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With the wide application of floating treatment wetland (FTW), the limited performance of FTWs should be improved. A comprehensive review is accordingly necessary to summarize the state-of-the-art on FTWs for performance improvement. An attempt has been made to gain information from literature about technologies to enhance the performance of FTWs. These technologies have been classified into three categories according to their mechanisms: 1) increasing the amount and activity of bacteria; 2) enhancing the growth of plant; and 3) configurable innovations. The design and application of each enhanced FTW have been discussed in detail. Thereafter, all the technologies have been compared and analyzed according to their improvement in pollutant removal and ecological effects. In summary, FTW with additional bio-carriers has a higher potential for future applications with the benefits of wide application conditions, scale-up potential, and the easy combination with other methods to further improve the removal efficiency. The stability and sustainability of these technologies should be further investigated., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Pyrrhotite is a promising electron donor for autotrophic denitrification. Using pyrrhotite as the substrate in constructed wetlands (CWs) can enhance the nitrogen removal performance in carbon-limited wastewater treatment. However, the role of plants in pyrrhotite-integrated CW is under debate as the oxygen released from plant roots may destroy the anoxic condition for autotrophic denitrification. This study compared pyrrhotite-integrated CWs with and without plants and identified the effects of plants' presence in nitrogen removal, pyrrhotite oxidized dissolution, and microbial community. The results show that plants enhanced the TN removal significantly (from 41.6 ± 3.9 % to 97.1 ± 2.6 %). Plants can accelerate the PAD in CW through the strengthening of pyrrhotite dissolution. Enriched functional (Thiobacillus and Acidiferrobacter) and a more complex bacterial co-occurrence network has been found in CW with plants. This study identified the role of plants in PAD acceleration, providing an in-depth understanding of pyrrhotite in CW systems., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Floating constructed wetlands (FCWs) have attained tremendous popularity for water purification purposes. However, FCW functions establishment in nutrients removal from carbon-limited wastewater, especially in cold weather, is still a challenge. Here, two drinking water treatment residual (DWTR) based biocarriers (B-I: DWTR cakes, B-II: DWTR cakes combined with woodchips) have been augmented into FCW to enhance the nutrients (N and P) removal performance. Compared to the traditional FCW, the intensified FCWs simultaneously achieved higher N and P removal efficiencies, with average pollutants removal of 52.16 ± 11.51% for TN and 92.72 ± 1.61% for TP in FCW-I and 57.65 ± 9.43% for TN and 92.17 ± 2.55% for TP in FCW-II, respectively, while their removal in FCW-III of 27.74 ± 7.11% for TN and 17.91 ± 9.27% for TP. B-II performed best in overcoming the negative influence of low temperature in nutrients removal. Mass balance budget indicated that most P was enriched in DWTR based biocarriers. Thus it is feasible to recycle and recover P from the surface water. Furthermore, P in the sediment can be changed from active P to stable P, mitigating the internal P release risk. This study can help to expand the understanding of the intensified FCWs and promote the practical application of FCWs., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The embedding microbial fuel cell (MFC) into constructed wetlands (CW) to form CW-MFC bears the potential to obtain bioelectricity and a clean environment. In this study, a bibliometric analysis using VOSviewer based on Web of Science data was conducted to provide an overview by tracing the development footprint of this technology. The countries, institutions, authors, key terms, and keywords were tracked and corresponding mapping was generated. From 2012 to September 2020, 442 authors from 129 organizations in 26 countries published 135 publications in 42 journals with total citation of 3139 times were found. The key terms analysis showed four clusters: bioelectricity generation performance, mechanism study, refractory pollutants removal, and enhanced conventional contaminants removal. Further research themes include exploring the biochemical properties of electrochemically active bacteria, emerging contaminants removal, effective bioelectricity harvest and the use, and biosensor development as well as scaling-up for real field application. The bibliometric results provide valuable references and information on potential research directions for future studies., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Bioelectricity production is always restricted by the limited cathode performance in integrated constructed wetland-microbial fuel cells (termed as electro-wetlands). Generally, the cathodes are located at the air-water interface for an oxygen-rich environment. However, its performance may still be unsatisfactory, resulting in a low bioelectricity production. After a long term trial in previous study, we recognised that the position of the electron collector in the cathode significantly affected the bioelectricity production in electro-wetlands. In this study, two cathode configurations of electron collector at the air-water interface and above water level for 1.5 cm, respectively, were evaluated for cell voltage and power density in a vertical up-flow electro-wetland. Results showed that maximum total power density was increased from 31 mW/m 2 to 165 mW/m 2 when the cathode electron collector was changed from the air-water interface to 1.5 cm above water level, proving that cathode configuration is the key factor in bioelectricity production., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

