Promoting the bio-cathode formation of a constructed wetland-microbial fuel cell by using powder activated carbon modified alum sludge in anode chamber

Advancement in constructed wetland microbial fuel cell process for wastewater treatment and electricity generation: a review

The constructed wetland coupled with a microbial fuel cell (CW-MFC) is a wastewater treatment process that combines contaminant removal with electricity production, making it an environmentally friendly option. This hybrid system primarily relies on anaerobic bioprocesses for wastewater treatment, although other processes such as aerobic bioprocesses, plant uptake, and chemical oxidation also contribute to the removal of organic matter and nutrients. CW-MFCs have been successfully used to treat various types of wastewater, including urban, pharmaceutical, paper and pulp industry, metal-contaminated, and swine wastewater. In CW-MFC, macrophytes such as rice plants, Spartina angalica, Canna indica, and Phragmites australis are used. The treatment process can achieve a chemical oxygen demand removal rate of between 80 and 100%. Initially, research focused on enhancing power generation from CW-MFC, but recent studies have shifted towards resource recovery from wastewater. This review paper provides an overview of the development of constructed wetland microbial fuel cell technology, from its early stages to its current applications. The paper also highlights research gaps and potential directions for future research.

Performance optimization for Pb(II) -containing wastewater treatment in constructed wetland-microbial fuel cell triggered by biomass dosage and Pb(II) level

Three identical sets of constructed wetland-microbial fuel cells (CW-MFCs) fabricated with biomass carbon source addition were constructed and underwent the short- and long-term experiments. For this, the efficacy of biomass dosage and Pb(II) concentration towards Pb(II) removal and concurrent bioelectricity production of CW-MFCs were systematically explored. From the perspective of integrated capabilities and economic benefits, the solid biomass carbon sources equivalent to 500 mg/L COD was regarded as the optimal dosage, and the corresponding device was labeled as CW-MFC-2. For the short-term experiment, the closed-circuit CW-MFC-2 produced maximum output voltages and power densities in a range of 386-657 mV and 1.55 × 103-6.31 × 103 mW/m2 with the increasing Pb(II) level, respectively. Also, Pb(II) removal up to 94.4-99.6% was obtained in CW-MFC-2. With respect to long-term experiment, Pb(II) removal, the maximum output voltage, and power density of CW-MFC-2 ranged from 98.7 to 99.2%, 322 to 387 mV, and 3.28 × 102 to 2.26 × 103 mW/m2 upon 200 mg/L Pb(II) level, respectively. The migration results confirmed the potential of substrate and biomass for Pb(II) adsorption and fixation. For the cathode, Pb(II) was fixed and removed via binding to O. This study enlarges our knowledge of effective modulation of CW-MFCs for the treatment of high-level Pb(II)-containing wastewater and bioelectricity generation via adopting desirable biomass dosage.

Advances in microbial electrochemistry-enhanced constructed wetlands

Constructed wetland (CW) is an effective ecological technology to treat water pollution and has the significant advantages of high impact resistance, simple construction process, and low maintenance cost. However, under extreme conditions such as low temperature, high salt concentration, and multiple types of pollutants, some bottlenecks exist, including the difficulty in improving operating efficiency and the low pollutant removal rate. Microbial electrochemical technology is an emerging clean energy technology and has the similar structure and pollutant removal mechanism to CW. Microbial electrochemistry combined with CW can improve the overall removal effect of pollutants in wetlands. This review summarizes characterization methods of microbial electrochemistry-enhanced constructed wetland systems, construction methods of different composite systems, mechanisms of single and composite systems, and removal effects of composite systems on different pollutants in water bodies. Based on the shortcomings of existing studies, the potential breakthroughs in microbial electrochemistry-enhanced constructed wetlands are proposed for developing the optimization solution of constructed wetlands.

