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•High removal efficiencies of COD, TN and TP in electrolysis-integrated constructed wetlands (E-CWs) were obtained.•Performance of MFC-CWs was slightly better than that of ...EC-CWs.•Higher microbial community diversity and richness in E-CWs driven higher pollutants removal.•Functional genes related to nitrogen transformation were greatly enriched in CWs by electrolysis.
The molecular mechanism of contaminant removal in different electrolysis -integrated constructed wetlands (CWs) was explored. Electrolysis (microbial fuel cells (MFC) and direct current (EC))-integrated CWs achieved high removal efficiencies for chemical oxygen demand (COD; 82.18% in MFC-CWs and 81.57% in EC-CWs), total nitrogen (TN; 75.08% in MFC-CWs and 69.19% in EC-CWs) and total phosphorus (TP; 92.56% in MFC-CWs and 92.86%), which was higher than that in CWs. Additionally, MFC-CWs had an average voltage of 384.56 ± 44.49 mV with the highest power density of 977 mW m−2. The pollutant removal performance of the MFC-CWs was better than that of the EC-CWs. Microorganisms in electrolysis-integrated CWs, especially in the MFC-CWs, gained higher diversity and richness than those in CWS. However, the effects between MFC and EC for CWs were different. In addition, nitrogen functional genes in electrolysis-integrated CWs were significantly more abundant than those in the CWs, and the electron transfer rate also increased. Combined analyses of microorganisms and functional genes revealed that the main contributors to nitrogen removal were anaerobic ammoxidation, ammonia oxidation, denitrification, and dissimilatory nitrate reduction to ammonium (DNRA) for CWs, anaerobic ammoxidation, ammonia oxidation, denitrification and DNRA for EC-CWs, anaerobic ammoxidation, ammonia oxidation and denitrification for MFC-CWs
Constructed wetlands have the capacity to degrade a host of contaminants of emerging concern through photodegradation via sunlight produced reactive oxygen species. Dissolved organic matter (DOM) is ...a critical intermediary in photodegradation as it influences the production of reactive oxygen species. In this study, the photochemical behavior of DOM of wastewater treated in constructed wetlands was characterized. Whole water samples and fractionated DOM were characterized using SUVA254, spectral slope ratios, excitation emission matrix fluorescence spectroscopy (EEMs), and proton nuclear magnetic resonance (1H NMR). Photoreactivity was assessed by measuring formation rates and steady state concentrations of hydroxyl radical (•OH), singlet oxygen (1O2), and the triplet excited states of DOM (3DOM⁎). The effluent was observed to transition from a microbially sourced protein-like DOM to a terrestrial DOM with higher aromaticity. Size exclusion chromatography revealed an 18% increase in larger molecular weight fractions of vegetated wetland effluent DOM. Additionally, wetland effluent DOM was observed to have a 32% increase in the aromatic region of 1H NMR spectra as compared to untreated wastewater. 1H NMR analysis also indicated an increase in the complexity of wetland effluent DOM. Fluorescence intensity fraction of the protein-like Peak T (Ex/Em:278/342 nm) of EEMs decreased by 16% from the untreated wastewater to wetland effluent. A negative correlation between the percent fluorescence of Peak T (Ex/Em:278/342 nm) and Peaks A (Ex/Em:245/460 nm), C (Ex/Em:336/435 nm), and M (Ex/Em:312/400 nm) of the excitation emission spectra confirmed the transition from a spectrum of pure wastewater to a spectrum characteristic of terrestrially derived DOM. Microbial uptake of bio-labile DOM and leaching of humic like substances from vegetated wetland cells were the predominant processes involved in this transition. This transition coincided with an increase in the formation rates of 1O2 and 3DOM⁎ and in the steady state concentration of 1O2.
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•Wastewater treatment constructed wetland processed DOM to a heterogenous terrestrial composition.•DOM transformation had a corresponding effect on wetland photoreactivity.•Wetland processed DOM had higher photo-generation of singlet oxygen (1O2) and triplet excited states of DOM (3DOM⁎).•Microbial assimilation of bio-labile DOM and DOM leaching from plant material influenced DOM transformation.
