic conditions through the degradation of aniline, an amination product of nitrobenzene, using an electrogenic respiration system. The microbial catabolism and ammonification were significantly enhanced by exposing the bioanode to air. Based on 16S rRNA gene sequencing and GeoChip analysis, our results indicated that aerobic aniline degraders and electroactive bacteria were enriched in suspension and inner electrode biofilm, respectively. The suspension community had a significantly higher relative abundance of catechol dioxygenase genes contributing to aerobic aniline biodegradation and reactive oxygen species (ROS) scavenger genes to protect from oxygen toxicity. The inner biofilm community contained obviously higher cytochrome c genes responsible for extracellular electron transfer. Additionally, network analysis indicated the aniline degraders were positively associated with electroactive bacteria and could be the potential hosts for genes encoding for dioxygenase and cytochrome, respectively. This study provides a feasible strategy to enhance nitrogen-containing organics ammonification and offers new insights into the microbial interaction mechanisms of micro-aeration assisted with electrogenic respiration.

Simultaneous removal of nitrate, nitrobenzene and aniline from groundwater in a vertical baffled biofilm reactor

The challenge of simultaneous removal of nitrobenzene (NB), aniline (AN) and nitrate from groundwater in a single bioreactor is mainly attributed to the persistence of AN to degradation with anoxic denitrification conditions. In this work, simultaneous removal of NB (100 μM), AN (100 μM) and nitrate (1 mM) was achieved within 8 h with a COD/N ratio of 8 in a vertical baffled biofilm reactor (VBBR). By setting DO concentration at 0.4-0.5 mg L^-1 to create a micro-aerobic condition, NB removal rate was accelerated without accumulation of AN, and AN could serve as electron donors for denitrification after ring cleavage. High-throughput sequencing showed that biofilm was predominated by denitrifiers (Luteimonas, Planctomyces, Thiobacillus, Thauera and so on) and NB-degrading bacteria (Pseudomonas), and biodiversity varied vertically along the height of the reactor. A dominantly anaerobic pathway for reducing NB to AN was identified by PICRUSt analysis, as the predicted genes involved in aerobic transformation of NB were several magnitudes lower than those in the anaerobic pathway. This study provided a new insight to the role of oxygen in robust bioremediation groundwater contaminated with NB, AN and nitrate.

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.

A tartrate-EDTA-Fe complex mediates electron transfer and enhances ammonia recovery in a bioelectrochemical-stripping system

Traditional bioelectrochemical systems (BESs) coupled with stripping units for ammonia recovery suffer from an insufficient supply of electron acceptors due to the low solubility of oxygen. In this study, we proposed a novel strategy to efficiently transport the oxidizing equivalent provided at the stripping unit to the cathode by introducing a highly soluble electron mediator (EM) into the catholyte. To validate this strategy, we developed a new kind of iron complex system (tartrate-EDTA-Fe) as the EM. EDTA-Fe contributed to the redox property with a midpoint potential of -0.075 V (vs. standard hydrogen electrode, SHE) at pH 10, whereas tartrate acted as a stabilizer to avoid iron precipitation under alkaline conditions. At a ratio of the catholyte recirculation rate to the anolyte flow rate (R_C-A) of 12, the NH₄ ⁺-N recovery rate in the system with 50 mM tartrate-EDTA-Fe complex reached 6.9 ± 0.2 g N m^-2 d^-1, approximately 3.8 times higher than that in the non-EM control. With the help of the complex, our system showed an NH₄ ⁺-N recovery performance comparable to that previously reported but with an extremely low R_C-A (0.5 vs. 288). The strategy proposed here may guide the future of ammonia recovery BES scale-up because the introduction of an EM allows aeration to be performed only at the stripping unit instead of at every cathode, which is beneficial for the system design due to its simplicity and reliability.

Bioelectrochemical catabolism of triclocarban through the cascade acclimation of triclocarban-hydrolyzing and chloroanilines-oxidizing microbial communities

Chlorinated antimicrobial triclocarban (3,4,4'-trichlorocarbanilide, TCC) is an emerging refractory contaminant omnipresent in various environments. Preferential microbial hydrolysis of TCC to chloroanilines is essential for its efficient mineralization. However, the microbial mineralization of TCC in domestic wastewater is poorly understood. Here, the bioelectrochemical catabolism of TCC to chloroanilines (3,4-dichloroaniline and 4-chloroaniline) and then to CO₂ was realized through the cascade acclimation of TCC-hydrolyzing and chloroanilines-oxidizing microbial communities. The biodegradation of chloroanilines was obviously enhanced in the bioelectrochemical reactors. Pseudomonas, Diaphorobacter, and Sphingomonas were the enriched TCC or chloroanilines degraders in the bioelectrochemical reactors. The addition of TCC enhanced the synergistic effect within functional microbial communities based on the feature of the phylogenetic ecological networks. This study provides a new idea for the targeted domestication and construction of functionally differentiated microbial communities to efficiently remove TCC from domestic wastewater through a green and low-carbon bioelectrochemical method.

Integration of microbial electrochemical systems and photocatalysis for sustainable treatment of organic recalcitrant wastewaters: Main mechanisms, recent advances, and present prospects

In recent years, microbial electrochemical systems (MESs) have demonstrated to be an environmentally friendly technology for wastewater treatment and simultaneous production of value-added products or energy. However, practical applications of MESs for the treatment of recalcitrant wastewater are limited by their low power output and slow rates of pollutant biodegradation. As a novel technology, hybrid MESs integrating biodegradation and photocatalysis have shown great potential to accelerate the degradation of bio-recalcitrant pollutants and increase the system output. In this review, we summarize recent advances of photo-assisted MESs for enhanced removal of recalcitrant pollutants, and present further discussion about the synergistic effect of biodegradation and photocatalysis. In addition, we analyse in detail different set-up configurations, discuss mechanisms of photo-enhanced extracellular electron transfer, and briefly present ongoing research cases. Finally, we highlight the current limitations and corresponding research gaps, and propose insights for future research.

