Constructed Wetland-microbial Fuel Cell Research Articles

Variation of graphene/titanium dioxide concentration as electrocatalyst for an oxygen reduction reaction in constructed wetland-microbial fuel cells

Constructed wetlands-microbial fuel cells (CW-MFC) are an innovative technology used for simultaneous bioelectricity generation and wastewater treatment. This is possible due to the installation of macrophytes in an electrode configuration, in which electroactive microorganisms use organic substrates as biofuel. One way to improve the electrochemical performance of CW-MFCs is through the impregnation of cathodic electrocatalysts. Therefore, in this study the bioelectricity production capacity of CW-MFCs was evaluated from the oxygen reduction reaction (ORR). For this study, the concentrations 0 (CW-MFC1), 0.5 (CW-MFC2), and 1 mg/cm2 (CW-MFC3) of graphene/titanium dioxide (G/TiO2) as electrocatalyst on the cathodes were evaluated. Using the Koutecky-Levich analysis, it was determined that the ORR transfer mechanism arises via a 4-electron pathway. The electrokinetic parameters of Tafel slope, charge transfer coefficient, and exchange current density determined the efficiency of the ORR, registering 92 mV/dec, 0.93 (α), and 2.30 x10-3 mA/cm2, respectively for CW-MFC3. The highest electrochemical performance was obtained at a concentration of 1 mg/cm2 (CW-MFC3) of G/TiO2, generating 144 mW/m2 of power density, 157 Ω of internal resistance, −150 mV of anodic potential, and 383 mV of cathodic potential. The surface modification carried out on the cathodes resulted in a catalytic increase in the ORR.

Study on the Removal Characteristics of IBP and DCF in Wastewater by CW-MFC with Different Co-Substrates

Pharmaceuticals and Personal Care Products (PPCPs) constitute a group of compounds that are challenging to break down and potentially pose risks to both ecosystems and human health when they accumulate in water bodies. This study established and operated small-scale constructed wetland–microbial fuel cells (CW-MFCs) continuously for 60 days, maintaining a hydraulic retention time (HRT) of 3 days. The research aimed to assess the treatment efficiency of wastewater containing Ibuprofen (IBP) and Diclofenac (DCF) using different co-substrates (glucose, sucrose, and sodium acetate) and to analyze the impact of these co-substrates on the composition of bacterial communities within the CW-MFC. After 60 days of operation, CW-MFC achieved removal rates of 89.29% for IBP and 84.10% for DCF. The elimination of IBP was primarily dependent on co-metabolic degradation processes occurring in both the anode and cathode, while DCF removal relied on anodic co-metabolism. Additionally, various co-substrates have an influence on the bacterial community diversity of the anode and cathodes. The possible bacterial groups involved in PPCP degradation were identified. In summary, Glu was identified as a more suitable co-substrate for CW-MFC in the removal of IBP and DCF, while SA as a co-substrate favored the induction and enrichment of EAB in the anodes. These findings offer valuable insights into the potential of CW-MFC for mitigating emerging contaminants.

Iron-sulfur mediated antibiotic resistance genes attenuation and autotrophic denitrification mechanisms in bioelectrochemical systems

Aiming at the problems of antibiotic resistance genes (ARGs) transfer, mobile gene elements (MGEs) and nitrogen removal in livestock wastewater, pyrite was introduced into the bioelectrochemical constructed wetland, mainly focusing on the mechanism of ARGs transfer and autotrophic denitrification in bioelectrochemical system. The results indicated that pyrite promoted the degradation of antibiotics while inhibiting the efflux of ARGs and MGEs in effluent. The removal rate of antibiotics in pyrite-mediated constructed wetland coupled with microbial fuel cell (PCW-MFC) was 26.84 % and 21.20 % higher than constructed wetland-microbial fuel cell (CW-MFC) and pyrite-mediated constructed wetland (PCW). Metagenomic analysis revealed that the abundance of ARGs in effluent and anodic microorganism in PCW-MFC was effectively controlled by inhibiting the expression of genes encoding antibiotic efflux (macB, tetA, smeS). The expression levels of periplasmic nitrate reduction genes (napA, napB) and encoding cytochrome c nitrite reductase small subunit genes (nrfH) in PCW-MFC were much higher than CW-MFC. The total expression of ARGs in CW-MFC anode biofilms was 35.77 % higher than PCW-MFC, indicating that the system can effectively reduce the spread of ARGs and abate environmental risks. The findings can provide theoretical reference for the control of ARGs and efficient nitrogen removal in livestock wastewater.

