Application Of Constructed Wetlands Research Articles

Constructed wetlands combined with microbial fuel cells (CW-MFCs) as a sustainable technology for leachate treatment and power generation.

The physical and chemical treatment processes of leachate are not only costly but can also possibly produce harmful by products. Constructed wetlands (CW) has been considered a promising alternative technology for leachate treatment due to less demand for energy, economic, ecological benefits, and simplicity of operations. Various trends and approaches for the application of CW for leachate treatment have been discussed in this review along with offering an informatics peek of the recent innovative developments in CW technology and its perspectives. In addition, coupling CW with microbial fuel cells (MFCs) has proven to produce renewable energy (electricity) while treating contaminants in leachate wastewaters (CW-MFC). The combination of CW-MFC is a promising bio electrochemical that plays symbiotic among plant microorganisms in the rhizosphere of an aquatic plant that convert sun electricity is transformed into bioelectricity with the aid of using the formation of radical secretions, as endogenous substrates, and microbial activity. Several researchers study and try to find out the application of CW-MFC for leachate treatment, along with this system and performance. Several key elements for the advancement of CW-MFC technology such as bioelectricity, reactor configurations, plant species, and electrode materials, has been comprehensively discussed and future research directions were suggested for further improving the performance. Overall, CW-MFC may offer an eco-friendly approach to protecting the aquatic environment and come with built-in advantages for visual appeal and animal habitats using natural materials such as gravel, soil, electroactive bacteria, and plants under controlled condition.

Applying biochar coupled with pyrite substrates simultaneously enhanced nutrient and heavy metal removal in constructed wetland: Performance and mechanism

Wastewater polluted by heavy metals with low C/N ratio posed a big challenge to constructed wetlands (CWs) for sustainable advanced wastewater purification. In this study, biochar coupled with pyrite was successfully applied in CWs to simultaneously remove organics, total nitrogen (TN), total phosphorus (TP) and heavy metals, with the highest removal efficiency of 95.78%, 98.78%, 96.22% and 99.91%, respectively. Batch tests proved that the complexation of ferric hydroxide from pyrite oxidation played an important role in TP and heavy metals removal. Meanwhile, fluorescence excitation-emission matrix combined with parallel factor analysis (EEM-PARAFAC) further manifested that protein-like substances contributed a lot to heavy metals stabilization. Moreover, the multiplication of Proteobacteria, Chloroflexi at phylum level and Dechloromonas at genus level, which were capable of heterotrophic or autotrophic nitrate reducing process indicated that the denitrification capacity of CWs was significantly enhanced by biochar and pyrite. This study provided a feasible insight into the application of CWs with biochar and pyrite addition to enhance the treatment of low C/N wastewater.

Promoting Aquatic Health in Constructed Wetlands: Removal of Pathogens and Nitrogen

Due to urbanization and population growth, freshwater resources have become a long-term concern for most developing countries. With the growth of population, the demand for fresh water is increasing and the requirement for sewage treatment is also increasing. In recent years, the demand for sewage recycling has increased sharply. Constructed wetlands (CWs) are an effective sewage treatment system with low energy consumption, minimal maintenance requirements, and a low operation cost, which will meet the current demand for the removal of nutrients and pathogens. The application of CWs in sewage treatment has attracted more and more attention because it is also a nature-based solution (NbS). These systems are capable of removing not only nitrogen (N) and phosphorus (P), but also pathogen indicators, such as fecal coliform and Escherichia coli. The presence of these indicators also suggests the influx of other pathogens into aquatic systems, thereby threatening aquatic ecological health. However, research on the removal of pathogens in CWs is relatively scare and their removal mechanisms are not fully understood. Despite their widespread application, the role of plants in CWs, particularly in the specific mechanism of pathogens and nitrogen removal, remains largely unknown. This article will help us to better understand this technology and provide help for our further research. In this paper, the coupled denitrification mechanism between microorganisms and plants in the process of nitrogen transformation was discussed. Plants affect nitrogen transformation microorganisms by releasing oxygen and secretions from their roots and provide substrates for bioremediation. The removal effects of different types of CWs on pathogen and nitrogen species were also summarized. Overall, the removal effect of subsurface flow wetlands outperforms that of surface flow wetlands, with multi-stage wetland systems being the most effective. The main factors affecting the removal of pathogens and nitrogen species in CWs include plants, substrates, operating parameters, UV radiation, temperature, water composition, and pH. Finally, the research frontiers on the removal of pathogens in CWs were prospected.

