Search Results (86)

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

Water pollution caused by petroleum-derived volatile organic compounds such as benzene, toluene, ethylbenzene, and xylenes (BTEX), as well as methyl tert-butyl ether (MTBE), poses a growing threat to aquatic ecosystems and human health. These contaminants, together with the organic matter and nutrients present in municipal wastewater, highlight the need for sustainable treatment technologies adapted to tropical conditions. This study evaluated the removal efficiency of BTEX, MTBE, and conventional pollutants using hybrid constructed wetlands (HCWs) that combine vertical subsurface flow (VSSF-CW) and horizontal subsurface flow (HSSF-CW) systems. Two plant species—Heliconia latispatha and Phragmites australis—were tested, along with a polyculture and an unvegetated control. The hybrid systems treated synthetic influents formulated to simulate contaminated municipal wastewater. Parameters including COD, TSS, N–NH₄⁺, N–NO₃⁻, P–PO₄³⁻, BTEX, and MTBE were monitored and analyzed using ANOVA and Tukey’s test (p < 0.05). Vegetated systems achieved COD removal efficiencies exceeding 85%, compared with 72% in the control. Phragmites australis obtained the highest removal of suspended solids (92 ± 3%) and ammonium nitrogen (88 ± 2%), whereas Heliconia latispatha exhibited superior phosphorus removal (84 ± 4%). The polyculture displayed a synergistic effect, achieving removal rates of 93% for benzene, 91% for toluene, and 88% for MTBE, with statistically significant differences relative to the control (p < 0.05). In conclusion, hybrid constructed wetlands planted with Heliconia latispatha and Phragmites australis demonstrated high efficiency and stability in removing BTEX, MTBE, and conventional pollutants under tropical conditions, positioning themselves as a sustainable, low-cost, and esthetically valuable treatment alternative. Full article

Decontamination of wastewater, industrial effluents, stormwater, and graywater can be carried out through the use of natural or constructed wetlands. In either case, the natural functions of soil, vegetation, and organisms are widely applied for the treatment of contaminated water. In particular, in the physical design of a constructed wetland, several operational factors must be adjusted with the aim of reducing pollution levels. Although various fully customized design methodologies have been developed and reported in the literature, they often fail to meet the required decontamination objectives. In this context, the application of the NSGA-II evolutionary algorithm is adequate to optimize the physical design of a horizontal subsurface flow wetland for graywater treatment, focusing specifically on the removal of biodegradable organic matter (BOD⁵). Four competing objectives are considered: minimizing physical volume and total design cost, while maximizing contaminant removal efficiency and graywater flow rate. Five constraint functions are also incorporated: removal efficiency greater than 95%, physical volume below 1000 m³, flow rate above 10 m³/d, a limit on total construction cost of MXN 1,000,000, and maintaining a length-to-width ratio greater than or equal to 2 but less than or equal to 4. The proposed methodology generates a wide set of non-dominated solutions, visualized through Pareto surfaces, which highlight the trade-offs among different objectives. This approach offers the possibility of selecting optimal designs under specific conditions, which underscores the limitations of conventional single-solution models. The results show that the methodology consistently achieved removal efficiencies above 95%, with construction costs within budget and physical volumes below the established limit, offering a more versatile and cost-effective alternative. This work demonstrates that the integration of NSGA-II into wetland design is an effective and adaptable strategy, capable of providing sustainable alternatives for graywater treatment and constituting a valuable decision-making tool. Full article

