Bioenergy generation and degradation pathway of phenanthrene and anthracene in a constructed wetland-microbial fuel cell with an anode amended with nZVI

Potentialities of manganese ore and iron-carbon particles for pharmaceuticals and personal care products removal in electroactive constructed wetland

This study explores the use of manganese ore, iron-carbon particles (Fe-C), and gravel as anode fillers in electroactive constructed wetlands (ECWs) to treat wastewater containing pharmaceuticals and personal care products (PPCPs) including ciprofloxacin (CIP), ofloxacin (OFL), and naproxen (NPX), while also assessing bioelectricity production. Although the presence of PPCPs reduced pollutant removal and electricity generation, ECWs outperformed conventional CWs. Specifically, Fe-C ECWs (FC-ECWs) achieved high COD and NPX removal efficiencies of 90.15 % and 62.25 %, respectively, along with the highest power density of 13.25 mW/m2. In contrast, manganese ore ECWs (Mn-ECWs) were more effective at removing NH4+-N, CIP, and OFL, with removal efficiencies of 42.08 %, 67.12 %, and 61.60 %, respectively. Notably, ECWs also facilitated the accumulation of qnrS resistance genes. FC-ECWs promoted both qnrS and intI gene expression, while Mn-ECWs inhibited the spread of antibiotic resistance genes (ARGs). Microbial analysis revealed that Firmicutes in Fe-C correlated with increased bioelectricity production. Additionally, genera like Enterobacter and Proteiniclasticum might act as ARG hosts. These findings highlight the innovation of using different anode fillers to optimize both pollutant removal and bioelectricity generation in ECWs, while also addressing the critical issue of ARG proliferation in wastewater treatment systems.

Advancements in constructed wetland technology: a state-of-the-art review on bio-electrochemical processes, tidal flow dynamics, and resilience to shock loads

This research article presents a comprehensive examination of recent advancements in constructed wetland technology, with a primary focus on bio-electrochemical processes, including electrolysis and microbial fuel cells, as well as the impact of tidal flow and shock loads on the constructed wetland performance. To date, extensive studies and in-depth analyses in these aspects are limited, highlighting a significant research gap. Electrolysis is explored for its efficacy in dephosphorization and denitrification, particularly under conditions of low carbon availability. Additionally, microbial fuel cell technology is investigated for its dual benefits of bioenergy generation and climate change mitigation. The tidal flow component is highlighted for its ability to create anaerobic, anoxic, and aerobic environments within and between cells, crucial for effective nitrogen removal. The study emphasizes the importance of constructed wetland resilience to shock loads, whether from increased discharge due to rainfall or heightened contaminant levels. The research employs bibliographic analysis and microbial community profiling and investigates factors such as nutrient removal, polarization curves, and the effects of flood/rest and flood/drain in tidal flow. Furthermore, the article delves into the impacts of hydraulic and organic shock loads on constructed wetland systems, providing a comprehensive overview of the current state of the field.

Electroactive biofilm communities in microbial fuel cells for the synergistic treatment of wastewater and bioelectricity generation

Increasing industrialization and urbanization have contributed to a significant rise in wastewater discharge and exerted extensive pressure on the existing natural energy resources. Microbial fuel cell (MFC) is a sustainable technology that utilizes wastewater for electricity generation. MFC comprises a bioelectrochemical system employing electroactive biofilms of several aerobic and anaerobic bacteria, such as Geobacter sulfurreducens, Shewanella oneidensis, Pseudomonas aeruginosa, and Ochrobacterum pseudiintermedium. Since the electroactive biofilms constitute a vital part of the MFC, it is crucial to understand the biofilm-mediated pollutant metabolism and electron transfer mechanisms. Engineering electroactive biofilm communities for improved biofilm formation and extracellular polymeric substances (EPS) secretion can positively impact the bioelectrochemical system and improve fuel cell performance. This review article summarizes the role of electroactive bacterial communities in MFC for wastewater treatment and bioelectricity generation. A significant focus has been laid on understanding the composition, structure, and function of electroactive biofilms in MFC. Various electron transport mechanisms, including direct electron transfer (DET), indirect electron transfer (IET), and long-distance electron transfer (LDET), have been discussed. A detailed summary of the optimization of process parameters and genetic engineering strategies for improving the performance of MFC has been provided. Lastly, the applications of MFC for wastewater treatment, bioelectricity generation, and biosensor development have been reviewed.

The introduction of nano zero-valent iron in constructed wetlands simultaneously enhanced the removal of perfluorooctanoic acid (PFOA) and nutrients

Constructed wetland (CW) serve as the final ecological barrier for hazardous materials entering the natural water environment. Due to the ecological toxicity and difficult bioutilization characteristics of perfluorooctanoic acid (PFOA) itself, CW technology faces great challenges in the field of PFOA remediation. In this study, nano zero-valent iron (nZVI) was introduced into CWs to explore the mechanism of the synergistic removal of PFOA and nutrients in nZVI-CW system. The results indicated that the addition of 10 mg/L nZVI improved the removal efficiency of CW for 1 and 10 mg/L PFOA, with an average removal rate increased by 3.53-8.70%. The transformation products in CW effluents were qualitatively detected using HPLC-Q-TOF-MS, suggesting that the degradation of PFOA may involve decarboxylation, hydrolysis, redox, elimination, substitution and intramolecular rearrangement processes. The presence of nZVI enhanced the average removal rates of NH4+-N, NO3--N and TP by 2.78-18.4% in CWs. The increase in key substrate enzyme activity confirmed the stimulating effect of nZVI on microbial activity. The addition of nZVI facilitated the growth and enrichment of hydroautotrophic denitrifying bacteria, nitrat-dependent iron-oxidizing bacteria, and dissimilatory iron-reducing bacteria. Two types of dissimilatory iron-reducing bacteria (Geobacter and Acinetobacter) may be potential PFOA-degrading bacteria. Additionally, signaling pathways related to carbohydrate metabolism, energy metabolism, and xenobiotic degradation and metabolism exhibited higher abundance in the nZVI treated groups.

From local bacterial communities to energy: application of microbial fuel cells in laboratory experimentation

It is well known that bacterial communities are an essential component to maintain the balance of terrestrial ecosystems due to the functions and services performed by microorganisms in the environment. The research seeking on alternative energy sources has shown that bacterial communities can bioconvert the chemical energy of an organic substrate into electrical energy, within devices known as microbial fuel cells. For this reason, this class project allows students of Biotechnology, Environmental Science, and Microbiology to apply the appropriate methodology to develop a class project throughout an environmental bacterial community capable of generating electrical energy.

Constructed wetland microbial fuel cell as enhancing pollutants treatment technology to produce green energy

The persistent challenge of water pollution, exacerbated by slow progress in ecofriendly technologies and accumulating pollutants, underscores the need for innovative solutions. Constructed Wetland Microbial Fuel Cell (CW-MFC) emerges as an intriguing environmental technology capable of adressing this issue by eliminating contaminants from wastewater while simultaneously producing green energy as an additional bonus. In recent years, CW-MFC technology has gained attention due to its sustainability and promising prospects for a circular waste-free industry. However, due to various technological and biological challenges, it has not yet achieved wide-scale application. This review examines the current state of CW-MFC technology and identifies both biotic and abiotic strategies for optimization through operational and structural improvements affecting biocomponents. Our review highlights several key findings: (1) Plants play an important role in reducing the system's inner resistance through mechanisms such as radial oxygen loss, evapotranspiration, and high photosynthetic flow, which facilitate electroactive bacteria and affect redox potential. (2) Plant characteristics such as root porosity, phloem and aerenchyma development, chlorophyll content, and plant biomass are key indicators of CW-MFC performance and significantly impact both pollutant removal and energy harvesting. (3) We expand the criteria for selecting suitable plants to include mesophytes and C3 pollutant-tolerant species, in addition to traditional aquatic and C4 plants. Additionally, the review presents several technical approaches that enhance CW-MFC efficiency: (1) design optimization, (2) use of novel materials, and (3) application of external electrical fields, aeration, light, and temperature adjustments. CW-MFCs are capable of nearly complete elimination of a wide range of contaminants, including organic matter (84 % ± 10), total nitrogen (80 % ± 7) and phosphorus (79 % ± 18) compounds, metals (86 % ± 10), pharmaceuticals (87 % ± 7), dyes (90 % ± 8), and other complex pollutants, while generating green energy. We hope our findings will be useful in optimizing CW-MFC design and providing insights for researchers aiming to advance the technology and facilitate its future scaling.

