Constructed Wetland Technology 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.

Oilfields produced water and constructed wetlands technology: a comprehensive review

ABSTRACT Produced water has elevated levels of salts, metals, and organic constituents and is seen as a waste byproduct in the oil and gas industry. This comprehensive review summarizes (1) the potential impact, (2) produced water management, and (3) identifies current research thrust areas in future efforts. Complementary treatment systems involving chemical and biological techniques offer significant advantages. The review emphasizes the application of these technologies and their performance in meeting regulatory standards. Cost, energy consumption, chemical use, and operational complexity are recognized challenges in both the water treatment industry and the oil and gas industry. It highlights the need for further research and for the optimization of processes to enhance their efficiency. The integration of conventional methods with advanced treatment processes is also explored, with a vision toward developing hybrid systems for improved treatment efficiency. Overall, complementary systems show great promise for the treatment of produced water, but further advancements, sustainability considerations, and integration with other technologies are essential for their successful implementation in large-scale applications. Maintaining expertise and awareness of water treatment issues in the oil and gas industry can help reclamation identify new technologies and solutions to technical challenges that may benefit the oilfield water treatment industry.

Efficiency with Constructed Wetlands System Using Water Ferns (Azolla microphylla) to Treat Laundry Wastewater

This research aims to analyze the efficiency of processing liquid waste from the laundry industry using the Free Water Surface Constructed Wetland (FWS) system with Azolla microphylla plants. The research method used is experimental research by manipulating independent variables and controlling other relevant variables, as well as observing the effect on the dependent variable. Laundry waste samples were taken from Berkah Laundry, Puri Gading, Bekasi. The results showed that the biomass of Azolla microphylla plants increased significantly from day 0 to day 12, with a growth rate between 0.0289 – 0.0477 grams/day and plant density between 185.19 ind/m2 – 277.78 ind/m2. The influent BOD concentration of laundry liquid waste during the acclimatization stage ranged from 5.89 – 10.54 mg/L, while the effluent BOD ranged from 4.35 – 6.98 mg/L, with the highest efficiency reaching 33.8%. The constructed wetland system with Azolla microphylla plants has proven to be effective in reducing pollutant content in liquid waste, with a BOD removal efficiency of 11.1% - 17.7% and COD of 14.5% - 39%. The conclusion of this research is that the use of artificial wetlands with Azolla microphylla plants can be an effective and environmentally friendly alternative solution for processing liquid waste from the laundry industry. The implications of this research show the potential for applying constructed wetland technology in the clothes washing industry to reduce the negative impact of waste on the environment.

Application and prospect analysis of microbial fuel cell technology

As global energy demand grows and environmental problems intensify, the search for clean, renewable energy solutions becomes especially urgent. This article reviews microbial fuel cell (MFCs) technology, a new type of clean energy technology that uses microbial metabolic activity to convert organic matter into electricity. Compared with traditional fossil fuel power generation methods, MFCs have significant advantages such as low pollution, low noise, and renewable. The working principle of MFCs, including the reaction process of anode and cathode, as well as the key factors affecting the performance of MFCs, such as the choice of anode and cathode materials, are discussed. In addition, the coupling applications of MFCs with other technologies, such as photocatalysis, electrofenton technology, microbial electrolysis (MEC) and constructed wetland technology, are discussed, which provide new possibilities for improving wastewater treatment efficiency and expanding the application field of MFC. Finally, the challenges and future development direction of MFCs technology are prospected, and key research directions such as improving energy conversion efficiency, reducing cost and enhancing system stability are pointed out.

Treatment of eutrophic water in pyrite-filled constructed wetland integrated with microelectrolysis driven by iron/sulfur cycle: Performance and mechanism

This study developed a microelectrolysis-integrated constructed wetland with pyrite filler around the cathode (e-PCW) to treat eutrophic water. Results indicated that e-PCW effectively enhanced pyrite dissolution, converting solid-phase electron donors into bioavailable forms, thereby facilitating the enrichment of various denitrifying bacteria on pyrite surfaces. Importantly, iron-reducing and sulfur-reducing bacteria attached to the pyrite surfaces enhanced the conversion of ferric iron and sulfate, thereby driving iron and sulfur cycles and promoting electron transfer. Therefore, synergistic effects of pyrite and microelectrolysis made e-PCW achieve higher total nitrogen (TN) and total phosphorus (TP) removal efficiencies. With a hydraulic retention time of 24 h, the highest removal efficiencies of TN and TP achieved 78% and 75%, respectively. Furthermore, when eutrophic water containing high concentration of algae was fed into e-PCW, it consistently demonstrated superior TN and TP removal capabilities. This work provides a valuable approach to optimizing constructed wetland technology for treating eutrophic water.