A double-edged sword: Constructed wetland-microbial fuel cells promote organics removal via entrapment

Recently, constructed wetland-microbial fuel cells (CW-MFCs) are found to enhance the organics removal via the connection of the external circuit. Yet, it is unclear why the energy output is unmatched with the enhancement of the organics removal. This study compared the dynamic changes of the organics in a CW-MFC microcosm operated under the close circuit and open circuit. As a result, the close circuit facilitated the organics removal by 9 % before the proportional discharge of carbon metabolites. This suggested that organics entrapment should account for the huge loss of carbon recovery; and closing the external circuit could further promote the organics entrapment. Besides, polyhydroxybutyrate was found accumulated in the MFC culture experiment, evidencing that the fed-batch mode of operation could result in a feast-famine pattern of microbial metabolism. Despite the fast organics entrapment during the first hours, prolonging the operation time would lead to continuous carbon gas emission, along with the substantially elevated coulombic efficiency. Together, these results explained the substantial COD removal enhancement with low electricity yield, and cautioned the safe use of the MFC integration to spare the system from overaccumulation of organics.

Accelerated Pb(II) removal and concurrent bioelectricity production via constructed wetland-microbial fuel cell: Structural orthogonal optimization and microbial response mechanism

In this study, a novel constructed wetland-microbial fuel cell (CW-MFC) filled with biomass carbon sources was established to elucidate the impacts of orthogonal configuration of multiple constraints towards wastewater purification and bioelectricity generation under Pb(II) stress. As a result, the optimal structural layouts of CW-MFC were granular activated carbon, Iris pseudacorus and 20 cm of electrode spacing, respectively. The homologous system yielded a favorable Pb(II) removal efficiency of 99.05 %, a maximum output voltage of 394.3 mV and power density of 4468.40 mW/m2, respectively. The migration results highlighted the major contribution of substrate and biomass to Pb(II) adsorption and fixation. Likewise, Pb(II) was immobilized on the cathode via potential binding to O. A visible enrichment of electroactive bacteria (Clostridium, Geobacter, Pseudomonas) and metal-resistant bacteria (Novosphingobium, Aeromonas) was noted. Also, microorganisms modulated the intracellular transport, chemotactic and antioxidant systems by engaging in the metabolic processes of carbohydrate, glutathione, pyruvate, etc. The microbial analysis signified that the genera enriched in disparate regions of CW-MFC-6 regulated the metabolic processes to facilitate their activities and resistance to Pb(II) stress, thereby synergistically enhancing the integrated capability of closed-circuit device. This study was dedicated to elucidating the microbial response mechanism of structural orthogonal optimization of CW-MFC, and providing a theoretical guidance for an effective regulation of Pb(II)-containing wastewater treatment.

Impact of separate concentrations of polyethylene microplastics on the ability of pollutants removal during the operation of constructed wetland-microbial fuel cell

Microplastics (MPs) in water pose a great threat to the ecological environment, but the impact of MPs on constructed wetland microbial fuel cells (CW-MFCs) has not been studied, so in order to fill the research gap and enrich the research in the field of microplastics, a 360-day experiment was designed to determine the operating status of CW-MFCs at different concentrations (0, 10, 100 and 1000 μg/L) polyethylene microplastics (PE-MPs) at different times, focusing on the changes of the CW-MFCs' ability to handle pollutants, power production performance and microbial composition. The results showed that with the accumulation of PE-MPs, the removal effect of COD and TP did not change significantly, and that the removal rate was maintained at around 90% and 77.9% respectively, within 120 d of operation. What's more, the denitrification efficiency increased (from 4.1% to 19.6%), but with the passage of time, it decreased significantly (from 7.16% to 31.9%) at the end of the experiment, while oxygen mass transfer rate was significantly increased. Further analysis showed that the accumulation of PE-MPs did not affect the current power density significantly with the changes of time and concentration, but the accumulation of PE-MPs would inhibit the exogenous electrical biofilm and increase the internal resistance, thereby affecting the electrochemical performance of the system. In addition, the results of microbial PCA showed that the composition and the activity of the microorganisms were changed under the action of PE-MPs, that the microbial community in CW-MFC showed a dose effect on the input of PE-MPs, and that the relative abundance of nitrifying bacteria with time was significantly affected by PE-MPs concentration. The relative abundance of denitrifying bacteria decreased over time, but PE-MPs promoted the reproduction of denitrifying bacteria, which was consistent with the changes in nitrification and denitrification rates. The removal modes of EP-MPs by CW-MFC include the adsorption and the electrochemical degradation, with two isothermal adsorption models of Langmuir and Freundlich being constructed in the experiment, and the electrochemical degradation process of EP-MPs being simulated. In summary, the results show that the accumulation of PE-MPs can induce a series of changes in substrate, microbial species and activity of CW-MFCs, which in turn affects the pollutant removal efficiency and power generation performance during its operation.