Interrelation between macrophytes roots and cathode in constructed wetland-microbial fuel cells: Further evidence

As an essential component in constructed wetland-microbial fuel cells (CW-MFC) system, the macrophytes play multiple roles in bioelectricity generation and decontaminants performance. However, the interrelation between macrophytes roots and cathode has not been fully investigated despite the fact that plant cultivation strategy is a critical issue in practice. For the first time, this study was designed to explore the interaction between macrophytes and cathode in CW-MFC by planting Cyperus altrnlifolius at relatively different positions from the cathode. The results showed that plants exhibited higher bioelectricity generation and dramatically improved pollution removal, as well as the improved richness and diversity of cathode microbes. More significantly, the relative locations between the plant roots and the cathode could lead to different cathode working patterns, while the optimal cathode pattern "plant root-assisted bio- & air-cathode" was formed when the plant roots are directly placed on the air-cathode layer in CW-MFC. The insight into the plant root and cathode relationship lies in whether the "multi-function cathode" can be established. This study contributes to increase the knowledge regarding the presence and behavior of plant roots and cathode throughout a CW-MFC system.

Removal of Cr(vi) and p-chlorophenol and generation of electricity using constructed wetland-microbial fuel cells based on Leersia hexandra Swartz: p-chlorophenol concentration and hydraulic retention time effects

Heavy metals and phenolic compounds existing in polluted wastewater are a threat to the environment and human safety. A downflow Leersia hexandra Swartz constructed wetland-microbial fuel cell (DLCW-MFC) was designed to treat polluted wastewater containing Cr(vi) and p-chlorophenol (4-CP). To determine the effect of 4-CP concentration and hydraulic retention time (HRT) on the performance of the DLCW-MFC system, the wastewater purification, electricity generation, electrochemical performance, and L. hexandra growth status were studied. Addition of 17.9 mg L-1 4-CP improved the power density (72.04 mW m-2) and the charge transfer capacity (exchange current, 4.72 × 10-3 A) of DLCW-MFC. The removal rates of Cr(vi) and 4-CP at a 4-CP concentration of 17.9 mg L-1 were 98.8% and 38.1%, respectively. The Cr content in L. hexandra was 17.66 mg/10 plants. However, a 4-CP concentration of 35.7 mg L-1 inhibited the removal of Cr(vi) and the growth of L. hexandra, and decreased the electricity generation (2.5 mW m-2) as well as exchange current (1.21 × 10-3 A) of DLCW-MFC. An increase in power density and removal of Cr(vi) and 4-CP, along with an enhanced transport coefficient of L. hexandra, was observed with HRT. At an optimal HRT of 6.5 d, the power density, coulomb efficiency, and exchange current of DLCW-MFC were 72.25 mW m-2, 2.38%, and 4.99 × 10-3 A, respectively. The removal rates of Cr(vi) and 4-CP were 99.0% and 78.6%, respectively. The Cr content and transport coefficient of L. hexandra were 4.56 mg/10 plants and 0.451, respectively. Thus, DLCW-MFC is a promising technology that can be used to detoxify polluted wastewater containing composite mixtures and synchronously generate electricity.

Intensifying anoxic ammonium removal by manganese ores and granular active carbon fillings in constructed wetland-microbial fuel cells: Metagenomics reveals functional genes and microbial mechanisms

The conventional biological ammonium removal process is challenged for lack of electron acceptors. A lab-scale integrated constructed wetland coupled with microbial fuel cells (CW-MFC) filling manganese ores (MO) and granular active charcoal (GAC) has been developed, named CW-CM. It enhanced the nitrogen removal two times over the control. A metagenomic-based study illustrated the functional genes and taxonomic groups related to N transformations, explored metabolic mechanisms of nitrogen and carbon sources, and then revealed some characteristics of the extracellular electron transfer (EET). Many nitrifying bacteria and autotrophic and heterotrophic denitrifiers were enriched in CW-CM. Furthermore, most nitrification and denitrification reactions except for the conversion of ammonium to hydroxylamine were significantly enhanced in CW-CM. Glycolysis and the TCA cycle were also improved. Overall, a novel anoxic ammonia removal process was achieved in the experimental group with no need of anammox functional bacteria and anammox key genes.

