Subsurface Flow Wetlands Research Articles

Integration of Coagulation–flocculation(with Natural Coagulant) to Constructed Wetlands for Color Removal from Tequila Vinasses

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 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.

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.

Mitigation of Sugar Industry Wastewater Pollution: Efficiency of Lab-Scale Horizontal Subsurface Flow Wetlands

Mitigation of Sugar Industry Wastewater Pollution: Efficiency of Lab-Scale Horizontal Subsurface Flow Wetlands

Treatment Effect of Long-Term Subsurface-Flow Constructed Wetland on Mariculture Water and Analysis of Wetland Bacterial Community

To improve the quality of natural seawater to meet the needs of aquaculture production, a large-scale subsurface-flow constructed wetland (HSFCW) was constructed and operated stably for 2 years to understand the reasons for its purification effect on natural seawater. The results of the study showed that the system could maintain a high purification effect on natural seawater during aquaculture; the average removal rates of COD, TSS, TN, NH4+-N, and DON (organic nitrogen) were 22.29%, 49.33%, 36.94%, 10.88%, and 44.08%, respectively. Additionally, the HSFCW could effectively remove harmful algae such as Cyanobacteria; the removal rate of dominant algae species in Cyanobacteria was 90.33–97.93%. The pyrosequencing of 16S ribosomal DNA revealed that Proteobacteria, Nitrospirae, and Chloroflexi were the main and key bacterial phyla in the system. Members of these key gates are regarded as playing important roles in resisting water purification. The study results suggest that the subsurface-flow wetland system can effectively improve seawater quality and reduce the density of harmful algae cells.

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.

Removal of Contaminants in Stormwater via Subsurface-Flow Wetlands: A Review with Focus on Nutrients, Heavy Metals, and PFAS

Removal of Contaminants in Stormwater via Subsurface-Flow Wetlands: A Review with Focus on Nutrients, Heavy Metals, and PFAS

Treatment of Slaughterhouse Wastewater through a Series System: Upflow Anaerobic Reactor and Artificial Wetland

Slaughterhouse wastewater is characterized by high concentrations of organic matter. This creates a need to explore methods for its treatment before discharge. This study evaluated the efficiency of an integrated treatment process consisting of a laboratory-scale upflow anaerobic sludge blanket reactor and a pilot-scale horizontal subsurface flow wetland. This treatment was used for (i) the removal of organic matter through anaerobic–aerobic microbiological processes, (ii) the conversion of organic matter from hydraulic processes, and (iii) for bioremediation and phytoremediation. The treatment system was evaluated at hydraulic retention times (HRTs) of 7.5, 5.0, and 2.5 d; during the investigation, the influence of the HRTs on the removal efficiency of the system was evaluated. High efficiencies of 85% and 75% were obtained for CODT and BOD, respectively, at an HRT of 7.5 d. The highest overall efficiency for the removal of total solids was observed at an HRT of 2.5 d. The results obtained confirm the feasibility of implementing the suggested system as an alternative for the adequate and sustainable treatment of slaughterhouse wastewater, and the system can be applied to slaughterhouses with similar conditions to those in this study.

Study on the impact of hydraulic loading rate (HLR) on removal of nitrogen under low C/N condition by modular moving bed constructed wetland (MMB-CW) system