Performance optimization of two-stage constructed wetland-microbial fuel cell system for the treatment of high-concentration wastewater.

Constructed wetland-microbial fuel cell (CW-MFC) has attracted much attention because of its dual functions of wastewater treatment and energy recovery. However, its performance in treating high-concentration wastewater is degraded by the decreased dissolved oxygen at the cathode and insufficient electron acceptors. In this study, two CW-MFC systems with cathodic aeration were connected in series to investigate the effects of aeration rate and hydraulic retention time (HRT) on the removal of pollutants and the performance of electricity production in high-concentration wastewater. Results showed that aeration enhanced NH4+-N and TP removal by 45.0-49.8% and 11.5-18.0%, compared with the unaerated condition, respectively. Meanwhile, no significant change regarding COD removal was observed. Aeration enhances the output voltage and power density of the system, especially the first stage CW-MFC, which improved the power production performance by 1 to 2 orders-of-magnitude. Increasing HRT improves the system's pollutant treatment efficiency and power generation performance for high-concentration wastewater. Still, the extension of HRT to 2days will not contribute much to improving the removal efficiency. Under optimized conditions, the maximum total removal rates of COD, NH4+-N, and TP for the two-stage tandem CW-MFC system were 99.3 ± 0.2%, 92.4 ± 1.6%, and 79.5 ± 3.4%, respectively. Meanwhile, the maximum output voltage and maximum power density of the first-stage CW-MFC were 405mV and 138.0mW/m3, respectively. In contrast, the maximum output voltage and maximum power density of the second stage are 105mV and 14.7mW/m3, respectively.

Influence of Electrodes Configuration on Hydraulic Characteristics of Constructed Wetland–Microbial Fuel Cell Systems Using Graphite Rods and Plates as Electrodes

Constructed wetland–microbial fuel cell coupling systems (CW–MFCs) have received significant academic interest in the last decade mainly due to the promotion of MFCs in relation to pollutants’ degradation in CWs. Firstly, we investigated the effect of hydraulic retention time (HRT) and electrode configuration on the flow field characteristics of CW–MFCs using graphite rods and plates as electrodes, as well as the optimization of electrode configuration using computational fluid dynamics (CFD) numerical simulation. The results showed that: (1) the apparent HRT was the most influential and decisive factor, with a contribution of over 90% for the average HRT of CW–MFCs; (2) anode spacing was the most influential factor for the hydraulic performance of CW–MFCs, with contributions of over 50% for water flow divergence and hydraulic efficiency (λ) and over 45% for effective volume ratio (e); (3) anode size was significant for e and λ, with a contribution of over 20%; (4) cathode position and cathode size had no statistically significant effect on the hydraulic performance of CW–MFCs. It was mainly through the blocking of water flows, flows around, compressing water flow channels and boundary layer separation that the MFC electrodes influenced the hydraulic characteristics of the flow field in CW–MFCs. Optimizing the flow field by optimizing the electrode configuration helped to facilitate electricity generation and pollutants’ removal in CW–MFCs. This study offers a scientific reference for improving the hydraulic performance of CW–MFCs, and it also provides a new research perspective for improving the wastewater treatment and electricity production performance of CW–MFCs.

