Search Results (30)

Microplastic pollution has emerged as a serious societal concern, posing risks to the environment, human health, and economies. Conventional wastewater treatment processes remove microplastics at various levels from physical removal (primary), biological degradation (secondary), and contaminant-specific removal (tertiary treatment). Nature-based solutions (NbSs) offer an ecologically friendly alternative that utilizes nature to remove microplastics from wastewater. Recent reviews either focus broadly on NBSs for wastewater, technological solutions for microplastics, or NbSs for microplastics, but rarely connect them systematically. This review presents an integrated review of the sources and impacts of microplastic pollution, NbS technologies for the removal of microplastics, challenges and prospects in utilizing NbSs, and the knowledge gaps. Primary sources of microplastics are intentionally produced at microscopic sizes, while secondary sources originate from the disintegration of larger plastic debris. Among the NbS technologies are constructed wetlands (horizontal subsurface flow, vertical flow, surface flow, microbial fuel cells, multistage) with up to 100% efficiency; green infrastructures (bioretention systems, green walls, permeable pavements, retention ponds) with up to 99% efficiency; macrophytes and microphytes with up to 94% microplastic removal rate. Despite the ecosystem services provided by NbSs, they are challenged by the decrease in efficiency in removing other contaminants, detection and evaluation of NbS performance, and non-technical factors (operations and maintenance, public acceptance, climate risks, and financing). The findings present insights on further research and policy recommendations aimed at facilitating the integration of NbSs into existing frameworks for the removal of microplastics from wastewater, promoting research and innovation, and ensuring sustainable practices for sustainable management of water resources. Full article

This study systematically compares the environmental and economic performance of three wastewater treatment systems: constructed wetlands (CWs), microbial fuel cells (MFCs), and their integration (CW–MFC). Lab-scale units of each system were constructed using a multi-media matrix (gravel, zeolite, and granular activated carbon), composite native wetland species (Juncus effusus, Iris sp., and Typha angustifolia), carbon-based electrodes (graphite), and standard inoculum for CW and CW–MFC. The MFC system employed carbon-based electrodes and proton-exchange membrane. The experimental design included a parallel operation of all systems treating domestic wastewater under identical hydraulic and organic loading rates. Environmental impacts were quantified across construction and operational phases using life cycle assessment (LCA) with GaBi software 9.2, employing TRACI 2021 and ReCiPe 2016 methods, while techno-economic analysis (TEA) evaluated capital and operational costs. The key results indicate that CW demonstrates the lowest global warming potential (142.26 kg CO₂-eq) due to its reliance on natural biological processes. The integrated CW–MFC system achieved enhanced pollutant removal (82.8%, 87.13%, 78.13%, and 90.3% for COD, NO₃, TN, and TP) and bioenergy generation of 2.68 kWh, balancing environmental benefits with superior treatment efficiency. In contrast, the stand-alone MFC shows higher environmental burdens, primarily due to energy-intensive material requirements and fabrication processes. TEA results highlight CW as the most cost-effective solution (USD 627/m³), with CW–MFC emerging as a competitive alternative when considering environmental benefits and operational efficiencies (USD 718/m³). This study highlights the potential of hybrid systems, such as CW–MFC, to advance sustainable wastewater treatment technologies by minimizing environmental impacts and enhancing resource recovery, supporting their broader adoption in future water management strategies. Future research should focus on optimizing materials and energy use to improve scalability and feasibility. Full article

Anthropogenic activities, such as agricultural, industrial, and domestic, generate wastewater, leading to environmental concerns. Wastewater constituents (organic matter, pathogens, pharmaceuticals, heavy metals, and nutrients) have a negative impact if not treated, harming ecosystems and human health. Phytoremediator plants are a good option for domestic wastewater treatment since they help remove pollutants through their physiological activities, which are highly related to anatomical adaptations due to their growth in humid habitats. Macrophytes are a useful tool when coupled with a bioelectrochemical constructed wetland and MFC (CW-MFC), which can enhance the removal efficiency of organic matter present in wastewater and promote higher bioelectricity due to the root activity of plants. This review aims to compare different aquatic macrophyte types in wastewater treatment efficiency and provide useful information for plant selection. Full article