There is little understanding of constructed wetlands (CWs) microbial community patterns in response to harvest management. Therefore, long-term impacts of harvesting Phragmites australis (Cav.) Trin. ex Steudel annually in November on the activity and community structure of microorganisms critical to the treatment efficiency of CW are elucidated. Findings show exponential increases in P. australis density and biomass with continuous harvesting, up to three times over unharvested CW. High-throughput pyrosequencing analysis demonstrates that plants harvesting improves the microbial community diversity and richness significantly, and more particularly, the relative abundance of Flavobacterium, Paenisporosarcina, and Povalibacter, which are extensively associated with CW performance. Consequently, increased plants biomass resulted in enhanced plants nutrients uptake in harvested (56.5 g N/m 2 , 5.5 g P/m 2 ) than unharvested CWs (17.5 g N/m 2 , 1.8 g P/m 2 ), whereas improved rhizosphere microclimates significantly enhanced nutrients removals in harvested CW (TN 109.9 g/m 2 vs 67.4 g/m 2 , TP 18.0 g/m 2 vs 13.0 g/m 2 )., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Substrate selection is one of the key technical issues for constructed wetlands (CWs), which works for wastewater treatment based mainly on the biofilm principle. In recent years, many alternative substrates have been studied and applied in CWs, and a review is conducive to providing updated information on CW R&D. Based on the intensive research work especially over the last 10 years on the development of emerged substrates (except for the three conventional substrates of soil, sand, and gravel) in CWs, this review was made. The substrates are categorized depending on their main roles in pollutant removal as ion-exchange substrates, P-sorption substrates, and electron donor substrates. Among these, reuse of various waste products as substrates was suggested due to their competitive pollutant removal efficiency and minimized waste disposal. Regarding substrate development, future research on avoiding substrate clogging to extend their lifetime in CWs is needed., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The low carbon/nitrogen (C/N) ratio and high nitrate content characteristics of agricultural runoff restricted the nitrogen removal in constructed wetlands (CWs). To resolve such problems, the economically- and easily-obtained Phragmites Australis (reeds) litters were applied and packed in the surface layer of a surface flow CW as external carbon sources. The results demonstrated that the introduction of the reeds straw increased the C concentration as a result of their decomposition during the CW operation, which will help the denitrification in the ensuing operation of an entire 148 days. The total nitrogen (TN) and Chemical Oxygen Demand (COD) () in the effluent reached the peak level of 63.2 mg/L and 83 mg/L at the fourth and the second day, respectively. Subsequently, the pollutants in the CW that were filled with straw decreased rapidly and achieved a stable removal after 13 days of operation. Moreover, the present study showed that the N removal efficiency increased with the increase of the hydraulic retention time (HRT). Under the HRT of four days, the CW presented 74.1 ± 6%, 87.4 ± 6% and 56.0 ± 6% removal for TN, NO₃⁻, and TP, respectively.

In this study, a high organic loading rate of 58-146 g BOD 5 /m 2  day with a hydraulic loading rate (HLR) of 1.63 m 3 /m 2  day and retention time (RT) of 16 h was achieved to maximize the treatment capacity of a four-stage alum sludge-based constructed wetland (CW) system. An alternative operation strategy, i.e., the first stage anaerobic up-flow and the remaining stage tidal flow with effluent recirculation, was investigated to achieve the goal with good treatment performance of 82% COD, 91% BOD 5 , 92% SS, 94% NH 4 -N, and 82% TN removal. Two kinetic models, i.e., first-order model and Monod plus continuous stirred-tank reactor (CSTR) flow model, were employed for predicting the removal dynamics. The results showed that the tidal flow strategy enhances oxygen transport and diffusion, thus improving reduction of organics and NH 4 -N. Effluent recirculation could further increase elimination of organics by extending the interaction time and also benefit the denitrification process. In addition, denitrification could be further enhanced by anaerobic up-flow in the first stage.