Transformation from biofiltration unit to hybrid constructed wetland-microbial fuel cell: Improvement of wastewater treatment performance and energy recovery

This study aimed to compare the performance of biofiltration, constructed wetland, and constructed wetland microbial fuel cell (CW-MFC). The transformation from a biofiltration unit to a hybrid CW-MFC was demonstrated with the advantages of improvement of wastewater treatment while generating electricity simultaneously. The introduction of plants to the upper region of the bioreactor enhanced the DO level by 0.8 mg/L, ammonium removal by 5 %, and COD removal by 1 %. The integration of electrodes and external circuits stimulated the degradation rate of organic matter in the anodic region (1 % without aeration and 3 % with aeration) and produced 5.13 mW/m3 of maximum power density. Artificial aeration improved the nitrification efficiency by 38 % and further removed the residual COD to an efficiency of 99 %. The maximum power density was also increased by 3.2 times (16.71 mW/m3) with the aid of aeration. In treating higher organic loading wastewater (3M), the maximum power density showed a significant increment to 78.01 mW/m3 (4.6-fold) and the COD removal efficiency was 98 %. The ohmic overpotential dominated the proportion of total loss (67-91 %), which could be ascribed to the low ionic conductivity. The reduction in activation and concentration loss contributed to the lower internal resistance with the additional aeration and higher organic loading. Overall, the transformation from biofiltration to a hybrid CW-MFC system is worthwhile since the systems quite resemble while CW-MFC could improve the wastewater treatment as well as recover energy from the treated wastewater.

Effect of External Aeration on Cr (VI) Reduction in the Leersia hexandra Swartz Constructed Wetland-Microbial Fuel Cell System

Cr (VI) is hazardous to humans and our environment. Leersia hexandra Swartz (L. hexandra) is the first wet chromium hyperaccumulator found in China. This study constructed the L. hexandra constructed wetland-microbial fuel cell (CW-MFC) system to treat Cr (VI) wastewater. It also determined the effects of different dissolved oxygen (DO) concentrations on power generation, pollutant removal, and Cr (VI) reduction. Cathode aeration promoted the voltage output and pollutant removal of the L. hexandra CW-MFC when the DO concentration was 4.5 mg·L−1: the highest voltage was 520 mV, the chemical oxygen demand (COD) removal rate was 93.73%, and the Cr (VI) removal rate was 97.77%. Moreover, the increase in the DO concentration improved the absorption of heavy metal Cr by the substrate and L. hexandra, and promoted the transformation from Cr (VI) to Cr (III). Chromium mostly exists as a residue with low toxicity and low mobility in L. hexandra and the substrate. This proves that the increased DO concentration promotes the redox reaction in the system and plants, reducing Cr (VI) to Cr (III). At the same time, the key micro-organism Geobacter that enhances the performance of the system and Cr (VI) reduction was found. The research results can provide a reference for the subsequent CW-MFC treatment of actual Cr-containing wastewater.

Innovative pilot-scale constructed wetland-microbial fuel cell system for enhanced wastewater treatment and bioelectricity production

In this study, a unique configuration of pilot scale constructed wetland-microbial fuel cell (CW-MFC) system was evaluated in terms of chemical oxygen demand (COD) removal from synthetic wastewater and bioelectricity generation. The system consists of nine individual CW-MFC units and two aerobic chambers configured in a fibre-reinforced rectangular tank (Total working volume-135.5 L). Typha angustifolia was used as wetland plant. To enhance electrical performance of the system, two auxiliary MFCs equipped with terracotta-based separator-electrode-assembly (SEA) were integrated into the anodic zone of each CW-MFC unit in addition to the conventional sediment-configured MFC. The system was evaluated in fed-batch and continuous up-flow modes of operations. All the CW integrated MFCs were studied individually without any combinations (parallel/series). In fed-batch mode, the CW-MFC unit of the system removed a maximum of 97.56 ± 1.6 % of COD from wastewater. The highest power and current densities achieved by the auxiliary MFCs were 58.55 mW/m2 and 229.6 mA/m2 respectively. In the continuous up-flow mode, the pilot-scale system treated around 4100 L of wastewater and exhibited a maximum of 82.8 ± 1.9 % COD removal efficiency. Whereas, the auxiliary MFCs attained the maximum power and current densities of 41.44 mW/m2 and 283.3 mA/m2 respectively. In both modes, the internal resistance of the auxiliary MFCs was found to be two times lower than that of the conventional sediment-configured MFCs of the system. The overall results manifested that the inclusion of SEAs and aerobic chambers in this innovative pilot-scale CW-MFC shows merit and improved the energetics of the system.