Although soil is mainly perceived as the basic component of agricultural production, it also plays a pivotal role in environmental protection and climate change mitigation. Soil ecosystems are the largest terrestrial carbon source and greenhouse gas emitters, and their degradation as a result of aggressive human activity exacerbates the problem of climate change. Application of microbial fuel cell (MFC) technology to soil-based ecosystems such as sediments, wetlands, farmland, or meadows allows for sustainable management of these environments with energy and environmental benefits. Soil ecosystem-based MFCs enable zero-energy, environmentally friendly soil bioremediation (with efficiencies reaching even 99%), direct clean energy production from various soil-based ecosystems (with power production reaching 334 W/m²), and monitoring of soil quality or wastewater treatment in wetlands (with efficiencies of up to 99%). They are also a new strategy for greenhouse gas, soil salinity, and metal accumulation mitigation. This article reviews the current state of the art in the field of application of MFC technology to various soil-based ecosystems, including soil MFCs, sediment MFCs, plant MFCs, and CW-MFCs (constructed wetlands coupled with MFCs). Full article

Constructed wetlands (CWs), serving as an advanced wastewater treatment system, play a vital role in both the emission and sequestration of diverse GHGs. However, there are few papers reviewing and analyzing developments in the field. In this study, bibliometrics were used as an essential tool for identifying and establishing connections among key elements within a discipline, as well as for analyzing the research status and developmental trends of the research fields. CiteSpace 6.3.1 was utilized to conduct an analysis of the references from the Web of Science Core Collection pertaining to GHG emissions from CWs over the period from 1993 to 2023. This study showed the following conclusions. (1) Organic nitrogen conversion produces N₂O, which is eventually transformed into N₂ and released from CWs. Anammox represents an attractive route for nitrogen removal. (2) The CO₂ is the final product of the oxidation of organic matter in the influent of CWs and can be fixed by plant photosynthesis. Anaerobic fermentation and CO₂ reduction produce CH₄. The two are emitted through aerenchyma transport, bubble diffusion, and other forms. (3) In the past 30 years, the number of publications and citation frequency shows an increasing trend. China and the United States published more papers. The top ten authors contributed to 20.607% of the total 1019, and the cooperation between different author groups needs to be strengthened. (4) The emerging burst keywords following 2020 are “microbial fuel cell” and “microbial community”, which highlights the current hotspots in research related to GHG emissions from CWs. (5) There is still a lack of long-term and applied discussion on the role of CWs in promoting GHG emission reduction. The relevant reaction conditions and mechanisms need to be explored and the possible research directions can be genetic regulation and information technology. Full article

This paper aims to comprehensively explore the performance and influencing factors of the constructed wetland–microbial fuel cell (CW-MFC) system when treating brine with different concentrations. The main objective is to determine how different salinity levels affect the operation and treatment efficiency of the CW-MFC system. The research results show that Bruguiera gymnorrhiza exhibits strong salt tolerance and can be used as a wetland plant for the CW-MFC system. The closed-circuit CW-MFC system with planted plants has the best performance, with a chemical oxygen demand (COD) removal rate of 84.8%, a total nitrogen (TN) removal rate of 68.12%, and a chloride ion (Cl⁻) removal rate of 29.96%. The maximum power density is 64.79% higher than that of the system without planted plants. The power generation performance of the system first increases and then decreases with the increase in salinity, while the internal resistance keeps decreasing. When the salinity is 2%, the power generation effect is the best, with an average output voltage of 617.3 ± 25.7 mV and a power density of 45.83 mW/m². The removal rates of COD and TN are inhibited with the increase in salinity, while the removal rate of total phosphorus (TP) is not significantly affected. The microbial community grows well under salt stress, but its structure is different. When the salinity is 1%, the optimal distance between electrodes is 10 cm. Considering the pollutant removal performance, the optimal hydraulic retention time is 3 days, and considering the power generation performance, the optimal hydraulic retention time is 2 days. This research provides important value for improving the performance of the CW-MFC system in treating brine. Full article

Hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP) are prevalent industrial wastewater contaminants that are recalcitrant to natural degradation and prone to migration in aquatic systems, thereby harming biological health and destabilizing ecosystems. Consequently, their removal is imperative. Compared to conventional chemical treatment methods, CW-MFC technology offers broader application potential. Leersia hexandra Swartz can enhance Cr (VI) and 4-CP absorption, thereby improving wastewater purification and electricity generation in CW-MFC systems. In this study, three CW-MFC reactors were designed with L. hexandra Swartz in distinct configurations, namely, stacked, multistage, and modular, to optimize the removal of Cr (VI) and 4-CP. By evaluating wastewater purification, electrochemical performance, and plant growth, the optimal influent hydraulic retention time (HRT) was determined. The results indicated that the modular configuration at an HRT of 5 days achieved superior removal rates and power generation. The modular configuration also supported the best growth of L. hexandra, with optimal photosynthetic parameters, and physiological and biochemical responses. These results underscore the potential of modular CW-MFC technology for effective detoxification of complex wastewater mixtures while concurrently generating electricity. Further research could significantly advance wastewater treatment and sustainable energy production, addressing water pollution, restoring aquatic ecosystems, and mitigating the hazards posed by Cr (VI) and 4-CP to water and human health. Full article

In this study, a constructed wetland was coupled with a microbial fuel cell to establish a coupled system known as the constructed wetland–microbial fuel cell (CW–MFC), utilized for the treatment of X-3B azo dye wastewater at varying concentrations. Experimental results indicated that the anodic region made the primary contributions to the discoloration of azo dyes and COD removal, with a contribution rate of 60.9–75.8% for COD removal and 57.8–83.0% for the effectiveness of discoloration. Additionally, the role of plants in the constructed wetland area could achieve the removal of small molecular substances and further discoloration. In comparison to open-circuit conditions, under closed-circuit conditions the CW–MFC effectively degraded X-3B azo dye wastewater. Under an external resistance of 2000 Ω, a maximum COD removal rate of 60.0% and a maximum discoloration rate of 85.8% were achieved for X-3B azo dye at a concentration of 100 mg/L. Improvements in the treatment efficiency of X-3B dye wastewater were achieved by altering the external resistance. Under an external resistance of 100 Ω and an influent concentration of X-3B of 800 mg/L, the COD removal rate reached 78.6%, and the decolorization rate reached 85.2%. At this point, the CW–MFC exhibited a maximum power density of 0.024 W/m³ and an internal resistance of 99.5 Ω. Spectral analysis and GC–MS results demonstrated the effective degradation of azo dyes within the system, indicating azo bond cleavage and the generation of numerous small molecular substances. Microbial analysis revealed the enrichment of electrogenic microorganisms under low external resistance conditions, where Geobacter and Trichococcus were dominant bacterial genera under an external resistance of 100 Ω, playing crucial roles in power generation and azo dye degradation within the system. Full article