Electrode Microbial Communities Associated with Electron Donor Source Types in a Bioelectrochemical System Treating Azo-Dye Wastewater

Bioelectrochemical systems (BESs) have been acknowledged to be an efficient technology for refractory pollution treatment. An electron donor is as an indispensable element of BES, and domestic wastewater (DW) has been proved as a cost-efficient and accessible alternative option to expensive carbon sources (such as acetate and glucose), yet its effect on microbial community evolution has not been thoroughly revealed. In this study, the electrode microbial communities from BESs treating azo dye wastewater fed by DW (RDW), acetate (RAc), and glucose (RGlu) were systematically revealed based on 16S rRNA Illumina MiSeq sequencing platform. It was found that there were significant differences between three groups in microbial community structures. Desulfovibrio, Acinetobacter, and Klebsiella were identified as the predominant bacterial genera in RDW, RAc, and RGlu, respectively. Methanosaeta, the most enriched methanogen in all reactors, had a relative lower abundance in RDW. Microbial communities in RAc and RGlu were sensitive to electrode polarity while RDW was sensitive to electrode position. Compared with pure substrates, DW increased the diversity of microbial community and, thus, may enhance the stability of electrode biofilm. This study provides an insight into the microbial response mechanism to the electron donors and provides engineering implications for the development of BES.

Coupling of membrane-based bubbleless micro-aeration for 2,4-dinitrophenol degradation in a hydrolysis acidification reactor

Micro-aeration hydrolysis acidification (HA) is an effective method to enhance the removal of toxic and refractory organic matter, but the difficulty in stable dosing control of trace oxygen limits its wide application. Membrane-based bubbleless aeration has been proved as an ideal aeration method because of its higher oxygen transfer rate, more uniform mass transfer, and lower cost than HA. However, the available information on its application in HA is limited. In this study, membrane-based bubbleless micro-aeration coupled with hydrolysis acidification (MBL-MHA) was exploited to investigate the performance of 2,4-dinitrophenol (2,4-DNP) degradation via comparing it with bubble micro-aeration HA (MHA) and anaerobic HA. The results indicated that the performances in MBL-MHA and MHA were higher than those in HA during the experiment. 2,4-DNP degradation rates under redox microenvironments caused by counter-diffusion in MBL-MHA (84.43∼97.28%) were higher than those caused by co-diffusion in MHA (82.41∼94.71%) under micro-aeration of 0.5-5.0 mL air/min. The 2,4-DNP degradation pathways in MBL-MHA were nitroreduction, deamination, aromatic ring cleavage, and fermentation, while those in MHA were hydroxylation, aromatic ring cleavage, and fermentation. Reduction/oxidation-related, interspecific electron transfer-related species, and fermentative species in MBL-MHA were more abundant than that in MHA. Ultimately, more reducing/oxidizing forces formed by more redox proteins/enzymes from these rich species could enhance 2,4-DNP degradation in MBL-MHA.

Mass transfer and reaction simultaneously enhanced airlift microbial electrolytic cell system with high gaseous o-xylene removal capacity

To overcome the limitation of mass transfer and reaction rate involved in the biodegradation of gaseous o-xylene, the airlift reactor and microbial electrolysis cell were integrated to construct an airlift microbial electrolysis cell (AL-MEC) system for the first time, in which the bioanode was modified by polypyrrole to further improve biofilm attachment. The developed AL-MEC system achieved 95.4% o-xylene removal efficiency at optimized conditions, and maintained around 75% removal efficiency even while the inlet o-xylene load was as high as 684 g m^-3 h^-1. The existence of O₂ exhibited a competition in electrons with the bioanode but a positive effect on ring-opening process in the o-xylene oxidation. The limitation of mass transfer had been overcome as the empty bed resistance time in the range of 20-80 s did not influence the system performance significantly. The microbial community analysis confirmed the o-xylene degradation microbes and electroactive bacteria were the dominant, which could be further enriched at 0.3 V against standard hydrogen electrode. This work revealed the feasibility of the AL-MEC system for the degradation of o-xylene and similar compounds, and provided insights into bioelectrochemical system design with high gaseous pollution removal capacity.

Treatment of hazardous organic amine wastewater and simultaneous electricity generation using photocatalytic fuel cell based on TiO2/WO3 photoanode and Cu nanowires cathode

Organic amines are regarded as high toxic, refractory chemicals due to the great damage on human body, and ecosystem. The treatment of organic amine wastewater involves the removal of total nitrogen and toxic organics simultaneously, which is one of the biggest difficulties in wastewater treatment. In this study, hazardous organic amine wastewater was purified by a photocatalytic fuel cell (PFC) with efficient nitrogen removal and organic degradation, and its chemical energy was recovered simultaneously based on hydroxyl radical (HO·) and chlorine radical (Cl·) reaction in a novel TiO₂/WO₃ and 3D Cu nanowires modified Cu foam (CuNWs/CF) system. TiO₂/WO₃ heterojunction as photoanode provided rapid charge separation and good stability, and the composite of poly-Si enhanced the light harvest and charge transfer. HO· played critical role in degrading organic amines, while Cl· was responsible for selectively oxidizing amine group or NH₄⁺ to N₂. Besides, trace amount of NO₂^- and NO₃^- formed by over-oxidation was eliminated on CuNWs/CF cathode due to large specific surface area and fast charge transfer. Moderate Cl^- concentration and initial pH had vital influence on strengthening Cl· and HO· generation in the system, and the optimal conditions were 50 mM NaCl and pH = 7. For methylamine, ethylamine and dimethylamine wastewater, the system showed total nitrogen removal efficiency of 94.93%, 91.81%, 93.10% and total organic carbon removal of 58.47%, 53.57%, and 56.71% within 2 h, respectively. Moreover, the corresponding maximum power densities of 2.49, 2.40, 2.27 mW cm^-2 were also generated, respectively. The study proposes an efficient, sustainable method for the treatment of hazardous organic amine wastewater and simultaneous energy recovery.

