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The current study was conducted to understand the sole role of graphite as a substrate material in a dual-chambered baffled electroactive wetland (EW) in the treatment of Methyl red dye-containing wastewater. The results obtained were compared with conventional gravel-based unplanted dual-chambered constructed wetlands (CW) at a lab scale. The highest dye decolorisation and COD removal efficiency achieved was 92.88 ± 1.6% and 95.78 ± 4.1%, respectively, in the electro-active wetland. Dissolved oxygen (DO) and pH conditions were appropriately maintained in both the microcosms because of separated aerobic and anaerobic chambers. UV–vis and gas chromatography-mass spectroscopy analysis revealed the production of by-products like 4-amino benzoic and N- N dimethyl phenyl-diamine of MR in microcosms and revealed further mineralisation of by-products in the aerobic zone of electroactive-wetland. Higher root growth of Cicer aerietinum and Vigna radiata was observed in the presence of effluents of baffled electroactive wetlands compared to constructed wetland, indicating a decrease in phytotoxicity. Metagenomic analysis revealed the abundance of potential microbes for MR and organic matter removal from phylum Proteobacteria, Firmicutes, Bacteroidetes, and Euryarchaeota. A batch adsorption study revealed a higher adsorption capability of graphite material in comparison to gravel. Hence, this study demonstrated that graphite is an appropriate substrate in electroactive wetland in facilitating microbial attachments and enhancing dye degradation, in addition to exhibiting superior adsorption quality. [ABSTRACT FROM AUTHOR]

Multiple anodes can significantly enhance the treatment potential of constructed wetlands coupled with a microbial fuel cell (CW-MFC) system, which has not yet been explored. Thus, the present study evaluates the potential of multi-anodes and single cathode-based CW-MFC at significantly higher organic loading rates for treatment performance and bioelectricity generation. For this purpose, two identical but different materials, i.e., graphite granules (GG) and granular activated charcoal (GAC), were used to set up multiple anodes and single cathode-based CW-MFCs. The graphite granules (GG)-based system is named CW-MFC (GG), and the granular activated charcoal (GAC) based system is named as CW-MFC (GAC). These systems were evaluated for chemical oxygen demand (COD), NH4+-N removal efficiency, and electrical output at relatively higher organic loading rates of 890.11 g COD/m3-d and 1781.32 g COD/m3-d. At an OLR of 890.11 g COD/m3-d, the treatment efficiency was found to be 24.8% more in CW-MFC (GAC) than CW-MFC (GG), whereas it was 22.73% more for CW-MFC (GAC) when OLR was increased to 1781.32 g COD/m3-d. Whereas, NH4+-N removal efficiency was more in CW-MFC (GG) i.e., 56.29 ± 7% and 56.09 ± 3.9%, compared to CW-MFC (GAC) of 36.59 ± 3.8% and 50.59 ± 7% at OLR of 890.11 g COD/m3-d and 1781.32 g COD/m3-d, respectively. A maximum power density of 48.30 mW/m3 and a current density of 375.67 mA/m3 was produced for CW-MFC (GAC) under an organic loading rate of 890.11 g COD/m3-d. [ABSTRACT FROM AUTHOR]

The present work designs a low-cost biological treatment strategy consisting of constructed wetlands (CWs) followed by entrapped algae (EA) for removing nutrients (PO43−, NO3−, and NH4+) and organic matters from high-strength wastewater. The CWs are efficient means for organic pollutant removal but face challenges in nutrient removal. Algae have a high growth rate and nutrient uptake capabilities from wastewater. The severe challenge that limits the use of algae for nutrient removal from wastewater is its post-treatment separation from wastewater. This work presents a strategy to address the described problems of CWs and algae-based system. It also assesses the performance of the system using synthetic wastewater. A combined system of CW followed by EA (CW-EA) was able to treat 86.0% of phosphate, 95.0% of nitrate, 74.0% of ammonium, and 87.0% of chemical oxygen demand (COD) from high-strength wastewater. [ABSTRACT FROM AUTHOR]

The present work is the first detailed study, which is about the performance of CW after MFC integration with it. The experiments were run in open and closed circuit mode for assessment purpose. The findings of this study indicate towards a more practical application of MFC in wastewater treatment along with electricity production. The closed circuit operations of CW–MFCs have performed 12–20% better than open circuit operation and 27–49% better than Normal-CW for chemical oxygen demand (COD) removal. The maximum power density of 320.8 mW/m 3 and current density of 422.2 mA/m 3 have been achieved in granular graphite anode and Pt coated carbon cloth cathode based CW–MFC. [ABSTRACT FROM AUTHOR]