Is constructed wetlands carbon source or carbon sink? Case analysis based on life cycle carbon emission accounting

Constructed wetlands (CWs) are widely used to polish the effluent of wastewater treatment plants and micro-polluted river or lake water. However, the impact of large-scale applications of CWs on carbon emissions is unclear. In this study, the carbon footprints of two full-scale hybrid CWs were determined based on life cycle assessment (LCA). Results showed that the carbon emission of CW ranged from 0.10 to 0.14 kg CO2-eq/m3, and was significantly correlated with the influent chemical oxygen demand loads and electricity consumption. However, CW would approach carbon neutrality during the service period when taking plant carbon sequestration into consideration. Compared with other advanced wastewater treatment technologies, CWs showed significant low-carbon emission and cost-effective benefits. This study clarified the role of CWs in the carbon cycle and would provide guidance for the construction and management of CWs.

FeCa-based layered double hydroxide, a high-performance phosphorus adsorbent in constructed wetlands and ecological dams - A pilot scale study

Research studies have modified traditional substances to seek fast-acting removal of phosphorus in constructed wetlands (CWs) and ecological dams, rather than develop a brand-new nano-adsorbent. This work synthesized FeCa-based layered double hydroxide (FeCa-LDH) with a chemical co-precipitation method, and the performance, mechanism and factors of phosphorus removal were investigated. FeCa-LDH showed a marked ability to adsorb phosphorus from waste water, with a removal efficiency of 94.4% and 98.2% in CWs and ecological dams, respectively. Both FTIR and XPS spectrum evidenced that FeCa-LDH removed phosphorus via electrostatic and hydrogen-bonding adsorption, as well as a coordination reaction and interlayer anion exchange. FeCa-LDH showed a higher capacity to remove phosphorus in alkaline and neutral waste water than in acid conditions. Co-occurrence anions, which influenced the efficiency of the phosphorus removal capacity are considered in the sequence below: CO32− ≈ HCO3− > SO42− > NO3−. Innovatively, FeCa-LDH was not affected by the low-temperature limitation for CWs, and phosphorus removal efficiency at 5 °C was almost equal to that at 25 °C. These results cast a new idea on the construction, application and phosphorus removal performance of CWs and ecological dams.

Trend and status of the NSFC funded projects for constructed wetlands in the last decade in China

The National Natural Science Foundation of China (NSFC) is the main agency for Chinese scientists to receive competitive public fund. An analysis of its funded projects in the field of constructed wetlands (CWs) can provide a novel perspective to insight into the R&D of CWs in China in the past decade. Here, we collect the information about the approved CW projects from multiple sources, while a total of 123 various types of CW projects were found during 2013–2022. The results show that nearly half of these projects were granted to support Chinese young scientists. However, most funded scientists are concentrated in economically developed regions of China, showing a trend of uneven regional development. In terms of publications, 515 publications were found from 123 NSFC-funded CW projects. The funded CWs projects focus more on pollution control, greenhouse gas (GHG) emission, low C/N ratio wastewater treatment, and wetland plants resources utilization. Based on the analysis of the R&D trend of funded projects, GHG emissions control, emerging contaminants removal, and larger-scale application of CWs may receive the NSFC funding in the future.

Constructed Wetlands for the Wastewater Treatment: A Review of Italian Case Studies

Wastewater is one of the major sources of pollution in aquatic environments and its treatment is crucial to reduce risk and increase clean water availability. Constructed wetlands (CWs) are one of the most efficient, environmentally friendly, and less costly techniques for this purpose. This review aims to assess the state of the art on the use of CWs in removing environmental pollutants from wastewater in Italy in order to improve the current situation and provide background for future research and development work. To evaluate the CWs performances, 76 research works (2001–2023) were examined, and the parameters considered were the type of wastewater treated, pollutants removed, macrophytes, and the kinds of CWs utilized. The pollutant removal efficiencies of all CWs reviewed showed remarkable potential, even though there are biotic and abiotic factor-driven performance variations among them. The number of articles published showed an increasing trend over time, indicating the research progress of the application of CWs in wastewater treatment. This review highlighted that most of the investigated case studies referred to pilot CWs. This finding suggests that much more large-scale experiments should be conducted in the future to confirm the potential of CWs in eliminating pollutants from wastewater.