Phytoremediation is a low-cost, environmentally friendly, and sustainable technology that can utilize vegetation and microorganisms to avoid eutrophication and purifying water environment. The ...ability of five different living aquatic plants of nitrogen (N), phosphorus (P), and chemical oxygen demand (CODcr) removal were investigated in pilot scale constructed wetlands (CWs). Aquatic plant mixes significantly improved CODcr removal and plant tissue uptake of nitrogen and phosphorus. The wetland performance of mixed plantings was also influenced by the specific species. The mixed planting of Phragmites australi, Nymphaea Colorado and Myriophyllum verticillatum (PNM)When assessing pollutant removal in CWs, PNM performed better within mixtures, a possible synergistic effect, while TNV Typha orientalis, Nymphaea Colorado, and Vallisneria natans (TNV) performed poorly, a possible antagonist effect. The nutrient uptake within plant tissues byunder mixed plants planting was always ahad synergistic effect. Mixed plantingAquatic plant mixes significantly increased the rhizosphere microbial diversity and promoted the growth of functional denitrifying flora.
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•Mixed planting significantly promoted CODcr removal, but had no effect on nitrogen and phosphorus removal.•Mixed planting of plants were always synergistic on plant uptake of nitrogen and phosphorus.•Mixed planting significantly increased the rhizosphere microbial diversity and promoted the growth of denitrifying flora.•Selecting the right mix of plants is an effective means to enhance the efficiency of CWs and improve eutrophication.
Recycled greenhouse nutrient solution requires treatment to prevent increased concentrations of both Na.sup.+ and Cl.sup.- ions from damaging crops or impacting the environment subsequent to its ...discharge. Constructed wetlands (CW) planted with species capable of hyper-accumulating Na.sup.+ and Cl.sup.- may be one viable treatment option. To mitigate the unwanted ions from CW, plant material may need to be harvested and removed. Research suggests that multiple harvests throughout the growing season can maximize the CW phytoremediation potential. To determine the ideal frequency of CW plant harvesting, an 18-week, outdoor microcosm experiment was conducted in which three wetland plant species, Juncus torreyi Coville. (Torrey's rush), Schoenoplectus tabernaemontani (C.C. Gmel.) Palla (softstem bulrush), and Typha latifolia L. (broad leaf cattail), were subjected to the following harvesting treatments: (i) one harvest, (ii) two harvests, and (iii) three harvests. The total amounts of Na.sup.+ and Cl.sup.- accumulated in the aboveground dry biomass per square meter of plant growth area were calculated. Treatments with the highest Na.sup.+ accumulation were as follows: T. latifolia with three harvests, 24.7 g m.sup.-2, T. latifolia with two harvests, 16.2 g m.sup.-2, J. torreyi with two harvests, 12.7 g m.sup.-2. Treatments with the highest Cl.sup.- accumulation were as follows: J. torreyi with two harvests, 111.3 g m.sup.-2, T. latifolia with three harvests, 94.8 g m.sup.-2, T. latifolia with two harvests, 81.4 g m.sup.-2. Harvesting, whether two or three times, increased the Na.sup.+ and Cl.sup.- accumulated by T. latifolia and J. torreyi but did not influence the Na.sup.+ and Cl.sup.- accumulation or growth of S. tabernaemontani. However, the average Na.sup.+ and Cl.sup.- removal efficiencies of the all treatments were low, between 1-5 % for Na.sup.+ and 7-15 % for Cl.sup.-, suggesting that phytodesalinization may not be the best option for Na.sup.+ and Cl.sup.- treatment.