Abstract: The research work reported here is about an innovative way of designing constructed wetlands (CW) for high removal rate of pollutants and to make them less land intensive. Influence of iron scrap (IS) and sulfate reducing bacterial enrichment (SRB) was studied in Canna indica planted CW microcosms. This is the first ever report which deals with such interaction for enhancing the performance of CW. Four sets of experiments were performed: first with normal-CW microcosm; second with SRB enriched CW microcosm; third with SRB and IS enriched, CW microcosm; and fourth with SRB and copper doped IS enriched CW microcosm. The microcosms were tested for color removal of methyl orange dye from synthetic wastewater. The SRB enriched CW achieved highest removal (99.5, 98.53, 97.05, 94.62, and 96.52%) and the normal-CW achieved lowest removal (93, 89.18, 48.72, 50.14, and 52.34%) from wastewater containing 500, 1000, 1500, 2000 and 2500mgl−1 dye respectively. Higher removal was achieved in SRB and IS enriched CW in comparison to other CW microcosms. At higher concentrations, enhancement in performance of SRB and SRB–IS enriched CW over normal CW was clearly achieved which was not observed in lower concentrations. During treatment of 2500mgl−1 dye containing wastewater, it was observed that the dye removal percentage was 37.02 higher in SRB-CW over normal-CW and 19.48% higher in SRB–IS-CW over SRB-CW in 24h of contact time. These results clearly revealed that higher removal rate of color of dye can be achieved in innovative constructed wetlands. [Copyright &y& Elsevier]

Abstract: The present study deals with comparative evaluation of three different plants species, i.e. Canna indica L., Typha angustifolia L. and Cyperus alternifolius L. planted vertical constructed wetlands (CWs) microcosms for Cu, Cr, Co, Ni and Zn removal from aqueous solution. The effects of depth of the gravel beds were also studied in order to explore possibilities of development of compact constructed wetlands. Linear regression analysis was carried out for predicting the final removal efficiencies by variation of the treatment time and the bed depth of filter materials. To determine the removal mechanism and mobility of heavy metals in constructed wetlands, accumulation of these metals in gravel, roots, stem and leaves of plant species were investigated. Results demonstrate that the wetland bed depth has significant, direct effect on final heavy metal removal efficiencies. Considering three different plant species, Zn removal was found to be highest (99.3% in T. angustifolia planted CWs in 72h of treatment time), and Co removal was found to be lowest (54.6% in T. angustifolia planted CW in 72h of treatment time). [Copyright &y& Elsevier]

Abstract: This research work deals with performance assessment of constructed wetlands-microbial fuel cell (CW-MFC) for electricity production and wastewater treatment. Microbial fuel cell consists of two chambers i.e. anaerobic and aerobic, where oxidation and reduction reactions take place. Constructed wetland also consists of aerobic and anaerobic zones where oxidation and reduction processes take place. These similarities in both technologies motivated us to design and develop a new type constructed wetland-microbial fuel cell. In this CW-MFC, the removal of dye and COD were investigated along with electricity generation. Experiments were performed in batch mode using different dye (methylene blue dye) concentration containing synthetic wastewater. Our results show that 76.2, 80.87, 69.29 and 93.15 percentage dye removal could be achieved after 96h of treatment of wastewater containing 2000, 1500, 1000 and 500mgl−1 initial concentration respectively. Also, the CW-MFC is able to remove 75% of COD form wastewater with 1500mgl−1 initial concentration of dye. The maximum power density of 15.73mWm−2 and maximum current density of 69.75mAm−2 could be achieved during treatment of 1000mgl−1 initial dye concentration containing wastewater. [Copyright &y& Elsevier]

Abstract: The present study was conducted to investigate the chromium and nickel removal from aqueous solutions in constructed wetland microcosms using Canna indica Lin. species. Effects of different hydraulic retention times (HRTs), initial metal concentrations and depth of gravel beds on removal of chromium and nickel were studied. Maximum removal of chromium and nickel was found to be 98.3(±0.32) and 96.2(±1.52) %, respectively, at initial concentrations of 10mgl−1 and at an HRT of 48h in 0.95m gravel bed depth constructed wetland microcosms. The attempt was made to know the possible mechanism of metals removal and their mobility within the plant. In order to reuse the exhausted gravel, desorption possibilities were tested. Desorption of 35, 25 and 33% of chromium and 60, 98 and 100% of nickel from gravel were achieved with 0.50mM EDTA, 0.1M HNO3 and 0.1M CaCl2 solutions, respectively. [Copyright &y& Elsevier]