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

Microbial fuel cells (MFCs) are an emerging technique presenting remarkable potential. In the current MFC, an electroactive biofilm anode was inoculated with activated sludge from a local municipal sewage treatment plant. The output voltage peaked at 0.60 V and 0.56 V in MFCs cultured with 2-chlorophenol (MFC-2-CP) and 2,4-dichlorophenol (MFC-2,4-DCP), respectively. The degradation and mineralization efficiency in MFC-2-CP were 100.0% and 82.0%, respectively. Based on the bacterial 16S rRNA gene sequence analysis, abundant Acinetobacter and Azospirillum existed during both the bioelectricity and biodegradation stages in MFC-2-CP, but different patterns were exhibited in MFC-2,4-DCP. The electrogenic bacteria relied on the electron transfer pathway of nicotinamide adenine dinucleotide dehydrogenase, succinate dehydrogenase and terminal oxidase, while the electrons were transferred to the extracellular electrode by cytochrome C, riboflavin, degradation products of CPs and flagella. 2-CP and 2,4-DCP were biodegraded into less toxic cyclohexanol via dichlorination, hydroxylation, and hydrogenation; hereafter, the ring was opened to generate long-chain hydrocarbons, and finally mineralized into CO₂ and H₂O. This work provided a new strategy for MFCs in power generation and contaminant treatment.

Resorcinol as a highly efficient aromatic electron donor in bioelectrochemical system

Bioelectrochemical systems (BESs) have been known as a promising technology for accelerating aromatic contaminants degradation and energy recovery. However, most existing studies concentrate on aromatics metabolized through a benzoyl-CoA pathway while those metabolized through other pathways are limited. In this work, resorcinol, a typical aromatic contaminant as well as a key central intermediate (other than benzoyl-CoA) involved in aromatics anaerobic biodegradation, was studied in BESs. Unlike the general impression of the relatively poor organic-to-current performance in the aromatics driven BESs, high efficiencies for resorcinol-fed BESs were observed with a current density and coulombic efficiency of up to 0.26 ± 0.05 mAcm^-2 and 74.3 ± 10.7%, respectively. The higher performance likely correlates to the readily fermentable property of resorcinol. Analysis of microbial communities in the biofilm suggests a syntrophic interaction between resorcinol-degrading bacteria (RDB) and anode-respiring bacteria (ARB) was involved in current generation. Additional tests involving the removal of accumulated acetate through fast resorcinol feeding indicates that a mechanism based on direct utilization of resorcinol for current generation may also exist. This study extends the knowledge for the fate of aromatics in BESs and indicates that aromatics entering into the resorcinol metabolic pathway can be treated efficiently with good energy recovery efficiency in BESs.

Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes

Chlorophenols (CPs) are highly toxic and refractory contaminants which widely exist in various environments and cause serious harm to human and environment health and safety. This review provides comprehensive information on typical CPs biodegradation technologies, the most green and benign ones for CPs removal. The known aerobic and anaerobic degradative bacteria, functional enzymes, and metabolic pathways of CPs as well as several improving methods and critical parameters affecting the overall degradation efficiency are systematically summarized and clarified. The challenges for CPs mineralization are also discussed, mainly including the dechlorination of polychlorophenols (poly-CPs) under aerobic condition and the ring-cleavage of monochlorophenols (MCPs) under anaerobic condition. The coupling of functional materials and degraders as well as the operation of sequential anaerobic-aerobic bioreactors and bioelectrochemical system (BES) are promising strategies to overcome some current limitations. Future perspective and research gaps in this field are also proposed, including the further understanding of microbial information and the specific role of materials in CPs biodegradation, the potential application of innovative biotechnologies and new operating modes to optimize and maximize the function of the system, and the scale-up of bioreactors towards the efficient biodegradation of CPs.

Microbial Interactions Drive the Complete Catabolism of the Antibiotic Sulfamethoxazole in Activated Sludge Microbiomes

Microbial communities are believed to outperform monocultures in the complete catabolism of organic pollutants via reduced metabolic burden and increased robustness to environmental challenges; however, the interaction mechanism in functional microbiomes remains poorly understood. Here, three functionally differentiated activated sludge microbiomes (S1: complete catabolism of sulfamethoxazole (SMX); S2: complete catabolism of the phenyl part of SMX ([phenyl]-SMX) with stable accumulation of its heterocyclic product 3-amino-5-methylisoxazole (3A5MI); A: complete catabolism of 3A5MI rather than [phenyl]-SMX) were enriched. Combining time-series cultivation-independent microbial community analysis, DNA-stable isotope probing, molecular ecological network analysis, and cultivation-dependent function verification, we identified key players involved in the SMX degradation process. Paenarthrobacter and Nocardioides were primary degraders for the initial cleavage of the sulfonamide functional group (-C-S-N- bond) and 3A5MI degradation, respectively. Complete catabolism of SMX was achieved by their cross-feeding. The co-culture of Nocardioides, Acidovorax, and Sphingobium demonstrated that the nondegraders Acidovorax and Sphingobium were involved in the enhancement of 3A5MI degradation. Moreover, we unraveled the internal labor division patterns and connections among the active members centered on the two primary degraders. Overall, the proposed methodology is promisingly applicable and would help generate mechanistic, predictive, and operational understanding of the collaborative biodegradation of various contaminants. This study provides useful information for synthetic activated sludge microbiomes with optimized environmental functions.