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. Full article

This study designed integrated constructed wetland–microbial fuel cell (CW–MFC) systems using activated carbon (AC) as both CW substrates and MFC anodes and investigated the structure-activity relationship of six kinds of commercial columnar AC, as well as the organics and nitrogen removal, microbial activity and diversity of CW–MFCs. Results showed that the nitrogen adsorption by AC tended to be a linear process in which physical adsorption played a leading role and micropores made great contributions. A higher specific surface area, developed mesopores, and oxygen functionalities were conducive to the capacitance properties of AC, while a higher specific surface area and developed micropores were conducive to reduce material resistance and improve ion permeability. Coconut-shell-based AC had both excellent nitrogen adsorption capacity and electrochemical properties, making it ideal as both CW substrates and MFC anodes for CW–MFCs. The electricity generation, coulombic efficiency, internal resistance, and organics and nitrogen removal of CW–MFCs were positively correlated with the total depth of AC anodes. The total depth of AC anodes can be determined based on the influent organics/nitrogen loadings and organics/nitrogen removal load of AC, and a relatively smaller depth of a single AC anode (5 cm) was recommended. The MFC effectively improved the enzymatic activity (by 10.33% dehydrogenase, 8.72% catalase, and 7.35% ammonia monooxygenase), nitrification/denitrification intensity (by 9.53%/6.68%), and microbial diversity (by 1.64–4.07%) of AC (MFC anodes) in CW–MFCs, while the depth of a single AC anode barely influenced the microbial activity and diversity. MFCs increased COD and NH₃-N removal in CW–MFCs by 11.60% and 3.4%, respectively. The increased total adsorption capacity of AC with the increase of its total depth narrowed the difference in COD removal resulting from the promotion of MFCs on organics degradation. MFCs increased TN removal in CW–MFCs by 5.29% through promoting denitrification in cathodes and enhancing NH₃-N assimilation in anodes. The phyla of EAB (Proteobacteria, Bacteroidetes, Firmicutes, and Acidobacteria) and genera of EAB (Citrobacter, Geobacter, and Pseudomonas) accounted for 85–86% and 15.58–16.64% of the microbial community on AC anodes in CW–MFCs, respectively. Full article

The tail wastewater from sewage treatment facilities usually lacks carbon sources, and its subsequent treatment for deep nitrogen removal is difficult in natural conditions. In this study, the constructed wetland (CW) was integrated with microbial fuel cell (MFC) with high-density polyethylene (HDPE) fillers as the main matrix to improve nitrogen removal under inefficient carbon source conditions. Compared with the regular MFC and CW systems, MFC-CW attained higher nitrogen removal under low-carbon source conditions. The influence of influent carbon/nitrogen ratio (C/N) on the denitrification and electricity-generation performance was explored. Although the increase of carbon source simultaneously improved chemical oxygen demand (COD), ammonia (NH₄⁺-N), nitrate (NO₃⁻-N) and TN removal, the power generation during the carbon source adjustment showed low relation with the variation of influent COD in the range of 40–120 mg/L. CW was more dependent on carbon sources, and the addition of bioelectrochemical systems into MFC-CW could reduce the dependence of nitrogen removal on carbon sources, especially under low carbon source conditions. These findings offer valuable insights into the potential applications of MFC-CW for tail water treatment, and its parameters for utilization in real CWs should be explored in future studies. Full article

Pharmaceuticals and Personal Care Products (PPCPs) constitute a group of compounds that are challenging to break down and potentially pose risks to both ecosystems and human health when they accumulate in water bodies. This study established and operated small-scale constructed wetland–microbial fuel cells (CW-MFCs) continuously for 60 days, maintaining a hydraulic retention time (HRT) of 3 days. The research aimed to assess the treatment efficiency of wastewater containing Ibuprofen (IBP) and Diclofenac (DCF) using different co-substrates (glucose, sucrose, and sodium acetate) and to analyze the impact of these co-substrates on the composition of bacterial communities within the CW-MFC. After 60 days of operation, CW-MFC achieved removal rates of 89.29% for IBP and 84.10% for DCF. The elimination of IBP was primarily dependent on co-metabolic degradation processes occurring in both the anode and cathode, while DCF removal relied on anodic co-metabolism. Additionally, various co-substrates have an influence on the bacterial community diversity of the anode and cathodes. The possible bacterial groups involved in PPCP degradation were identified. In summary, Glu was identified as a more suitable co-substrate for CW-MFC in the removal of IBP and DCF, while SA as a co-substrate favored the induction and enrichment of EAB in the anodes. These findings offer valuable insights into the potential of CW-MFC for mitigating emerging contaminants. Full article