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/m 2 ), which is 3.9 times higher than the value in GW system (17.14 mW/m 2 ). 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., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

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, R 2 =0.9710) and then from 500 to 1000mg/L (631.74±7.41 to 668.46±0.01mV, R 2 =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., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In the last 10 years, the microbial fuel cell (MFC) has been extensively studied worldwide to extract energy from wastewater via electricity generation. More recently, a merged technique of embedding MFC into a constructed wetland (CW) has been developed and appears to be increasingly investigated. The driving force to integrate these two technologies lies in the fact that CWs naturally possess a redox gradient (depending on flow direction and wetland depth), which is required by MFCs as anaerobic anode and aerobic cathode chambers. No doubt, the integration of MFC with a CW will upgrade the CW to allow it to be used for wastewater treatment and, simultaneously, electricity generation, making CWs more sustainable and environmentally friendly. Currently, published work shows that India, China, Ireland, Spain, Germany and Malaysia are involved in the development of this technology although it is in its infant stage and many technical issues are faced on system configuration, operation and maximisation of electricity production. This paper aims to provide an updated review and analysis of the CW-MFC development. Focuses are placed on the experience gained so far from different researchers in the literature and further research directions and proposals are discussed in great detail.

In the present study, a novel green bio-sorption reactor (GBR) was firstly proposed and preliminarily investigated by embedding constructed wetland (CW) into the aeration tank of the conventional activated sludge (CAS). This integrated novel system owns the striking features of adding carriers of wetland substrate (i.e. the dewatered alum sludge in this case) in CAS for robust phosphorus adsorption and enriching the biomass. Meanwhile, the "green" feature of this GBR imparted aesthetic value of CW to the CAS system. The preliminary 3-month trial of GBR based on a sequencing batch reactor (GB-SBR) with diluted piggery wastewater demonstrated an average removal of 96%, 99% and 90% for BOD, TP and TN, respectively. The comparison with moving bed biofilm reactor (MBBR) and integrated fixed-film activated sludge (IFAS) reflected the advantages of GBR over purification performance, aesthetic value and potential carbon sink. Moreover, the carriers used in the GBR are dewatered alum sludge which is in line with the policy of "recycle, reuse and reduce". Overall, this GBR undoubtedly offered a more sustainable and economical solution for retrofitting the aging CAS., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The outcome of competition between adjoining interspecific colonies of Phragmites and Typha in two large field pilot-scale free water surface (FWS) and subsurface flow (SSF) CWs is evaluated. According to findings, the effect of interspecific competition was notable for Phragmites australis, whereby it showed the highest growth performance in both FWS and SSF wetland. In a mixed-culture, P. australis demonstrates superiority in terms of competitive interactions for space between plants. Furthermore, the interspecific competition among planted species seemed to cause different ecological responses of plant species in the two CWs. For example, while relatively high density and shoot height determined the high aboveground dry weight of P. australis in the FWS wetland, this association was not evident in the SSF. Additionally, while plants nutrients uptake accounts for a higher proportion of the nitrogen removal in FWS, that in the SSF accounts for a higher proportion of the phosphorous removal., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

The performance of a field grassed swales (GSs) coupled with wetland detention ponds (WDPs) system was monitored under four typical rainfall events to assess its effectiveness on agricultural runoff pollution control in Taihu Basin, China. The results indicated that suspended solids (SS) derived from the flush process has significant influence on pollution loads in agricultural runoff. Determination of first flush effect (FFE) indicated that total suspended solids (TSS) and total phosphorus (TP) exhibited moderate FFE, while chemical oxygen demand (COD) and total nitrogen (TN) showed weak FFE. Average removal efficiencies of 83.5 ± 4.5, 65.3 ± 6.8, 91.6 ± 3.8, and 81.3 ± 5.8 % for TSS, COD, TN, and TP were achieved, respectively. The GSs played an important role in removing TSS and TP and acted as a pre-treatment process to prevent clogging of the subsequent WDPs. Particle size distributions (PSDs) analysis indicated that coarse particles larger than 75 μm accounted for 80 % by weight of the total particles in the runoff. GSs can effectively reduce coarse particles (≥75 μm) in runoff, while its removal efficiency for fine particles (<75 μm) was low, even minus results being recorded, especially for particles smaller than 25 μm. The length of GSs is a key factor in its performance. The WDPs can remove particles of all sizes by sedimentation. In addition, WDPs can improve water quality due to their buffering and dilution capacity during rainfall as well as their water purification ability during dry periods. Overall, the ecological system of GSs coupled with WDPs is an effective system for agricultural runoff pollution control.

