A schematic summary of the mechanism employed by the plants for the uptake and, degradation/detoxification of emerging PPCP contaminants, and the potential applications and advances in ...phytoremediation for the sustainable treatment of contaminated environments.
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•Man-made activities are responsible for extensive pollution of water reservoirs.•Enzymatic catalysis is the major key mechanism of contaminant removal.•Novel engineered wetlands can act as complementary wastewater treatment strategy.•Advanced genetic methodologies should be employed to improve phytoremediation.
The industrial revolution in the production of pharmaceuticals and personal care products (PPCPs) has significantly improved public health in recent years. However, this development has also led to water pollution because of the unintentional disposal of these synthetic chemicals, creating unacceptable sanitary conditions. Conventional wastewater treatment systems can eliminate most of the contaminants, however these are not efficient in removing PPCPs. Plant-based remediation is a simple, yet very effective and eco-friendly approach that can complement existing wastewater treatment. Phytoremediation of emerging contaminants is relatively new, and various key concepts including the uptake and detoxification mechanisms remain relatively unexplored compared with microbial processes. This review comprehensively discusses the latest studies on the biochemistry and application of phytoremediation for the removal of PPCPs from wastewater, focusing on the mechanisms of uptake and detoxification through the enzymatic biotransformation of PPCPs and the latest field applications using innovative engineered systems. Future research recommendations are addressed, including the need of topics warranting investigation in PPCPs interactions with plant tissues, their metabolic transformation in plants, development of new predictive uptake models and futuristic advancements involving the cutting-edge methodologies in genetic engineering for the realization of advanced phytoremediation technologies. This review is an effort to gather the scattered information on research updates of phytoremediation in recent decade to present an outlook of the emerging, green biotechnology for the rehabilitation of the environment.
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•CW can be integrated with MFC for wastewater treatment and electricity generation.•Aeration in cathode area will significantly benefit power generation.•The continuous flow CW-MFC ...with cathode aeration is worth further investigation.
This study has served as more encouraging signs that constructed wetlands (CWs) can incorporate microbial fuel cells (MFCs) into their design to produce electrical energy while treating wastewater. Two 3.7L CW-MFCs have been constructed to treat swine wastewater with one (System 1) operated in batch mode while the other (System 2) was operated in continuous, upward flow mode and incorporated air diffusion heads to aerate the cathode. System 1 removed, on average, 71.5% of COD (with initial concentration of 3190–7080mg/L) and produced a peak power density of 12.83μW/m2. The aeration of the cathode significantly enhanced the performance of the CW-MFC, with System 2 demonstrating an average of 76.5% COD removal (average influent COD concentration of 1058.45±420.89mg/L) with a peak power density of 9.4mW/m2.
This investigation is the first of its kind to evaluate the interrelation of sulphate (SO42-) 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 NH4+ 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.
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•Abundance of sulphate influences the treatment performance in CW-MFC.•Conductive material assisted the NH4+ 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.
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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.
The objective of water ecosystem management is shifting from halting water quality deterioration to promoting ecological rehabilitation. One area of growing attention within this context is to remove ...the refractory organics from water ecosystem. Bioelectrochemical system (BES) owns the capability for bioelectricity generation or value-added product production. Its combining with constructed wetland (BES-CW) was demonstrated a novel measure to remove refractory organics with the integration of exogenous electron donor/acceptor-electrodes. Therefore, the review summarized the former researches on the removal of refractory organics in BES-CWs. It comprehensively reveals the research evolution and degradation mechanisms, and extensively analyzes the response of performance to operational structure and conditions, followed by proposing feasible intensive strategies. Additionally, the sustainability of BES-CW was discussed through life cycle assessment and economic feasibility assessment. The limitations and future research directions of BES-CW for removing refractory organics in term of mechanisms, operational conditions and practical applications have been highlighted. It is expected to accelerate the transformation of BES-CW from laboratory to engineering applications.
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•BES-CW is being widely used for the removal of emerging refractory organics.•The mechanism of BES-CW for removing refractory organics relies on each unit synergy.•Intensive strategies focus on coupled device, operating mode and functional substrate.•BES-CW is deemed a sustainable process based on LCA and economic feasibility analysis.
Constructed wetlands for antibiotics and heavy metals removal have become important reservoirs of antibiotic resistance genes (ARGs) and heavy metal resistance genes (MRGs), especially in the ...substrates. Here, substrate-free hydroponic microcosms of Myriophyllum aquaticum were established; tetracyclines (TCs) and Cu(II) were added to evaluate the behaviours of ARGs and MRGs in the microcosms. Several ARGs, MRGs, and mobile genetic elements (MGE) were detected in the biofilms attached to the plants, ranging from 0.5 to 2.3 × 108 copies/g dry weight. ARGs and MRGs exhibited higher relative abundances in the effluent suspended solids (SS); however, their absolute amounts were much lower than those in conventionally constructed wetlands. Microcosms with TCs and Cu(II) exhibited a higher level of resistant genes than those with compound added singularly owing to co-selection pressure. The existence of TCs and copper significantly changed the microbial communities in the microcosms. The exogenous input of TC/Cu(II) and microbial community structure were the factors driving the occurrence of ARGs, whereas MRGs were more correlated with the copper addition. Thus, reducing the exogenous inputs of antibiotics /heavy metals and SS of the effluent is suggested for the mitigation of resistant genes in phytoremediation technologies working in the absence of conventional substrates.
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•Tetracyclines and Cu(II) were efficiently removed by the substrate-free systems.•Resistant genes emerged despite the lack of any substrate material.•The absolute amounts of resistant genes were much lower in the hydroponic system.•Gene abundances related to biofilm formation were significantly higher than control.•Reducing solids in effluents may minimise the introduction of these genes.
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•Realistic conditions than most of previous CW-MFC designs.•Artificial electron acceptors in anaerobic condition prompt the oxidation.•On average 33% higher COD removal in HSSF-CWs ...with MFCs.•Treatment improvement reconfirms the earlier lab-scale results of CW-MFC.•Bigger scale implementation of the concept is possible.
This work presents a new hybrid technology for treating wastewater along with electricity generation. The main objective of this work was to integrate a microbial fuel cell (MFC) into a horizontal subsurface constructed wetland (HSSF-CW-MFC) at a pilot scale for improving the wastewater treatment performance of HSSF-CW. The HSSF-CW-MFC was tested on three different organic loading rates: 0.15, 0.30, and 0.52 kg COD/m3/d at a set hydraulic retention time. The HSSF-CW-MFC was further studied for establishing the influence of electron transfer using conductive material (artificial electron acceptor) on wastewater treatment performance. During the efficient electron transfer (system run in closed-circuit operation), 33.7% higher chemical oxygen demand (COD) removal was achieved in comparison to the hindered electron transfer (system run in open circuit) condition. The results illustrate that efficient electron transfer from bottom anaerobic zones to the aerobic zone of the HSSF-CW helps in enhancing the treatment performance. The maximum power and current densities achieved were 11.67 mW/m3and 17.15 mA/m3, respectively.
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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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