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•EPS, microbial communities and its implications for clogging were investigated.•Total EPS quantity increased in SSFCWs by applying aeration with biochar addition.•Contents of ...different types of EPS decreased from upper to lower substrate layer.•Biochar and aeration enhanced the abundance of microbes but reduced the diversity.•Aeration and biochar addition may increase potential risks of clogging in SSFCWs.
Substrate clogging is regarded as one of the main influencing factors on the sustainable operation in subsurface flow constructed wetlands (SSFCWs). The accumulation of extracellular polymeric substances (EPS) produced by microbial metabolism may contribute to the substrate clogging due to the increasing formation of biofilms in CWs. In this study, the quantity and composition of EPS, and the distribution and variation of bacterial communities in different CW systems with and without aeration and biochar addition were comparatively investigated. Biochar and intermittent aeration addition could shift the production and compositions of EPS in SSFCW. Higher total EPS production was observed in CW with intermittent aeration and biochar (328 mg L−1), compared with control (241 mg L−1), CW with biochar addition (154 mg L−1) and CW with intermittent aeration (285 mg L−1). In addition, biochar addition could decrease the content of soluble EPS (S-EPS), and combination of biochar and aeration could increase the content of tightly B-EPS (TB-EPS). Four fluorescent components were identified in EPS samples by parallel factor (PARAFAC) analysis. The fluorescence intensity of tryptophan-like substance was maximum, followed by tyrosine-like substance and humic acid-like substance. The application of intermittent aeration and biochar improved the abundance of microbes but decreased the diversity of microbes. Moreover, higher relative abundance of some functional bacteria correlated with the nitrogen removal was found in biochar added intermittently aerated SSFCW. The obtained results revealed that intermittent aeration and biochar addition could enhance treatment performance, but might have a potential risk of substrate clogging in SSFCWs.
The aim of this study was to assess the environmental impact of microbial fuel cells (MFCs) implemented in constructed wetlands (CWs). To this aim a life cycle assessment (LCA) was carried out ...comparing three scenarios: 1) a conventional CW system (without MFC implementation); 2) a CW system coupled with a gravel-based anode MFC, and 3) a CW system coupled with a graphite-based anode MFC. All systems served a population equivalent of 1500 p.e. They were designed to meet the same effluent quality. Since MFCs implemented in CWs improve treatment efficiency, the CWs coupled with MFCs had lower specific area requirement compared to the conventional CW system. The functional unit was 1m3 of wastewater. The LCA was performed with the software SimaPro® 8, using the CML-IA baseline method. The three scenarios considered showed similar environmental performance in all the categories considered, with the exception of Abiotic Depletion Potential. In this impact category, the potential environmental impact of the CW system coupled with a gravel-based anode MFC was around 2 times higher than that generated by the conventional CW system and the CW system coupled with a graphite-based anode MFC. It was attributed to the large amount of less environmentally friendly materials (e.g. metals, graphite) for MFCs implementation, especially in the case of gravel-based anode MFCs. Therefore, the CW system coupled with graphite-based anode MFC appeared as the most environmentally friendly solution which can replace conventional CWs reducing system footprint by up to 20%. An economic assessment showed that this system was around 1.5 times more expensive than the conventional CW system.
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•MFCs implemented in CWs improve treatment efficiency and reduce surface requirement.•LCA of CWs coupled with MFCs and conventional CWs was performed.•CWs coupled with MFCs and conventional CWs showed similar environmental impacts.•MFCs implemented in CWs can reduce system footprint while keeping the environmental impacts low.•MFCs implemented in CWs are around 1.5 times more expensive than conventional CWs.
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•Role of anammox process in constructed wetland (CW) is discussed.•Nitrogen transformation and removal pathways in CWs via anammox process are discussed.•Various factors affecting N ...removal in CW via Anammox are discussed.•Anammox bacteria improve the total nitrogen removal efficiency of CW.•Macrophytes support anammox enrichment in CW systems.