Development of a Constructed Wetland for Greywater Treatment for Reuse in Arid Regions: Case Study in Rural Burkina Faso

This study implemented and assessed, over a period of four weeks, a full-scale constructed wetland designed to collect and treat the greywater for a rural household located in an arid environment typical of Africa’s Sahel region. The system was constructed from local materials and consisted of a shower room, a receiving basin, a pre-treatment filter, and a subsurface horizontal flow wetland planted with Chrysopogon zizanioides. Results showed the overall removal of organic matter was greater than 90%, and orthophosphate and ammonium were reduced by 73% and 60%, respectively, allowing for the treated water to retain some embedded nutrients. The removal efficiency of fecal bacteria varied from 3.41 (enterococci) to 4.19 (fecal coliforms) log10 units which meets World Health Organization Guidelines for restricted irrigation. Our assessment of the full-scale household constructed wetland technology adds to the relatively low number of constructed wetland studies conducted outside a laboratory setting. Furthermore, it supports efforts to promote safe reuse of an underutilized resource at the rural household level in Sub-Saharan Africa and other arid regions in the developing world, supporting prospects for using treated greywater for agricultural reuse in regions that experience water scarcity, climate variability, and land degradation.

Life Cycle Assessment of an Innovative Combined Treatment and Constructed Wetland Technology for the Treatment of Hexachlorocyclohexane-Contaminated Drainage Water in Hajek in the Czech Republic

The paper presents the results of an LCA analysis of the “Wetland+®” technology compared to conventional wastewater treatment technology. Wastewater contaminated with pesticide production residues from lindane was treated. The analysis is based on data from a full-scale Wetland+® installation located in Hajek, the Czech Republic. Conventional wastewater treatment technology was selected as a comparator. For the comparative system, data for the LCA came from design calculations assuming the location of such a system in the same place and function as the Wetland+® technology implemented. The LCA analysis was carried out using system boundaries covering the stages of construction and operation of the systems. The results indicate that with the Wetland+® technology, a system’s overall environment burdens are >11 times less than that of conventional wastewater treatment technology.

Treatment of pharmaceutical industry wastewater for water reuse in Jordan using hybrid constructed wetlands

Developing cost-efficient wastewater treatment technologies for safe reuse is essential, especially in developing countries simultaneously facing water scarcity. This study developed and evaluated a hybrid constructed wetlands (CWs) approach, incorporating tidal flow (TF) operation and utilising local Jordanian zeolite as a wetland substrate for real pharmaceutical industry wastewater treatment. Over 273 days of continuous monitoring, the results revealed that the first-stage TFCWs filled with either raw or modified zeolite performed significantly higher reductions in Chemical Oxygen Demand (COD, 58 %–60 %), Total Nitrogen (TN, 32 %–37 %), and Phosphate (PO4, 46 %–64 %) compared to TFCWs filled with normal sand. Water quality further improved after the second stage of horizontal subsurface flow CWs treatment, achieving log removals of 1.09–2.47 for total coliform and 1.89–2.09 for E. coli. With influent pharmaceutical concentrations ranging from 275 to 2000 μg/L, the zeolite-filled hybrid CWs achieved complete removal (>98 %) for ciprofloxacin, ofloxacin, erythromycin, and enrofloxacin, moderate removal (43 %–81 %) for flumequine and lincomycin, and limited removal (<8 %) for carbamazepine and diclofenac. The overall accumulation of pharmaceuticals in plant tissue and substrate adsorption accounted for only 2.3 % and 4.3 %, respectively, of the total mass removal. Biodegradation of these pharmaceuticals (up to 61 %) through microbial-mediated processes or within plant tissues was identified as the key removal pathway. For both conventional pollutants and pharmaceuticals, modified zeolite wetland media could only slightly enhance treatment without a significant difference between the two treatment groups. The final effluent from all hybrid CWs complied with Jordanian treated industry wastewater reuse standards (category III), and systems filled with raw or modified zeolite achieved over 95 % of samples meeting the highest water reuse category I. This study provides evidence of using hybrid CWs technology as a nature-based solution to address water safety and scarcity challenges.