Bioelectrochemical degradation of monoaromatic compounds: Current advances and challenges

Monoaromatic compounds (MACs) are typical refractory organic pollutants which are existing widely in various environments. Biodegradation strategies are benign while the key issue is the sustainable supply of electron acceptors/donors. Bioelectrochemical system (BES) shows great potential in this field for providing continuous electrons for MACs degradation. Phenol and BTEX (Benzene, Toluene, Ethylbenzene and Xylenes) can utilize anode to enhance oxidative degradation, while chlorophenols, nitrobenzene and antibiotic chloramphenicol (CAP) can be efficiently reduced to less-toxic products by the cathode. However, there still have several aspects need to be improved including the scale, electricity output and MACs degradation efficiency of BES. This review provides a comprehensive summary on the BES degradation of MACs, and discusses the advantages, future challenges and perspectives for BES development. Instead of traditional expensive dual-chamber configurations for MACs degradation, new single-chamber membrane-less reactors are cost-effective and the hydrogen generated from cathodes may promote the anode degradation. Electrode materials are the key to improve BES performance, approaches to increase the biofilm enrichment and conductivity of materials have been discussed, including surface modification as well as composition of carbon and metal-based materials. Besides, the development and introduction of functional microbes and redox mediators, participation of sulfur/hydrogen cycling may further enhance the BES versatility. Some critical parameters, such as the applied voltage and conductivity, can also affect the BES performance, which shouldn't be overlooked. Moreover, sequential cathode-anode cascaded mode is a promising strategy for MACs complete mineralization.

Turning harmful algal biomass to electricity by microbial fuel cell: A sustainable approach for waste management

Effective utilization of harmful algal biomass from eutrophic lakes is required for sustainable waste management and circular bioeconomy. In this study, Microcystis aeruginosa derived biomass served as an electron donor in the microbial fuel cell (MFC) for waste treatment and electricity generation. Bioelectrochemical performance of MFC fed with microalgae (MFC-Algae) was compared with MFC fed with a commercial substrate (MFC-Acetate). Complete removal of microcystin-LR (MC-LR) and high chemical oxygen demand (COD) removal efficiency (67.5 ± 1%) in MFC-Algae showed that harmful algal biomass could be converted into bioelectricity. Polarization curves revealed that MFC-Algae delivered the maximum power density (83 mW/m²) and current density (672 mA/m²), which was 43% and 45% higher than that of MFC-Acetate respectively. Improved electrochemical performance and substantial coulombic efficiency (7.6%) also verified the potential use of harmful algal biomass as an alternate MFC substrate. Diverse microbial community profiles showed the substrate-dependent electrogenic activities in each MFC. Biodegradation pathway of MC-LR by anodic microbes was also explored in detail. Briefly, a sustainable approach for on-site waste management of harmful algal biomass was presented, which was deprived of transportation and special pretreatments. It is anticipated that current findings will help to pave the way for practical applications of MFC technology.

Anoxic-biocathode microbial desalination cell as a new approach for wastewater remediation and clean water production

Bioelectrochemical systems are emerging as a promising and friendly alternative to convert the energy stored in wastewater directly into electricity by microorganisms and utilize it in situ to drive desalination. To better understand such processes, we propose the development of an anoxic biocathode microbial desalination Cell for the conversion of carbon- and nitrogen-rich wastewaters into bioenergy and to perform salt removal. Our results demonstrate a power output of 0.425 W m^-3 with desalination, organic matter removal and nitrate conversion efficiencies of 43.69, 99.85 and 92.11% respectively. Microbiological analysis revealed Proteobacteria as the dominant phylum in the anode (88.45%) and biocathode (97.13%). While a relatively higher bacterial abundance was developed in the anode chamber, the biocathode showed a greater variety of microorganisms, with a predominance of Paracoccus (73.2%), which are related to the denitrification process. These findings are promising and provide new opportunities for the development and application of this technology in the field of wastewater treatment to produce cleaner water and conserve natural resources.

Performance improvement and model of a bio-electrochemical system built-in up-flow anaerobic sludge blanket for treating β-lactams pharmaceutical wastewater under different hydraulic retention time

This paper focused on the performance of an up-flow bio-electrochemical system (UBES) for treating the β-lactams pharmaceutical wastewater under different hydraulic retention time (HRT). UBES is added a bio-electrochemical system below the three-phase separator based on up-flow anaerobic sludge blanket (UASB). Comparisons of chemical oxygen demand (COD) removal, accumulation of volatile fatty acid (VFA) and biogas production were investigated during the 316-day operation time, which was divided into five parts with HRT of 96 h, 72 h, 48 h, 36 h and 20 h, respectively. The average COD removal efficiency of UBES could reach 45.3 ± 7.5%, 72.2 ± 3.5%, 86.2 ± 1.4%, 75.9 ± 1.8% and 64.9 ± 2.0%, which were 2.4%, 6.1%, 6.4%, 10.2%, 8.7% more than those of UASB under different HRTs, respectively. Biogas production as well as methane production of UBES were significantly higher than UASB during the whole changing HRT process, the maximum methane yield of UBES was 0.31 ± 0.07 L/gCOD_removed. Accumulation of VFA in UBES was discovered to be lighter than UASB, the minimum average VFA in UBES was 131.9 ± 18.5 mg/L, which was obtained at HRT of 48 h. These results proved that UBES can slow down the inhibition of VFA on methanogens to make sure a good performance on COD removal and biogas production than UASB. Moreover, the relationships between methane production and VFA, biogas production and COD consumption were analyzed. A cost and benefit were analyzed for evaluating the potential of UBES in practical applications compared with UASB. Finally, radial basis function neural network (RBFNN) model was developed and fitted well with the experimental data, which can be employed to predict the effluent quality of the UBES and UASB.

Micro-aeration in anode chamber promotes p-nitrophenol degradation and electricity generation in microbial fuel cell

Biodegradation of recalcitrant organic compounds in microbial fuel cell (MFC) is limited, due to its strong electron affinity and persisted in anaerobic condition. In this study, Pseudomonas monteilii LZU-3 degraded p-nitrophenol (PNP) and generated current at 100 mg L^-1 of PNP in anode MFC with the addition of oxygen. The highest PNP degradation was 4, 37.75, and 99.89% in anaerobic, aerobic, and aerated anode of MFC respectively, at 7 h. The maximum voltage generation in aerated anode was 183 mV, which was comparatively higher than aerobic (150 mV) and anaerobic (68 mV). The qRT-PCR results confirmed that the oxygenase genes in strain LZU-3 were up-regulated from 17.51 to 39.39-fold at 1.6-4.5 mg L^-1 of oxygen concentrations resulted in PNP degradation in anode MFC. This study demonstrated that supplementation of oxygen into the anode MFC might be a potential approach for biodegradation of recalcitrant compounds and electricity generation.