Phosphorus (P) removal in constructed wetlands (CWs) is often low unless special substrates with high sorption capacities are used. However, the use of special substrates in vertical flow (VF) CWs has not been proved to enhance P sorption. Thus, two VF wetlands were designed to evaluate the potential for enhanced P removal from polluted urban river water, one with slag as substrate and the other as a control with gravel as substrate. Findings from batch experiments showed P sorption capacities of 3.15 gP/kg and 0.81 gP/kg, respectively, for steel slag and gravel. Different organic matter fractions played different roles in P sorption, the effects of which were significant only at high concentrations. Over a 220 days' operation, the VF-slag removed 76.0% of the influent total phosphorus (TP) at 0.159 g/m(2)·d and PO4-P of 70.9% at 0.063 g/m(2)·d, whereas the VF-gravel removed 65.0% at 0.136 g/m(2)·d and 48.6% at 0.040 g/m(2)·d, respectively. Therefore, the merit of using a steel slag substrate in VF wetlands can be significant for the removal of PO4-P.

Constructed wetlands (CWs) and microbial fuel cells (MFCs) are compatible technologies since both are reliant on the actions of bacteria to remove contaminants from wastewater. MFCs require the anode to remain anaerobic with the cathode exposed to oxygen while these redox conditions can develop naturally in CWs. For this reason, research into combining the two technologies (termed as CW-MFC) has emerged in recent years with the aim of improving the wastewater treatment capacity of wetlands while simultaneously producing electrical power. Based on the published work (although limited), this review aims to provide a timely, current state-of-the-art in CW-MFC while exploring future challenges and research directions., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

The choice of substrates with high adsorption capacity, yet readily available and economical is vital for sustainable pollutants removal in constructed wetlands (CWs). Two identical large-scale demonstration horizontal subsurface flow (HSSF) CWs (surface area, 340 m(2); depth, 0.6 m; HLR, 0.2 m/day) with gravel or slag substrates were evaluated for their potential use in remediating polluted urban river water in the prevailing climate of northwest China. Batch experiments to elucidate phosphorus adsorption mechanisms indicated a higher adsorption capacity of slag (3.15 g/kg) than gravel (0.81 g/kg), whereby circa 20 % more total phosphorus (TP) removal was recorded in HSSF-slag than HSSF-gravel. TP removal occurred predominantly via CaO-slag dissolution followed by Ca phosphate precipitation. Moreover, average removals of chemical oxygen demand and biochemical oxygen demand were approximately 10 % higher in HSSF-slag than HSSF-gravel. Nevertheless, TP adsorption by slag seemed to get quickly saturated over the monitoring period, and the removal efficiency of the HSSF-slag approached that of the HSSF-gravel after 1-year continuous operation. In contrast, the two CWs achieved similar nitrogen removal during the 2-year monitoring period. Findings also indicated that gravel provided better support for the development of other wetland components such as biomass, whereby the biomass production and the amount of total nitrogen (TN; 43.1-59.0 g/m(2)) and TP (4.15-5.75 g/m(2)) assimilated by local Phragmites australis in HSSF-gravel were higher than that in HSSF-slag (41.2-52.0 g/m(2) and 3.96-4.07 g/m(2), respectively). Overall, comparable pollutant removal rates could be achieved in large-scale HSSF CWs with either gravel or slag as substrate and provide a possible solution for polluted urban river remediation in northern China.