Efficient degradation of carbamazepine and metagenomic investigations of anodic biofilm in microbial fuel cells

Environmental contamination with carbamazepine is a considerable global problem. In this study, two-compartment microbial fuel cells (MFCs) were constructed to investigate the degradation performance of carbamazepine, and the degradation mechanism was further explored by using metagenomic analysis. The results showed that MFCs exhibited excellent carbamazepine removal performance and also generated electricity. The removal rate of carbamazepine reached 73.56% over the 72-h operation period, which was 3.09 times higher than that of the traditional anaerobic method, and the peak voltage of the MFCs could reach 416 mV. Metagenomics revealed significant differences in microbial community composition between MFCs and the traditional anaerobic method (p < 0.05), and Proteobacteria (81.57%) was predominant bacterial phyla during the degradation of carbamazepine by MFCs. Among them, the microbial communities at the genus level were mainly composed of Pseudomonas, Pusillimonas, Burkholderia, Stenotrophomonas, Methyloversatilis and Nitrospirillum. Kyoto Encyclopedia of genes and genomes (KEGG) metabolic pathway analysis showed that the number of genes related to carbon and nitrogen metabolism increased by 85.12% and 142.25%, respectively. Importantly, a greater number of genes of microbial grown on the surface of anode were assigned to denitrification and the degradation of aromatic compounds. This research provides a cost-effective method for treating wastewater contaminated with carbamazepin.

Modified basalt fiber filled in constructed wetland-microbial fuel cell: Comparison of performance and microbial impacts under PFASs exposure

Basalt fiber (BF) with modification of iron (Fe-MBF) and calcium (Ca-MBF) were filled into constructed wetland-microbial fuel cell (CW-MFC) for innovative comparison of improved performance under perfluorooctanoic acid (PFOA) exposure. More enhancement on nitrogen and phosphorus removal was observed by Fe-MBF than Ca-MBF, with significant increase of ammonium (NH4+-N) removal by 3.36-5.66 % (p < 0.05) compared to control, even under PFOA stress. Markedly higher removal efficiency of PFOA by 4.76-8.75 % (p < 0.05) resulted from Fe-MBF, compared to Ca-MBF and control BF groups. Besides, superior electrochemical performance was found in Fe-MBF group, with maximum power density 28.65 % higher than control. Fe-MBF caused higher abundance of dominant microbes on electrodes ranged from phylum to family. Meanwhile, ammonia oxidizing bacteria like Nitrosomonas was more abundant in Fe-MBF group, which was positively correlated to NH4+-N and total nitrogen removal. Some other functional genera involved in denitrification and phosphorus-accumulation were enriched by Fe-MBF on electrodes and MBF carrier, including Dechloromonas, Candidatus_Competibacter, and Pseudomonas. Additionally, there were more biomarkers in Fe-MBF group, like Pseudarcobacter and Acidovorax, conducive to nitrogen and iron cycling. Most functional genes of nitrogen, carbon, and sulfur metabolisms were up-regulated with Fe-MBF filling, causing improvement on nitrogen removal.

Simultaneous removal of phenanthrene and Pb using novel PPG-CNTs-nZVI beads

PPG-CNTs-nZVI bead was synthesized by polyvinyl alcohol, pumice, carbon nanotube, and guar gum-nanoscale zero-valent iron to be applied on simultaneously removal of polycyclic aromatic hydrocarbons (PAHs; phenanthrene) and heavy metals (Pb2+) via adsorption. The individual and simultaneous removal efficiency of phenanthrene and Pb2+ using the PPG-CNTs-nZVI beads was evaluated with a range of initial concentrations of these two pollutants. The kinetics and isotherms of phenanthrene and Pb2+ adsorption by the PPG-CNTs-nZVI beads were also determined. The PPG-CNTs-nZVI beads show reasonably high phenanthrene adsorption capacities (up to 0.16 mg/g), and they absorbed 85% of the phenanthrene (initial concentration 0.5 mg/L) in 30 min. High Pb2+ adsorption capabilities were also demonstrated by the PPG-CNTs-nZVI beads (up to 11.6 mg/g). The adsorption fits the Langmuir model better than the Freundlich model. The adsorption still remained stable with various ionic strength circumstances and a wide pH range (2-5). Additionally, the co-adsorption of phenanthrene and Pb2+ by the PPG-CNTs-nZVI beads resulted in synergistic effects. Particularly, phenanthrene-Pb2+ complex formation via π-cation interactions demonstrated a greater affinity than phenanthrene or Pb2+ alone. The present findings suggest that PPG-CNTs-nZVI beads may be effective sorbents for the simultaneous removal of PAHs and heavy metals from contaminated waters.

Biochar imparted constructed wetlands (CWs) for enhanced biodegradation of organic and inorganic pollutants along with its limitation

The remediation of polluted soil and water stands as a paramount task in safeguarding environmental sustainability and ensuring a dependable water source. Biochar, celebrated for its capacity to enhance soil quality, stimulate plant growth, and adsorb a wide spectrum of contaminants, including organic and inorganic pollutants, within constructed wetlands, emerges as a promising solution. This review article is dedicated to examining the effects of biochar amendments on the efficiency of wastewater purification within constructed wetlands. This comprehensive review entails an extensive investigation of biochar's feedstock selection, production processes, characterization methods, and its application within constructed wetlands. It also encompasses an exploration of the design criteria necessary for the integration of biochar into constructed wetland systems. Moreover, a comprehensive analysis of recent research findings pertains to the role of biochar-based wetlands in the removal of both organic and inorganic pollutants. The principal objectives of this review are to provide novel and thorough perspectives on the conceptualization and implementation of biochar-based constructed wetlands for the treatment of organic and inorganic pollutants. Additionally, it seeks to identify potential directions for future research and application while addressing prevailing gaps in knowledge and limitations. Furthermore, the study delves into the potential limitations and risks associated with employing biochar in environmental remediation. Nevertheless, it is crucial to highlight that there is a significant paucity of data regarding the influence of biochar on the efficiency of wastewater treatment in constructed wetlands, with particular regard to its impact on the removal of both organic and inorganic pollutants.

Urban wastewater oxidation by bioelectrochemical systems: To what extent does the inoculum matter?

Bioelectrochemical systems offer an environmental-friendly alternative to activated sludge for future wastewater treatment but have not yet reached technological maturity. This study aims to assess the long-term influence of the inoculation strategy on real urban wastewater treatment by bioelectrochemical systems, focusing on both process performances and biofilm assembly dynamics. Four inoculation strategies were investigated in triplicates during six consecutive batches to treat primary clarifier effluent at lab scale. At the studied anodic potential (0.05 vs SHE), no long-term impact of the inoculation strategy on the performances was observed. Indeed, after three batches, electrochemical (88.0 ± 3.9 % coulombic efficiencies) and treatment performances (30.8 ± 3.9 % COD removals) converged for all inoculation strategies. Consistently, the microbial compositions of the different biofilms converged, with selection being the main assembly process. For larger scale bioelectrochemical reactors, the use of wastewater as both substrate and inoculum would be the most convenient choice, since the other inoculation strategies only displayed short-term effects.

Effects of pH on simultaneous Cr(VI) and p-chlorophenol removal and electrochemical performance in Leersia hexandra constructed wetland-microbial fuel cell

Cr(VI) and p-chlorophenol (4-CP) are common pollutants in the aquatic environment but are difficult to degrade and have complex toxic effects. A downflow Leersia hexandra microbial fuel cell (DLCW-MFC) system was constructed to purify Cr(VI) and 4-CP polluted wastewater, as well as to investigate the effects of different pHs on Cr(VI) and 4-CP removal, electrochemical performance, physiological and biochemical responses, and Cr enrichment status of L. hexandra. The results showed that the DLCW-MFC had the highest Cr(VI) and 4-CP removal rates at pH 6.5, which were 99.0% and 78.6%, respectively. At the same time, 543 mV output voltage and 72.25 mW/m2 power density of the system were generated at pH 6.5, which were better than those at pH 7.4 and pH 5.8. The electrochemical performance result showed that pH 6.5 enhanced charge transfer ability and ion diffusion ability of the system. pH 6.5 also promoted growth and photosynthesis, and enhanced the Cr enrichment capacity (4.56 mg/10 plants) of L. hexandra. These results demonstrate that pH 6.5 was the optimum pH for the DLCW-MFC synchronous treatment of Cr(VI) and 4-CP as well as the generation of electricity. The DLCW-MFC designed in this study will provide a reference for purifying polluted wastewater and generating electricity.