Use of Vetevera Grass (Chrysopogon zizanioides) in a Constructed Wetland to Remove Heavy Metals from Kege Wet Coffee Processing Plant, Dale Woreda, Sidama Regional State, Ethiopia

Conventional methods for removing heavy metals from contaminated water are prohibitively expensive and, more significantly, ineffective, especially when the concentration of heavy metals is low. This paper evaluated the use of vetevera grass in a constructed wetland to remove Ca, Cd, Co, Cu, Cr, Fe, K, Mn, Na, Pb, and Zn metals from Kege Wet Coffee Processing Plant, Dale Woreda, Sidama Regional State, Ethiopia using a two vertical flows constructed wetland of 132 square meters in size with Eleven meters in length and 12 meters wide. The 11m * 3m * 1m open space between two constructed wetlands is developed. The second wetland was built, and it serves the same purpose as the previous one but discharges water into the river. The construction of the wetland is performed by digging 20 cm wide, and 30 cm apart furrows. vetiveria grasses was planted at 20 cm intervals. Heavy metals (Ca, Cd, Co, Cu, Cr, Fe, K, Mn, Na, Pb, and Zn) were measured from soil and plant samples from the inlet to the outlet sampling sites using standard procedures from two compartments (soil, and macrophytes) of constructed wetland. Findings indicated that Ca (460.0 ppm) had the highest mean concentration of heavy metals, whereas Ni (0.50 ppm) had the lowest in the soil sample. Metal absorption by vetiver grass is the highest concentration found in plant tissues grown in the following order k &gt; Ca &gt; Na &gt; Mn &gt; Fe &gt; Zn &gt; Cu &gt;Ni &gt;Cr in shoots. The order of the heavy metal contents in the roots of vetiver grass was k &gt; Ca &gt; Na &gt; Mn &gt; Fe &gt; Zn &gt; Cu &gt;Ni &gt;Cr. The plant was found to be effective at transferring Mn and Ni from the roots to the shoots based on translocation and bioconcentration, whereas it served as a potential phytostabilizer for Ca, Cu, Cr, Fe, K, Na, and Zn since the TF values are lower than 1, which show that vetiver grass prefers to accumulate heavy metals in the roots rather than the shoot and so supports its potential for phytostabilization. From the present study, it was evident that vetiver grass is an ideal candidate for wastewater treatment using constructed wetland technology.

Phytoremediation Performance with Ornamental Plants in Monocultures and Polycultures Conditions Using Constructed Wetlands Technology.

The assessment of constructed wetlands (CWs) has gained interest in the last 20 years for wastewater treatment in Latin American regions. However, the effects of culture systems with different ornamental species in CWs for phytoremediation are little known. In this study, some chemical parameters such as total suspended solids (TSS), chemical oxygen demand (COD), phosphate (PO4-P), and ammonium (NH4-N) were analyzed in order to prove the removal of pollutants by phytoremediation in CWs. The environmental impact index based on eutrophication reduction (EI-E) was also calculated to estimate the cause-effect relationship using CWs in different culture conditions. C. hybrids and Dieffenbachia seguine were used in monoculture and polyculture (both species mixed) mesocosm CWs. One hundred eighty days of the study showed that CWs with plants in monoculture/polyculture conditions removed significant amounts of organic matter (TSS and COD) (p > 0.05; 40-55% TSS and 80-90% COD). Nitrogen and phosphorous compounds were significantly lower in the monoculture of D. seguine (p < 0.05) than in monocultures of C. hybrids, and polyculture systems. EI-E indicator was inversely proportional to the phosphorous removed, showing a smaller environmental impact with the polyculture systems (0.006 kg PO₄3- eq removed) than monocultures, identifying the influence of polyculture systems on the potential environmental impacts compared with the phytoremediation function in monocultures (0.011-0.014 kg PO₄3- eq removed). Future research is required to determine other types of categories of environmental impact index and compare them with other wastewater treatment systems and plants. Phytoremediation with the ornamental plants studied in CWs is a good option for wastewater treatment using a plant-based cleanup technology.