[Display omitted] • Aluminium dross beads enhance practical utility of raw aluminium dross. • Efficiently removes pollutants from both flowing and stagnant water environments. • Maximum phosphate and ammonium removal achieved were 85 % and 93 %, respectively. • Treated water can prevent algal growth, ensuring safe water discharge. On global scale, eutrophication is one of the most prevalent environmental threats to water quality, primarily caused by elevated concentration of nutrients in wastewater. This study utilizes aluminum dross (AD), an industrial waste, to create a value-added material by improving its operational feasibility and application for removing phosphate and ammonium from water. The operational challenges of AD such as its powdered nature and effective operation under only extreme pH conditions were addressed by immobilizing in calcium alginate to form calcium alginate aluminium dross (Ca-Alg-Al dross) beads. These Ca-Alg-Al dross beads were further tested for phosphate and ammonium removal from natural wastewater in two different aqueous environment systems: (i) vertical flow constructed wetlands (VF-CWs) followed by Ca-Alg-Al dross beads fixed bed system and (ii) Ca-Alg-Al dross beads mounted floating constructed wetlands (FCW) for remediating polluted lentic ecosystems. Our results show maximum phosphate and ammonium removal of 85 ± 0.41 % and 93.44 %, respectively, in VF-CWs followed by Ca-Alg-Al dross beads fixed bed system. The Ca-Alg-Al dross beads mounted FCW system achieved maximum phosphate removal of 79.18 ± 8.56 % and ammonium removal of 65.45 ± 21.04 %. Furthermore, the treated water from the FCW system was assessed for its potential to inhibit algal growth by artificially inoculating treated water with natural algae to simulate eutrophic conditions. Interestingly, treated water from the FCW system was found capable of arresting the algal growth. Besides, scanning electron microscopy with energy dispersive X-ray (SEM-EDX) and Fourier transform infrared (FTIR) spectroscopy confirmed the functional groups and surface properties and probable participation of multiple mechanisms including ion exchange, electrostatic attraction, and ligand complexation for phosphate and ammonium removal. Overall, these results offer a promising way to utilize AD for high-end applications in wastewater treatment. [ABSTRACT FROM AUTHOR]

This study developed microbial fuel cell (MFC)-based hybrid constructed wetland systems using different filter media, i.e., organic (biochar), construction (sand), and rejected (iron particle, concrete particle, and stone dust) materials, and evaluated the performance of the developed systems for treating landfill leachate. The mean ammonium nitrogen (NH 4 –N), total nitrogen (TN), total phosphorus (TP), biochemical oxygen demand (BOD), chemical oxygen demand (COD) removal percentages within the hybrid systems ranged between 91 and 98%, 90 and 98%, 97 and 99%, 88 and 93%, 93 and 97%, respectively, despite higher pollutants concentration in leachate wastewater. The aerobic environment in the cathode compartment (due to intermittent load) and free-draining of wastewater (from cathode to anode compartment) supported electrochemically inactive, active pollutants removal in the electrodes integrated first stage vertical flow (VF) wetlands. The second stage electrodes integrated horizontal flow (HF) wetlands supported electrochemical-based organic removal and nitrification because of efficient organic removal in the previous VF wetland stages. Nitrogen, phosphorus accumulation percentages in plant tissues ranged between 0.3 and 7%, 0.4 and 14%, respectively. Nutrient removal was achieved through chemical and microbial routes. The biochar-packed VF wetland produced a maximum power density of 20.6 mW/m2. The coexistence of unsaturated, saturated media in the partially saturated HF wetland maintained the required environmental gradient between the electrodes and improved operational performance. [Display omitted] • Electrodes integrated hybrid wetlands treated landfill leachate. • Free-draining improved pollutant removal of the VF wetlands. • Filter media influenced bioenergy production in VF wetlands. • Media saturation controlled the operational performance in HF systems. [ABSTRACT FROM AUTHOR]