Wastewater generated by academic institutions poses an environmental burden due to its composition, including household, food-related waste, and potential microcontaminants such as pharmaceutical and laboratory chemicals. This study evaluated wastewater from eleven academic institutions. Horizontal subsurface flow constructed wetlands (HSFCWs) filled with locally sourced volcanic gravel were tested for treatment performance at a selected site, the University of Rwanda, College of Science and Technology (UR-CST). Six HSFCWs operated continuously for four months: two planted with Cyperus latifolius, two with Juncus effusus, and two unplanted. Academic wastewater showed average concentrations of 715 mg/L COD, 54 mg/L NH₄⁺-N, 9 mg/L NO₃⁻-N, and 32 mg/L PO₄³⁻-P. A 4-day hydraulic retention time was effective for the treatment process. The HSFCWs achieved removal efficiencies of 69–82% (COD), 66–87% (NH₄⁺-N), 69–90% (NO₃⁻-N), and over 90% for TSS and PO₄³⁻-P, emphasizing the strong physical and chemical purification capacity of volcanic gravel as confirmed by XRF analysis. Juncus effusus outperformed Cyperus latifolius in biomass (6667 vs. 4389 g/m²) and nutrient assimilation per unit area, removing 3.75× more TP and 1.46× more TN. The desorption capacity of the substrate enabled potential phosphorus recovery of up to 50%. Volcanic gravel-based CWs offer an effective, low-cost, and sustainable approach to wastewater treatment with potential for nutrient recovery. Full article

Constructed wetlands are nature-based technologies widely used for the treatment of wastewater and contaminated surface water. This study evaluated the efficiency of free water surface (FWS) and horizontal subsurface flow (HSSF) constructed wetlands in reducing the turbidity of mine spoil rainwater using the w-C* model. Different hydraulic retention times (2, 4, and 6 days) were tested, and the influence of macrophyte type and substrate on the w parameter was investigated. Model calibration was performed based on correlation coefficients (R), coefficient of determination (R²), Nash–Sutcliffe efficiency (NSE), and root mean square error (RMSE). The results indicated a 99% reduction in turbidity, with average values of R = 0.87 ± 0.05 (FWS) and 0.87 ± 0.03 (HSSF), and NSE of 0.76 ± 0.04 (FWS) and 0.74 ± 0.07 (HSSF), demonstrating good agreement between observed and predicted data. The settling rate (w) ranged from 0.16 to 0.40 m·d⁻¹ in FWS and from 0.20 to 0.70 m·d⁻¹ in HSSF, with the lowest value recorded in the control (0.09 m·d⁻¹). The best performances were observed in FWS-P with Pistia stratiotes (0.40 m·d⁻¹) and HSSF with Typha domingensis (0.70 m·d⁻¹), demonstrating that vegetation, combined with the use of medium-grain substrate (9.5–19.0 mm), enhances turbidity removal. The w-C* model proved to be a robust tool for describing the kinetics of suspended colloidal particle removal in constructed wetlands, providing valuable insights for optimizing hydraulic parameters and design criteria for full-scale application. Full article

As the discharge points of domestic sewage in rural areas are scattered with large fluctuations, constructed wetlands (CWs) are of great effectiveness in treating rural domestic wastewater. In this paper, horizontal subsurface flow modular constructed wetlands (HSSF-MCWs) with different filler combinations and plant species were constructed to analyze the pollutant removal effect on rural domestic wastewater. According to the fuzzy comprehensive evaluation method, the purification effect of the systems on rural domestic wastewater was evaluated for the selection of the best system. The decentralized rural domestic sewage treatment PPP project (Phase III) in Changshu was also monitored for field application. The results indicated that the red brick–volcanic rock (RB-VR) combination showed the best comprehensive removal effect on rural domestic wastewater, with the highest average removal rate of ammonia nitrogen (NH₄⁺-N 81.0 ± 2.5%) and total nitrogen (TN 64.5 ± 3.4%). The fuzzy comprehensive index (FCI) of the RB-VR systems with four rural plants ranged from 2.60 to 3.74, in which Myriophyllum elatinoides Gaudich. showed the optimum long-term purification effect. The water quality and economic analysis results of the pilot project in Changshu indicated that the overall influent concentration was low with large fluctuations, and the qualified effluent rate was relatively low. Moreover, the equipment investment accounted for 51.24% of the overall construction investment of the project, so more economical equipment (1 m³/day and 20 m³/day) should be adopted in rural domestic wastewater treatment. Full article