Microbial electrochemical system: an emerging technology for remediation of polycyclic aromatic hydrocarbons from soil and sediments

Worldwide industrialization and other human activities have led to a frightening stage of release of hazardous, highly persistent, toxic, insoluble, strongly adsorbed to the soil and high molecular weight ubiquitous polycyclic aromatic hydrocarbons (PAHs) in soils and sediments. The various conventional remediation methods are being used to remediate PAHs with certain drawbacks. Time taking process, high expenditure, excessive quantities of sludge generation, and various chemical requirements do not only make these methods outdated but produce yet much resistant and toxic intermediate metabolites. These disadvantages may be overcome by using a microbial electrochemical system (MES), a booming technology in the field of bioremediation. MES is a green remediation approach that is regulated by electrochemically active microorganisms at the electrode in the system. The key advantage of the system over the conventional methods is it does not involve any additional chemicals, takes less time, and generates minimal sludge or waste during the remediation of PAHs in soils. However, a comprehensive review of the MES towards bioremediation of PAHs adsorbed in soil and sediment is still lacking. Therefore, the present review intended to summarize the recent information on PAHs bioremediation, application, risks, benefits, and challenges based on sediment microbial fuel cell and microbial fuel cell to remediate mount-up industrial sludge, soil, and sediment rich in PAHs. Additionally, bio-electrochemically active microbes, mechanisms, and future perspectives of MES have been discussed.

Phenanthrene removal from a spent sediment washing solution in a continuous-flow stirred-tank reactor

The issue of polycyclic aromatic hydrocarbons (PAHs) is widespread in marine sediments involving ecological systems and human health. Sediment washing (SW) has proven to be the most effective remediation approach for sediments polluted by PAHs, such as phenanthrene (PHE). However, SW still raises waste handling concerns due to a considerable amount of effluents generated downstream. In this context, the biological treatment of a PHE- and ethanol-containing spent SW solution can represent a highly efficient and environmentally-friendly strategy, but its knowledge is still scarce in scientific literature and no studies have so far been conducted in continuous mode. Therefore, a synthetic PHE-polluted SW solution was biologically treated in a 1 L aerated continuous-flow stirred-tank reactor for 129 days by evaluating the effect of different pH values, aeration flowrates and hydraulic retention times as operating parameters over five successive phases. A PHE removal efficiency of up to 75-94% was achieved by an acclimated PHE-degrading consortium mainly composed of Proteobacteria, Bacteroidota and Firmicutes phyla through biodegradation following the adsorption mechanism. PHE biodegradation, mainly occurring via the benzoate route due to the presence of PAH-related-degrading functional genes and a phthalate accumulation up to 46 mg/L, was also accompanied by a reduction of dissolved organic carbon and ammonia nitrogen above 99% in the treated SW solution.

The race between classical microbial fuel cells, sediment-microbial fuel cells, plant-microbial fuel cells, and constructed wetlands-microbial fuel cells: Applications and technology readiness level

Microbial fuel cell (MFC) is an interesting technology capable of converting the chemical energy stored in organics to electricity. It has raised high hopes among researchers and end users as the world continues to face climate change, water, energy, and land crisis. This review aims to discuss the journey of continuously progressing MFC technology from the lab to the field so far. It evaluates the historical development of MFC, and the emergence of different variants of MFC or MFC-associated other technologies such as sediment-microbial fuel cell (S-MFC), plant-microbial fuel cell (P-MFC), and integrated constructed wetlands-microbial fuel cell (CW-MFC). This review has assessed primary applications and challenges to overcome existing limitations for commercialization of these technologies. In addition, it further illustrates the design and potential applications of S-MFC, P-MFC, and CW-MFC. Lastly, the maturity and readiness of MFC, S-MFC, P-MFC, and CW-MFC for real-world implementation were assessed by multicriteria-based assessment. Wastewater treatment efficiency, bioelectricity generation efficiency, energy demand, cost investment, and scale-up potential were mainly considered as key criteria. Other sustainability criteria, such as life cycle and environmental impact assessments were also evaluated.

Recovery of electron and carbon source from agricultural waste corncob by microbial electrochemical system to enhance wastewater denitrification

The denitrification process in wastewater treatment plants (WWTPs) is limited by insufficient carbon sources. Agricultural waste corncob was investigated for its feasibility as a low-cost carbon source for efficient denitrification. The results showed that the corncob as the carbon source exhibited a similar denitrification rate (19.01 ± 0.03 gNO₃^--N/m³d) to that of the traditional carbon source sodium acetate (19.13 ± 0.37 gNO₃^--N/m³d). When filling corncob into a microbial electrochemical system (MES) three-dimensional anode, the release of corncob carbon sources was well controlled with an improved denitrification rate (20.73 ± 0.20 gNO₃^--N/m³d). Carbon source and electron recovered from corncob led to autotrophic denitrification and heterotrophic denitrification occurred in the MES cathode, which synergistically improved the denitrification performance of the system. The proposed strategy for enhanced nitrogen removal by autotrophic coupled with heterotrophic denitrification using agricultural waste corncob as the sole carbon source opened up an attractive route for low-cost and safe deep nitrogen removal in WWTPs and resource utilization for agricultural waste corncob.

Sustained-release nitrate combined with microbial fuel cell: A novel strategy for PAHs and odor removal from sediment

Nitrate addition is a biostimulation technique that can improve both the oxidation of acid volatile sulfide (AVS) through autotrophic denitrification and the biodegradation of polycyclic aromatic hydrocarbons (PAHs) via heterotrophic denitrification. However, during the remediation, parts of the dissolved nitrate in the sediment migrates from the sediment to the overlying water, leading to the loss of effective electron acceptor. To overcome this limitation, a combined approached was proposed, which involved nitrocellulose addition and a microbial fuel cell (MFC). Results indicated the nitrate could be slowly released and maintained at a higher concentration over long term. In the combined system, the removal efficiencies of PAHs and AVS were 71.56% and 89.76%, respectively. Furthermore, the voltage attained for the MFC-nitrocellulose treatment was maintained at 146.1 mV on Day 70, which was 5.37 times higher than that of the MFC-calcium nitrate treatment. Sediments with nitrocellulose resulted in lower levels of nitrate and ammonium in the overlying water. Metagenomic results revealed that the combined technology improved the expression of nitrogen-cycling genes. The introduction of MFC inhibited sulfide regeneration during incubation by suppressing the enzyme activity like EC4.4.1.2. The enhanced biostimulation provided potential for in-situ bioremediation utilizing MFC coupled with slow-released nitrate (i.e., nitrocellulose) treatment.

Atomically Dispersed ZnN5 Sites Immobilized on g-C3 N4 Nanosheets for Ultrasensitive Selective Detection of Phenanthrene by Dual Ratiometric Fluorescence

Ultrasensitively selective detection of trace polycyclic aromatic hydrocarbons (PAHs) like phenanthrene (PHE) is critical but remains challenging. Herein, atomically dispersed Zn sites on g-C₃ N₄ nanosheets (sZn-CN) are constructed by thermal polymerization of a Zn-cyanuric acid-melamine supramolecular precursor for the fluorescence detection of PHE. A high amount (1.6 wt%) of sZn is grafted in the cave of CN with one N vacancy in the form of unique Zn(II)N₅ coordination. The optimized sZn-CN achieves a wide detection range (1 ng L^-1 to 5 mg L^-1 ), ultralow detection limit (0.35 ng L^-1 , with 5-order magnitude improvement over CN), and ultrahigh selectivity toward PHE even among typical PAHs based on the built PHE-CN dual ratiometric fluorescence method. By means of in situ Fourier transform infrared spectroscopy, time-resolved absorption and fluorescence spectroscopy, and theoretical calculations, the resulting superior detection performance is attributed to the favorable selective adsorption of PHE on as-constructed atomic Zn(II)N₅ sites via the ionic cation-π interactions (Zn^δ+ C₂ ^δ- type), and the fluorescence quenching is dominated by the inner filter effect (IFE) from the multilayer adsorption of PHE at low concentrations, while it is done by the protruded photogenerated electron-transfer process, as well as IFE from the monolayer adsorption of PHE at ultralow concentration.