This investigation is the first of its kind to evaluate the interrelation of sulphate (SO 4 2-) with conductive materials as well as their individual and synergetic effects on the removal of ammonium and organic pollutants in electroactive wetlands, also known as constructed wetland (CW) - microbial fuel cell (MFC). The role of MFC components in CW was investigated to treat the sulphate containing wastewater under a long-term operation without any toxicity build-up in the system. A comparative study was also performed between CW-MFC and CW, where sulphate containing wastewater (S-replete) and without sulphate wastewater (S-deplete) was assessed. The S-replete showed high NH 4 + removal than the S-deplete, and the requesnce of removal was: CW-MFC-replete > CW-MFC-deplete > CW-replete > CW-deplete. The chemical oxygen demand (COD) removal was high in the case of CW-MFC-replete, and the sequence of removal was CW-MFC-replete > CW-MFC-deplete > CW-deplete > CW-replete. X-ray photon spectroscopic study indicates 0.84% sulphur accumulation in CW-MFC-replete and 2.49% in CW-replete, indicating high sulphur precipitation in CW without the MFC component. The high relative abundance of class Deltaproteobacteria (7.3%) in CW-MFC-replete along with increased microbial diversity (Shannon index = 3.5) rationalise the symbiosis of sulphate reducing/oxidising microbes and its impact on the treatment performance and electrochemical activity. [Display omitted] • Abundance of sulphate influences the treatment performance in CW-MFC. • Conductive material assisted the NH 4 + removal that enhances in presence of sulphate. • CW-MFC with sulphate was inhabited with diverse microbial community. • Abundance of sulphate impacts the electron transfer in CW-MFC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxido-reductive azo reductase enzyme of plant treat orgaic pollutants. • Plant uptake and storage in stem cells also play role in treatment of pollutants. • Plants do chemisorption of MR dye as indicated by pseudo-second order kinetics. • C. indica shows high tolerance towards MR azo dye toxicity. • Planted CW system peform better than non planted CW. Direct role of macrophyte (aquatic plant) in constructed wetlands has been an issue of serious debate in organic pollutant treatment for last many decades. The present study was performed to investigate the direct role of plants using azo dye methyl red (MR) as a model organic pollutant in constructed wetlands. The study was performed using widely used wetland macrophyte Canna indica L. (Cannaceae) in constructed wetlands with multiple controls experiments. Dye decolourization and ultraviolet–visible spectroscopy (UV–Vis) study revealed that about 99.0 % removal of MR occurred in presence of plants. Results show that C. indica based CW system was able to remove 99.0 % of colour and 75.0 % of COD while the system without C. indica was able to remove 73.6 % of colour and 42.0 % of COD. Simultaneously, accumulation of MR was also observed in the cells of C. indica stem at the end of experimental period. Gas chromatography–mass spectrometry (GC–MS) analysis established that the cleavage of mutagenic azo bond occurred due to the presence of plants. Instead, in absence of plants though discolouration took place, but breakdown of azo bond was not found. Kinetic models depict that plants perform chemisorption mechanism for degradation of MR. Negligible reduction in plant growth and regulatory functions stated that the wetland plants can phyto-remediate and withstand such concentration of MR (50 mg/L) provided during the study. The study affirms that wetland plants can play a direct role in degradation and detoxification of organics pollutant. Results from the experiment revealed that plants play a direct role for the treatment of organic pollutants in constructed wetland treatment system. [ABSTRACT FROM AUTHOR]

In less than a decade, bioelectrochemical systems/microbial fuel cell integrated constructed wetlands (electroactive wetlands) have gained a considerable amount of attention due to enhanced wastewater treatment and electricity generation. The enhancement in treatment has majorly emanated from the electron transfer or flow, particularly in anaerobic regions. However, the chemistry associated with electron transfer is complex to understand in electroactive wetlands. The electroactive wetlands accommodate diverse microbial community in which each microbe set their own potential to further participate in electron transfer. The conductive materials/electrodes in electroactive wetlands also contain some potential, due to which, several conflicts occur between microbes and electrode, and results in inadequate electron transfer or involvement of some other reaction mechanisms. Still, there is a considerable research gap in understanding of electron transfer between electrode-anode and cathode in electroactive wetlands. Additionally, the interaction of microbes with the electrodes and understanding of mass transfer is also essential to further understand the electron recovery. This review mainly deals with the electron transfer mechanism and its role in pollutant removal and electricity generation in electroactive wetlands. • The review provides a comprehensive understanding of electroactive wetlands. • Challenge and future research direction of electroactive wetlands are discussed. • Technical aspects of electron flow in electroactive wetlands are provided. • Mechanism of enhanced pollutant removal and electricity generation are discussed. [ABSTRACT FROM AUTHOR]