An integrated hybrid system was developed, incorporating sedimentation, anaerobic digestion, biological filtration, and a two-stage hybrid subsurface flow constructed wetland, horizontal subsurface flow constructed wetland (HSSFCW) and vertical subsurface flow constructed wetland (VSSFCW), to treat rural sewage in southern Jiangsu. To optimize nitrogen and phosphorus removal, the potential of six readily accessible industrial and agricultural waste byproducts—including plastic fiber (PF), hollow brick crumbs (BC), blast furnace steel slag (BFS), a zeolite–blast furnace steel slag composite (ZBFS), zeolite (Zeo), and soil—was systematically evaluated individually as substrates in vertical subsurface flow constructed wetlands (VSSFCWs) under varying hydraulic retention times (HRTs, 0–120 h). The synergy among substrates, plants, and microbes, coupled with the effects of hydraulic retention time (HRT) on pollutant degradation performance, was clarified. Results showed BFS achieved optimal comprehensive pollutant removal efficiencies (97.1% NH₄⁺-N, 76.6% TN, 89.7% TP, 71.0% COD) at HRT = 12 h, while zeolite excelled in NH₄⁺-N/TP removal (99.5%/94.5%) and zeolite–BFS specializing in COD reduction (80.6%). System-wide microbial analysis revealed organic load (sludges from the sedimentation tank [ST] and anaerobic tanks [ATs]), substrate type, and rhizosphere effects critically shaped community structure, driving specialized pathways like sulfur autotrophic denitrification (Nitrospira) and iron-mediated phosphorus removal. Annual engineering validation demonstrated that the optimized strategy of “pretreatment unit for phosphorus control—vertical wetland for enhanced nitrogen removal” achieved stable effluent quality compliance with Grade 1-A standard for rural domestic sewage discharge after treatment facilities, without the addition of external carbon sources or exogenous microbial inoculants. This low-carbon operation and long-term stability position it as an alternative to energy-intensive activated sludge or membrane-based systems in resource-limited settings. Full article

Nature-based solutions represent a decentralized wastewater treatment proposal, offering diverse mechanisms for effectively removing emerging contaminants, particularly acidic pharmaceuticals. This study evaluated the performance of acidic-drug (diclofenac, fenofibrate, ibuprofen, gemfibrozil, fenoprofen, naproxen, and indomethacin) removal from wastewater using a surface-flow constructed wetland with an organic bed (Eichhornia crassipes (Mart.) Solms, 18 ind/m²), and a horizontal subsurface-flow constructed wetland, divided into three sections. The process was complemented by two stabilization ponds and other horizontal subsurface-flow wetlands using papyrus (Cyperus papyrus L., 8–13 ind/m²) and tezontle as support media. The industrial-scale system (67.8 m²) was fed with wastewater at a rate of 1.33 m³/d with a hydraulic time retention of about 5.8 days. Drugs were quantified by gas chromatography. The results showed that gemfibrozil and indomethacin were completely removed (100%), while diclofenac (73%) and naproxen (94%) showed significant removals. Fenoprofen was not removed. Ibuprofen and fenofibrate showed increased concentrations, resulting in negative removals due to anoxic conditions (ibuprofen) and a slightly neutral pH (fenofibrate). These findings underscore the system’s ability to improve water quality by removing most acidic drugs, suggesting that the hybrid design is particularly effective in treating specific wastewater contaminants. Full article

Constructed wetlands (CWs) are cost-effective and sustainable systems for wastewater treatment, but their hydraulic performance remains a critical challenge. In this study, a lab-scale baffled horizontal subsurface flow constructed wetland was modeled using Computational Fluid Dynamics to investigate the effects of aeration strategies on hydraulic performance, focusing on aeration rates and positions. A gas–liquid two-phase flow system was modeled using the Euler–Euler approach with the Darcy–Forchheimer model in OpenFOAM, simulating 15 cases with varying aeration rates (0.1–0.3 m³/day) and positions (middle of channels vs. bends at the ends of baffles). Results show that the introduction of aeration influenced hydraulic efficiency (HE) and the Morrill Dispersion Index (MDI). Without aeration, the baseline HE was already high (HE = 0.9297) due to the optimized baffle configuration. However, aeration further improved performance, with HE increasing to 0.9594 and MDI decreasing from 1.6087 to 1.4000 when aeration was applied at bends (Position C) at 0.3 m³/day. Aeration at bends was more effective than mid-channel aeration, promoting uniform flow distribution and reducing short-circuiting. These findings highlight the importance of aeration positioning and provide insights for optimizing CW design to balance energy consumption and hydraulic performance. Full article