Improving performance of pilot-scale ecological bed coupled with microbial electrochemical system for urban tail water treatment

Recycling urban tail water for ecological base flow and landscape use offers a reliable solution for the problem of water resource shortage. But the long-term direct discharge of urban tail water can aggravate the eutrophication of surface water based on the present drainage standard of sewage plant. It is of great significance to develop low-cost and low-energy ecological technologies as transitional region between urban tail water and surface water. In this study, a pilot-scale ecological bed coupled with microbial electrochemical system (EB-MES) was established to treat urban tail water deeply. The system was operated for 96 days from June to September. Average TN removal efficiency in EB-MES under the condition of submerged plant coupled closed-circuit MES could reach 59.0 ± 16.6 %, which was 82.7 % and 38.1 % higher than that of open-circuit EB-MES and MES without plants, respectively. Microbial community structure testing indicated that multiple nitrogen metabolic mechanisms occurred in the system, including nitrification, electrode autotrophic denitrification, anammox, simultaneous nitrification and denitrification, and aerobic denitrification, which results in better denitrification efficiency under tail water. Our research provided a novel ecological technology with advantages of high-efficiency, low-energy and low-carbon and verified the feasibility in pilot scale for application in the advanced treatment of urban tail water.

Enhanced benzofluoranthrene removal in constructed wetlands with iron- modified biochar: Mediated by dissolved organic matter and microbial response

Polycyclic aromatic hydrocarbons (PAHs) pose a high risk to ecosystems owing to their adverse environmental effects. The use of biochar in constructed wetlands (CWs) to remove PAH has received increased interest, but is frequently challenging because of saturation adsorption. To enhance the microbial degradation, electron acceptors are provided. This study aimed to remove a representative PAH, benzofluoranthrene (BbF), using iron-modified biochar as a supplement to the CW substrate. Results revealed that iron-mediated biochar based CWs increased the removal of BbF by 20.4 % and ammonium by 25.6 %. The BbF retained in substrate with biochar (36.6 % higher content) and further removed with iron modification (40.6 % lower content). Iron-modified biochar increased dissolved organic carbon content, particularly low-aromaticity, and low-molecular-weight organic matters (25.7 % higher tryptophan-like material), which contributed to PAH degradation by microorganisms. Microbial analysis confirmed that iron-mediated biochar enriched the abundance of microbes (e.g., Cellulomonas, Actinotalea, and Sphingomonas) and key enzymes (e.g., catA, lipV, and sdhA) that are involved in PAH degradation. Higher proportion of iron-reducing bacteria (e. g., Thiobacillus, Rhodobacter) played a significant role in driving microbial iron cycle, which was beneficial for PAHs removal. Based on the results, we confirmed that the use of iron-modified biochar in CWs enhance PAH removal.

Enhanced nickel removal and synchronous bioelectricity generation based on substrate types in microbial fuel cell coupled with constructed wetland: performance and microbial response

In this study, an attempt was made to clarify the impact of substrates on the microbial fuel cell coupled with constructed wetland (CW-MFC) towards the treatment of nickel-containing wastewater. Herein, zeolite (ZEO), coal cinder (COA), ceramsite (CER), and granular activated carbon (GAC) were respectively introduced into lab-scaled CW-MFCs to systematically investigate the operational performances and microbial community response. GAC was deemed as the most effective substrate, and the corresponding device yielded favorable nickel removal efficiencies over 99% at different initial concentrations of nickel. GAC-CW-MFC likewise produced a maximum output voltage of 573 mV, power density of 8.95 mW/m², and internal resistance of 177.9 Ω, respectively. The strong adsorptive capacity of nickel by GAC, accounting for 54.5% of total contaminant content, was mainly responsible for the favorable nickel removal performances of device GAC-CW-MFC. The high-valence Ni²⁺ was partially reduced to elemental Ni⁰ on the cathode, which provided evidence for the removal of heavy metals via the cathodic reduction of CW-MFC. The microbial community structure varied considerably as a result of substrates addition. For an introduction of GAC into the CW-MFC, a remarkably enriched population of genera Thermincola, norank_f__Geobacteraceae, Anaerovorax, Bacillus, etc. was noted. This study was dedicated to providing a theoretical guidance for an effective regulation of CW-MFC treatment on nickel-containing wastewater and accompanied by bioelectricity generation via the introduction of optimal substrate.

Recovery trajectories of the bacterial community at distances in the receiving river under wastewater treatment plant discharge

Microbes in rivers are an important part of the biogeochemical cycle in aquatic ecosystems, and understanding the major factors that influence the composition of microbial communities has an important role in assessing and improving ecosystem functioning. A high-throughput 16 S rRNA gene sequencing technique was employed to sequence bacterial communities in 21 sediment samples and 21 water samples from an urban river WWTP (wastewater treatment plant) discharge. A systematic study of changes in bacterial community composition in downstream river sediment and water was conducted. The study found that compared with the bacterial diversity in the natural upstream area of the wastewater outfall, the bacterial diversity in the sediment lower reaches decreased significantly, while the bacterial abundance and diversity in the water increased significantly. The Mantel test and redundancy analysis showed that the downstream distance and physicochemical properties were significantly related to the succession of bacterial communities in the sediment downstream of the WWTP discharge. Among them, TOC (total organic carbon) was the most important factor affecting the change in the bacterial community in the downstream sediment. The physicochemical properties were significantly correlated with the succession of bacterial communities in the water downstream of the WWTP discharge. Among them, TN (total nitrogen), PO₄^3--P (phosphorus phosphate) and TP (total phosphorus) were the main factors that affected the change in the bacterial community in the downstream water. Key taxa in the co-occurrence network at different distances downstream reflected the depth of the effect of the WWTP effluent on the bacterial community. The bacterial community in the lower reaches of the river sediment showed a strong recovery ability under the influence of pollutants, while the bacterial community in the lower reaches of the river water was difficult to recover under the influence of pollutants. In general, pollutants contained in effluent are the key to changing the composition of bacterial communities in the lower reaches of the river, but exogenous bacteria in effluent are not. This study provides a basis for further improving the effluent discharge standards of WWTPs in the future.

Enhanced removal of aged and differently functionalized polystyrene nanoplastics using ball-milled magnetic pinewood biochars

In this study, simple and environmentally friendly magnetic biochars were successfully prepared by ball-milling biochar with Fe₃O₄ nanoparticles to remove NPs from water. The magnetic biochars synthesized at various pyrolysis temperatures of 300 °C (MBC300), 500 °C (MBC500), and 700 °C (MBC700) were used to eliminate the unmodified (PS), aged under UV radiation (UVPS), amine-modified (PS-NH₂) and carboxylate-modified (PS-COOH) polystyrene NPs of 100 nm in size. Results showed that the removal efficiency of MBC300, MBC500, and MBC700 for PS were 43.67, 82.73 and 57.02%, which were 3.01, 5.76, and 3.10 times greater than that of corresponding pristine biochars at the same temperatures, respectively, and the strongest removal efficiency of MBC500 was 95.2% since it has the largest specific surface area and abundant oxygen-containing functional groups. The surface properties of the NPs affected their removal, and the PS-NH₂ had the highest removal rate using magnetic biochars. Compared to pristine biochars, the magnetic biochars displayed faster adsorption kinetics. The Langmuir maximum adsorption capacity of magnetic biochars for NPs were 107.7181-229.5772 mg/g, much greater than those of the pristine biochars (55.4602-80.3096 mg/g). Mechanism analysis revealed that the hydrophobicity, electrostatic attraction, H-bonding formation and π-π conjunction between the NPs and MBCs contributed to the adsorption process. This work highlights the promising potential of ball milling to be used as a simple technique for the preparation of magnetic biochar to remove NPs, especially NPs with various surface groups.