Constructed wetland (CW) is regarded as one of the major sustainable eco-technologies that offers robust and effective remediation of several types of contaminants. Nevertheless, when viewed from the aspect of nitrogen removal, the remediation efficiency of CWs is quite unsatisfactory and exhibits considerably fluctuating total nitrogen removal efficiencies ranging between 40% and 70%. Moreover, N2O production from nitrification and denitrification is inevitable in CWs. Anaerobic ammonium oxidation (Anammox) is an eco-friendly technology whose energy autarky and excellent nitrogen removals are well known. Consequently, its integration in CWs along with different system modifications like biochar addition, microbial fuel cell (MFC) incorporation for bioelectricity production, and degradation of organic pollutants, besides phytoremediation, could be one of the potential solutions to overcome the shortcomings of CWs. Although low temperature and electrode biological reaction can decrease the efficiency of MFC coupled anammox-CW systems. Different studies have discussed the contribution of anammox in various nitrogen transformation and removal pathways like simultaneous partial nitrification, anammox, and denitrification (SNAD), Partial nitrification-anammox (PN/A), Partial denitrification-anammox (PD/AMX) for efficient N removal. Limited nitrification and denitrification in response to low oxygen transfer and carbon source is one of the major limitations of CWs. However, this opens opportunities for anammox integration as it requires low dissolved oxygen (DO) and no carbon source to eliminate nitrogen. Macrophytes including Typha and Phragmites species were found promising for anammox enrichment while studying several CW systems. This provides a way forward for future researchers to investigate associated challenges and put together a cost-effective approach for reducing nitrogen.
There is an urgent need to develop low-cost technology for effective wastewater treatment and its further disinfection to the level that makes it economically useful. This work has designed and ...evaluated the various types of constructed wetlands (CWs) followed by a slow sand filter (SSF) for wastewater treatment and disinfection. The studied CWs were, CWs with gravels (CW-G), free water surface-CW (FWS-CWs), and CWs integrated microbial fuel cell (MFC) with granular graphite (CW-MFC-GG) planted with Canna indica plant species. These CWs were operated as secondary wastewater treatment technologies followed by SSF for disinfection purposes. The highest total coliform removal was observed in the combination of CW-MFC-GG-SSF which achieved a final concentration of 172 CFU/100 mL, whereas faecal coliform removal was 100 % with the combinations of CW-G-SSF and CW-MFC-GG-SSF, achieving 0 CFU/100 mL in the effluent. In contrast, FWS-SSF achieved the lowest total and faecal coliform removal attaining a final concentration of 542 CFU/100 mL and 240 CFU/100 mL, respectively. Furthermore, E. coli were detected as negative/absent in CW-G-SSF and CW-MFC-GG-SSF, while it was positive for FWS-SSF. In addition, the highest turbidity removal was achieved in CW-MFC-GG and SSF combination of 92.75 % from the municipal wastewater influent turbidity of 82.8 NTU. Furthermore, in terms of overall treatment performance of CW-G-SSF and CW-MFC-GG-SSF, these systems were able to treat 72.7 ± 5.5 % and 67.0 ± 2.4 % of COD and 92.3 % and 87.6 % of phosphate, respectively. Additionally, CW-MFC-GG also exhibited a power density of 85.71 mA/m3 and a current density of 25.71 mW/m3 with 700 Ω of internal resistance. Thus, CW-G and CW-MFC-GG followed by SSF could be a promising solution for enhanced disinfection and wastewater treatment.
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•Demonstrated low-cost technology for efficient wastewater treatment and disinfection in field•CW, CW-MFC, and FWS were used as secondary treatment followed by SSF as tertiary level treatment.•CW-MFC-GG-SSF gained highest TC and FC removal with 172 and 0 CFU/100 mL in effluent, respectively.•CW-G showed highest volume reduction, thus conducive to clogging and reduced life span in long run.•CW-G-BSSF and CW-MFC-GG-SSF effluent pass stringent regulations for reuse in agriculture purposes
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•Pollutants were removed via CWs periodically under day-night alterations.•Day-night alterations shifted the rhizosphere microbial community in CWs.•Keystone bacteria relevant to C, ...N, and P metabolism had higher abundance during the daytime.•Microbial metabolism promoted pollutant removal more at night than during the daytime.•Environmental factors exerted a significant influence in driving rhizosphere microbial processes.