Landfill leachate treatment employing normal and electrode-integrated constructed wetlands is difficult due to the presence of significant amounts of organic compounds, which frequently impede the progression of microbial-based aerobic pollutant removal pathways. As a result, this study examines the effect of supplementary air availability via intermittent and continuous aeration strategies in improving organic, nutrient, and coliform removals of the unplanted, planted (normal and electrode-integrated) two-stage tidal flow constructed wetlands designed to treat landfill leachate. The constructed wetlands were filled with coal and biochar media and planted with Canna indica. Mean chemical oxygen demand (COD), total nitrogen (TN), total phosphorus (TP), and coliform removal percentages of the externally aerated two-stage unplanted, only planted, planted-microbial fuel cell integrated constructed wetland systems ranged between 96 and 99%, 82 and 93%, 91 and 98%, 86 and 96%, respectively, throughout the experimental campaign. External aeration inhibited the development of a dominant anaerobic environment within the media of the wetland systems and improved overall pollutant removal. The electrode-integrated planted tidal flow wetlands produced better effluent quality than the unplanted or only planted tidal flow systems without electrode assistance. The first stages of the three wetland systems achieved an additional 5–7% COD, 7–12% TN, and 15–22% coliform removal during the continuous aeration period compared to the corresponding performance of the intermittent aeration phase. The pollutant removal performance of the second-stage wetlands decreased during the continuous aeration phase. The media composition supported electrochemically active and inactive microbial-based pollutant removal routes and the chemical adsorption of pollutants. Nitrogen and phosphorus accumulation percentage in plant tissues was low, i.e., 0.4–2.2% and 0.04–0.8%, respectively. During the continuous aeration period, the electrode-integrated tidal flow constructed wetlands achieved higher power density production, i.e., between 859 and 1432 mW (mW)/meter3(m3). This study demonstrates that external aeration might improve pollutant removal performance of the normal, electrodes integrated tidal flow-based constructed wetlands when employed for high organic-strength wastewater treatment such as landfill leachate. [Display omitted] • Normal and electrode-assisted aerated tidal flow wetlands treated leachate. • Plants, electrodes, and aeration have a positive synergistic effect on performance. • 96–99% COD, 82–94% TN, 91–98% TP, and 86–96% coliform removals were achieved. • The nutrient accumulation percentage in plant tissues ranged between 0.02 and 2.2%. • A maximum power density production of 1572 mW/m3 was recorded. [ABSTRACT FROM AUTHOR]

[Display omitted] • Conductive biochar prompts electricity generation, and treatment efficiency. • CWs produced biomass can be reutilized in developing advanced CW-MFCs. • Plasma process produces highly electroactive biochar in few minutes. • Conductive biochar prompts microbial electron transfer and improved redox reaction. • Biochar synthesis processes influence the physico-(electro)chemical properties. This study demonstrates two sustainable processes to produce electroactive biochars and their application in electroactive constructed wetlands (CWs) for providing a circular route for biomass utilization and technology up-gradation for wastewater treatment along with electricity generation. With the use of Canna indica biomass generated in CWs operation, the current study produced two different biochars that differ in their physico-(electro)chemical properties related to the preparation method used. This study used plasma based processing to produce ultrafast biochar (PB) within a few minutes resulting in more crystalline biochar with high electrical conductivity compared to the amorphous biochar material produced by using the drum kiln processed biochar (KB) method. These biochars were used in developing electroactive constructed wetlands coupled with microbial fuel cells (CW-MFC) and were operated in batch mode together with commercial granular graphite (GG) substrate-based CW-MFC as control. PB was developed from high-temperature plasma processing in 6.0 min, whereas KB was prepared in bulk amount from semi-controlled combustion process in kiln method and took 3–4 days before final biochar preparation. Electrical conductivity (EC) of the biochar and GG material were found to be in the order of PB > GG > KB, indicating PB as a highly conductive material that assisted in microbial electron transfer. Accordingly, the highest current and power densities of 628 mA m-3 and 126 mW m-3, respectively, were also achieved with PB. The COD removal of 72.42 ± 2.61 %,72.32 ± 2.98 % and 59.91 ± 3.21 % was found in CW-MFC-GG, CW-MFC-KB and CW-MFC-PB microcosms, respectively. [ABSTRACT FROM AUTHOR]

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 NO 3 −, NH 4 + and PO 4 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 NH 4 + and 69.03 ± 10.14% of PO 4 3−. The additional sand filter provided anaerobic situation favorable for removal of NO 3 − 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. Image 1 • Realistic three-stage design of algal assisted CW-MFC integrated with sand filter. • Electron conductive materials in anaerobic condition prompt the oxidation of pollutants. • The algal cathode attributed to nutrients uptake. • Synergistic single system approach to treat organic and nutrient pollutants. [ABSTRACT FROM AUTHOR]

• A comprehensive review on the constructed wetland integrated microbial fuel cell technology. • Insights into design aspects and operational parameters of CW-MFC. • Associated challenges of CW-MFC and futuristic applications. • Electroactive bacteria as bio-electrocatalysts catalysing high removal kinetics. 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. [ABSTRACT FROM AUTHOR]