The importance of rest phase and pollutant removal mechanism of tidal flow constructed wetlands (TFCW) in rural grey water treatment

This paper explored the effects of the rest phase of tidal flow constructed wetlands (TFCW) on pollutant removal and microbial communities, and further analyzed the mechanism of TFCW removal of pollutants from grey water. The results showed that the removal rate of organic matter was 69.91 ± 2.44% in the control group (NR-TFCW) without the rest phase, 94.95 ± 1.17% in the experimental group (TFCW), and 96.95 ± 2.43% in the control group (P-TFCW) with the ventilation pipe enhanced rest phase. Limiting and enhancing the oxygen supply in the emptying stage of TFCW will enhance the overlap rate of microorganisms in the upper, middle and lower layers of the reactor. Enhancing the rest phase of TFCW leaded to better aerobic removal of organic matter in the microbial community, while limiting the rest phase of TFCW results in the opposite. In addition, the species overlap rate of the top, middle and bottom layers of NR-TFCW (69.98%) and P-TFCW (54.29%) was higher than that of TFCW (11.34%). The removal of organic matter by TFCW mainly relied on the adsorption of biochar in the flood phase, and the microorganisms aerobic degraded the organic matter adsorbed on the biochar in the rest phase. And thus form a continuous cycle of adsorption and biological regeneration. The microbial community in TFCW did not have the ability to nitrify, but had the ability to remove phosphorus. Ammonia nitrogen in the influent was adsorbed by biochar or converted into cytoplasm. While the phosphorus in the influent was adsorbed by the biochar, it was also being biologically removed.

Enhanced performance and microbial interactions of shallow wetland bed coupling with functional biocathode microbial electrochemical system (MES)

It is essential to remediate the polluted urban river, which endangers the aquatic creatures and affected human body's senses. The treatment wetland combined with microbial electrochemical system (MES) used for the remediation is becoming a new research focus due to its ideal pollutants removal efficiency and small footprint. Here this paper provided a kind of novel shallow wetland bed coupling with close-circuit microbial electrochemical system (WB-CMES) to remove pollutants in surface water. In contrast to the shallow wetland bed coupling with open-circuit MES (WB-OMES) and the shallow wetland bed without MES (WB), the enhancing effects and pollutants removal pathway were evaluated. After 62-day operation, average TN removal efficiency in WB-CMES was 87.7%, which was 19.7% and 13.8% higher than that of WB-OMES and WB respectively. The rate coefficient k of NO₃^--N degradation in WB-CMES was 1.6 and 1.8 times higher than that in WB-OMES and WB. The results of chlorophyll, protein and superoxide dismutase (SOD) in WB-CMES were 27.3%, 44.3% and 12.9% higher than those in WB. The microbial community structure analysis indicated that electroactive bacteria on anode like Desulfobulbus could oxidize organics and generate electrons to compensate cathode, meanwhile, cathode could enrich more species of functional bacteria like Rhodobacter, Pirellula, Hyphomicrobium, Thauera, which had a synergistic effect on oxygen reduction, nitrogen removal and plant growth. The results indicated that oxygen produced by submerged plants could be utilized by the oxygen-reducing functional biocathode of MES and the proper aerobic and anoxic environment might enhance nitrate removal mainly through simultaneous nitrification and denitrification (SND), aerobic denitrification and anammox. This research provided a novel technology with advantages of simple operation, flexible configuration, easy scale-up and low cost for application in remediation of highly polluted surface water.

Cedar Wood-Based Biochar: Properties, Characterization, and Applications as Anodes in Microbial Fuel Cell

In this study, the relationship between pyrolysis temperature of woody biomass and physicochemical properties of derived biochar was investigated for microbial fuel cell (MFC) application. Physical and chemical properties of biochar were characterized for different pyrolysis temperatures. Results showed that biochar obtained at 400 °C was not conductor, while biochars prepared at 600 °C, 700 °C, and 900 °C exhibited decreased electrical resistivity of (7 ± 6) × 10³ Ω.m, (1.8 ± 0.2) Ω.m, and (16 ± 3) × 10^-3 Ω.m, respectively. Rising pyrolysis temperature from 400 to 700 °C exhibited honeycomb-like macroporous structures of biochar with an increase in the specific surface area from 310 to 484 m².g^-1. However, the production of biochar at 900 °C reduced its specific surface area to 136 m².g^-1 and caused the loss of the ordered honeycomb structure. MFCs using anodes based on biochar prepared at 900 °C produced maximum power densities ((9.9 ± 0.6) mW.m^-2) higher than that obtained with biochar pyrolyzed at 700 °C ((5.8 ± 0.1) mW.m^-2) and with conventional carbon felt anodes ((1.9 ± 0.2) mW.m^-2). SEM images of biochar-based anodes indicated the clogging of macropores in honeycomb structure of biochar prepared at 700 °C by growth of electroactive biofilms, which might impede the supply of substrate and the removal of metabolites from the inside of the electrode. These findings highlight that electrical conductivity of biochar is the major parameter for ensuring efficient anodes in microbial fuel cell application. Schematic representation of cedar wood-based biochar and its application as anode in MFC.

Pilot scale microbial fuel cells using air cathodes for producing electricity while treating wastewater

Microbial fuel cells (MFCs) can generate electrical energy from the oxidation of the organic matter, but they must be demonstrated at large scales, treat real wastewaters, and show the required performance needed at a site to provide a path forward for this technology. Previous pilot-scale studies of MFC technology have relied on systems with aerated catholytes, which limited energy recovery due to the energy consumed by pumping air into the catholyte. In the present study, we developed, deployed, and tested an 850 L (1400 L total liquid volume) air-cathode MFC treating domestic-type wastewater at a centralized wastewater treatment facility. The wastewater was processed over a hydraulic retention time (HRT) of 12 h through a sequence of 17 brush anode modules (11 m² total projected anode area) and 16 cathode modules, each constructed using two air-cathodes (0.6 m² each, total cathode area of 20 m²) with the air side facing each other to allow passive air flow. The MFC effluent was further treated in a biofilter (BF) to decrease the organic matter content. The field test was conducted for over six months to fully characterize the electrochemical and wastewater treatment performance. Wastewater quality as well as electrical energy production were routinely monitored. The power produced over six months by the MFC averaged 0.46 ± 0.35 W (0.043 W m^-2 normalized to the cross-sectional area of an anode) at a current of 1.54 ± 0.90 A with a coulombic efficiency of 9%. Approximately 49 ± 15 % of the chemical oxygen demand (COD) was removed in the MFC alone as well as a large amount of the biochemical oxygen demand (BOD₅) (70%) and total suspended solid (TSS) (48%). In the combined MFC/BF process, up to 91 ± 6 % of the COD and 91 % of the BOD₅ were removed as well as certain bacteria (E. coli, 98.9%; fecal coliforms, 99.1%). The average effluent concentration of nitrate was 1.6 ± 2.4 mg L^-1, nitrite was 0.17 ± 0.24 mg L^-1 and ammonia was 0.4 ± 1.0 mg L^-1. The pilot scale reactor presented here is the largest air-cathode MFC ever tested, generating electrical power while treating wastewater.

Simultaneously enhanced removal of PAHs and nitrogen driven by Fe2+/Fe3+ cycle in constructed wetland through automatic tidal operation

The lack of dissolved oxygen and weak substrate removal capacity in constructed wetlands (CW) leads to terrible removal of nitrogen and polycyclic aromatic hydrocarbons (PAHs). In this study, automatic tidal flow CW microcosms were constructed by improving the oxygen environment (siphon and air-duct) and substrate (magnetite) to enhance purification performance and the mechanism was explored. The results showed that the addition of air-duct could improve the oxygen collection and thus improved the NH₄⁺ removal efficiency. Additionally, nitrogen removal was improved greatly due to the simultaneous nitrification and denitrification in aerobic layer with the addition of magnetite. Mass balance indicated the microbial degradation dominated (32-62%) the removal of PAHs. Metagenomic analysis proved the existence of magnetite enhanced the number of PAHs-degrading bacteria, functional groups and metabolic pathways and thus greatly improved the microbial degradation of PAHs. Furthermore, Fe²⁺/Fe³⁺ cycle played an important role in promoting the anaerobic degradation of PAHs, which might be served as an electron conduit to establish the direct interspecies electron transfer between iron-reducing bacteria (e.g. Deltaproteobacteria bacterium) and Anaerolineae bacterium to degrade PAHs efficiently. This study provided better understanding of the simultaneous removal of PAHs and nitrogen in tidal flow CWs.