Glyphosate (GLY) is the most widely used herbicide in agriculture worldwide, posing a significant contamination risk to rivers, lakes, wetlands, and soils. Its ultimate fate represents a potential threat to the health of both terrestrial and aquatic ecosystems. This study evaluated the removal efficiency of glyphosate and conventional pollutants in mesocosm-scale horizontal subsurface flow-constructed wetlands planted with Canna indica, Heliconia psittacorum, and Alpinia purpurata in runoff water contaminated with glyphosate. Additionally, the study examined the performances of these species in monoculture and polyculture settings of tropical ornamental plants. Canna indica exhibited the highest growth (up to 160 cm) in both monoculture and polyculture conditions, as well as the highest removal efficiencies for total nitrogen (TN), total phosphorus (TP), and phosphate (PO₄³⁻), achieving a 91%, 93%, and 98% removal, respectively. Polyculture systems demonstrated a superior ammonium removal efficiency, reaching 94%. Alpinia purpurata (>5 ppm after 40 days) and Heliconia psittacorum (>5 ppm after 200 days) were the most effective species for glyphosate removal. Glyphosate can be effectively removed from aquatic environments through constructed wetlands planted with ornamental species, offering a sustainable approach to mitigating herbicide contamination in water bodies. Full article

This study investigates the performance of large-scale ornamental treatment wetlands (TW) for the treatment of municipal wastewater in the municipality of Nautla, Veracruz, Mexico, specifically within a contaminated estuary in the Gulf of Mexico. The research employed a treatment wetland system that integrates mixed flow methods, including vertical subsurface flow (VSSF) and horizontal subsurface flow (HSSF), to optimize operational, maintenance, and energy costs. Over a monitoring period from 15 October 2022 to 17 September 2023, the system achieved remarkable efficiencies in the removal of chemical oxygen demand (COD), NH₃-N, NH₄-N, NO₂-N, NO₃-N, total nitrogen (TN), with removal rates of 93.37%, 93.37%,91.36%, 91.29%, 95.74%, 97.36%, 71.69%, 92.26% and 91.45%, respectively. The effluent complied with the water quality standards established by the official Mexican standard NOM-001-SEMARNAT-2021, demonstrating the effectiveness of this TW configuration in treating water characterized by high chemical oxygen demand, nitrogen, and phosphorus levels. The results are especially relevant for tropical climates, where high temperatures and humidity can affect microbial activity and nutrient cycling, potentially enhancing treatment performance and reducing construction and management costs. This research highlights the viability of ornamental treatment wetlands as a sustainable solution for wastewater treatment in tropical climates and provides valuable information for future implementation and design criteria. Full article

Landfill leachate contains various organic and inorganic substances resulting from the decomposition of solid waste. The treatment of this complex mixture is an imperative need for environmental protection. This study used five pilot-scale horizontal subsurface flow (HSF) constructed wetland (CW) units to treat landfill leachate. The main objective was the evaluation of the performance of CW units in the removal of pollutants. The effect of porous media (gravel and zeolite), plants (common reed and cattail), and hydraulic residence time (HRT, 8 and 10 days) were investigated. Two pilot-scale CW units differed in HRT, two in porous media, and three in planting. The results showed that the planted CW units had higher organic matter (OM) and nitrogen (TKN, NH₄-N) removal compared with the unplanted unit. The 10-day HRT CW unit had higher average removal rates for all pollutants compared with the CW unit with an 8-day HRT. Finally, the CW unit with zeolite (25%, by volume) in the fill material showed higher average removal rates for OM and nitrogen compared to the unit with gravel. Full article