Initial concept and embodiment to develop modular constructed wetland: A unique and promising solution to sustainability transitions in water management

Constructed Wetlands (CWs) were widely used as nature-based solution to effectively remove contaminants from wastewater, while offering benefits for ecological value and landscape services. However, one limited factor for practical applications of CW technology is the conventional construction style, which is a laborious and complex civil engineering. As such, an idea of modular CW (MCW) was proposed and embodiment was made for different scales of treatment wetland projects. This paper introduces the MCW concept and the efforts made to realize it. MCW is a revolutionary approach in wastewater treatment that combines efficiency, adaptability, and environmental sustainability. MCW represents a paradigm shift from traditional CWs, offering a pre-fabricated, modular solution that simplifies the complexities of civil engineering in wastewater management. These prefabricated modular structures, assembled off-site and installed on-site, provide a streamlined, flexible, and user-friendly alternative to conventional CWs. The innovative design of MCWs incorporates advanced substrates and technologies, integrating enhanced processes such as intermittent aeration, tidal flow, and circulating reflux. This novel approach significantly improves pollutant removal efficiency, reduces land usage, and addresses clogging issues through rapid module replacement. The paper comprehensively delved into the structural, substrate, plant, and operational aspects of MCWs. It highlights the environmental and economic benefits of MCWs, emphasizing their role as a cost-effective, environmentally-friendly solution for wastewater treatment. The study concludes by underscoring the potential of MCWs in spearheading new research and development in sustainable wastewater management, marking a new generation in CW systems.

Research Trends and Future Prospects of Constructed Wetland Treatment Technology in China

With the intensification of water pollution problems worldwide, constructed wetlands, as a green, efficient, and energy-saving wastewater treatment technology, have gradually attracted the wide attention of scholars at home and abroad. In order to better understand and master the research trends of constructed wetland treatment technology in China and promote its development, the literature from 2000 to 2023 in the CNKI database and the Web of Science (WoS) database (located in China) were selected as research objects. Then, CiteSpace software (6.2.R4) was used to visualize and analyze the literature, revealing the research trends and hot areas of constructed wetland treatment technology in China. Then, the optimized way of operation effect of constructed wetland was discussed to provide a theoretical and technical basis for the wide application of constructed wetland technology in our country. The results indicate that the annual publication volume of research on constructed wetlands in China is showing a rapid upward trend. Among them, the Chinese literature mainly focuses on how to improve the application effect of constructed wetlands on nitrogen and phosphorus removal of rural domestic wastewater by matching different wetland plants or developing combined processes. The English literature from the Web of Science (WoS) database mainly focuses on how to remove emerging pollutants, such as heavy metals and resistance genes in wastewater in China, by changing the filling matrix and microbial community structure or developing new processes, and the related mechanisms have been discussed. One of the hot spots for the future research of constructed wetlands in China is to vigorously develop microbial fuel cells, and try to overcome the problem of poor purification efficiency of constructed wetlands under complex conditions such as low temperature, low carbon-nitrogen ratio, and high pollution load. In order to strengthen its application, the specific optimization methods can be divided into two categories: self-optimization strategies such as increasing oxygen supply and transfer, providing electron donor matrix, preventing matrix blockage, and combination processes coupled with anaerobic treatment and other technologies.

Developing a novel lightweight substrate for constructed treatment wetland: The idea and the reality

The cost-effective and environmentally friendly substrates play an important role in functioning constructed wetlands (CWs). This study innovatively composes aluminum sludge and polyurethane under the action of a catalyst to develop a novel lightweight substrate (Al-NLS), which is expected to be used as a main substrate in CWs. The driving force of it lies in reducing construction costs of CWs in practice, while offering a flexible and considerably efficient substrate in CW. The bulk density of the resultant Al-NLS was apparently reduced by about 80 % compared with common substrate of gravel. The static adsorption experiments showed that the adsorption behavior of Al-NLS on phosphorus (P) was in accordance with Langmuir isotherm (with maximum P adsorption capacity of 1.12 mg/g,) and quasi-second-order kinetic models. The use of Al-NLS as a single stage wetland substrate to treat real domestic wastewater has favorable removal efficiencies of COD (65.9–74.3 %), TP (86.9–98.6 %), NH4+-N (61.1–52.2 %) and TN (35.4–45.6 %). The mechanisms of P removal onto Al-NLS were examined by various physiochemical characterizations of Al-NLS and raw alum sludge, which revealed that P adsorption was via forming Hydroxy-Al by ion exchange. In addition, high throughput sequencing analysis revealed that Al-NLS had positive impact on the richness and diversity of microbial community for pollutants removal, while the abundance of key functional bacteria such as proteobacteria and bacteroidota was higher in the longer retention time of CW (HRT = 2 days). These results indicated that Al-NLS could be used as a new alternative substrate in CWs technology.