Traditional constructed wetlands often exhibit low nitrogen removal efficiency when treating low C/N wastewater, prompting the need for targeted technological innovation. Modular moving bed constructed wetlands (MMB-CWs) have demonstrated superior performance, achieving over 15% higher TN removal compared to traditional subsurface flow wetlands, even without the addition of carbon, further research is required to fully understand the operational effects of different hydraulic loads and the underlying nitrogen removal mechanisms. To address this gap, the contrast performance of MMB-CWs with three different substrate addition ratios 90% (unit A), 60% (unit B), 30% (unit C) was studied under low C/N conditions and different hydraulic loading rates (HLRs). Results show that there are no significant differences in TN removal among the three systems at 250 mm/d and 500 mm/d. NH4+-N and NO3--N removal rates don't significantly decrease (p>0.05). High HLR leads to significantly lower effluent NO2--N concentrations. HLR minimally affects CODCr removal, with unit C exhibiting better resistance. Functional gene analysis reveals a minor role of nitrification, emphasizing the crucial role of anaerobic ammonium oxidation. The copy number of the Anammox gene is 1.2–4.0 times that of the NIR gene, with a larger ratio in the secondary unit, indicating that denitrification is mainly driven by Anammox. The dominant genera in the first unit are Azospira, Thauera, and Denitratisoma, while Defluviicoccus, Mycobacterium, and Nocardioides dominate the ceramsite and biochar of the second unit. The addition of biochar enhances the composition and abundance of microbial communities in the system, and as biochar addition increases, the removal rates of NH4+-N and TN gradually increase, ensuring effective denitrification under varying loads.

Performance of a multi-stage hybrid wetland system for the treatment of a dairy effluent

This work evaluates the performance of a pilot-scale hybrid wetland (HW) system for the effluent treatment from a dairy industry, located in Santa Fe (Argentina). The system consists of three stages in a serial configuration: vertical flow (S1) – free water surface (S2) – horizontal subsurface flow (S3) wetlands. The HW was operated during nine months. Wastewater, plant and sediment samples were taken from the system. Main pollutant concentrations were determined in wastewater. N and P concentrations were determined in plant tissues and in sediments to evaluate the accumulation in the system. The mean COD, BOD, TN, and TP removals in the whole HW system were 91 %, 94 %, 76 %, and 64 %, respectively. Organic matter concentration decreased due to aerobic and anaerobic degradation processes in all stages, mainly in S2. S1 presented proper conditions for nitrogen compounds interconversions by ammonification and nitrification processes. The highest total nitrogen removal was achieved in S2. Plant uptake contributed significantly to nutrient retention in S2 and S3. In S2, sediment did not participate significantly in nutrient retention. Phosphorus removal showed the lowest system efficiency. The obtained results determine the system performance under site-specific conditions, which contributes to the scaling process of the treatment wetland.

Effect of greywater treated by horizontal subsurface flow wetlands planted with Chrysopogon zizanioides and Andropogon gayanus on the germination of tomato (Lycopersicon esculentum Mill.) seeds under Sahelian climate

Greywater reuse for agricultural irrigation may contribute to reduce pressure on scarce freshwater sources and the use of chemical fertilizers in Sahelian countries. However, treatment methods that reduce the harmful effects of untreated greywater are essential for sustainable agriculture. This study aims to evaluate greywater treatment capacity by Horizontal Subsurface Flow wetlands (HSSF) planted with Chrysopogon zizanioides (HSSF-C) and Andropogon gayanus (HSSF-A), and to investigate the suitability of the effluents on the germination of tomato seeds. Three pilot-scale HSSF (planted with Chrysopogon zizanioides or Andropogon gayanus and an unplanted (control)) were designed and their removal efficiencies of organic matter, nutrients and fecal bacteria were evaluated. Principal component analysis showed planted systems provided higher removal efficiencies than the unplanted system. HSSF-A showed the best performance for removal of organic (COD, BOD5) and mineral (NO3−, NH4+) matter while HSSF-C showed the best performance for removal of phosphorus compounds and fecal indicators (thermotolerant coliforms, E. coli). HSSF-UP showed the lowest performance for removal of all parameters. The reduction of thermotolerant coliforms and E. coli were significantly greater in the two planted systems and exceeded 2 log10 removal. However, no significant difference was observed between the planted and unplanted HSSF for fecal indicators. Furthermore, germination rates obtained with greywater treated by HSSF were higher than 80%, approaching that obtained using distilled water, while the lower germination rates were observed with seeds irrigated with raw greywater (58%). This is a clear indication of the beneficial effect of treated greywater by HSSF wetlands on seeds germination. In addition, residual content of fecal indicators and physicochemical characteristics of the treated greywater are compliant with WHO reuse guidelines for restricted irrigation. The results demonstrate the possibility of using constructed wetlands for greywater treatment and its reuse in gardening in Sahelian countries.