Effectiveness of constructed wetland integrated with microbial fuel cell for domestic wastewater treatment and to facilitate power generation

Constructed wetlands (CWs) have gained a lot of attention for wastewater treatment due to robustness and natural pollutant mitigation characteristics. This widely acknowledged technology possesses enough merits to derive direct electricity in collaboration with microbial fuel cell (MFC), thus taking advantage of microbial metabolic activities in the anoxic zone of CWs. In the present study, two identical lab-scale CWs were selected, each having 56 L capacity. One of the CW integrated with MFC (CW-MFC) contains two pairs of electrodes, i.e., carbon felt and graphite plate. The first pair of CW-MFC consists of a carbon felt cathode with a graphite plate anode, and the second pair contains a graphite plate cathode with a carbon felt anode. The other CW was not integrated with MFC and operated as a traditional CW for evaluating the performance. CW-MFC and CW were operated in continuous up-flow mode with a hydraulic retention time of 3 days and at different organic loading rates (OLRs) per unit surface area, such as 1.45 g m^-2 day^-1 (OLR-1), 2.43 g m^-2 day^-1 (OLR-2), and 7.25 g m^-2 day^-1 (OLR-3). The CW-MFC was able to reduce the organic matter, phosphate, and total nitrogen by 92%, 93%, and 70%, respectively, at OLR of 1.45 g m^-2 day^-1, which was found to be higher than that obtained in conventional CW. With increase in electrochemical redox activities, the second pair of electrodes made way for 3 times higher power density of 16.33 mW m^-2 as compared to the first pair of electrodes in CW-MFC (5.35 mW m^-2), asserting carbon felt as a good anode material to be used in CW-MFC. The CW-MFC with carbon felt as an anode material is proposed to improve the electro-kinetic activities for scalable applications to achieve efficient domestic wastewater treatment and electricity production.

A taxonomy of design factors in constructed wetland-microbial fuel cell performance: A review

The past decade has seen the rapid development of constructed wetland-microbial fuel cell (CW-MFC) technology in many aspects. The first publication on the combination of constructed wetland (CW) and microbial fuel cell (MFC) appeared in 2012, subsequently, research on the subject has grown exponentially to improve the performance of CW-MFCs in their dual roles of wastewater treatment and power generation. Although significant research has been conducted on this technology worldwide, a comprehensive and critical review of effective controlling parameters is lacking. More broadly, research is needed to draw up-to-date conclusions on recent developments and to identify knowledge gaps for further studies. This review paper systematically enumerates and reviews research studies published in this area to determine the key design factors and their role in CW-MFC performance. Moreover, a taxonomy of all CW-MFC design parameters has been synthesised from the literature. Importantly, this original work provides a comprehensive conceptual framework for future researchers, designers, builders, and users to understand CW-MFC technology. Within the taxonomy, parameters are placed in three main categories (physical/environmental, chemical, and biological/electrochemical) and comprehensive details are given for each parameter. Finally, a comprehensive summary of the parameters has been tabulated showing their impact on CW-MFC operation, design recommendations from literature, and the significant research gaps that this review has identified within the existing literature. It is hoped that this paper will provide a clear and rich picture of this technology at its current stage of development and furthermore, will facilitate a deeper understanding of CW-MFC performance for long-term and large-scale development.