POLLUTION REMOVAL CAPACITIES OF AQUATIC PLANT SPECIES IN THE DATONG WETLAND PARK IN NORTH CHINA

The purification effect of a natural wetland landscape is often low when the focus is placed on the landscape effect. The effective combination of constructed wetland technology with landscape construction is challenging. Taking the Yuhe Wetland Park in Datong, Shanxi Province, China, as an example, the COD, phosphorus, and nitrogen removal capacities of aquatic plant species were determined, as well as the effects of the soil and the microbial communities. The highest COD and P removal capacity was observed for Typha orientalis Presl. which the purification rate reached 76.9% and 76.6%, and the highest N removal capacities were found for Scirpus validus Vahl., the rate of purification was 83.4%. Gram-negative bacteria were dominant.

Study on the Effect of AO-Coupled Constructed Wetlands on Conventional and Trace Organic Pollutant Treatment.

In this study, a pilot-scale integrated process was developed, which combined the integrated biological contact oxidation technology (AO) and the improved constructed wetland technology. The results showed significant removal efficiency for both conventional and trace organic pollutants. The average removal efficiencies for COD, NH4+-N, and TP were 78.52, 85.95, and 49.47%, respectively. For trace organic pollutants, triclocarban, triclosan, and sulfadiazine, the removal efficiencies reached 60.14, 57.42, and 84.29%, respectively. The AO stage played a crucial role in removing trace organic pollutants, achieving removal efficiencies of 37.28, 43.44, and 83.82% for triclocarban, triclosan, and sulfadiazine, respectively. Subsequent treatment using improved constructed wetland technology with coal slag + gravel fillers demonstrated the highest removal efficiency, with average efficiencies of 68.66, 63.38, and 81.32% for triclocarban, triclosan, and sulfadiazine, respectively. Correlation analysis revealed positive correlations between temperature, precipitation, and the removal efficiency of COD, NH4+-N, and TP, while negative correlations were observed with the removal efficiency of triclocarban, triclosan, and sulfadiazine. Furthermore, the influent concentrations of triclocarban and triclosan were significantly negatively correlated with the removal efficiency of COD and TP. The presence of triclocarban and triclosan potentially reduced the microbial diversity and hindered sludge sedimentation performance.

A survey on constructed wetland publications in the past three decades.

Decentralised wastewater treatment systems, such as constructed wetlands, are becoming increasingly popular these days because they are more economical and cost-effective than conventional plants. The primary objective of this review paper is to determine the number of studies that have been conducted on constructed wetlands, specifically 'free water surface flow constructed wetlands', 'horizontal subsurface flow constructed wetlands', 'vertical subsurface flow constructed wetlands', and 'hybrid constructed wetlands'. In addition, the paper examines the status of research publications on constructed wetlands by country, author, and journal. Based on the review, it has been found that although constructed wetland technology is economical and cost-effective, it is still not among the top 10 effluent treatment methods. Compared to other constructed wetland systems, 'hybrid constructed wetlands' have received minimal attention. Based on the search results, 4639 documents published between 1989 and 2021 have been extracted from the online edition of SCI-EXPANDED, Web of Science. The documents associated with constructed wetlands are divided into eight main document types. Articles and proceedings papers are the most common document type, accounting for 93% of all publications, followed by reviews (4%), meeting abstracts (1.3%), corrections (0.56%), editorial materials (0.38%), news items (0.2%), letters (0.04%), and book reviews (0.02%).

Chromium and Zinc removal from synthetic industrial wastewater in pilot-scale constructed wetlands planted with Cyperus odoratus L

Introduction: Constructed wetlands (CWs) are a recognized technology to treat industrial wastewater. Objective: A pilot system of two horizontal subsurface flow CWs was used to remove Cr and Zn from industrial synthetic wastewater. Method: The study was carried out at Universidad del Atlántico in Barranquilla, Colombia. Two containers of 0.375 m2 were filled with a gravel bed (~10 mm and 40% of porosity) and a 0.3 m water column. One container was planted with Cyperus odoratus L. and another without plants was used as a control. Results: The removal efficiency of Cr and Zn was 93% and 96% in the CW planted, respectively and 67% and 98% removal were obtained in the unplanted system with statistical differences (P&lt;0,05). The observed difference in biomass production (0.1 and 0.6 kg/m2) could be related to seasonal weather that could have favored the growth of the plant. C. odoratus reached a Translocation Factor greater than 1.5 for Cr and Zn, which is greater than that, reported by others for Cyperus species. However, a Bioconcentration Factor &gt; 13.6 for Zn and &lt; 7.7 for Cr indicated that C. odoratus is an accumulator species for Cr and Zn. Sorption metal processes in gravel can be occurring due to the high removal efficiency of Zn in unplanted systems Conclusions: These results show that C. odoratus could be recommended for use in constructed wetlands technology due to fast-growing and absorption and translocation heavy metals capacity.