Dyeing wastewater treatment in horizontal-vertical constructed wetland using organic waste media

A hybrid constructed wetland (CW) system with horizontal and vertical flow combination was evaluated for treating carbon-deficient synthetic dyeing wastewater containing 100 mg/L Reactive Yellow 145 dye. Organic waste products such as cow manure and wood chips were added as media in horizontal CW, and gravel as vertical CW media. Horizontal and vertical CWs were planted with Typha angustifolia. Horizontal CW was operated in continuous mode at hydraulic retention time (HRT) of 3 d and vertical CW in batch mode at 1 d HRT. The results suggested the potential application of a cost-effective horizontal-vertical hybrid CW to remove azo dyes from low-carbon dyeing wastewater. In horizontal CW, organic media was used as the carbon source for microbial dye degradation, resulting in 90% colour removal in the absence of available carbon in dyeing wastewater. Proteobacteria, Firmicutes and Bacteroidetes played a dominant role in dye degradation in horizontal CW. Vertical CW removed dye degradation organics, 69% ammonium-nitrogen and 39% organic-nitrogen. Phytotoxicity assays indicated toxicity reduction along the CW treatment path.

Constructed wetland challenges for the treatment of industrial wastewater in smart cities: A sensitive solution

Since last few years, the Constructed Wetlands (CWs) are beingemployed as a green as well as sustainablemethod to treat different types of wastewater released from industrial sources in smart cities. Particularly for small villages and isolated areas, CWs provide an energy- and land-efficient alternative to traditional treatment systems. There are still many questions regarding the effective implementation of these systems and their long-term viability. This study aims to offer and inspire sustainable options for the effectiveness and use of CWs by thoroughly evaluating their application and the most recent developments in their sustainable design and operation for wastewater treatment. First, a brief explanation of the definition, classification, and application of current CWs has been given. The relationship between the operational needs and design criteria of CWs, such as substrate types, hydraulic retention time, water depth, plant species, hydraulic load, and feeding mechanism, and the operation's sustainability for treating wastewater has then been examined. Growing knotweed plants, which bind dye particles in the soil and take up heavy metal ions for better growth, as well as reducing the detrimental effects of dyes and heavy metals, are some of the sustainability initiatives for those wetland technologies that are outlined in this paper. If employed, this approach can clean wastewater in smart cities and metropolitan regions that are polluted by industrial waste water very well with a single expenditure. Future research on improving the sustainability and stability of CWs is also emphasised as being crucial.

A novel constructed wetland based on iron carbon substrates: performance optimization and mechanisms of simultaneous removal of nitrogen and phosphorus.

In recent years, the combination of iron carbon micro-electrolysis (ICME) with constructed wetlands (CWs) for removal of nitrogen and phosphorus has attracted more and more attention. However, the removal mechanisms by CWs with iron carbon (Fe-C) substrates are still unclear. In this study, the Fe-C based CW (CW-A) was established to improve the removal efficiencies of nitrogen and phosphorus by optimizing the operating conditions. And the removal mechanisms of nitrogen and phosphorus were explored. The results shown that the removal rates of COD, NH4+-N, NO3--N, TN, and TP in CW-A could reach up to 84.4%, 94.0%, 81.1%, 86.6%, and 84.3%, respectively. Wetland plants and intermittent aeration have dominant effects on the removal of NH4+-N, while the removal efficiencies of NO3--N, TN, and TP were mainly affected by Fe-C substrates, wetland plants, and HRT. XPS analysis revealed that Fe(0)/Fe2+ and their valence transformation played important roles on the pollutants removal. High-throughput sequencing results showed that Fe-C substrates and wetland plants had considerable impacts on the microbial community structures, such as richness and diversity of microorganism. The relative abundance of autotrophic denitrification bacteria (e.g., Denitatsoma, Thauera, and Sulfuritalea) increased in CW-A than CW-C. The electrons and H2/[H] produced from Fe-C substrates were utilized by autotrophic denitrification bacteria for NO3--N reduction. Microbial degradation was the main removal mechanism of nitrogen in CW-A. Removal efficiency of phosphorus was enhanced resulted from the reaction of phosphate with iron ion. The application of CWs with Fe-C substrates and plants presented great potential for simultaneous removal of nitrogen and phosphorus.