Biochar-Based Subsurface-Flow Wetland from Crumb Rubber Scrap in Treatment of Landfill Leachate

Biochar-Based Subsurface-Flow Wetland from Crumb Rubber Scrap in Treatment of Landfill Leachate

Wetland water quality assessment of eco-engineered landscaping practices: a case study of constructed wetland parks in Hangzhou

Abstract Urban constructed water quality treatment (WQT) wetlands are often applied to be integrated with ecological engineered landscaping (EEL) measures for wastewater treatments. This study aims to identify the interrelationships between the hydrological factors and pollutant removal contributions of typical WQT wetlands at each WQT stage, i.e., subsurface flow wetlands (SSF), vertical flow wetlands (VF), free surface flow wetland (FSF), floating wetland island (FWI), aeration ponds (APs), and ornamental ponds (OPs) in four typical wetland parks in Hangzhou, China. Water quality indices (WQIs) of wetland parks have been monitored. Interactive comparisons and correlations between hydrological indicators and WQIs (i.e., pH, DO, NH3-N, CODCr, and TP) are developed, while the removal contribution of each WQI was explained. It is found that each stage had heterogeneous effects on wastewater treatment due to various geo-ecological factors, including hydraulic conditions, plant type, and microbial microenvironment, whereas the temperature of waterbodies affected WQT performances at full sites in all seasons. Three corresponding EEL guiding principles were derived, i.e., optimising the EEL measures, adapting planting methods, and incorporating multifunctional design and adaptive management. The findings will be helpful for improving the efficacy of WQT stages as one of the potential ecosystem services provided by wetland parks.

Persistent Trace Organic Contaminants Are Transformed Rapidly under Sulfate- and Fe(III)-Reducing Conditions in a Nature-Based Subsurface Water Treatment System.

Subsurface treatment systems, such as constructed wetlands, riverbank filtration systems, and managed aquifer recharge systems, offer a low-cost means of removing trace organic contaminants from treated municipal wastewater. To assess the processes through which trace organic contaminants are removed in subsurface treatment systems, pharmaceuticals and several major metabolites were measured in porewater, sediment, and plants within a horizontal levee (i.e., a subsurface flow wetland that receives treated municipal wastewater). Concentrations of trace organic contaminants in each wetland compartment rapidly declined along the flow path. Mass balance calculations, analysis of transformation products, microcosm experiments, and one-dimensional transport modeling demonstrated that more than 60% of the contaminant removal could be attributed to transformation. Monitoring of the system with and without nitrate in the wetland inflow indicated that relatively biodegradable trace organic contaminants, such as acyclovir and metoprolol, were rapidly transformed under both operating conditions. Trace organic contaminants that are normally persistent in biological treatment systems (e.g., sulfamethoxazole and carbamazepine) were removed only when Fe(III)- and sulfate-reducing conditions were observed. Minor structural modifications to trace organic contaminants (e.g., hydroxylation) altered the pathways and extents of trace organic contaminant transformation under different redox conditions. These findings indicate that subsurface treatment systems can be designed to remove both labile and persistent trace organic contaminants via transformation if they are designed and operated in a manner that results in sulfate-and Fe(III)-reducing conditions.

Robust control of water quality in horizontal sub-surface flow wetlands using decentralized quantitative feedback theory based controller

This paper addresses the regulation of water quality influencers such as Organic Nitrogen, Ammonia Nitrogen, Nitrate Nitrogen, Dissolved Organic Carbon and Dissolved Oxygen for a sub-surface flow horizontal wetland in a controlled environment. The plant uncertainty is quantified by using measurement data. The robust control of the process is achieved using a decentralized quantitative feedback theory based control strategy. The control structure also employs a feed-forward mechanism to minimize loop interactions and feedback control to ensure stability, tracking and disturbance rejection. The numerical simulations and hardware-in-loop implementation show that the performance specifications are robustly met.