The characteristics of nitrogen (N) and phosphorus (P) removal were studied during the 2-year operation of a free water surface flow wetland of 900 m² with hydraulic loading of 0.1 m/d to evaluate its potential to treat water from an urban stream polluted with municipal and industrial wastewater. Attention was focused on the removal of dissolved N and P by harvesting plants (local Phragmites australis and Typha orientalis) at the end of each growing season. According to findings, the removals of N and P increased from 47.1% and 17.6%, respectively, in the 1st year to 52.3% and 32.4%, respectively, in the 2nd year. Increments of N and P removal were largely attributable to plant biomass, which increased from an average dry weight of 1.77 kg/m² in the 1st year to 3.41 kg/m² in the 2nd year. The amount of nutrients assimilated by plants in the 2nd year was almost double that of the 1st year. Increasing biomass in the 2nd year also improved redox conditions in the substrate layer, which contributed to increasing the efficiency of N removal. Compared with T. orientalis, P. australis was more competitive and adapted to conditions in the wetland better; it regenerated more vigorously and contributed more to nutrient removal.

Globally, alum sludge is an easily, locally and largely available by-product from water treatment plants where aluminium sulphate is used as the coagulant for raw water purification. Owing to the high content of Al ions (29.7±13.3% dry weight) in alum sludge and the strong affinity of Al ions to adsorb various pollutants especially phosphorus (P), alum sludge (in the form of dewatered cakes) has been investigated in recent years as a low-cost alternative substrate in constructed wetland (CW) systems to enhance the treatment efficiency especially for high strength P-containing wastewater. Long-term trials in different scales have demonstrated that the alum sludge-based CW is a promising technique with a two-pronged feature of using 'waste' for wastewater treatment. Alum sludge cakes in CW can serve as a medium for wetland plant growth, as a carrier for biofilm development and as a porous material for wastewater infiltration. After the intensive studies of the alum sludge-based CW system, this paper aims to address the key issues and concerns pertaining to this kind of CW system. These include: (1) Is alum sludge suitable for reuse in CWs? (2) Is Al released from the sludge a concern? (3) What is the lifespan of the alum sludge in CWs? (4) How can P be recovered from the used alum sludge? (5) Does clogging happen in alum sludge-based CW systems and what is the solution?

By integrating microbial fuel cells (MFCs) into constructed wetlands (CWs) the need and cost of building a reactor are eliminated, while CWs provide the simultaneous redox conditions required for optimum MFC performance. Two single-stage MFC-CWs, with dewatered alum sludge cake as the main wetland medium for enhanced phosphorus removal, were operated to determine the effects of electrode separation and flow regimes on power production and wastewater treatment. When the anode is buried and the cathode is at the air-water interface the system is inhibited by a large ohmic resistance resulting from the increased electrode separation. By placing the cathode directly above the anode and operating the system with simultaneous up-flow into the anode and down-flow into the cathode the ohmic resistance is reduced. The chemical oxygen demand (COD) removal efficiency was, however, reduced to 64% (compared with 79%). A two-stage system was subsequently run for fuller wastewater treatment and increased power production. The results indicate that a two-stage MFC-CW can increase the normalized energy recovery and improve removal efficiencies of COD, total nitrogen, NH4⁺, total phosphorus and reactive phosphorus to 93 ± 1.7%, 85 ± 5.2%, 90 ± 5.4%, 98 ± 5.3% and 99 ± 2.9%, respectively.

A series of large pilot constructed wetland (CW) systems were constructed near the confluence of an urban stream to a larger river in Xi'an, a northwestern megacity in China, for treating polluted stream water before it entered the receiving water body. Each CW system is a combination of surface-and subsurface-flow cells with local gravel, sand or slag as substrates and Phragmites australis and Typha orientalis as plants. During a one-year operation with an average surface loading of 0.053 m(3)/(m(2)·day), the overall COD, BOD, NH3-N, total nitrogen (TN) and total phosphorus (TP) removals were 72.7% ± 4.5%, 93.4% ± 2.1%, 54.0% ± 6.3%, 53.9% ± 6.0% and 69.4% ± 4.6%, respectively, which brought about an effective improvement of the river water quality. Surface-flow cells showed better NH3-N removal than their TN removal while subsurface-flow cells showed better TN removal than their NH3-N removal. Using local slag as the substrate, the organic and phosphorus removal could be much improved. Seasonal variation was also found in the removal of all the pollutants and autumn seemed to be the best season for pollutant removal due to the moderate water temperature and well grown plants in the CWs., (Copyright © 2014 The Research Centre for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.)