Constructed wetlands (CWs), as nature-based wastewater treatment systems, continuously maintain exchanges of material and energy with the natural environment. However, it is unclear how pollutant removal performance in CWs occurs in response to diurnal variation. Herein, we investigated the effects of day-night alterations on the rhizosphere microbial community in CWs. The results revealed that a dynamic alternate mechanism existed in the inner environment when the CWs were in steady operation, which was validated by rhythmic changes in the core microbial community, microbial metabolism activity, and pollutant removal shown in this study. The results showed that pollutant removal (e.g., total nitrogen) due to microbial processes was 1.31 times higher under daytime conditions than under nighttime conditions. Core microbial taxa of the rhizosphere that evolved with circadian rhythm (e.g., Chloroflexus and Beijerinckia) were mostly associated with carbon, nitrogen, phosphorus, and energy metabolism, with lower average relative abundance identified at night. Although higher activity of microbial metabolism was also observed in the daytime, nighttime conditions demonstrated higher gene levels that were related to carbon and nitrogen metabolic functions. Structural equation model (SEM) analysis further suggested that environmental factors exerted a significant influence in driving microbial processes for pollutant removal and that the microbial community played a greater role in promoting pollutant removal under nighttime conditions than under daytime conditions.
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•IVCW could achieve simultaneous nitrogen and antibiotic removal.•Sulfamethoxazole (SMX) removal exceeds 95% primarily via biodegradation.•Enrichment of Pseudomonas, Bradyrhizobium, ...Sphingomonas, Luteimonas for SMX removal.•SMX transforms nitrogen transformation process to favor ANAMMOX.
This study aims to provide insights into the fate and effects of the antibiotic sulfamethoxazole (SMX) on nitrogen transformation processes in integrated vertical-flow constructed wetlands (IVCW), which is useful to create strategies to improve their degradation and combat antibiotic resistance dissemination. Findings indicated chronic exposure to SMX to cause moderate deterioration of IVCW performance for nitrogen removal (p < 0.05), with average TN removal efficiency reductions of circa 10%. High-throughput sequencing and network analysis demonstrated chronic exposure of antibiotics to impact functional bacteria, ammonium oxidizing bacteria (AOB) and ANAMMOX, significantly. ANNAMMOX emerged as a potential pathway of nitrogen removal in the IVCW, albeit with considerable accumulation of NO3−-N (12.76 mg/L) and carbon deficiency (C/N = 0.99). Nonetheless, IVCW provides a promising technology for the advanced treatment of antibiotic-containing wastewater, demonstrated by a high and stable removal efficiency (circa 95%) of sulfamethoxazole. Biodegradation, primarily in the first stage of the IVCW, represented the major removal pathway of SMX. Microbial network analysis and the enrichment of Pseudomonas, Bradyrhizobium, Sphingomonas and Luteimonas demonstrated potential for the biodegradation of SMX. These results provide a theoretical reference for the enhancement of nitrogen and antibiotics removal in constructed wetlands.
•ECW could reduce the overall environmental impacts by 49.2% than conventional CW.•ECW could significantly reduce indirect and direct N2O emission.•Electricity consumption became the main ...environmental impacts source in all CWs.•ECW could save the overall costs of 61.8% and area of 65.0% than conventional CW.
The sustainability of the integrated bioelectrochemical-constructed wetland system (ECW) is still debatable. In this study, the environmental impact and economic performance of the conventionally constructed wetland (CW) and ECW were conducted using the life cycle assessment method. The results showed that both CW and ECW had significant impacts on the aquatic environment, especially on marine aquatic ecotoxicity. Although the application of the electrode module, especially the power supply, increased 118.0% of the environmental impacts from construction materials due to the massive use of plastics and metals, the overall environmental impact of ECW was 49.2% lower than that of the CW and the total global warming potential of ECW were mitigated by 69.1% compared with the CW. In terms of cost, the ECW could reduce 61.8% of the total cost when reaching the same effluent standard with the CW, indicating that ECW was environmentally and economically feasible.