Removal of microcystin (MC-LR) in constructed wetlands integrated with microbial fuel cells: Efficiency, bioelectricity generation and microbial response

Microcystins (MCs) pollution caused by cyanobacteria harmful blooms (CHBs) has posed short- and long-term risks to aquatic ecosystems and public health. Constructed wetlands (CWs) have been verified as an effective technology for eutrophication but the removal performance for MCs did not achieve an acceptable level. CWs integrated with microbial fuel cell (MFC-CWs) were developed to intensify the nutrient and Microcystin-LR (MC-LR) removal efficiencies in this study. The results indicated that closed-circuit MFC-CWs (T1) exhibited a better NO₃^--N, NH₄⁺-N, TP and MC-LR removal efficiency compared to that of open-circuit MFC-CWs (CK, i.e., traditional CWs). Therein, a MC-LR removal efficiency of greater than 95% was observed in both trials in T1. The addition of sponge iron to the anode layer of MFC-CWs (T2) improved only the NO₃^--N removal and efficiency bioelectricity generation performance compared to T1, and the average effluent MC-LR concentration of T2 (1.14 μg/L) was still higher than the provisional limit concentration (1.0 μg/L). The microbial community diversity of T1 and T2 was simplified compared to CK. The relative abundance of Sphingomonadaceae possessing the degradation capability for MCs increased in T1, which contributed to the higher MC-LR removal efficiency compared to CK and T2. While the relative abundance of electrochemically active bacteria (EAB) (i.e., Desulfuromonadaceae and Desulfomicrobiaceae) in the anode of T2 was promoted by the addition of sponge iron. Overall, this study suggests that integrating MFC into CWs provides a feasible intensification strategy for eutrophication and MCs pollution control.

High removal efficiencies of antibiotics and low accumulation of antibiotic resistant genes obtained in microbial fuel cell-constructed wetlands intensified by sponge iron

Using microbial fuel cells with constructed wetlands (MFC-CWs) for eliminating antibiotics has recently attracted extensive attention. However, antibiotic removal efficiencies in MFC-CWs must be enhanced, and the accumulation of antibiotic resistant genes (ARGs) remains an unmanageable issue. This study tries to enhance the antibiotic removal in synthetic wastewater and reduce ARGs by adding sponge iron (s-Fe⁰) and calcium peroxide to the anode and cathode of MFC-CWs, respectively, and/or simultaneously. The results demonstrated that adding s-Fe⁰ and calcium peroxide to MFC-CWs could improve the removal efficiencies of sulfamethoxazole (SMX) and tetracycline (TC) by 0.8-1.3% and 6.0-8.7%. Therein, s-Fe⁰ also significantly reduced 84.10-94.11% and 49.61-60.63% of total sul and tet genes, respectively. Furthermore, s-Fe⁰ improved the voltage output, power density, columbic efficiency, and reduced the internal resistance of reactors. The intensification to the electrode layers posed a significant effect on the microbial community composition and functions, which motivated the shift of antibiotic removal, accumulation of ARGs and bioelectricity generation in MFC-CWs. Given the overall performance of MFC-CWs, adding s-Fe⁰ to the anode region of MFC-CWs was found to be an effective strategy for removing antibiotics and reducing the accumulation of ARGs.

Bioelectrochemical process for simultaneous removal of copper, ammonium and organic matter using an algae-assisted triple-chamber microbial fuel cell

Considering the adverse effect of heavy metals (such as Cu²⁺) on biological wastewater treatment processes, an algae-assisted triple-chamber microbial fuel cell (MFC) was established to remove Cu²⁺, COD and nitrogen sequentially, and also generate electricity. About 86.2% of the Cu²⁺ was removed in the first cathodic chamber, and the remaining Cu²⁺ was largely eliminated by algal uptake, contributing to an overall Cu²⁺ removal rate of 99.9% across the whole system. The nitrogen removal rate reached 79% in the system. The majority of the ammonium was assimilated by algae, and nitrogen oxides formed during the light period were denitrified at the cathode in the dark period. The variation in electrode potentials indicated that the cathode and anode potentials not only depended on the respective substrate concentrations, but also affected each other. The influence of algae on the microbial communities was greater than that of Cu²⁺ or the system structure. Devosia, Thauera, Pseudomonas, Acinetobacter and Flavobacterium may influence nitrogen removal, while Delftia, Thauera and Pseudomonas may play an important role in power generation. The present study has developed a practical method for removing pollutants from the wastewater containing heavy metals.

A review of the bioelectrochemical system as an emerging versatile technology for reduction of antibiotic resistance genes

Antibiotic contamination and the resulting resistance genes have attracted worldwide attention because of the extensive overuse and abuse of antibiotics, which seriously affects the environment as well as human health. Bioelectrochemical system (BES), a potential avenue to be explored, can alleviate antibiotic pollution and reduce antibiotic resistance genes (ARGs). This review mainly focuses on analyzing the possible reasons for the good performance of ARG reduction by BESs and potential ways to improve its performance on the basis of revealing the generation and transmission of ARGs in BES. This system reduces ARGs through two pathways: (1) the contribution of BES to the low selection pressure of ARGs caused by the efficient removal of antibiotics, and (2) inhibition of ARG transmission caused by low sludge yield. To promote the reduction of ARGs, incorporating additives, improving the removal rate of antibiotics by adjusting the environmental conditions, and controlling the microbial community in BES are proposed. Furthermore, this review also provides an overview of bioelectrochemical coupling systems including the BES coupled with the Fenton system, BES coupled with constructed wetland, and BES coupled with photocatalysis, which demonstrates that this method is applicable in different situations and conditions and provides inspiration to improve these systems to control ARGs. Finally, the challenges and outlooks are addressed, which is constructive for the development of technologies for antibiotic and ARG contamination remediation and blocking risk migration.

A review of recent advances in electrode materials for emerging bioelectrochemical systems: From biofilm-bearing anodes to specialized cathodes

Bioelectrochemical systems (BES), mainly microbial fuel cells (MEC) and microbial electrolysis cells (MFC), are unique biosystems that use electroactive bacteria (EAB) to produce electrons in the form of electric energy for different applications. BES have attracted increasing attention as a sustainable, low-cost, and neutral-carbon option for energy production, wastewater treatment, and biosynthesis. Complex interactions between EAB and the electrode materials play a crucial role in system performance and scalability. The electron transfer processes from the EAB to the anode surface or from the cathode surface to the EAB have been the object of numerous investigations in BES, and the development of new materials to maximize energy production and overall performance has been a hot topic in the last years. The present review paper discusses the advances on innovative electrode materials for emerging BES, which include MEC coupled to anaerobic digestion (MEC-AD), Microbial Desalination Cells (MDC), plant-MFC (P-MFC), constructed wetlands-MFC (CW-MFC), and microbial electro-Fenton (BEF). Detailed insights on innovative electrode modification strategies to improve the electrode transfer kinetics on each emerging BES are provided. The effect of materials on microbial population is also discussed in this review. Furthermore, the challenges and opportunities for materials scientists and engineers working in BES are presented at the end of this work aiming at scaling up and industrialization of such versatile systems.

The impact of national energy structure on the concentrations, environmental behavior, and sources of polycyclic aromatic hydrocarbons in riverine and coastal sediments of the Beibu Gulf, China

In this study, polycyclic aromatic hydrocarbons (PAHs) were measured in sediments of the Beibu Gulf in 2017 to investigate sources and a risk assessment. The results showed the total PAH concentration (∑₁₆PAHs) in sediments of the Beibu Gulf in 2017 (17.6 ± 16.7 ng g^-1) was significantly lower than that in 2010 (47.8 ± 27.4 ng g^-1). The ∑₁₆PAHs concentrations varied spatially within the Beibu Gulf, impacted by point source pollution. The results of adsorption/desorption and water-air partitioning suggest that the environmental behavior of PAHs in the Beibu Gulf is affected by atmospheric deposition and sediment-water partitioning. A risk assessment showed that the PAHs in sediments were within a safety threshold. Three source apportionment methods show that oil spills and oil and biomass burning were the most important (>83.8%) sources of PAHs in sediments of the Beibu Gulf.