Achieving effective total nitrogen (TN) removal is one of the major challenges faced by constructed wetlands (CWs). To address this issue, multiple "tides" were proposed in a single stage tidal flow constructed wetland (TFCW). With this adoption, exceptional TN removal (85% on average) was achieved under a high nitrogen loading rate (NLR) of around 28 g Nm(-2)day(-1), which makes the proposed system an adequate option to provide advanced wastewater treatment for peri-urban communities and rural area. It was revealed that the multiple "tides" not only promoted TN removal performance, but also brought more flexibility to TFCWs. Adsorption of NH4(+)-N onto the wetland medium (during contact period) and regeneration of the adsorption capacity via nitrification (during bed resting) were validated as the key processes for NH4(+)-N conversion in TFCWs. Moreover, simultaneous nitrification denitrification (SND) was found to be significant during the bed resting period. These findings will provide a new foundation for the design and modeling of nitrogen conversion and oxygen transfer in TFCWs., (© 2013.)

Novel alum sludge-based floating treatment wetland (FTW) was developed to enhance the purification performances of natural water bodies, i.e., rivers, lakes, and ponds. Polyurethane was applied to foam the lightweight alum sludge based-substrate (PU-AL) of FTW through the response surface method. Three FTWs configurations were created for a half-year lab-scale operation, and the PU-AL FTW presents the greatest purification performance in the removal rate of chemical oxygen demand (COD) of 62.58 ± 6.65%, total nitrogen (TN) of 53.31 ± 4.65%, and total phosphorus (TP) of 45.39 ± 4.69%. PU-AL substrate could enhance the nutrient removal performance of existing FTW by providing a proper media for microbial and plants' growth. This study provides a good solution and showcase not only from a natural water restoration point of view but also from the waterworks sludge management view for a better understanding of FTWs and good applications in engineering practice. [ABSTRACT FROM AUTHOR]

A multiple bio-cathodes constructed wetland-microbial fuel cell (CW-MFC) system, aiming for higher power production and therefore the improved N removal, was investigated in this study. As the bio-cathode number increased from 1 to 3, the energy losses on both anode and cathode showed a significant decrement (from 97.85 mV to 46.09 mV for anode and from 221.5 mV to 45.89 mV for cathode, respectively). Accordingly, the maximum power density of the system showed a notable increase from 12.56 to 26.16 mW/m 2 . In addition to the improved electrical performance, enhanced simultaneous nitrification & denitrification process was triggered due to the influence of the bioelectrical derived interaction between power production and systematic nitrification rate ( r Ni ) and denitrification rate ( r De ). Insight into the nitrification & denitrification process has been given that r Ni increased from 98.59 ± 4.53 mg/(m 2 ·d) of the control system to 179.11 ± 7.65 mg/(m 2 ·d) of three bio-cathodes system while r De increased from 89.64 ± 4.57 mg/(m 2 ·d) to 163.55 ± 11.88 mg/(m 2 ·d). Correction analysis showed that the amount of electrical related nitrogen removal is almost linearly correlated to the produced electricity. Overall, this study presented a promising strategy and provided insight for higher energy production and the enhanced nitrogen removal from the newly established CW-MFC system. [ABSTRACT FROM AUTHOR]

This study investigates the ability of four alum sludge-based constructed wetlands, incorporating microbial fuel cell technology, to achieve high organic and nutrient removal from swine slurry while simultaneously producing electricity. As a cross-comparison the effects of electrode spacing and flow pattern are investigated. By providing a simultaneous upflow–downflow regime the maximum power density is boosted by 70% to 0.268 W/m 3 and an ammonium removal efficiency of 75% is achieved. However, the COD removal efficiency falls to 64% compared with 80%, 79% and 81% achieved by operating with a continuous upflow regime in the other three systems of the study. The alum sludge wetland medium showed an enhanced capacity to immobilise phosphorous with total phosphorous and reactive phosphorous removal rates of 85–86% and 89–90%, respectively. Accordingly, multi-stage hybrid CW-MFC systems and alternative operational strategies are discussed and recommended for full nutrient and organic removal. [ABSTRACT FROM AUTHOR]

Highlights: [•] 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. [ABSTRACT FROM AUTHOR]