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Surface-flow constructed wetlands (CWs) are systems that replicate the nutrient reduction processes of natural wetlands and are considered suitable measures to reduce the nutrient losses from ...agricultural drainage discharge to surface waters. The present study aimed to investigate the biogeochemical stability of phosphorus (P) in three CWs. Intact soil cores were collected from each CW zone and included the soil and the sediment layer (average 28 mm thickness) formed by deposition of the incoming sediments with the water flow. Soil and sediment layer were analysed geochemically, including bulk density, pH, and total contents of carbon, nitrogen, P as well as different extracts of iron (Fe), aluminium and P. In situ measurements of soil redox potential, dissolved oxygen concentration and temperature were carried out in the CWs during 16 months. Grab water samples were collected across the CWs for determination of P species, total Fe, sulphate and pH. Soil core analysis revealed that the major P storage in the CWs was attributed to retention of Fe-bound P in the sediment layer. The Fe and total P (TP) retention differed significantly between CWs (11–63 g Fe m−2 yr−1 and 1–9 g TP m−2 yr−1). Amorphous Fe oxides constituted the major P sorbent fraction in the soil and sediments of all CWs, and the higher P sorption capacity in the sediment layer demonstrated the continuous supply of P sorbents to this layer. The stability of Fe-bound P in the anaerobic sediments seemed to be controlled by the high molar ratios of bicarbonate-dithionite extractable Fe (FeBD) to associated P, which varied from 21 to 49, and the presence of an aerobic sediment-water interface.
•Phosphorus sorption capacity (mass basis) generally increased in the sediment layer.•Sediments were generally less saturated with phosphorus than the underlying soil.•Phosphorus deposition was mainly associated with particles and iron.•Oxygen concentration at the sediment-water interface varied seasonally.•Reactive phosphorus in the water tended to increase under low oxygen concentration.
Combined sewer overflows (CSOs) are a major source of surface water pollution and degradation. This is particularly visible where sewage collection with combined sewer and centralized treatment are ...well established, such as in Europe and North America: an overwhelming number of surface water bodies are in insufficient status of ecology, hydrology and physico-chemical parameters. Therefore, several countries have started implementing constructed wetlands (CWs) as mainstream on-spot treatment. This paper summarizes the main design approaches that can be adopted. We identified eight different schemes for the implementation of CSO-CWs, based on our international experience and documented by a literature analysis. The performance review includes conventional water quality parameters, as well as pathogen and emergent contaminant removal. Furthermore, modelling tools for advanced design and for understanding a wide applicability of these green infrastructures are presented. This paper also provides a review on other side benefits offered by the adoption of Nature-Based Solutions for CSO treatment, such as ecosystem services, and the most common issues related to their operation and maintenance. Our analysis has produced a list of key factors for design and operation, all derived from full-scale installations in operation up to more than ten years.
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•Combined sewer overflows (CSOs) convey significant pollutant loads to water bodies.•Constructed wetlands (CWs) are Nature-Based Solutions for CSO pollution control.•Review gives state-of-the-art of CSO-CWs based on research and year-long practice.•CSO-CWs show effective removal of conventional, emerging and pathogenic pollutants.•CSO-CWs can provide other ecosystem services (e.g. flood protection, biodiversity).
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•Plant uptake of pollutants was similar in CW-MFCs under open- and close-circuit.•Live plants enhanced the power output by 68–97% compared with unplanted CW-MFC.•Iris improved removal ...of COD, N, and power density by 43, 66, and 97% in the CW-MFC.•Dead Hya. harms the CW-MFC by releasing pollutants and lowering power production.•Phragmites improved COD removal and power density by 28.38% and 68.02%.
The aim of this study was to determine the role of plants on pollutant removal and bioelectricity production in the treatment of municipal wastewater with constructed wetland matrix incorporating microbial fuel cells (CW-MFCs) compared to traditional CWs. Multi-anode unplanted and planted CW-MFCs (Iris pseudacorus, Hyacinth pink, and Phragmites australis) were established in fed-batch mode. CW-MFC modules with established vegetation had high treatment efficiencies with COD, NO3−-N, NH4+-N, and PO43−-P removal of 46.9–51.6%, 94.8–97.4%, 43.2–71.5%, and 96.0–97.6%, respectively, compared to 36.6%, 89.9%, 43.0%, 97.1% in the unplanted wetland module, respectively. More efficient pollutant removal and higher power production were correlated with higher plant growth. The highest maximum power density achieved was 25.14 mW/m2 in the multi-anode CW-MFC planted with Iris pseudacorus at highest plant height (1635 cm). The CW-MFC planted with Iris pseudacorus enhanced NH4+-N removal by 66.2% and significantly contributed to bioelectricity generation by 97.5% compared to the unplanted CW-MFC. The results highlight the significant role of growing plants in the CW-MFC matrix in strengthening the bioenergy output compared with enhancement in wastewater treatment in CW-MFCs. Future studies should focus on improvement in cathode potential over a long-term operation and minimize the negative role of withered plants on the planted CW-MFCs.
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