Investigating effect of proton-exchange membrane on new air-cathode single-chamber microbial fuel cell configuration for bioenergy recovery from Azorubine dye degradation

One of the biggest challenges of using single-chamber microbial fuel cells (MFCs) that utilize proton-exchange membrane (PEM) air cathode for bioenergy recovery from recalcitrant organic compounds present in wastewater is mainly attributed to their high internal resistance in the anodic chamber of the single microbial fuel cell (MFC) configurations. The high internal resistance is due to the small surface area of the anode and cathode electrodes following membrane biofouling and pH splitting conditions as well as substrate and oxygen crossover through the membrane pores by diffusion. To address this issue, the fabrication of new PEM air-cathode single-chamber MFC configuration was investigated with inner channel flow open assembled with double PEM air cathodes (two oxygen reduction activity zones) coupled with spiral-anode MFC (2MA-CsS-AMFC). The effect of various proton-exchange membranes (PEMs), including Nafion 117 (N-117), Nafion 115 (N-115), and Nafion 212 (N-212) with respective thicknesses of 183, 127, and 50.08 μ, was separately incorporated into carbon cloth as PEM air-cathode electrode to evaluate their influences on the performance of the 2MA-CsS-AMFC configuration operated in fed-batch mode, while Azorubine dye was selected as the recalcitrant organic compound. The fed-batch test results showed that the 2MA-CsS-AMFC configuration with PEM N-115 operated at Azorubine dye concentration of 300 mg L^-1 produced the highest power density of 1022.5 mW m^-2 and open-circuit voltage (OCV) of 1.20 V coupled with enhanced dye removal (4.77 mg L h^-1) compared to 2MA-CsS-AMFCs with PEMs N-117 and N-212 and those in previously published data. Interestingly, PEM 115 showed remarkable reduction in biofouling and pH splitting. Apart from that, mass transfer coefficient of PEM N-117 was the most permeable to oxygen (K_O = 1.72 × 10^-4 cm s^-1) and PEM N-212 was the most permeable membrane to Azorubine (K_A = 7.52 × 10^-8 cm s^-1), while PEM N-115 was the least permeable to both oxygen (K_O = 1.54 × 10^-4) and Azorubine (K_A = 7.70 × 10^-10). The results demonstrated that the 2MA-CsS-AMFC could be promising configuration for bioenergy recovery from wastewater treatment under various PEMs, while application of PEM N-115 produced the best performance compared to PEMs N-212 and N-117 and those in previous studies of membrane/membrane-less air-cathode single-chamber MFCs that consumed dye wastewater.

Simultaneous debromination and mineralization of bromophenol in an up-flow electricity-stimulated anaerobic system

Due to highly recalcitrant and toxicological nature of halogenated organic compounds, conventional anaerobic dehalogenation is often limited by low removal rate and poor process stability. Besides, the reduction intermediates or products formed during dehalogenation process, which are still toxic, required further energy-intensive aerobic post-treatment. In this study, an up-flow electricity-stimulated anaerobic system (ESAS) was developed by installing cathode underneath and anode above to realize simultaneous anaerobic debromination and mineralization of 4-bromophenol (4-BP). When cathode potential was -600 mV, high TOC removal efficiency (98.78 ± 0.96%), complete removal of 4-BP and phenol could be achieved at 4-BP loading rate of 0.58 mol m^-3 d^-1, suggesting debrominated product of 4-BP from cathode (i.e., phenol) would be utilized as the fuel by the bioanode of ESAS. Under high 4-BP loading rate (2.32 mol m^-3 d^-1) and low electron donor dosage (4.88 mM), 4-BP could be completely removed at acetate usage ratio as low as 4.21 ± 1.42 mol acetate mol^-1 4-BP removal in ESAS, whereas only 13.45 ± 1.38% of 4-BP could be removed at acetate usage ratio as high as 31.28 ± 3.38 mol acetate mol^-1 4-BP removal in control reactor. Besides, electrical stimulation distinctly facilitated the growth of various autotrophic dehalogenation species, phenol degradation related species, fermentative species, homoacetogens and electrochemically active species in ESAS. Moreover, based on the identified intermediates and the bacterial taxonomic analysis, possible metabolism mechanism involved in enhanced anaerobic debromination and mineralization of 4-BP in ESAS was proposed.

Effects of glucose and starch on the toxicity of nitrobenzene to plants and microbes in constructed wetlands

Photosynthetic pigment content, antioxidant enzyme activities of plants, microbial enzyme activities and community structure were analyzed to investigate the effects of glucose and starch on the toxicity of nitrobenzene (NB) to plants and microbes in constructed wetlands (CWs). As the influent NB concentration increased from 10 mg/L to 100 mg/L, the NB removal efficiency of the blank group decreased from 97.1% to 75.02%. However, the NB removal efficiencies of the external carbon source groups were maintained at nearly 100%. External carbon sources accelerated the transformation process of NB to aniline (AN), thus decreasing NB toxicity to the microbes and plants. When the influent NB concentration reached 100 mg/L, the NB removal rates and NB reductase activities of the external carbon source groups were 2.4 times and 4 times higher, respectively, than those of the blank group. Most of the dominant genera found in the three CWs could reduce nitroaromatics to the corresponding aromatic amines according to the results of high-throughput sequencing. The performance of NB removal in the CWs indicated the potential of CWs for NB treatment and the necessity of external carbon sources under high NB concentrations.