Leachate resulting from the decomposition of organic waste is still a challenging problem, especially in landfill management. Constructed wetlands (CW) are effective, economical, and environmentally ...friendly options to treat landfill leachate. Biochar added into CW as a pollutant adsorbent in leachate treatment. This study aimed to determine the effectiveness of sub-surface flow CW amended with biochar in reducing leachate pollutants. Biochar was synthesized from crumb rubber scrap waste using pyrolysis. The variation biochar in CW i.e. CW0 without biochar as a control system, CW1 10% biochar, CW2 20% biochar, and CW3 30% biochar. Leachate samples flowed into each CW reactor for 10 days of retention time. The scanning electron showed that the biochar pores ranged from 5-10 կm, containing elements of C, O, Ca, N, Mg, Al, Si, and Fe. Some elements have greater cumulative mass and atomic percentage values i.e. C 34.51%, O 26.54%, and Ca 21.85%. The result of CW treatment showed that the CW system was able to remove 76-88% BOD5, 70-87% COD, and 67-81% TSS. The addition of biochar in CW increased pollutant removal by 7-14%, showing that biochar is able to increase pollutant adsorption in wastewater and improve CW performance. Furthermore, converting organic waste into biochar is highly recommended as a sustainable way to generate useful resources.
The hybrid systems were developed in the 1960s but their use increased only during the late 1990s and in the 2000s mostly because of more stringent discharge limits for nitrogen and also more complex ...wastewaters treated in constructed wetlands (CWs). The early hybrid CWs consisted of several stages of vertical flow (VF) followed by several stages of horizontal flow (HF) beds. During the 1990s, HF–VF and VF–HF hybrid systems were introduced. However, to achieve higher removal of total nitrogen or to treat more complex industrial and agricultural wastewaters other types of hybrid constructed wetlands including free water surface (FWS) CWs and multistage CWs have recently been used as well. The survey of 60 hybrid constructed wetlands from 24 countries reported after 2003 revealed that hybrid constructed wetlands are primarily used on Europe and in Asia while in other continents their use is limited. The most commonly used hybrid system is a VF–HF constructed wetland which has been used for treatment of both sewage and industrial wastewaters. On the other hand, the use of a HF–VF system has been reported only for treatment of municipal sewage. Out of 60 surveyed hybrid systems, 38 have been designed to treat municipal sewage while 22 hybrid systems were designed to treat various industrial and agricultural wastewaters. The more detailed analysis revealed that VF–HF hybrid constructed wetlands are slightly more efficient in ammonia removal than hybrid systems with FWS CWs, HF–VF systems or multistage VF and HF hybrid CWs. All types of hybrid CWs are comparable with single VF CWs in terms of NH4-N removal rates. On the other hand, CWs with FWS units remove substantially more total nitrogen as compared to other types of hybrid constructed wetlands. However, all types of hybrid constructed wetlands are more efficient in total nitrogen removal than single HF or VF constructed wetlands.
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•Hybrid constructed wetlands are mostly used in Europe and Asia.•The most common hybrid system is a VF–HF combination.•Hybrid constructed wetlands are more efficient than single HF or VF units for removal of TN.
The aim of this study was to assess the environmental impact of three alternatives for wastewater treatment in small communities. To this end, a Life Cycle Assessment (LCA) was carried out comparing ...a conventional wastewater treatment plant (i.e. activated sludge system) with two nature-based technologies (i.e. hybrid constructed wetland and high rate algal pond systems). Moreover, an economic evaluation was also addressed. All systems served a population equivalent of 1500 p.e. The functional unit was 1 m3 of water. System boundaries comprised input and output flows of material and energy resources for system construction and operation. The LCA was performed with the software SimaPro®8, using the ReCiPe midpoint method. The results showed that the nature-based solutions were the most environmentally friendly alternatives, while the conventional wastewater treatment plant presented the worst results due to the high electricity and chemicals consumption. Specifically, the potential environmental impact of the conventional wastewater treatment plant was between 2 and 5 times higher than that generated by the nature-based systems depending on the impact category. Even though constructed wetland and high rate algal pond systems presented similar results in terms of environmental impact, the latter showed to be the less expensive alternative. Nevertheless, the constructed wetland system should be preferred when land occupation is of major concern, since it has a smaller footprint compared to the high rate algal pond alternative.