Use of Biochar-Based Cathodes and Increase in the Electron Flow by Pseudomonas aeruginosa to Improve Waste Treatment in Microbial Fuel Cells

In this paper, we tested the combined use of a biochar-based material at the cathode and of Pseudomonas aeruginosa strain in a single chamber, air cathode microbial fuel cells (MFCs) fed with a mix of shredded vegetable and phosphate buffer solution (PBS) in a 30% solid/liquid ratio. As a control system, we set up and tested MFCs provided with a composite cathode made up of a nickel mesh current collector, activated carbon and a single porous poly tetra fluoro ethylene (PTFE) diffusion layer. At the end of the experiments, we compared the performance of the two systems, in the presence and absence of P. aeruginosa, in terms of electric outputs. We also explored the potential reutilization of cathodes. Unlike composite material, biochar showed a life span of up to 3 cycles of 15 days each, with a pH of the feedstock kept in a range of neutrality. In order to relate the electric performance to the amount of solid substrates used as source of carbon and energy, besides of cathode surface, we referred power density (PD) and current density (CD) to kg of biomass used. The maximum outputs obtained when using the sole microflora were, on average, respectively 0.19 Wm−2kg−1 and 2.67 Wm−2kg−1, with peaks of 0.32 Wm−2kg−1 and 4.87 Wm−2kg−1 of cathode surface and mass of treated biomass in MFCs with biochar and PTFE cathodes respectively. As to current outputs, the maximum values were 7.5 Am−2 kg−1 and 35.6 Am−2kg−1 in MFCs with biochar-based material and a composite cathode. If compared to the utilization of the sole acidogenic/acetogenic microflora in vegetable residues, we observed an increment of the power outputs of about 16.5 folds in both systems when we added P. aeruginosa to the shredded vegetables. Even though the MFCs with PTFE-cathode achieved the highest performance in terms of PD and CD, they underwent a fouling episode after about 10 days of operation, with a dramatic decrease in pH and both PD and CD. Our results confirm the potentialities of the utilization of biochar-based materials in waste treatment and bioenergy production.

Application of constructed wetlands in the PAH remediation of surface water: A review

Polycyclic aromatic hydrocarbons (PAHs) pose adverse risks to ecosystems and public health because of their carcinogenicity and mutagenicity. As such, the extensive occurrence of PAHs represents a worldwide concern that requires urgent solutions. Wastewater treatment plants are not, however, designed for PAH removal and often become sources of the PAHs entering surface waters. Among the technologies applied in PAH remediation, constructed wetlands (CWs) exhibit several cost-effective and eco-friendly advantages, yet a systematic examination of the application and success of CWs for PAH remediation is missing. This review discusses PAH occurrence, distribution, and seasonal patterns in surface waters during the last decade to provide baseline information for risk control and further treatment. Furthermore, based on the application of CWs in PAH remediation, progress in understanding and optimising PAH-removal mechanisms is discussed focussing on sediments, plants, and microorganisms. Wetland plant traits are key factors affecting the mechanisms of PAH removal in CWs, including adsorption, uptake, phytovolatilization, and biodegradation. The physico-chemical characteristics of PAHs, environmental conditions, wetland configuration, and operation parameters are also reviewed as important factors affecting PAH removal efficiency. Whilst significant progress has been made, several key problems need to be addressed to ensure the success of large-scale CW projects. These include improving performance in cold climates and addressing the toxic threshold effects of PAHs on wetland plants. Overall, this review provides future direction for research on PAH removal using CWs and their large-scale operation for the treatment of PAH-contaminated surface waters.

Electrochemical performance and response of bacterial community during phenanthrene degradation in single-chamber air-cathode microbial fuel cells

Polycyclic aromatic hydrocarbons have attracted considerable attention for their carcinogenic, teratogenic, and mutagenic properties in humans. Phenanthrene is one of the most abundant polycyclic aromatic hydrocarbons in aquatic environments. In this study, different concentrations of phenanthrene were degraded by single-chamber air-cathode microbial fuel cells. The electrochemical parameter of microbial fuel cells and biofilm changes on the anode were observed. The results showed that the addition of phenanthrene reduced the power output of the microbial fuel cell which affected the process of microbial electricity generation. Meanwhile, microorganisms destroyed the original structure of phenanthrene through anaerobic metabolism, and achieved good average degradation of 94.9-98.4%. Observation of the anodic biofilm found that the microbes had tolerance to phenanthrene and the biofilm exhibited to be well-constructed. Bacterial community distribution showed a decrease in the relative abundance of Acidovorax and Aquamicrobium, whereas the relative content of the main electroactive organism, Geobacter, increased by a factor of three. The results show that it is feasible for microbial fuel cells to biodegrade phenanthrene, and provide some references for the changes of microbial community during degradation process.

Pathways regulating the enhanced nitrogen removal in a pyrite based vertical-flow constructed wetland

In this study, two vertical constructed wetland using natural pyrite (P-VFCW) and quartz sand (C-VFCW) as substrate were constructed, and the enhanced nitrate removal mechanism by pyrite was further investigated. Results showed that the nitrate removal efficiency (NRE) of P-VFCW was 4% higher than that of C-VFCW with a C/N of 0. Interestingly, the difference on NRE between CWs markedly enlarged with C/N and hydraulic retention time (HRT) simultaneously increasing. At a COD/N of 6 and HRT of 24 h, the effluent average NO₃^--N and NO₂^--N concentrations in P-VFCW and C-VFCW were 2.36 ± 2.64 mg/L/1.34 ± 1.28 mg/L, 9.20 ± 6.91 mg/L/5.57 ± 3.68 mg/L, respectively, revealing pyrite could promote heterotrophic denitrification and avoid nitrite accumulation. After the whole operation, a better growth of Canna indica occurred in P-VFCW. High-throughput sequencing implied that denitrifying bacteria (Comamonas), iron oxidation and reduction microorganism (Thiobacillus) and the rhizosphere microorganism differed in CWs.

Two-stage hybrid constructed wetland-microbial fuel cells for swine wastewater treatment and bioenergy generation

A newly emerged alum sludge-based hybrid constructed wetland-microbial fuel cells (CW-MFCs), i.e. vertical upflow CW coupled MFC as 1st stage and horizontal subsurface flow CW coupled MFC as 2nd stage (VFCW-MFC + HSSFCW-MFC), was firstly developed for swine wastewater treatment and electricity generation. Swine wastewater and multi-set air-cathodes were applied to investigate the pollutants removal behavior and the power production. Six-month trial suggested that the overall removal efficiency of SS, COD, NH₄⁺-N, NO₃^--N, TN, TP and PO₄^3--P was 76 ± 12.4, 72 ± 7.4, 59 ± 28.3, 69 ± 25.6, 47 ± 19.7, 85 ± 9.5 and 88 ± 8.7%, respectively. The two stages hybrid system (VFCW-MFC + HSSFCW-MFC) continuously generated electrical power with average voltages of 0.44 ± 0.09 and 0.34 ± 0.09 V, and power densities of 33.3 ± 13.81 and 9.0 ± 2.5 mW/m³ in 1st and 2nd stage, respectively. The average net energy recovery (NER) of 1st stage and 2nd stage is in turn 0.91 ± 0.16 and 2.76 ± 0.70 Wh/kg·COD. It indicates that the hybrid CW-MFCs has higher removal efficiency than single stage CW-MFC, while 1st stage plays the major role both in pollutants removal and power generation.

Removal of sulfamethoxazole and tetracycline in constructed wetlands integrated with microbial fuel cells influenced by influent and operational conditions

Constructed wetlands integrated with microbial fuel cells (MFC-CWs) have been recently developed and tested for removing antibiotics. However, the effects of carbon source availability, electron transfer flux and cathode conditions on antibiotics removal in MFC-CWs through co-metabolism remained unclear. In this study, four experiments were conducted in MFC-CW microcosms to investigate the influence of carbon source species and concentrations, external resistance and aeration duration on sulfamethoxazole (SMX) and tetracycline (TC) removal and bioelectricity generation performance. MFC-CWs supplied with glucose as carbon source outperformed other carbon sources, and moderate influent glucose concentration (200 mg L^-1) resulted in the best removal of both SMX and TC. Highest removal percentages of SMX (99.4%) and TC (97.8%) were obtained in MFC-CWs with the external resistance of 700 Ω compared to other external resistance treatments. SMX and TC removal percentages in MFC-CWs were improved by 4.98% and 4.34%, respectively, by increasing the aeration duration to 12 h compared to no aeration. For bioelectricity generation performance, glucose outperformed sodium acetate, sucrose and starch, with the highest voltages of 386 ± 20 mV, maximum power density (MPD) of 123.43 mW m^-3, and coulombic efficiency (CE) of 0.273%. Increasing carbon source concentrations from 100 to 400 mg L^-1, significantly (p < 0.05) increased the voltage and MPD, but decreased the internal resistance and CE. The highest MPD was obtained when the external resistance (700 Ω) was close to the internal resistance (600.11 Ω). Aeration not only improved the voltage and MPD, but also reduced the internal resistance. This study demonstrates that carbon source species and concentrations, external resistances and aeration duration, all play vital roles in regulating SMX and TC removal in MFC-CWs.