Treatment of tequila vinasse mixed with domestic wastewater in two types of constructed wetlands.

Tequila vinasse (TV) is a high-strength effluent generated during the production of tequila, with a chemical oxygen demand (COD) concentration of up to 74 g/L. In this study, the treatment of TV was evaluated in a 27-week study in two types of constructed wetlands (CWs), namely horizontal subsurface flow wetlands (HSSFWs) and vertical upflow wetlands (VUFWs). The pre-settled and neutralized TV was diluted at 10, 20, 30, and 40% with domestic wastewater (DWW). Volcanic rock (tezontle) was used as the substrate and Arundo donax and Iris sibirica as emergent vegetation. The two systems showed similar high removal efficiencies for COD, biochemical oxygen demand (BOD5), turbidity, total suspended solids (TSS), true colour (TC), electrical conductivity (EC), and total nitrogen (TN). The highest average percentages of removal were obtained at 40% of dilution: 95.4 and 95.8% for COD, 98.1 and 98.2% for turbidity, 91.8 and 95.9% for TSS, and 86.5 and 86.4% for TC in the HSSFWs and the VUFWs, respectively. This study demonstrates the potential of CWs for TV treatment as a major step in a treatment system.

Pollutant removal modeling in a hybrid wetland system for industrial wastewater treatment

Modeling of treatment wetlands allows the prediction of system behavior and facilitates large-scale design by evaluating the effects of modifying the operating parameters. The aim of this study was to calibrate and verify applicable models in vertical flow (VF) and horizontal subsurface flow (HSSF) wetlands -first and second stage of the hybrid wetland (HW) system- operating in site-specific environmental conditions. Stepwise multiple linear regression analysis, oxygen demand model, and k-C* model, were applied to each stage of the HW system as appropriate. All models were calibrated and verified based on the data observed by monitoring the HW system. Afterwards, simulations were performed at each stage of the HW system. The simulations show the dependence of nitrification on the availability of NH4+-N and also that both, the increase in Org-N and COD loading, affect the efficiency of nitrification in the VF stage. In the HSSF stage, simulations show that the increase in hydraulic or pollutants loading rate has a positive impact on the performance of the system. The fit achieved in the models was satisfactory and the results obtained by simulation provide a useful tool to evaluate the performance of the HW system in different possible operating scenarios.

The effects of cold frozen conditions on nitrogen removal and transformation in wetlands purifying wastewater: Insights from combined full- and pilot-scale observations

In wastewater treatment, wetlands are regarded as cost-efficient and sustainable purification systems. Currently, different types of wetland are used for year-round treatment of municipal wastewater (the polishing step after the secondary or tertiary units) in cold climate regions. However, there is a lack of understanding regarding the effect of freezing cold conditions on pollutant removal processes, in particular regarding those linked to nitrogen cycling. This study evaluated the effect of cold winter conditions on contaminant removal, with a focus on nitrogen transformation and removal in a pond-type surface flow wetland with reed (Reed-SF) and a peat-based horizontal subsurface flow (Peat-HSSF) wetland. Year-round full-scale wetland monitoring was complemented with pilot-scale laboratory experiments, which allowed to follow the cold-climate induced effects on contaminant removal and nitrogen processes, along with other water quality, environmental, and microbial parameters. Overall, it was observed that the effect of cold climate conditions on nitrogen removal was dependent on the wetland type in combination with the quality of the inflow water. When treating ammonium (NH4) rich wastewater, removal of total nitrogen (Ntot), as well as NH4, was higher in the Peat-HSSF than in the Reed-SF wetland. Under frozen conditions, NH4 removal decreased slightly but remained positive in the pilot Peat-HSSF, whereas it declined and even turned into leaching in the pilot Reed-SF wetland. Conditions encountered in the Peat-HSSF wetlands (high abundances of active nitrifying bacteria, high levels of dissolved oxygen (DO) and redox potential) supported nitrification, which continued under cold conditions. Whereas in the Reed-SF, a low abundance of active nitrifying bacteria was found, especially in the water column under frozen conditions. DO here was low and decreased in cold conditions with ice cover.