Creating tidal flow via siphon for better pollutants removal in a microbial fuel cell-constructed wetland

Oxygen is the electron acceptor in cathode chamber of microbial fuel cell-constructed wetland system (MFC-CW). The objective of the study lies in creating a "tidal flow" (TF) in cathode chamber via a siphon to enhance the oxygen diffusion, thus promoting the system performance. A laboratory scale MFC-CW with a siphon driven TF recirculation was proposed and designed. It allows the variable water level being created in four operational modes. The results demonstrated the significance of the siphon which was reflected by the attractive wastewater treatment performance. Compared with the tested four operational modes under the same hydraulic condition, the highest total nitrogen removal efficiency of 96.32% and COD removal efficiency of 92.37% were achieved, respectively, in 1st full siphon recirculation mode (FSR) and 2nd FSR operation mode. Indeed, the water level variation range played an important role in pollutants removal performance. Reduced water level variation of the TF in cathode chamber hindered excessive oxygen diffusion into MFC-CW and thus adversely affected the system performance. It is clear that the siphon is a wiser input to bring about the better treatment performance, but it is believed that the enhanced microbial activities behind the oxygen promotion is the driven force to exhibiting a better performance in the MFC-CW system.

An algal assisted constructed wetland-microbial fuel cell integrated with sand filter for efficient wastewater treatment and electricity production

In this study we report on a three-stage design of algal assisted constructed wetland -microbial fuel cell incorporated sand filter for efficient treatment of wastewater and bioelectricity generation, simulating a core of it. It aims for the complete removal of organic matter and other inorganic pollutants such as NO₃^-, NH₄⁺ and PO₄^3-. The conductive material equipped anode region of constructed wetland (CW) performed better for organic removal, and the system efficiently removed COD up to 96.37 ± 2.6%. The algal biomass passively aerated the cathode region and resulted in efficient removal of 85.14 ± 10.73% of NH₄⁺ and 69.03 ± 10.14% of PO₄^3-. The additional sand filter provided anaerobic situation favorable for removal of NO₃^- up to 68.41 ± 7.63%. The maximum power and current densities achieved in the system were 33.14 mW m^-3 and 235.0 mA m^-3, respectively.

Pathways regulating nitrogen removal in constructed ditch wetlands: effects of different inflow ratios and artificial aeration

Constructed ditch wetland (CDW) is a combination of idle ditch and constructed wetland, which is typically used in rural areas to remove pollutants from domestic wastewater. However, its low total nitrogen (TN) removal remains a pressing issue. To enhance total nitrogen removal, an approach of supplying water at two locations in the CDW at different influent flow ratios, combined with artificial aeration, was proposed to adjust carbon and oxygen distribution in the system. The highest average TN removal was achieved at low influent concentration (CDW4; influent flow ratio 1:2). The removal of TN in winter and spring were 58.93 and 83.26%, respectively. The distribution of carbon sources in the back zone enhanced denitrification. Of the high influent concentration treatments, CDW2 (2:1) achieved 16.97% more TN removal on average compared with CDW1 (3:0), after extra artificial aeration was applied in the front zone. However, nitrification was a limiting step in the system, which became the primary problem preventing pollutant purification. Moreover, nitrifying bacteria abundance was negatively correlated to the influent flow ratio and autotrophic denitrifying bacterial abundance was positively correlated to the influent flow ratios. Graphical abstract.

Operation mechanism of constructed wetland-microbial fuel cells for wastewater treatment and electricity generation: A review

Constructed wetland-microbial fuel cells (CWL-MFCs) are eco-friendly and sustainable technology, simultaneously implementing contaminant removal and electricity production. According to intensive research over the last five years, this review on the operation mechanism was conducted for in-depth understanding and application guidance of CWL-MFCs. The electrochemical mechanism based on anodic oxidation and cathodic reduction is the core for improved treatment in CWL-MFCs compared to CWLs. As the dominant bacterial community, the abundance and gene-expression patterns of electro-active bacteria responds to electrode potentials and contaminant loadings, further affecting operational efficiency of CWL-MFCs. Plants benefit COD and N removal by supplying oxygen for aerobic degradation and rhizosphere secretions for microorganisms. Multi-electrode configuration, carbon-based electrodes and rich porous substrates affect transfer resistance and bacterial communities. The possibilities of CWL-MFCs targeting at recalcitrant contaminants like flame retardants and interchain interactions among effect components need systematic research.