The presence of nanoplastics (NPs) in wastewater poses a considerable risk to ecosystems. Although constructed wetlands (CWs) have the potential to removal NPs, their efficiency is limited by ...insufficient consideration of ecosystem integrity. Herein, three typical benthic fauna (Corbicula fluminea, Chironomus riparius and Tubifex tubifex) were added to CWs to improve the ecological integrity of CWs, and further enhance the ecological benefits. Results indicated that the addition of C. fluminea, C. riparius and T. tubifex increased NPs removal by 19.14 %, 17.02 %, and 15.76 % than that without benthic faunas, respectively. Based on fluorescence signal analysis, the presence of benthic fauna could intake NPs, and enhanced the adsorption of NPs by plants. The addition of C. fluminea significantly increased catalase (1541.82 ± 41.35 U/g), glutathione S-transferase (0.34 ± 0.02 U/g), and superoxide dismutase (116.33 ± 6.91 U/g) activities (p < 0.05) as a defense mechanism against NPs-induced oxidative stress. Metagenomic analysis revealed that the abundances of key enzymes involved in glycolysis, the tricarboxylic acid cycle, and polystyrene metabolism pathways were increased when C. fluminea was added, corresponding to the microbial degradation of NPs. Overall, the results of this study implied that the benthic fauna can efficiently remove NPs from wastewater in CWs.
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•Benthic fauna increased removal efficiency of NPs in CWs by 17.33 %.•Changes of biological enzyme decreased NPs-induced oxidative stress.•Abundance of microbes that has the capacity to remove NPs was enhanced.•C. fluminea increased the abundances of key enzymes that involved in metabolic pathways.
•Plastic particles affect nitrogen removal while mitigating the release of N2O.•Large plastics reduce N2O release by impeding CO2 assimilation and NH2OH reduction.•Nanoplastics affect N metabolism by ...disrupting N-ion transmembrane transport.•Nanoplastics block the key N-removing enzyme activity, hindering N2O production.
Constructed wetlands (CWs) have been proven to effectively immobilize plastic particles. However, little is known about the differences in the impact of varying sized plastic particles on nitrous oxide (N2O) release, as well as the intervention mechanisms in CWs. Here, we built a lab-scale wetland model and introduced plastic particles of macro-, micro-, and nano-size at 100 μg/L for 370 days. The results showed that plastic particles of all sizes reduced N2O release in CWs, with the degrees being the strongest for the Nano group, followed by Micro and Macro groups. Meanwhile, 15N- and 18O-tracing experiment revealed that the ammoxidation process contributed the most N2O production, followed by denitrification. While for every N2O-releasing process, the contributing proportion of N2O in nitrification-coupled denitrification were most significantly cut down under exposing to macro-sized plastics and had an obvious increase in nitrifier denitrification in all groups, respectively. Finally, we revealed the three mechanism pathways of N2O release reduction with macro-, micro-, and nano-sized plastics by impacting carbon assimilation (RubisCO activity), ammonia oxidation (gene amo abundance and HAO activity), and N-ion transmembrane and reductase activities, respectively. Our findings thus provided novel insights into the potential effects of plastic particles in CWs as an eco-technology.
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•Nitrogen removal in constructed wetlands is achieved mainly through microorganisms.•Coupling of nitrogen transformation functional microorganisms in nitrogen removal conserves oxygen ...and energy.•The activity and diversity of nitrifiers and denitrifiers are significantly affected by plant species.•Coupling mechanisms for which substrates play the role of electron donor enhancing microbial denitrification are emphasized.•Microbial autotrophic denitrification induced by Fe, S, H and other inorganic elements can improve nitrogen removal rates.
Nitrogen removal through microorganisms is the most important pathway in constructed wetlands (CWs). In this review, we summarize the microbial coupling mechanisms of nitrogen removal, which are the common methods of nitrogen transformation. The electron pathways are shortened and consumption of oxygen and energy is reduced during the coupling of nitrogen transformation functional microorganisms. The highly efficient nitrogen removal mechanisms are cultivated from the design conditions in CWs, such as intermittent aeration and tidal flow. The coupling of microorganisms and substrates enhances nitrogen removal mainly by supplying electrons, and plants affect nitrogen transformation functional microorganisms by the release of oxygen and exudates from root systems as well as providing carriers for microbial attachment. In addition, inorganic elements such as Fe, S and H act as electron donors to drive the autotrophic denitrification process in CWs.
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