Enhanced bisphenol S anaerobic degradation using an NZVI-HA-modified anode in bioelectrochemical systems

As a substitute for bisphenol A (BPA), bisphenol S (BPS) has a longer half-life, higher chemical inertness and better skin permeability than BPA, and it also has a strong endocrine disruption effect. Relatively few studies have focused on the main processing technology for BPS biodegradation, and the findings indicate that the biodegradation efficiency of BPS was relatively low. Therefore, this paper used an NZVI-HA composite-modified bio-anode to enhance the anaerobic degradation of BPS in a Bioelectrochemical Systems (BES). The results showed that the degradation efficiency of BPS was improved from 31.1% to 92.2% with the NZVI-HA modification compared with the control group (CC-BES). FTIR and XPS analyzes demonstrated that HA can accelerate the reduction rate of Fe³⁺ and increase the ratio of Fe²⁺/Fe³⁺. In addition, HA can form Fe-O-HA complexes with NZVI to promote electron transfer. An analysis of the NZVI-HA-BES intermediate metabolites revealed that complex modification properties altered the BPS degradation pathway. An analysis of microbial diversity indicated that the bacteria related to the degradation of BPS may be Terrimonas, Lysobacter, and Acidovorax.

Mapping the field of constructed wetland-microbial fuel cell: A review and bibliometric analysis

The embedding microbial fuel cell (MFC) into constructed wetlands (CW) to form CW-MFC bears the potential to obtain bioelectricity and a clean environment. In this study, a bibliometric analysis using VOSviewer based on Web of Science data was conducted to provide an overview by tracing the development footprint of this technology. The countries, institutions, authors, key terms, and keywords were tracked and corresponding mapping was generated. From 2012 to September 2020, 442 authors from 129 organizations in 26 countries published 135 publications in 42 journals with total citation of 3139 times were found. The key terms analysis showed four clusters: bioelectricity generation performance, mechanism study, refractory pollutants removal, and enhanced conventional contaminants removal. Further research themes include exploring the biochemical properties of electrochemically active bacteria, emerging contaminants removal, effective bioelectricity harvest and the use, and biosensor development as well as scaling-up for real field application. The bibliometric results provide valuable references and information on potential research directions for future studies.

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

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

Green choline amino acid ionic liquids aqueous two-phase extraction coupled with synchronous fluorescence spectroscopy for analysis naphthalene and pyrene in water samples

A novel aqueous two-phase extraction method has been established for the determination of polycyclic aromatic hydrocarbons in water sample. This method was based on the extraction of naphthalene and pyrene from water by means of choline amino acid ionic liquids aqueous two-phase system and their determination by synchronous fluorescence spectroscopy. In synchronous fluorescence spectroscopy, the fluorescence peaks of naphthalene and pyrene were completely separated to meet the requirement of simultaneous determination. For this method, good linear calibration curves of naphthalene and pyrene were obtained in the range of 0.50-10.0, 0.05-5.0 μg mL^-1, respectively, and limits of detection were 0.211, 0.012 μg mL^-1, respectively. The proposed method was successfully applied for the simultaneous determination of naphthalene and pyrene in water samples, which was considered as an excellent green analysis according Analytical Eco-Scale.

The Utility of Electrochemical Systems in Microbial Degradation of Polycyclic Aromatic Hydrocarbons: Discourse, Diversity and Design

Polycyclic aromatic hydrocarbons (PAHs), especially high molecular weight PAHs, are carcinogenic and mutagenic organic compounds that are difficult to degrade. Microbial remediation is a popular method for the PAH removal in diverse environments and yet it is limited by the lack of electron acceptors. An emerging solution is to use the microbial electrochemical system, in which the solid anode is used as an inexhaustible electron acceptor and the microbial activity is stimulated by biocurrent in situ to ensure the PAH removal and avoid the defects of bioremediation. Based on the extensive investigation of recent literatures, this paper summarizes and comments on the research progress of PAH removal by the microbial electrochemical system of diversified design, enhanced measures and functional microorganisms. First, the bioelectrochemical degradation of PAHs is reviewed in separate and mixed PAH degradation, and the removal performance of PAHs in different system configurations is compared with the anode modification, the enhancement of substrate and electron transfer, the addition of chemical reagents, and the combination with phytoremediation. Second, the key functional microbiota including PAH degrading microbes and exoelectrogens are overviewed as well as the reduced microbes without competitive advantage. Finally, the typical representations of electrochemical activity especially the internal resistance, power density and current density of systems and influence factors are reviewed with the correlation analysis between PAH removal and energy generation. Presently, most studies focused on the anode modification in the bioelectrochemical degradation of PAHs and actually more attentions need to be paid to enhance the mass transfer and thus larger remediation radius, and other smart designs are also proposed, especially that the combined use of phytoremediation could be an eco-friendly and sustainable approach. Additionally, exoelectrogens and PAH degraders are partially overlapping, but the exact functional mechanisms of interaction network are still elusive, which could be revealed with the aid of advanced bioinformatics technology. In order to optimize the efficacy of functional community, more advanced techniques such as omics technology, photoelectrocatalysis and nanotechnology should be considered in the future research to improve the energy generation and PAH biodegradation rate simultaneously.

Antibiotic resistance genes, bacterial communities, and functions in constructed wetland-microbial fuel cells: Responses to the co-stresses of antibiotics and zinc

The effects of the continuous accumulation of Zinc (Zn) on the fate of antibiotic resistance genes (ARGs) in constructed wetland-microbial fuel cells (CW-MFCs) remain unclear. In this study, the impacts of Zn addition and a circuit mode on antibiotic removal, occurrence of ARGs, the bacterial community, and bacterial functions were investigated in three groups of CW-MFCs. The results showed that continuous Zn exposure enriched the target ARGs during the initial stage, while excessive Zn accumulation decreased antibiotic removal and the abundance of ARGs. A principal component analysis demonstrated that ARGs and the bacterial community distribution characteristics were significantly impacted by the mass accumulation of antibiotics and Zn, as well as the circuit mode. A redundancy analysis, partial least squares path modeling, and Procrustes analysis revealed that the accumulation of antibiotics and Zn, the composition of the bacterial community, the circuit mode, and the abundance of intI associated with horizontal gene transfer jointly contributed to the distributions of ARGs in the electrodes and effluent. Moreover, continuous exposure to Zn decreased the bacterial diversity and changed the composition and function of the bacterial community predicted using PICRUSt tool. The co-occurrence of ARGs, their potential hosts and bacterial functions were further revealed using a network analysis. A variation partition analysis also showed that the accumulation of target pollutants and the circuit mode had a significant impact on the bacterial community composition and functions. Therefore, the interaction among ARGs, the bacterial community, bacterial functions, and pollutant accumulations in the CW-MFC was complex. This study provides useful implications for the application of CW-MFCs for the treatment of wastewater contaminated with antibiotics and heavy metals.

Desorption process and morphological analysis of real polycyclic aromatic hydrocarbons contaminated soil by the heterogemini surfactant and its mixed systems

Surfactant-enhanced remediation (SER) is an efficient and low-cost technology for polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study assessed the desorption processes and effects of Heterogemini surfactant (Dodecyldimethylammonium bromide/tetradecyldimethylammonium bromide, DBTB), two traditional surfactants (Hexadecyl trimethyl ammonium bromide, CTAB; Sorbitan monolaurate, Span 20) and their mixed systems on the real PAHs-contaminated soil from an abandoned coking plant, as well they were analyzed micro morphologically. DBTB had greater desorption capability for PAHs and favorable interaction with the traditional surfactants confirmed by reaction parameters β^m and Gibbs. Whether for total PAHs (TPAHs) or different molecular weight PAHs, the mixed system Span 20/DBTB had larger molar solubilization ratio (MSR) and partition coefficient (K_m) than CTAB/DBTB, the highest desorption rate for TPAHs reaching 68.83%. Additionally, microscopic morphology showed micelles of Span 20/DBTB were more dispersed and formed strings easily, explaining its good desorption capability. What resulted demonstrated the feasibility of DBTB, a novel Heterogemini surfactant, and its mixed systems remediating PAHs-contaminated soil of abandoned industrial site.