Abstract: A tidal flow constructed wetland system was investigated for the removal of organic matter and ammoniacal-nitrogen from diluted piggery wastewater. The results demonstrated that the operation of tidal flow enhanced the transfer of oxygen into wetland matrices. The supply of oxygen by the operation (473gO2/m2d) matched the demand for wastewater treatment. The overall oxygen consumption rate in the system was considerably higher than the typical rate obtainable in conventional wetlands; most oxygen being used for the decomposition of organic matter. Compared with conventional systems, the tidal flow system demonstrated greater efficiency in the removal of organic matter. Significant nitrification did not take place, although 27–48% ammonia was removed from the wastewater. Immobilization by microbial cells and adsorption were the likely routes to remove ammonia under the specific experiment conditions. Percentage removals of BOD5, NH4–N and SS increased after effluent recirculation at a ratio of 1:1 was employed. [Copyright &y& Elsevier]

The review paper sis based on the analysis or nearly 700 research papers published during 2019 and the first half of 2020 and indexed by Web of Science under the password "constructed wetlands for wastewater treatment". Out of this number 132 papers dealing with "new" topics such as new wastewaters treated in constructed wetlands (CW), new filtration materials, role of vegetation, floating treatment wetlands, microbiology of CW, greenhouse gas emissions from CWs, sustainability and secondary benefits of CWs. For the deeper analysis the supporting literature from previous periods has been cited. The analysis indicates increasing popularity and diversification of types and tasks of CWs. This supports the need for further research of processes and design-related properties of CWs. The research in full scale CWs and long-term studies are only rare and in order to upgrade the CWs technology, research must be also carried out in the field under full-scale conditions. [Display omitted] • The paper evaluates 131 papers on constructed wetlands research in 2019 and 2020. • Less than 10% of the experiments is done in the full-scale constructed wetlands. • Vegetation may play more important role than expected. • Microbiology is affected by wastewater, filtration substrate, type of the wetland, vegetation. • Floating wetlands are still lacking the design and operational parameters. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Siphon was firstly applied for creating "tidal flow" in MFC-CW studies. • Different effluent recirculation modes in cathode chamber of MFC-CW were investigated. • Higher COD and nitrogen removals were obtained in siphon/"tidal flow" mode. • It is the oxygen in cathode chamber to control the treatment performance. [ABSTRACT FROM AUTHOR]

Constructed wetland (CW) works mostly depending on biological and biochemical processes. No doubt, these processes are affected by climate conditions. This is a challenge and that is why this review was made. By inspecting most of the published full-scale investigations of the CWs worldwide, it seems that the nitrogen is the most sensitive parameter to be affected in the cold climate, while organic matter and phosphorus remain relatively less affected. The low-temperature and oxygen shortcoming are together inhibited the biota activities. To face such situation, a wide range of possible intensification strategies from CW structure and operation related intensification (controlled tidal flow, batch operation, effluent recirculation, etc.) are discussed. Indeed, the effects of cold climate on CWs are an integrated issue without single solution. Future studies on the combination of multiple approaches and optimizing suitable microcosms as well as reasonable design and intensification considerations in cold climate CWs are necessary. Unlabelled Image • CW in cold climate is a challenge with low biological activities being the most affecting issue. • Integrated solutions can be applied, mainly in system modification and operational intensification. • Aeration, substrates combination, bioaugmentation, and operational tailor-made strategies are desirable. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel Fe-C tidal flow system boosts NH 4 +-N and TN removal in constructed wetlands. • Tidal operation promoted Fe cycling and microbe enrichment, enhancing denitrification. • Fe-C release Fe2+ via galvanic cell reaction to promote denitrification and Feammox. • Notable increase in Fe-reducing, autotrophic denitrifying bacteria and gene abundance. • Autotrophic denitrification pathway enhances TN removal while reducing N 2 O emissions. This study focused on developing a tidal flow constructed wetland (CW) with an iron-carbon (Fe-C) substrate to enhance nitrogen removal efficiency. The results demonstrated significant improvements in the removal of NH 4 +-N and TN in the iron-carbon tidal flow constructed wetland (IC-TFCW) compared to traditional gravel CW. IC-TFCW achieved a 23.82 % and 31.01 % more effective removal, resulting in reductions of 82.45 % and 74.13 %, respectively. The large specific surface area and electron transfer effect of the Fe-C substrate facilitated pollutant retention and proliferation of denitrifying microorganisms. However, the Fe-C substrate inhibited plant growth and rhizosphere microorganisms, reducing plant nitrogen uptake by 2.69-fold. Galvanic cell reaction in the Fe-C substrate facilitated the release of iron and its oxides and promoted iron cycling under the alternating aerobic-anoxic conditions induced by tidal flow. This led to the enrichment of autotrophic denitrifying and Fe-reducing bacteria by 14.89 and 1.1 times, and increase in the relative abundance of denitrification genes nar (narG, narH, narI) and nap (napA, napB) by 60.94 %. The Fe2+ released during the galvanic cell reaction contributed electrons to denitrification, while the reduction of Fe3+ facilitated the Anammox process, resulting in the Feammox reaction. This created an autotrophic denitrification pathway (autotrophic denitrification and Feammox), synergizing with the heterotrophic denitrification pathway and the iron cycling process to significantly increase TN removal and reduce N 2 O emissions per unit of TN removed by up to 36.99 %. These findings elucidate the various denitrification pathways present in CW and provide insights into improving denitrification efficiency. [ABSTRACT FROM AUTHOR]