A Critical Review on Economical and Sustainable Solutions for Wastewater Treatment Using Constructed Wetland

Pollutant removal by the mechanism of constructed wetland has led to low cost, highly efficient wastewater treatment technology. Constructed wetlands (CWs) are artificial engineered systems that mimic like natural wetlands. CW’s have been used in previous research to treat a broad range of waste streams at large-scale for low-cost application in wastewater management. Generally, the most literature has targeted a particular class of mechanism or the other due to lack of generalized techniques for wastewater management using CWs. This work focuses on to introductory information and review on concept of CWs based on the latest mechanisms for the wastewater treatment to inspire economical and sustainable solutions to water based environmental problems. This research emphasis CW mechanism, construction, design, and applications of CWs as well as optimization of CWs for the treatment of wastewater. This review also highlights the study with different treatment stages of CWs for removing pollutants from different types of wastewaters.

Strategies for enhancing phosphorous removal in Vertical Flow Constructed Wetlands.

Constructed wetlands (CWs) are among the fastest emerging treatment methods for wastewater treatment. Unlike their organics and nitrogen removal capacities, the potential of CWs as a sink for phosphorous is still debatable. In this study, the secondary data from several CWs treating domestic sewage were compiled and assessed. Curves were plotted between orthophosphate-phosphorous (PO43--P) loading and the corresponding removal rates. Other factors affecting PO43--P removal like depth of the CW, surface area, organic loading rate etc. Were also analyzed. Removal rates of PO43--P were conforming to a linear positive relation with the loading rates. Pea gravel as a CW medium performed consistently well (60-80% removal) for a wide range of influent PO43--P loading (0.5-1.5g/m3-d). The increased depth of the wetland appears to favor phosphate removal. PO43--P removal was found to be correlated with outlet dissolved oxygen, total Kjeldahl nitrogen removal and effluent nitrate. The study suggests that proper design, optimal organic loading and suitable pre-treatment may increase the applicability of CWs for phosphate removal from domestic wastewater. Larger area requirements can also be avoided by increasing their depth while keeping the volume of the filter media the same.

A review on constructed wetlands-based removal of pharmaceutical contaminants derived from non-point source pollution

In the current decade, Non-Point Source (NPS) pollution has become a critical global problem in both developing and developed countries. As a result of diverse human activities, NPS pollution has led to an excessive supply of inorganic nutrients (e.g., phosphorus, nitrogen, and metals) and organic compounds (e.g., pharmaceutical compounds and pesticides) into soils and surface waters which change the water quality. Continuous discharge of pollutants by NPS source mainly affects the soil and aquatic ecosystem, damaging the food chain and food web that exist in this Earth planet. On such a serious note, methods to mitigate the pollutants derived from NPS sources or treatment methods could effectively reduce the contaminant load. Recently, the use of constructed wetlands (CWs) for bioremediation purposes has been gaining considerable attention in many countries since they mostly mimic the natural and eco-friendly process for mitigating various types of pollutants. Although their successful use in the treatment of point source pollutants is well documented, information on the performance of CWs for treating organic pollutants, particularly pharmaceutical residues, is still not adequately summarized. Therefore, this paper focuses on outlining and reviewing the current information related to the use of CWs in mitigating pharmaceutical contaminants (PCs) in soil and water reservoirs. Firstly, we summarized the key aspects on sources, occurrence, fate, and ecotoxicological effects of most common pharmaceuticals derived by NPS pollution. The second objective deals with the significance of plants present in CWs that help PCs remove via various possible mechanisms. Thirdly, we discuss the roles and importance of other factors (e.g., microorganism, temperature, and substrate) to remove PCs efficiently. Overall, this review highlights the current state-of-art of CWs for mitigating NPS-derived PCs and presses the area where future research is required to make the CWs application more successful shortly.

Contribution of Constructed Wetlands for Reclaimed Water Production: A Review

Freshwater scarcity is a growing threat to sustainable development, which can be mitigated by adequate management of water resources. Agriculture and related activities consist in the main use of freshwater, but several other human activities present relevant contributions. Because most of the water uses imply the generation of resultant wastewater, the production and use of reclaimed water by appropriate technologies can be part of the solution to that issue. Considering that the use of constructed wetlands (CWs) can be a relevant contribution to the production of reclaimed water, as an eco-friendly alternative to costly advanced water treatment technologies, this work is a review of the last decade of literature on the use of CWs to produce reclaimed water. The results point to a usual focus on the production of reclaimed water for agriculture or urban spaces irrigation. In order to potentiate a broader application of CWs, some directions of future research and use of this green technology are proposed.