Microbial Fuel Cell stack performance enhancement through carbon veil anode modification with activated carbon powder

The chemical energy contained in urine can be efficiently extracted into direct electricity by Microbial Fuel Cell stacks to reach usable power levels for practical implementation and a decentralised power source in remote locations. Herein, a novel type of the anode electrode was developed using powdered activated carbon (PAC) applied onto the carbon fibre scaffold in the ceramic MFC stack to achieve superior electrochemical performance during 500 days of operation. The stack equipped with modified anodes (MF-CV) produced up to 37.9 mW (21.1 W m-3) in comparison to the control (CV) that reached 21.4 mW (11.9 W m-3) showing 77% increase in power production. The novel combination of highly porous activated carbon particles applied onto the conductive network of carbon fibres promoted simultaneously electrocatalytic activity and increased surface area, resulting in excellent power output from the MFC stack as well as higher treatment rate. Considering the low cost and simplicity of the material preparation, as well as the outstanding electrochemical activity during long term operation, the resulting modification provides a promising anode electrocatalyst for high-performance MFC stacks to enhance urine and waste treatment for the purpose of future scale-up and technology implementation as an applied off-grid energy source.

Assessing the factors influencing the performance of constructed wetland-microbial fuel cell integration

Constructed wetland coupled microbial fuel cell (CW-MFC) systems integrate an aerobic zone and an anaerobic zone to treat wastewater and to generate bioenergy. The concept evolves based on the principles of constructed wetlands and plant MFC (one form of photosynthetic MFC) technologies, of which all contain plants. CW-MFC have been used in a wide range of application since their introduction in 2012 for wastewater treatment and electricity generation. However, there are few reports on the individual components and their performance on CW-MFC efficiency. The performance and efficiency of this technology are significantly influenced by several factors such as the organic load and sewage composition, hydraulic retention time, cathode dissolved oxygen, electrode materials and wetland plants. This paper reviews the influence of the macrophyte (wetland plants) component, substrate material, microorganisms, electrode material and hydraulic retention time (HRT) on CW-MFC performance in wastewater treatment and electricity generation. The study assesses the relationship between these parameters and discusses progress in the development of this integrated system to date.

Electricity production and the analysis of the anode microbial community in a constructed wetland-microbial fuel cell

The objective of this study is to assess bioelectricity generation, pollutant removal (COD, ammonium, nitrate) and the bacterial communities on anodes in constructed wetlands coupled with microbial fuel cells (CW-MFCs), through feeding the systems with three different types of synthetic wastewater (system 1: normal wastewater; system 2: ammonium-free wastewater; system 3: nitrate-free wastewater). Three CW-MFCs were operated with different wastewater concentrations and hydraulic retention times (HRTs) over a long time period (6 months). The results indicate that the maximum open circuit voltage (775.63 mV) and maximum power density (0.628 W m⁻³) were observed in system 3 (period 3), and that bioenergy production was inhibited in system 2, when feeding with ammonium-free wastewater continuously. COD removal rates in the three systems were similar during each period and ranged from 82.2 ± 6.8% to 98.3 ± 2.2%. Ammonium removal occurred at the air cathode of the CW-MFCs through nitrification, and a higher level of ammonium removal was found in system 1 (period 3) compared with the others. Meanwhile, denitrification occurred at the anaerobic anode of the CW-MFCs, and a large amount of nitrate was removed effectively. The highest nitrate removal rate was 98.8 ± 0.5% in system 2 (period 3). Additionally, four genera related to electricity generation were detected at the anode: Geothrix; Desulfovibrio; Desulfobulbus; and Geobacter. The relative abundances of Desulfovibrio, Desulfobulbus and Geothrix gradually increased during the three periods in system 3, which might be beneficial for bioelectricity generation. Further investigations are needed to optimize the CW-MFC performance and explain the mechanism behind the pollutant degradation and electron motion in the CW-MFCs.