The importance of harvest management for the growth and development of plants and nutrients removal in constructed wetlands (CWs) is highly controversial. This study evaluated the effects of annual harvesting on the growth and productivity of local Phragmites australis in northwestern China. Growth characteristics such as shoot density, biomass and height were studied using two pilot-scale surface-flow CWs over a two-year operation period. Plants were kept unharvested in one CW for comparative studies with the second CW, which was harvested at the end of the growing season. Each CW of 400 m 2 was operated with a hydraulic loading of 34 m 3 /d for the treatment of water from an urban river polluted with municipal and industrial wastewater. The harvested CW recorded a higher shoot density (175 shoots/m 2 ), biomass (1.4 kg/m 2 ) and peak height (3.4 m) than the unharvested one (130 shoots/m 2 , 1.2 kg/m 2 and 3.2 m). The overall nutrients removals were also slightly higher for the harvested CW (46.0% TN and 38.1% TP) than the unharvested CW (40.6% TN and 29.1% TP). Plants harvesting in the first year improved nutrients removal by plant uptake (41.9 g N/m 2 and 3.7 g P/m 2 versus 37.3 g N/m 2 and 3.2 g P/m 2 ) as well as in the substrate layer (216.9 g N/m 2 and 8.0 g P/m 2 versus 191.0 g N/m 2 and 5.7 g P/m 2 ) during the second year. Nonetheless, the increase in nutrients removal by harvesting was minimal. [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]

• Woodchips substrates supplement the carbon source for denitrification. • The COD release rate and sustainability of woodchips are variable. • Woodchips reduced the ORP of CW, enhancing the denitrification of annamox. • The combined substrates realized the simultaneous denitrification and dephosphorization. The lack of carbon source in the denitrification process with low C/N wastewater is the main factor limiting the denitrification efficiency in constructed wetlands (CWs). However, the traditional method of adding liquid carbon source is often costly and facing the risk of secondary pollution. This study attempted to solve this problem by adding woodchips sustained-release carbon sources as part of the substrate, together with the dewatered alum sludge as the main wetland substrate to the baffle subsurface flow constructed wetland (BSFCW). The effects of woodchips on denitrification capacity, effluent COD and nitrogen transfer and transformation were studied. Results showed that the removal rates of ammonia nitrogen (NH 4 +-N), nitrate nitrogen (NO 3 −-N), total nitrogen (TN) and total phosphorus (TP) were 19.0%–75.3%, 63.6%–96.1%, 61.94%–74.4%, 75.0%–98.8%, respectively, when the C/N ratio varies between 0.93 and 1.87. The two-dimensional contour simulation of pollutants concentration in the system indicated that: i) the release rate of COD by woodchips decreased with the time; ii) woodchips reduced the oxidation reduction potential (ORP) of CW system, creating favorable conditions for the denitrification; iii) the closer the woodchips filling position to the inlet, the higher the denitrification efficiency of the system. The combination of dewatered alum sludge and woodchips substrates realized the simultaneous denitrification and dephosphorization of the BSFCW system. This study is of great significance for the treatment of low C/N wastewater containing considerable even high strength P. [ABSTRACT FROM AUTHOR]