Impact of influent strengths on nitrous oxide emission and its molecular mechanism in constructed wetlands treating swine wastewater

Constructed wetlands (CWs) can remove nitrogen (N) through plant assimilation and microbial nitrification and denitrification, while it also releases large greenhouse gas nitrous oxide (N2O) into the atmosphere. However, N2O emissions and the underlying microbial mechanisms of CWs when treating high-strength wastewater have not been systematically surveyed. Here, the effect of three influent strengths on N2O emissions in a pilot-scale CW treatment of swine wastewater was determined and the underlying microbial mechanisms were explored. The results showed that the removal rates of ammonium (NH4+) and total nitrogen (TN) increased significantly with the increasing influent strengths, however, the ratio of N2O emission/TN removal rose by 1.5 times at the same time. Quantitation of microorganisms responsible for N-cycle in the sediment indicated that the abundance of ammonia-oxidizing bacteria (AOB) in high influent strengths (COD, 962.38 ± 3.05 mg/L; NH4+, 317.89 ± 4.24 mg/L) was 51.6-fold compared with that in low influent strengths (COD, 516.94 ± 4.18 mg/L; NH4+, 100.65 ± 2.65), and AOB gradually replaced ammonia-oxidizing archaea (AOA) to dominate ammonia oxidizers. Structural equation models demonstrated that NO2− accumulations promoted the ratio of AOB/AOA, which further led to an increase in the ratio of N2O emission/TN removal. It is worth noting both the N removal rates and N2O emissions increased with the increasing influent strength. To obtain reduced N2O emissions, pretreatment technology for strength reduction should be supplemented before high-strength wastewater enters the CWs. This study may shed new light on the sustainable operation and application of CWs.

The Interaction Effects of Aeration and Plant on the Purification Performance of Horizontal Subsurface Flow Constructed Wetland.

Aeration and plants exhibit influence on the water purification performance in constructed wetlands (CWs). However, the interaction between aeration and plants on enhancing performance of domestic sewage treatment is unclear. Our study aims to optimize the combination of aeration position and plant species, promoting the extensive and effective application of CWs. Herein, six horizontal subsurface flow (HSSF) CWs small scale plots were established and divided into two groups according to the plant (i.e., Canna indica and Iris sibirica). To adjust the distribution of dissolved oxygen (DO) in CWs, each group had three plots of HSSF CWs. One plot was aerated at the bottom of the first quarter of the filtration chamber, one plot was aerated at the bottom of the inflow chamber, and the remaining plot was not aerated as a control. Results showed that aeration at the bottom of the first quarter filtration chamber could contribute to the highest removal efficiency of chemical oxygen demand (COD), ammonium nitrogen (NH4+-N) and total nitrogen (TN). The COD, NH4+-N, and TN removal percentages decreased with the drop in temperature. However, the plot aerated at the bottom of the first quarter filtration chamber with I. sibirica exhibited the best average CODCr, NH4+-N and TN removal percentages in both the warm season (83.6%, 82.7% and 76.8%) and the cool season (66.3%, 44.1% and 43.8%). Therefore, this study indicated that the combination of aerating at the bottom of the first quarter filtration chamber and planting with I. sibirica in the HSSF CWs would be a promising way forward for wastewater treatment, especially in low temperature seasons.

Performance Efficiency of Conventional Treatment Plants and Constructed Wetlands towards Reduction of Antibiotic Resistance.

Domestic and industrial wastewater discharges harbor rich bacterial communities, including both pathogenic and commensal organisms that are antibiotic-resistant (AR). AR pathogens pose a potential threat to human and animal health. In wastewater treatment plants (WWTP), bacteria encounter environments suitable for horizontal gene transfer, providing an opportunity for bacterial cells to acquire new antibiotic-resistant genes. With many entry points to environmental components, especially water and soil, WWTPs are considered a critical control point for antibiotic resistance. The primary and secondary units of conventional WWTPs are not designed for the reduction of resistant microbes. Constructed wetlands (CWs) are viable wastewater treatment options with the potential for mitigating AR bacteria, their genes, pathogens, and general pollutants. Encouraging performance for the removal of AR (2–4 logs) has highlighted the applicability of CW on fields. Their low cost of construction, operation and maintenance makes them well suited for applications across the globe, especially in developing and low-income countries. The present review highlights a better understanding of the performance efficiency of conventional treatment plants and CWs for the elimination/reduction of AR from wastewater. They are viable alternatives that can be used for secondary/tertiary treatment or effluent polishing in combination with WWTP or in a decentralized manner.