Sediment Fungal Communities of Constructed Wetlands Dominated by Zizania latifolia and Phragmites communis and Their Effect on Organic Pollutant Removal

The purpose of the study was to investigate the relationship between wetland plants and fungal communities with a focus on their combined functions to remove organic pollutants. Two constructed wetland (CW) systems, covering a total area of 4.24 hm2, were established to treat the agricultural non-point source pollution using, respectively, Zizania latifolia (CW1) and Phragmites communis (CW2) as the dominant plant species. The obtained results showed that CW1 performed much better than CW2 in terms of promoting the abundance and diversity of the sediment fungal community identified by high-throughput sequencing technology. The enhanced fungal activity was shown to be one of the main factors that raised the pollutant removal rates and reduced the contents of the target pollutants (COD, TN, TP and NH4+-N) to levels below the stipulated national standards. Significant differences in abundant fungi were observed between the CW units and their inlet and outlet sampling sites, indicating that the plant species and pollutant concentrations were the key factors affecting the diversity and activity of the sediment fungal community. The findings of the study provided not only a better understanding of the plant–fungi symbiotic system but also useful information for the development of CW technology.

A review of emerged constructed wetlands based on biochar filler: Wastewater purification and carbon sequestration/greenhouse gas reduction

Constructed wetlands (CWs) are a promising ecological wastewater treatment technology. The method of biochar (BC) filler to enhance CWs has been widely researched in the past decade. This article summarizes the applications of BC-added CWs technology and consolidates the various impacts of BC filler on the operation of CWs, which can be divided into two aspects. One is to enhance the wastewater purification performance of CWs ecosystems, and the other is to improve the abilities of CWs to sequester carbon and reduce greenhouse gas (GHG) emissions. These two aspects are precisely among the environmental challenges facing humanity globally. The BC prepared from CWs plants used as CWs filler can solve excess biomass in CWs. Moreover, the large specific surface area of BC, excellent adsorption performance, and good biocompatibility improve the sewage treatment effect of CWs. The BC has a high potential for stimulating the growth of CWs plants, biomass carbon sequestration, inhibition of organic carbon mineralization in CWs substrates, and reducing GHG emissions, which mitigates global climate change. In short, the BC-added CWs is a technology that combines wastewater purification and carbon sequestration/GHG reduction. This study provides solid references for the engineering promotion of CWs based on BC filler.

Enhanced nitrogen removal via biochar-mediated nitrification, denitrification, and electron transfer in constructed wetland microcosms.

This study investigated the effect of biochar on real domestic wastewater treatment by constructed wetlands (CWs). To evaluate the role of biochar as a substrate and electron transfer medium on nitrogen transformation, three treatments of CW microcosms were established: conventional substrate (T1), biochar substrate (T2), and biochar-mediated electron transfer (T3). Nitrogen removal increased from 74% in T1 to 77.4% in T2 and 82.1% in T3. Nitrate generation increased in T2 (up to 2 mg/L) but decreased in T3 (lower than 0.8 mg/L), and the nitrification genes (amoA, Hao, and nxrA) in T2 and T3 increased by 132-164% and 129-217%, respectively, compared with T1 (1.56 × 104- 2.34 × 107 copies/g). The nitrifying Nitrosomonas, denitrifying Dechloromonas, and denitrification genes (narL, nirK, norC, and nosZ) in the anode and cathode of T3 were significantly higher than those of the other treatments (increased by 60-fold, 35-fold, and 19-38%). The genus Geobacter, related to electron transfer, increased in T3 (by 48-fold), and stable voltage (~150 mV) and power density (~9 uW/m2) were achieved. These results highlight the biochar-mediated enhancement of nitrogen removal in constructed wetlands via nitrification, denitrification, and electron transfer, and provide a promising approach for enhanced nitrogen removal by constructed wetland technology.