Combined photoelectrocatalytic microbial fuel cell (PEC-MFC) degradation of refractory organic pollutants and in-situ electricity utilization

A new photoelectrocatalytic (PEC) and microbial fuel cell (MFC) process was developed and applied to simultaneously remove refractory organic pollutants (i.e., phenol and aniline) from wastewater while recovering energy for in-situ utilization. The current generated by the MFC process was applied to drive the PEC reaction. Compared with single PEC or MFC processes, the PEC-MFC combined process showed higher pollutant and chemical oxygen demand (COD) removal capacities and electricity production. Over 95% of the phenol or aniline was removed by these process, even at high initial concentrations. The COD removal efficiencies for phenol and aniline were ca. 96% (from 700 to 29 mg L^-1) and 70% (from 165 to 49 mg L^-1), respectively. Although the PEC process showed a limited contribution to phenol and aniline removals (16.5% and 43%, respectively), the utilization of PEC-treated phenol or aniline streams resulted in a MFC with higher voltage output, higher coulombic efficiency, maximal volumetric power density, and lower internal resistance as compared to untreated water. High-performance liquid chromatography coupled with mass spectrometry measurements revealed quinones/hydroquinones and low molecular weight organic acids to be produced as intermediates after the PEC process, which could improve the production of electricity in the MFC.

Bioelectricity generation using microalgal biomass as electron donor in a bio-anode microbial fuel cell

In this study, microalgal biomass waste (Chlorella regularis) was treated while simultaneously producing bioelectricity in a microbial fuel cell (MFC). Algal biomass was the sole electron donor and was enriched with easily biodegradable proteins (46%) and carbohydrates (22%). The generated power density was 0.86 W/m² and the columbic efficiency reached ∼61.5%.The power generation could be further increased to 1.07 W/m² by using a biomass waste concentration enhancement strategy with maximum chemical oxygen demand (COD) removal of ∼65.2%. Via direct comparison, the power generation and COD removal capability of the algal-fed MFC was close to that of the commercial acetate-fed MFC. The algae-fed MFC presented superior electrochemical characteristics that were attributed to the complicated composition of the biomass anolyte. It possessed a multiple anode respiring bacterial group and diverse microbial community. Hence, this study provides a new strategy for the utilization of microalgal biomass as a bioresource.

Simultaneous anaerobic and aerobic transformations of nitrobenzene

Aerobic biodegradation of nitrobenzene (NB) produces nitrophenol (NP), which has stronger toxicity than NB. Anaerobic biodegradation of NB produces aniline (AN), which has weaker toxicity, but is a dead-end product in anaerobic conditions. Accumulation of AN should be overcome by coupling anaerobic and aerobic transformations: NB is transformed to AN in an anaerobic zone of the bioreactor, and AN is then transformed in an aerobic zone. A vertical baffled bioreactor (VBBR) was employed for NB biodegradation with a controlled dissolved oxygen (DO) concentration. NB biodegradation was accelerated by simultaneous anaerobic and aerobic transformations, since AN was biotransformed by a mono-oxygenase reaction. Adding exogenous electron donor (acetate) enhanced NB removals when the DO concentration was ∼0.5 mg/L, because the donor accelerated mono-oxygenations of NB and AN. Coupling anaerobic and aerobic transformations can be a valuable strategy for biodegrading organic compounds that undergo aerobic and anaerobic biotransformations.

Micro-oxygen bioanode: An efficient strategy for enhancement of phenol degradation and current generation in mix-cultured MFCs

It is controversial to introduce oxygen into anode chamber as oxygen would decrease the CE (Coulombic efficiency) while it could also enhance the degradation of aromatics in microbial fuel cell (MFCs). Therefore, it is important to balance the pros and cons of oxygen in aromatics driven MFCs. A R_MO (micro-oxygen bioanode MFC) was designed to determine the effect of oxygen on electricity output and phenol degradation. The R_MO showed 6-fold higher phenol removal efficiency, 4-fold higher current generation than the R_AN (anaerobic bioanode MFC) at a cost of 26.9% decline in CE. The Zoogloea and Geobacter, which account for phenol degradation and current generation, respectively, were dominated in the R_MO bioanode biofilm. The biomass also showed great difference between R_MO and R_AN (114.3 ± 14.1 vs. 2.2 ± 0.5 nmol/g). Therefore, different microbial community, higher biomass as well as the different degradation pathway were suggested as reasons for the better performance in R_MO.

Enhanced performance and microbial community analysis of bioelectrochemical system integrated with bio-contact oxidation reactor for treatment of wastewater containing azo dye

Feasibility and superiority of the bioelectrochemical system integrated with biocontact oxidation (BES-BCO) for degradation and/or mineralization of azo dyes have been confirmed. In this study, the effects of hydraulic retention time (HRT), applied voltage, and dissolved oxygen (DO) concentration at the bioanode on the performance of BES-BCO and traditional BES were investigated. Using the response surface methodology, the optimum values of HRT, applied voltage, and DO concentration at the bioanode of BES-BCO were investigated to obtain the maximum decolouration and COD removal efficiency and minimum specific energy consumption (SEC). The microbial community structure in BES-BCO was studied for analyzing the change following the introduction of oxygen. The optimised solution was an applied voltage of 0.59V, HRT of 12h, and DO concentration of 0.96mg/L at the bioanode. Under such conditions, the DE, COD removal efficiency, and SEC values were 94.62±0.63%, 89.12±0. 32%, and 687.57±3.86J/g, respectively. In addition, after changing from BES to BES-BCO, the bacterial community structure of the bioanode underwent significant changes. Several aerobic aniline-degrading bacteria and anode-respiration bacteria (ARB) were found to dominate the community of the anode biofilm. The results showed that the removal of azo dye degradation by-products was closely correlated with the o-bioanode and the BCO bacterial community structure.