The Sustainable Treatment Effect of Constructed Wetland for the Aquaculture Effluents from Blunt Snout Bream (Megalobrama amblycephala) Farm

In aquaculture, constructed wetland (CW) has recently attracted attention for use in effluent purification due to its low running costs, high efficiency and convenient operation,. However, less data are available regarding the long-term efficiency of farm-scale CW for cleaning effluents from inland freshwater fish farms. This study investigated the effectiveness of CW for the removal of nutrients, organic matter, phytoplankton, heavy metals and microbial contaminants in effluents from a blunt snout bream (Megalobrama amblycephala) farm during 2013–2018. In the study, we built a farm-scale vertical subsurface flow CW which connected with a fish pond, and its performance was evaluated during the later stage of fish farming. The results show that CW improved the water quality of the fish culture substantially. This system was effective in the removal of nutrients, with a removal rate of 21.43–47.19% for total phosphorus (TP), 17.66–53.54% for total nitrogen (TN), 32.85–53.36% for NH4+-N, 33.01–53.28% NH3-N, 30.32–56.01% for NO3−-N and 42.75–63.85% for NO2−-N. Meanwhile, the chlorophyll a (Chla) concentration was significantly reduced when the farming water flowed through the CW, with a 49.69–62.01% reduction during 2013–2018. However, the CW system only had a modest effect on the chemical oxygen demand (COD) in the aquaculture effluents. Furthermore, concentrations of copper (Cu) and lead (Pb) were reduced by 39.85% and 55.91%, respectively. A microbial contaminants test showed that the counts of total coliform (TC) and fecal coliform (FC) were reduced by 55.93% and 48.35%, respectively. In addition, the fish in the CW-connected pond showed better growth performance than those in the control pond. These results indicate that CW can effectively reduce the loads of nutrients, phytoplankton, metals, and microbial contaminants in effluents, and improve the water quality of fish ponds. Therefore, the application of CW in intensive fish culture systems may provide an advantageous alternative for achieving environmental sustainability.

Improving the quality of stabilization pond effluents using hybrid constructed wetlands

Water shortage and excessive use of water resources in arid and semi-arid regions, such as Iran, highlights the importance of using treated wastewater, especially for the highly demanding agricultural sector. Constructed wetlands (CWs) are among green technologies that offer an efficient and cost-effective wastewater treatment. This study investigates the complementary treatment of effluent from the Fooladshahr wastewater treatment plant, Isfahan, Iran, using pilot-scale CWs with horizontal (H-CW) and horizontal-vertical flow (HV-CW). The performance of two substrates, pumice and gravel, and the effect of using plants (Phragmites australis) was compared. Maximum removal efficiencies of total suspended solids (TSS) and biochemical oxygen demand (BOD5) were observed in the case of unplanted and planted HV-CW with pumice bed, respectively. In the case of gravel bed, planted H-CWs demonstrated maximum chemical oxygen demand (COD) removal efficiency. The highest mean outflow concentrations for TSS, BOD5 and COD were obtained in unplanted H-CW with pumice bed, likely due to shorter retention times compared to HV-CWs, as well as due to the absence of plants providing the required physicochemical and biological conditions for high performance treatment. Phosphate (PO43−) removal efficiency demonstrated seasonal dependency, where the highest values were obtained in warm seasons. In the case of fecal coliforms (FC), no significant differences were observed between the studied HV-CWs during the whole study period. Based on our results, planted H-CW with gravel bed provided an optimum removal efficiency while requiring a smaller footprint and lower expenditure than HV-CWs. This study demonstrates the application of CWs as an affordable solution for treating domestic wastewater for various reuse application in developing countries with water crisis, such as Iran.

Application of constructed wetlands in treating rural sewage from source separation with high-influent nitrogen load: a review.

Constructed wetlands (CWs) are characterized by low construction cost, convenient maintenance and management, and environmentally friendly features. They have emerged as promising technologies for decentralized sewage treatment across rural areas. Source separation of black water and gray water can facilitate sewage recycling and reuse of reclaimed water, reduce the size of treatment facilities, and lower infrastructure investment and operating cost. This is consistent with the concept of sustainable development. However, black water contains high concentrations of ammonia nitrogen, and the denitrification capacity of CWs is not excellent due to insufficient carbon source. Therefore, application of CWs for black water treatment faces challenges. This article provides a review on the progress in CWs for treatment of the sewage with high-influent nitrogen load, with emphasis on the commonly used strengthening means and the role of plants in nitrogen removal via CWs. The current issues of rural sewage treatment with high-influent nitrogen load by CWs are also assessed. Finally, the challenges and perspectives are discussed for the optimization of CWs-enhanced denitrification strategies.