The effect of aeration on treatment efficiency and bioenergy generation of septic-tank effluent in constructed wetland-microbial fuel cell

This study examines the effect of different rates and modes of supplementary aeration on the treatment of synthetic septic tank effluent in a lab-scale unplanted constructed wetland-microbial fuel cell (CW-MFC) along with bioenergy generation. The experiment was conducted in 4 sequential phases; 1) the cell was operated with no aeration (NA), 2&3) the cathode layer was continuously aerated under different aeration rates (CA-I and CA-II), and 4) the cathode layer was intermittently aerated (IA). Results showed that the dissolved oxygen gradient caused by IA formed aerobic and anoxic zones in CW-MFC and promoted total nitrogen removal. The best performance was observed with intermittent aeration where the maximum removal efficiencies of COD (96.8 ± 3.3 %), TN (62.3 ± 2.1 %), TKN (68.3 ± 2.0 %), and NH3 (64.8 ± 2.3 %) were achieved. Furthermore, this treatment efficiency corresponded with enhanced bioenergy generation under the IA regime, achieving maximum power output (7.5 mW/m2), highest average voltage output (0.399 ± 0.02 V), Coulombic efficiency (1.94 %), and normalized energy recovery (1.4 Wh/m3). Continuous aeration, however, induced an adverse effect on energy generation due to excessive oxygen penetration into the anode region. Nitrate accumulation was also observed as a sign of an incomplete denitrification process under the continuous aeration regime. Overall, it can be concluded that the intermittently aerated CW-MFC not only lowers operational costs but improves effectiveness in terms of the nitrogen removal process in the treatment of septic tank effluent.

Effects of multiple key factors on the performance of petroleum coke-based constructed wetland-microbial fuel cell

In this study, two constructed wetland-microbial fuel cells (CW-MFC), including a closed-circuit system (CCW-MFC) and an open-circuit system (OCW-MFC) with petroleum coke as electrode and substrate, were constructed to explore the effect of multiple key factors on their operation performances. Compared to a traditional CW, the CCW-MFC system showed better performance, achieving an average removal efficiency of COD, NH4+-N, and TN of 94.49 ± 1.81%, 94.99 ± 4.81%, and 84.67 ± 5.6%, respectively, when the aeration rate, COD concentration, and hydraulic retention time were 0.4 L/min, 300 mg/L, and 3 days. The maximum output voltage (425.2 mV) of the CCW-MFC system was achieved when the aeration rate was 0.2 L/min. In addition, the CCW-MFC system showed a greater denitrification ability due to the higher abundance of Thiothrix that might attract other denitrifying bacteria, such as Methylotenera and Hyphomicrobium, to participate in the denitrifying process, indicating the quorum sensing could be stimulated within the denitrifying microbial community.

Enhanced degradation of ibuprofen in an integrated constructed wetland-microbial fuel cell: treatment efficiency, electrochemical characterization, and microbial community dynamics.

Over the past few decades, there has been a growing concern regarding the fate and transport of pharmaceuticals, particularly antibiotics, as emerging contaminants in the environment. It has been proposed that the presence of antibiotics at concentrations typically found in wastewater can impact the dynamics of bacterial populations and facilitate the spread of antibiotic resistance. The efficiency of currently-used wastewater treatment technologies in eliminating pharmaceuticals is often insufficient, resulting in the release of low concentrations of these compounds into the environment. In this study, we addressed these challenges by evaluating how different influent ibuprofen (IBU) concentrations influenced the efficiency of a laboratory-scale, integrated constructed wetland-microbial fuel cell (CW-MFC) system seeded with Eichhornia crassipes, in terms of organic matter removal, electricity generation, and change of bacterial community structure compared to unplanted, sediment MFC (S-MFC) and abiotic S-MFC (AS-MFC). We observed that the addition of IBU (5 mg L-1) resulted in a notable decrease in chemical oxygen demand (COD) and electricity generation, suggesting that high influent IBU concentrations caused partial inhibition for the electroactive microbial community due to its complexity and aromaticity. However, CW-MFC could recover from IBU inhibition after an acclimation period compared to unplanted S-MFC, even though the influent IBU level was increased up to 20 mg L-1, suggesting that plants in CW-MFCs have a beneficial role in relieving the inhibition of anode respiration due to the presence of high levels of IBU; thus, promoting the metabolic activity of the electroactive microbial community. Similarly, IBU removal efficiency for CW-MFC (i.e., 49-62%) was much higher compared to SMFC (i.e., 29-42%), and AS-MFC (i.e., 20-22%) during all experimental phases. In addition, our high throughput sequencing revealed that the high performance of CW-MFCs compared to S-MFC was associated with increasing the relative abundances of several microbial groups that are closely affiliated with anode respiration and organic matter fermentation. In summary, our results show that the CW-MFC system demonstrates suitability for high removal efficiency of IBU and effective electricity generation.