Constructed wetland–microbial fuel cell coupling systems (CW–MFCs) have received significant academic interest in the last decade mainly due to the promotion of MFCs in relation to pollutants’ degradation in CWs. Firstly, we investigated the effect of hydraulic retention time (HRT) and electrode configuration on the flow field characteristics of CW–MFCs using graphite rods and plates as electrodes, as well as the optimization of electrode configuration using computational fluid dynamics (CFD) numerical simulation. The results showed that: (1) the apparent HRT was the most influential and decisive factor, with a contribution of over 90% for the average HRT of CW–MFCs; (2) anode spacing was the most influential factor for the hydraulic performance of CW–MFCs, with contributions of over 50% for water flow divergence and hydraulic efficiency (λ) and over 45% for effective volume ratio (e); (3) anode size was significant for e and λ, with a contribution of over 20%; (4) cathode position and cathode size had no statistically significant effect on the hydraulic performance of CW–MFCs. It was mainly through the blocking of water flows, flows around, compressing water flow channels and boundary layer separation that the MFC electrodes influenced the hydraulic characteristics of the flow field in CW–MFCs. Optimizing the flow field by optimizing the electrode configuration helped to facilitate electricity generation and pollutants’ removal in CW–MFCs. This study offers a scientific reference for improving the hydraulic performance of CW–MFCs, and it also provides a new research perspective for improving the wastewater treatment and electricity production performance of CW–MFCs. Full article

Electrocoagulation (EC) has gained increasing attention as an effective and environmentally friendly technique for purifying water and wastewater. This review provides a comprehensive analysis of the recent literature on EC and identifies new trends and potentials for further research. Initially, the nature of EC and its operating parameters are discussed, while the research trends are analyzed using the Scopus database and VOSviewer software. From 1977 to 2022, 2691 research articles and review papers on EC for water/wastewater treatment were published, with the number of publications increasing from 2 in 1977 to 293 in 2022. In the past five years, most studies focused on treatment performance and the mechanism of EC systems. However, recent emphasis has been placed on combining EC with other treatment processes and addressing emerging pollutants. The innovative applications of EC are highlighted, including the removal of microplastics and per/polyfluoroalkyl substances, the power supply of EC via microbial fuel cells (MFCs) and electro-wetlands (EWs), and the application of power management systems in EC. The review concludes with suggestions for further research to enhance the technology and expand its scope of applications. Full article

Cr (VI) is hazardous to humans and our environment. Leersia hexandra Swartz (L. hexandra) is the first wet chromium hyperaccumulator found in China. This study constructed the L. hexandra constructed wetland-microbial fuel cell (CW-MFC) system to treat Cr (VI) wastewater. It also determined the effects of different dissolved oxygen (DO) concentrations on power generation, pollutant removal, and Cr (VI) reduction. Cathode aeration promoted the voltage output and pollutant removal of the L. hexandra CW-MFC when the DO concentration was 4.5 mg·L⁻¹: the highest voltage was 520 mV, the chemical oxygen demand (COD) removal rate was 93.73%, and the Cr (VI) removal rate was 97.77%. Moreover, the increase in the DO concentration improved the absorption of heavy metal Cr by the substrate and L. hexandra, and promoted the transformation from Cr (VI) to Cr (III). Chromium mostly exists as a residue with low toxicity and low mobility in L. hexandra and the substrate. This proves that the increased DO concentration promotes the redox reaction in the system and plants, reducing Cr (VI) to Cr (III). At the same time, the key micro-organism Geobacter that enhances the performance of the system and Cr (VI) reduction was found. The research results can provide a reference for the subsequent CW-MFC treatment of actual Cr-containing wastewater. Full article