The objective of this study is to assess bioelectricity generation, pollutant removal and the bacterial communities on anodes in constructed wetlands coupled with microbial fuel cells, through feeding the systems with three different types of synthetic wastewater.

Microbial Electrochemical Technologies for Wastewater Treatment: Principles and Evolution from Microbial Fuel Cells to Bioelectrochemical-Based Constructed Wetlands

Microbial electrochemical technologies (MET) rely on the presence of the metabolic activity of electroactive bacteria for the use of solid-state electrodes for oxidizing different kinds of compound that can lead to the synthesis of chemicals, bioremediation of polluted matrices, the treatment of contaminants of interest, as well as the recovery of energy. Keeping these possibilities in mind, there has been growing interest in the use of electrochemical technologies for wastewater treatment, if possible with simultaneous power generation, since the beginning of the present century. In the last few years, there has been growing interest in exploring the possibility of merging MET with constructed wetlands offering a new option of an intensified wetland system that could maintain a high performance with a lower footprint. Based on that interest, this paper explains the general principles of MET, and the different known extracellular electron transfer mechanisms ruling the interaction between electroactive bacteria and potential solid-state electron acceptors. It also looks at the adoption of those principles for the development of MET set-ups for simultaneous wastewater treatment and power generation, and the challenges that the technology faces. Ultimately, the most recent developments in setups that merge MET with constructed wetlands are presented and discussed.

Effect of biochar on bio-electrochemical dye degradation and energy production

The effect of coconut shell biochar on dye degradation in a microbial fuel cell (MFC) was investigated in the present study. Two different doses of biochar (0.5 g and 1 g) and one control without bio-char were studied. The highest COD removal efficiency was about 77.7% (0.5 g biochar), maximum current (1.07 mA) and voltage (722 mV) were obtained with 1 g biochar. Biofilm optical microscopy characterization revealed the micro colonies intricate plate-like structures. High adsorbent dosage might provide a high surface area for biofilm to generate electricity. BET results of coconut shell biochar showed the maximum surface area of 0.9669 m²/g and macroporosity (0.0032 cm³/g). The overall results highlighted the possibility of using biochar as an additive in MFC for efficient dye degradation.

Influence of glass wool as separator on bioelectricity generation in a constructed wetland-microbial fuel cell

To figure out the impact of the separator on the electrical performance of the newly established constructed wetland-microbial fuel cell (CW-MFC), two parallel upflow CW-MFC systems, with and without glass wool (GW), were set up in this study. System performances in terms of bioelectricity production were monitored for more than 4 months. Results showed that the highest voltage was achieved in non-separator (NS) system (465.7 ± 4.2 mV with electrode spacing of 5 cm), which is 48.9% higher than the highest value generated in GW system (312 ± 7.0 mV with electrode spacing of 2 cm). The highest power density was produced in NS system (66.22 mW/m²), which is 3.9 times higher than the value in GW system (17.14 mW/m²). The diffusion of oxygen from the open air was greatly hindered by the biofilm formed under the cathode. This kind of biofilm can be severed as the "microbial separator", playing the same role in a real separator.

First study to explore the feasibility of applying microbial fuel cells into constructed wetlands for COD monitoring

Chemical oxygen demand (COD) is one of the major targets to remove in constructed wetlands (CWs) system. Traditional method for COD measurement is a complex, time-consuming and highly toxic reagents participated procedure. In this study, microbial fuel cell (MFC) was successfully integrated into CW for indicating COD concentration. Results showed that there are two linear correlations between bioelectrical signals (output voltage from MFC) and COD concentration (acetate), which are COD from 0 to 500mg/L (101.99±7.42 to 631.74±7.41mV, R²=0.9710) and then from 500 to 1000mg/L (631.74±7.41 to 668.46±0.01mV, R²=0.9245). Furthermore, results also revealed the specificity of the system in terms of different types of carbon source. Overall, this work presented the feasibility of using CW-MFC for in-situ sensing COD during the wastewater treatment process, which will be a promising technique for water quality monitoring within CWs.