Peat Soil Ecosystem Restoration for Development of a Wetland- a review

Constructed wetlands are sustainable wastewater treatment technology and have been used to treat a variety of wastewaters for decades, including domestic and industrial wastewaters. They take advantage of many of the same processes that occur in natural wetlands but do so in a more controlled or engineered system. To date, surface flow and subsurface flow wetlands are the two main categories of constructed wetland applications. On the other hand, peat soil is the decomposed organic matter that have built up over thousands of years, with high moisture content. Peat soil management is imperative to maintain the mire ecosystem. The use of rhizosphere biodegradation, phyto-stabilization and phyto-accumulation have shown the possibility of improving water quality of wetland associated with peat soil. Thus, the aim of this work is to present a review in the role of constructed wetland system for peat soil management and the water quality as restoration measures of the peat soil ecosystem to promote its suitability for agricultural purpose.

A TESTING STUDY OF WASTE WATER TREATMENT USING REED BED SYSTEM

Following industrialisation, a number of companies generate poisonous waste materials are carelessly dumped into streams and rivers, harming both aquatic and terrestrial life. In this study, a reed bed system for harmful metal removal from industrial waste water was examined. In the Amrutha water treatment plant, a vertical subsurface flow wetland was created to remove hazardous metals from industrial effluent. For the Wetland system, phragmites Karka was employed, and the substrates used were granite and washed sand. Hydraulic retention times of 5, 9, 10, 14, and 18 days were used to record treatment performance. You can create a waste water treatment facility in your own garden with a reed bed sewage system. It must be used in conjunction with a septic tank in order to function as a sewage system. Two reed beds are required for a reed bed sewage system to function properly. One bed must fill for a while while the other drains, and then the process must be reversed. The results indicated that the hazardous metals gradually decreased as the retention times increased. The reed bed rate removal ranges from 36.8% to 61.5%. These findings support the phragmites karka reed plant's ability to effectively treat industrial effluent.

Characteristics of resistome and bacterial community structure in constructed wetland during dormant period: A fullscale study from Annan wetland

As a green technology, constructed wetlands (CWs) can provide a low-cost solution for wastewater treatment. Either as a standalone treatment or integrated with conventional treatment, nutrients, antibiotic resistant bacteria (ARB)/antibiotic resistance genes (ARGs) can be removed by CW efficiently. While, few studies have focused on characteristics of resistome and bacterial community (BC) structure in CW during dormant period. Therefore, in this study, Annan CW (a full-scale hybrid CW) was selected to characterize resistome and BC during dormant period. The profiles of bacteria / ARGs were monitored in combination of shotgun sequencing and metagenomic assembly analysis. And multidrug ARGs are the most abundant in Annan CW, and surface flow wetland had the relatively high ARG diversity and abundance compared with subsurface flow wetland and the front pond. The most dominant phylum in CW is Proteobacteria, while the other dominant phylum in three parts have different order. COD, TP, TN, ARGs, and mobile genetic genes (MGEs) were removed by subsurface flow CW with better performance, but virulent factors (VFs) were removed by surface flow CW with better performance. Based on the spatiotemporal distribution of ARGs, the internal mechanism of ARGs dynamic variation was explored by the redundancy analysis (RDA) and variation partitioning analysis (VPA). BCs, MGEs and environmental factors (EFs) were responsible for 45.6 %, 28.3 % and 15.4 % of the ARGs variations. Among these factors, BCs and MGEs were the major co-drivers impacting the ARG profile, and EFs indirectly influence the ARG profile. This study illustrates the specific functions of ARG risk elimination in different CW components, promotes a better understanding of the efficiency of CWs for the reduction of ARG and ARB, contributing to improve the removal performance of constructed wetlands. And provide management advice to further optimize the operation of CWs during dormant period.