Effects of surface charge, hydrophilicity and hydrophobicity on functional biocathode catalytic efficiency and community structure

The bioelectrotransformation efficiency of various organic matters and corresponding electrode biofilm community formation as well as electron transfer efficiency in bioelectrochemical systems (BESs) with different modified electrodes has been extensively studied on the anode side. However, the effects of cathode interface characteristics towards the BESs bioelectrotransformation performance remain poorly understood. In this study, the nitrobenzene-reducing biocathode catalytic efficiency and community structure in response to different modified electrodes (control: hydrophobic and no charge; -SH: hydrophobic and single negative charge; -NH₂: hydrophilic and single positive charge -NH-NH₂: hydrophilic and double positive charges) were investigated. The biocathode transformation efficiency of nitrobenzene (NB) to aniline (AN) (E_NB-AN) was affected by the nature of electrode interface as well as the biocathode community formation and structure. Cathodes with hydrophilic surface and positive charges have performed well in the bioelectrotransformation experiments, and especially made an outstanding performance when inorganic NaHCO₃ was supplied as carbon source and cathode as the sole electron donor. Importantly, the hydrophilic surfaces with positive charges were dominated by the electroactive nitroaromatic reducers (Enterococcus, Desulfovibrio and Klebsiella) with the relative abundance as high as 72.20 ± 1.87% and 74.86 ± 8.71% for -NH₂ and -NH-NH₂ groups respectively. This could explain the higher E_NB-AN in the hydrophilic groups than that of the hydrophobic -SH modified group. This study provides new insights into the effects of electrode interface characteristics on the BESs biocathode performance and offers some suggestions for the future design for the improvement of bioelectroremediation performance.

Substantial enhancement of anaerobic pyridine bio-mineralization by electrical stimulation

Due to highly recalcitrant and toxicological nature of pyridine, the conventional anaerobic bioprocess is often limited by low removal rate and poor process stability. In this study, an electricity-assisted anaerobic system was developed in order to enhance biodegradation of pyridine from wastewater. The results showed that the performance and stability of the anaerobic reactor was remarkably improved for pyridine biodegradation with the applied direct current of 0.3 mA, where the efficiencies of pyridine and total organic carbon removal as well as NH₄⁺-N formation were as high as 100.0%, 96.1 ± 1.2% and 60.1 ± 2.1% respectively. The compact biofilm due to electrical stimulation as well as the microaerobic environment in the bioanode might promote pyridine bio-mineralization in the anaerobic reactor. Moreover, the species related to pyridine biodegradation (Desulfovibrio, Dokdonella, Hydrogenophaga, and Paracoccus) were enriched in the anodic biofilm, which would be another reason for better reactor performance. This study demonstrated that electrical stimulation would be a potential alternative for the enhancement of pyridine removal from wastewater in anaerobic systems.

Sequential reduction/oxidation of azo dyes in a three-dimensional biofilm electrode reactor

By combining sequential anaerobic-aerobic reactor and penetrable cathode-anode operation, a novel anaerobic/aerobic sequencing three-dimensional biofilm electrode reactor (3D-BER) was developed to evaluate the degradation of azo dye reactive brilliant red X-3B (RBRX-3B). In the bottom cathodic region, anaerobic reductive conditions and H₂ were produced for the bioreduction of azo dyes; in the top anodic region, aerobic oxidative conditions and O₂ were produced for the mineralization of dye intermediates. Due to the supply of electrical power, electrons could be mediated via electrolysis of water or directly transfer between electrodes and microbe cells. The biofilm immobilized on the surface of the cathode utilized electrode or H₂ as electron donors and accelerated the rate of RBRX-3B reduction, and the decolorization rate was significantly increased 2.6-3.7 fold, reaching at 2.52-3.39 mol/m³/d at an energy consumption of 0.15 kWh/mol RBRX-3B. RBRX-3B was reductively cleaved into aromatic amines at the biocathode and these amines were effectively removed at the bioanode. Acute toxicity tests showed that the intermediates of RBRX-3B were more toxic when compared with the initial influent, and the 3D-BER effluent exhibited much lower toxicity (5% inhibition of bioluminescence of Vibrio fisheri) than the electrochemical and biological effluent (65% and 30% inhibition, respectively). These findings suggest the novel 3D-BER may provide a promising alternative to remove azo dyes in dyeing wastewater.

Microbial community composition and electricity generation in cattle manure slurry treatment using microbial fuel cells: effects of inoculum addition

Microbial fuel cell (MFC) is a sustainable technology to treat cattle manure slurry (CMS) for converting chemical energy to bioelectricity. In this work, two types of allochthonous inoculum including activated sludge (AS) and domestic sewage (DS) were added into the MFC systems to enhance anode biofilm formation and electricity generation. Results indicated that MFCs (AS + CMS) obtained the maximum electricity output with voltage approaching 577 ± 7 mV (~ 196 h), followed by MFCs (DS + CMS) (520 ± 21 mV, ~ 236 h) and then MFCs with autochthonous inoculum (429 ± 62 mV, ~ 263.5 h). Though the raw cattle manure slurry (RCMS) could facilitate electricity production in MFCs, the addition of allochthonous inoculum (AS/DS) significantly reduced the startup time and enhanced the output voltage. Moreover, the maximum power (1.259 ± 0.015 W/m²) and the highest COD removal (84.72 ± 0.48%) were obtained in MFCs (AS + CMS). With regard to microbial community, Illumina HiSeq of the 16S rRNA gene was employed in this work and the exoelectrogens (Geobacter and Shewanella) were identified as the dominant members on all anode biofilms in MFCs. For anode microbial diversity, the MFCs (AS + CMS) outperformed MFCs (DS + CMS) and MFCs (RCMS), allowing the occurrence of the fermentative (e.g., Bacteroides) and nitrogen fixation bacteria (e.g., Azoarcus and Sterolibacterium) which enabled the efficient degradation of the slurry. This study provided a feasible strategy to analyze the anode biofilm formation by adding allochthonous inoculum and some implications for quick startup of MFC reactors for CMS treatment.