Energy capture and nutrients removal enhancement through a stacked constructed wetland incorporated with microbial fuel cell

To improve the sustainability of constructed wetlands (CWs), a novel tiered wetland system integrated with a microbial fuel cell (MFC) was developed in this study. Compared to the single stage CW, chemical oxygen demand (COD) removal efficiency was improved from 83.2% to 88.7%. More significantly, this tiered system significantly enhanced total nitrogen removal efficiency (an increase from 53.1% to 75.4%). In terms of MFC integration, a gradually decreased performance in electricity production was observed during its 3 months of operation (the voltage dropped from nearly 600 mV to less than 300 mV), which resulted in a reduction of power density from around 2 W/m³ to less than 0.5 W/m³. The deterioration in performance of the air-cathode is the main reason behind this, since the electrode potential of the cathode under open circuit reduced from 348.5 mV to 49.5 mV while the anode potential kept constant at around -400 mV. However, in spite of its electrical performance reduction, it was proved that MFC integration enhanced COD removal and the nitrification process. Further work is needed to improve the stability and feasibility of this new system.

Carbon-Based Microbial-Fuel-Cell Electrodes: From Conductive Supports to Active Catalysts

Microbial fuel cells (MFCs) have attracted considerable interest due to their potential in renewable electrical power generation using the broad diversity of biomass and organic substrates. However, the difficulties in achieving high power densities and commercially affordable electrode materials have limited their industrial applications to date. Carbon materials, which can exhibit a wide range of different morphologies and structures, usually possess physiological activity to interact with microorganisms and are therefore fast-emerging electrode materials. As the anode, carbon materials can significantly promote interfacial microbial colonization and accelerate the formation of extracellular biofilms, which eventually promotes the electrical power density by providing a conductive microenvironment for extracellular electron transfer. As the cathode, carbon-based materials can function as catalysts for the oxygen-reduction reaction, showing satisfying activities and efficiencies nowadays even reaching the performance of Pt catalysts. Here, first, recent advancements on the design of carbon materials for anodes in MFCs are summarized, and the influence of structure and surface functionalization of different types of carbon materials on microorganism immobilization and electrochemical performance is elucidated. Then, synthetic strategies and structures of typical carbon-based cathodes in MFCs are briefly presented. Furthermore, future applications of carbon-electrode-based MFC devices in the energy, environmental, and biological fields are discussed, and the emerging challenges in transferring them from laboratory to industrial scale are described.

Role of macrophyte and effect of supplementary aeration in up-flow constructed wetland-microbial fuel cell for simultaneous wastewater treatment and energy recovery

This study investigates the role of plant (Elodea nuttallii) and effect of supplementary aeration on wastewater treatment and bioelectricity generation in an up-flow constructed wetland-microbial fuel cell (UFCW-MFC). Aeration rates were varied from 1900 to 0mL/min and a control reactor was operated without supplementary aeration. 600mL/min was the optimum aeration flow rate to achieve highest energy recovery as the oxygen was sufficient to use as terminal electron acceptor for electrical current generation. The maximum voltage output, power density, normalized energy recovery and Coulombic efficiency were 545.77±25mV, 184.75±7.50mW/m³, 204.49W/kg COD, 1.29W/m³ and 10.28%, respectively. The variation of aeration flow rates influenced the NO₃^- and NH₄⁺ removal differently as nitrification and denitrification involved conflicting requirement. In terms of wastewater treatment performance, at 60mL/min aeration rate, UFCW-MFC achieved 50 and 81% of NO₃^- and NH₄⁺ removal, respectively. E. nuttallii enhanced nitrification by 17% and significantly contributed to bioelectricity generation.