Surface runoff in mining areas transports dissolved and suspended particles into water bodies, known as mine spoil rainwater, contributing to increases in turbidity. The aim of this study was to evaluate the effectiveness of horizontal flow wetlands, free water surface (FWS), and subsurface flow (HSSF) in reducing turbidity >1500 NTU from a synthetic mine spoil rainwater. Macrophytes, support media, hydraulic retention time (HRT), and hydraulic loading rate (HLR) were analyzed. The HSSF T. domingensis in gravel #1 achieved a 99% reduction for 4-day HRT, with residual turbidity of 7 ± 3 NTU for 27.43 L m⁻² d⁻¹ HLR. The FWS P. stratiotes achieved a 99% reduction for 6-day HRT, with residual turbidity of 11 ± 5 NTU for 36.53 L m⁻² d⁻¹ HLR. P. stratiotes free root structures promoted interception of suspended colloidal particles, resulting in a better performance. The dense root structure of T. domingensis spreading through the pores of the substrate provided better efficiency than N. humboldtiana. However, N. humboldtiana proved to be promising as a native species. The use of small granulometry alkaline support media (9 to 19 mm) was highlighted. Therefore, this research proves the efficiency of constructed wetlands in reducing high turbidity and provides optimized parameters for this technology application. Full article

The aim of this study was to evaluate a natural coagulant, Moringa oleifera seeds (MOC), to reduce the color concentration in treated tequila vinasses (TVs). TV-A was the effluent of horizontal subsurface flow wetlands (HSSFW); TV-B was the effluent of vertical up-flow wetlands (VUFW); and TV-C was the effluent of vertical down-flow constructed wetlands (VDFW). Raw TVs were also evaluated with MOC. Jar tests were performed to find the optimal dose and pH value for apparent color (AC) removal. With the optimal dose and pH for each type of TV, tests were performed in triplicate to evaluate the removal of apparent color (AC), true color (TC), turbidity, total suspended solids (TSS), chemical oxygen demand (COD), and electrical conductivity (EC). For TV-A and TV-B, the optimal values were 1 g/L of MOC and pH 8, and the removals were 52%, 43%, 50% and 72% of AC, turbidity, TC, and TSS, respectively. For TV-C, the optimal values were 2.5 g/L and pH 5, with removals of 66%, 73%, and 98% for AC, TC, and TSS, respectively. For TV-D, the MOC had no coagulant effect in any of the experimental conditions evaluated, probably due to the high concentration of turbidity and TSS in the raw vinasses, which prevented the interaction between MOC and melanoidins. Deeper studies are required to understand and evaluate those factors that influence MOC efficiency so that the coagulation–flocculation process can be optimized. Full article

Untreated domestic wastewater from rural areas poses significant risks to ecosystems and human health. Constructed wetlands (CWs) are a viable alternative for this wastewater treatment, enhancing nitrogen removal using substrates as carbon sources. This process is particularly beneficial for wastewater with low carbon-to-nitrogen (C/N) ratios, making the treated water suitable for agricultural irrigation. In this study, a Horizontal Subsurface Flow CW (HSF-CW) was evaluated using Canna hybrids and a mixed substrate of gravel and endocarp from oil palm fruit (EOP) as a carbon source to leverage its abundance in the region. It was also determined that the effluent complies with the permissible limits set by Resolution 1207 of 2014 from the Colombian Ministry of Environment and Sustainable Development, which establishes environmental standards for wastewater treatment to ensure environmental protection and enable safe reuse in agricultural irrigation. The key parameters analyzed included organic contaminants, heavy metals, nutrients, and microbiological indicators. Removal efficiencies of up to 91%, 94%, 98%, 52%, 73%, 78%, and 75% were achieved for BOD, TSS, total phosphorus, nitrates, nitrites, ammonium, and total nitrogen, respectively, demonstrating the CW’s strong performance in contaminant removal and meeting most standards for agricultural irrigation. Although the carbon source was not highly efficient, the overall system performance supports its viability for improving water quality and promoting sustainable agricultural practices in rural areas. Full article