Effects of flow pattern, Leersia hexandra, and circuit mode on the Cr(Ⅵ) removal capacity, electricity generation performance, and microbial community of constructed wetland-microbial fuel cells

Cr(Ⅵ) can harm the environment and human health due to its high toxicity. Constructed wetland-microbial fuel cells (CW-MFCs) systems are cheap and effective tools for wastewater purification and electricity generation with broad application prospects. This study investigated the Cr(VI) removal performance, electricity generation performance, and microbial community of up-flow, up-down flow, and down-flow CW-MFCs with the hyperaccumulator Leersia hexandra and open and closed circuit modes. The power density of the down-flow CW-MFC with L. hexandra was higher (64.2 mW/m2) than that of the CW-MFC without plants (52.05 mW/m2) and CW-MFCs with other flow patterns under exposure to 40 mg/L Cr(Ⅵ). The down-flow CW-MFC with L. hexandra had a higher current response and charge transfer capability, which enhanced the abundance of electricigens (e.g., Acinetobacter) in the anode. The Cr(VI) wastewater treatment performance of the down-flow CW-MFC with L. hexandra was superior to that of CW-MFCs with other flow patterns. L. hexandra and the closed circuit mode can enhance the Cr(VI) wastewater treatment performance of the CW-MFC, which stems from the photosynthesis and enrichment capacity of L. hexandra and the positive effect of the closed circuit on the performance of L. hexandra. Cr(Ⅵ)-reducing bacteria (e.g., Acinetobacter, Simplicispira, Propionivibrio, Comamonas, and Rhizobium) were abundant in the cathode. The higher wastewater purification and electricity generation performance of the down-flow CW-MFC stems from the stronger charge transferability and current response associated with its unique flow pattern.

Constructed Wetland Coupled Microbial Fuel Cell: A Clean Technology for Sustainable Treatment of Wastewater and Bioelectricity Generation

The availability of clean water and the depletion of non-renewable resources provide challenges to modern society. The widespread use of conventional wastewater treatment necessitates significant financial and energy expenditure. Constructed Wetland Microbial Fuel Cells (CW-MFCs), a more recent alternative technology that incorporates a Microbial Fuel Cell (MFC) inside a Constructed Wetland (CW), can alleviate these problems. By utilizing a CW’s inherent redox gradient, MFC can produce electricity while also improving a CW’s capacity for wastewater treatment. Electroactive bacteria in the anaerobic zone oxidize the organic contaminants in the wastewater, releasing electrons and protons in the process. Through an external circuit, these electrons travel to the cathode and produce electricity. Researchers have demonstrated the potential of CW-MFC technology in harnessing bio-electricity from wastewater while achieving pollutant removal at the lab and pilot scales, using both domestic and industrial wastewater. However, several limitations, such as inadequate removal of nitrogen, phosphates, and toxic organic/inorganic pollutants, limits its applicability on a large scale. In addition, the whole system must be well optimized to achieve effective wastewater treatment along with energy, as the ecosystem of the CW-MFC is large, and has diverse biotic and abiotic components which interact with each other in a dynamic manner. Therefore, by modifying important components and optimizing various influencing factors, the performance of this hybrid system in terms of wastewater treatment and power generation can be improved, making CW-MFCs a cost-effective, cleaner, and more sustainable approach for wastewater treatment that can be used in real-world applications in the future.

Enhanced Swine Wastewater Treatment by Constructed Wetland—Microbial Fuel Cell Systems

This paper studies the effects of planting plants and coupled microbial fuel cells (MFCs) on the decontamination capacity and purification mechanism of constructed wetlands (CWs). Four systems were set, namely CW-without plants (A1), CW-with plants (A2), CW-MFC-without plants (A3) and CW-MFC-with plants (A4). The daily reductions per unit area of chemical oxygen demand (COD) were 48.72 ± 5.42, 51.26 ± 4.10, 53.49 ± 5.44 and 58.54 ± 4.16 g·(d·m2)−1, respectively. The daily reductions per unit area of nitrogen (N) were 11.89 ± 0.73, 12.38 ± 0.76, 12.24 ± 0.79 and 13.61 ± 1.07 g·(d·m2)−1, respectively. After studying the pollutant removal efficiency, it was found that the unit area of A4 removes the highest number of pollutants, improving the area efficiency of the wetland system and fundamentally alleviating the disadvantage of the large land footprint of wetland processes. The average output voltages of A3 and A4 were 568.29 and 717.46 mV, respectively, and the maximum power densities were 4.59 and 15.87 mW/m3, respectively. In addition, after high-throughput analysis of microbial samples, anaerobic ammonia oxidising (anammox) bacteria were found to remove N from the system in the anaerobic anode region.