Efficient treatment of aniline containing wastewater in bipolar membrane microbial electrolysis cell-Fenton system

Aniline-containing wastewater can cause significant environmental problems and threaten the humans's life. However, rapid degradation of aniline with cost-efficient methods remains a challenge. In this work, a novel microbial electrolysis cell with bipolar membrane was integrated with Fenton reaction (MEC-Fenton) for efficient treatment of real wastewater containing a high concentration (4460 ± 52 mg L^-1) of aniline. In this system, H₂O₂ was in situ electro-synthesized from O₂ reduction on the graphite cathode and was simultaneously used as source of OH for the oxidation of aniline wastewater under an acidic condition maintained by the bipolar membrane. The aniline was effectively degraded following first-order kinetics at a rate constant of 0.0166 h^-1 under an applied voltage of 0.5 V. Meanwhile, a total organic carbon (TOC) removal efficiency of 93.1 ± 1.2% was obtained, revealing efficient mineralization of aniline. The applicability of bipolar membrane MEC-Fenton system was successfully demonstrated with actual aniline wastewater. Moreover, energy balance showed that the system could be a promising technology for removal of biorefractory organic pollutants from wastewaters.

Polarity inversion of bioanode for biocathodic reduction of aromatic pollutants

The enrichment of specific pollutant-reducing consortium is usually required prior to the startup of biocathode bioelectrochemical system (BES) and the whole process is time consuming. To rapidly establish a non-specific functional biocathode, direct polar inversion from bioanode to biocathode is proposed in this study. Based on the diverse reductases and electron transfer related proteins of anode-respiring bacteria (ARB), the acclimated electrochemically active biofilm (EAB) may catalyze reduction of different aromatic pollutants. Within approximately 12 d, the acclimated bioanodes were directly employed as biocathodes for nitroaromatic nitrobenzene (NB) and azo dye acid orange 7 (AO7) reduction. Our results indicated that the established biocathode significantly accelerated the reduction of NB to aniline (AN) and AO7 to discolored products compared with the abiotic cathode and open circuit controls. Several microbes possessing capabilities of nitroaromatic/azo dye reduction and bidirectional electron transfer were maintained or enriched in the biocathode communities. Cyclic voltammetry highlighted the decreased over-potentials and enhanced electron transfer of biocathode as well as demonstrated the ARB Geobacter containing cytochrome c involved in the backward electron transfer from electrode to NB. This study offers new insights into the rapid establishment and modularization of functional biocathodes for the potential treatment of complicated electron acceptors-coexisting wastewaters.

Evaluation of anaerobic sludge volume for improving azo dye decolorization in a hybrid anaerobic reactor with built-in bioelectrochemical system

A hybrid anaerobic reactor with built-in bioelectrochemical system (BES) has been verified for efficiently treating mixed azo dye wastewater, yet still facing many challenges, such as uncertain reactor construction and insufficient electron donors. In this study, an up-flow hybrid anaerobic reactor with built-in BES was developed for acid orange 7 (AO7) containing wastewater treatment. Cathode and real domestic wastewater both served as electron donor for driving azo dye decolorization. The decolorization efficiency (DE) of AO7 (200 mg/L) in the hybrid reactor was 80.34 ± 2.11% with volume ratio between anaerobic sludge and cathode (VR_slu:cat) of 0.5:1 and hydraulic retention time (HRT) of 6 h, which was 15.79% higher than that in BES without sludge zone. DE was improved to 86.02 ± 1.49% with VR_slu:cat increased to 1:1. Further increase in the VR_slu:cat to 1.5:1 and 2:1, chemical oxygen demand (COD) removal efficiency was continuously improved to 28.78 ± 1.96 and 32.19 ± 0.62%, but there was no obvious DE elevation (slightly increased to 87.62 ± 2.50 and 90.13 ± 3.10%). BES presented efficient electron utilization, the electron usage ratios (EURs) in which fluctuated between 11.02 and 13.06 mol e^-/mol AO7. It was less than half of that in sludge zone of 24.73-32.06 mol e^-/mol AO7. The present work optimized the volume ratio between anaerobic sludge and cathode that would be meaningful for the practical application of this hybrid system.

Improving the extracellular electron transfer of Shewanella oneidensis MR-1 for enhanced bioelectricity production from biomass hydrolysate

Direct electricity production from biomass hydrolysate by microbial fuel cells (MFC) holds great promise for the development of the sustainable biomass industry.

Azo dye decolorization in an up-flow bioelectrochemical reactor with domestic wastewater as a cost-effective yet highly efficient electron donor source

A major challenge of employing bioelectrochemical system (BES) for reductively degrading recalcitrant contaminants in industrial wastewater is lacking sufficient electron donors. In this work, domestic wastewater (DW) was demonstrated to efficiently drive BES for implementing the decolorization of azo dye, acid orange 7 (AO7). Side benefit was the simultaneous treatment of DW. Decolorization efficiency in BES fed with DW (R_DW) was found to be comparable with that either fed with glucose (R_Glu) or acetate (R_Ac). Much lower reductant usage ratio was observed in R_DW. As a result, when the ratio of electron donors to azo dye decreased to 4.4 mol COD mol^-1 AO7, DE of R_DW kept over 90% while DEs of R_Ac and R_Glu were significantly dropped due to the insufficient electrons donation. Besides serving as electron donor, DW was proved to also provide some conductivity and buffer capacity. Accordingly, DE of R_DW was less deteriorated when fully removing the external buffer slats. This study comprehensively revealed the feasibility and superiority of DW as a cost-effective electron donor source in BES and brings this technology closer to the practice.

Microbial fuel cells as pollutant treatment units: Research updates

Microbial fuel cells (MFC) are a device that can convert chemical energy in influent substances to electricity via biological pathways. Based on the consent that MFC technology should be applied as a waste/wastewater treatment unit rather than a renewable energy source, this mini-review discussed recent R&D efforts on MFC technologies for pollutant treatments and highlighted the challenges and research and development needs. Owing to the low power density levels achievable by larger-scale MFC, the MFC should be used as a device other than energy source such as being a pollutant treatment unit.

Relieving the fermentation inhibition enables high electron recovery from landfill leachate in a microbial electrolysis cell

The energy value of the organic matter in landfill leachate can be captured with a microbial electrolysis cell (MEC), which oxidizes organic compounds at an anode and generates H₂gas at a cathode.

Increasing power density and dye decolorization of an X-3B-fed microbial fuel cell via TiO2 photocatalysis pretreatment

With pretreatment via photocatalysis, the output power density of MFC increased and more X-3B was removed.