Performance assessment of constructed wetland-microbial fuel cell for treatment of mariculture wastewater containing heavy metals

Mariculture wastewater poses potential risks to the sustainability of the coastal environment. In this study, different types of constructed wetland-microbial fuel cells (CW-MFC), including up-flow CW-MFC (UCW-MFC), down-flow CW-MFC (DCW-MFC), and hybrid up-flow/down-flow CW-MFCs (HCW-MFC) were constructed to evaluate their efficiency to treat mariculture wastewater containing heavy metals (Cu and Zn). The results showed that both the UCW-MFC and DCW-MFC operated with aeration demonstrated better removal performance for conventional pollutants. The presence of heavy metals in wastewater reduced the removal of NH4+-N and total inorganic nitrogen, but had no significant effect on the removal of chemical oxygen demand (COD) and total phosphorus (TP). The HCW-MFC had better removal performance than the UCW-MFC and DCW-MFC, especially when treating heavy metal containing wastewater. All systems had excellent removal performance for (Cu2+ and Zn2+), resulting in concentrations below the first discharge standard. All the systems produced S2-, which could react with Cu2+/Zn2+ to form CuS/ZnS, leading to the removal of heavy metals from the systems. The average output voltage of the three systems was 561.64 ± 16.64 mV for UCW-MFC, 634.73 ± 9.33 mV for DCW-MFC, and 1074.88 ± 49.90 mV for HCW-MFC, respectively. In addition, the maximum power density (PAmax) increased by 160.81 % and 44.16 % in HCW-MFC compared to those of UCW-MFC and DCW-MFC systems, respectively. Further, connecting the three systems successfully derived a light-emitting diode to emit light, which indicated that CW-MFC systems have promising application prospects for both pollutant removal as well as energy recycling.

Electroactive constructed wetland using Fe3C as an anodic exogenous electron donor: Performance and mechanisms

Constructed wetland microbial fuel cells (CW-MFCs) are promising for removing trace contaminants. We investigated using Fe3C as an anodic exogenous electron donor in a CW-MFC to remove bisphenol A (BPA). BPA removal and electricity production were used to evaluate the CW-MFC performance, and bacterial high-throughput sequencing was used to investigate the microbial response. The experimental system removed BPA (91.62 ± 0.85 %), chemical oxygen demand (76.44 ± 2.25 %), total phosphorus (98.40 ± 0.17 %), and ammonium nitrogen (91.62 ± 0.85 %). It also had a high voltage (352.13 ± 31.48 mV) and power density (3.88 mW/m2), and relatively high coulombic efficiency (3.31 %). Fe3C addition enhanced bacterial cooperation and community stability, and increased the abundance of electroactive and ferric ammonium oxidation bacteria (Desulfovibrio and Geobacter). These changes explained the improved water purification effect and electricity production. Fe3C as an anodic electron donor in CW-MFCs is promising for practical applications.

Mechanism of Fe-C micro-electrolysis substrate to improve the performance of CW-MFC with different factors: Insights of microbes and metabolic function.

Constructed wetland-microbial fuel cell (CW-MFC) is a novel technology for wastewater treatment with electrical generation. This work proposed a Fe-C micro-electrolysis substrate (Fe-C) with biomass modified ceramsite to enhance pollutants removal and electricity generation. The key influencing factors were revealed, and the COD, NH4+-N, and TP removal efficiency was respectively increased by 10.2, 8.1 and 8.78% with 76% higher power output at optimal conditions (e.g. OLR 52.5g/(m2.d), HRT 48h, and aeration rate 800mL/min). Fe-C based substrates improved the microenvironments in CW-MFC, including dissolved oxygen (DO) and oxidation-reduction potential (ORP) lowering and electron transfer facilitation. These contributed to the enrichment of critical microorganisms and metabolic activities. The abundance of functional bacteria (i.e. Geobacter, Thauera and Dechloromonas) were evidently increased. Additionally, the energy metabolism and other functional genes encoding cytochrome c (ccoN), nitrite reductase (nirD) and phosphate transporter (pstA) were all stimulated.