Performance of a constructed wetland as an upstream intervention for stormwater runoff quality management

Virtual sample generation empowers machine learning-based effluent prediction in constructed wetlands

The design of constructed wetlands (CWs) is critical to ensure effective wastewater treatment. However, limited availability of reliable data can hamper the accuracy of CW effluent predictions, thus increasing design costs and time. In this study, a novel effluent prediction framework for CWs is proposed, utilizing data dimensionality reduction and virtual sample generation. By using four the machine learning algorithms (Cubist, random forest, support vector regression, and extreme learning machine), important features of CW design are identified and used to build prediction models. The extreme learning machine algorithm achieved the highest determination coefficient and lowest error, identifying it as the most suitable algorithm for effluent prediction. A multi-distribution mega-trend-diffusion algorithm with particle swarm optimization was employed to generate virtual samples. These virtual samples were then combined with real samples to retrain the prediction model and verify the optimization effect. Comparative analysis demonstrated that the integration of virtual samples significantly improved the prediction accuracy for ammonium and chemical oxygen demand. The root mean square error decreased by averages of 60.5% and 42.1%, respectively, and the mean absolute percentage error by averages of 21.5% and 23.8%, respectively. Finally, a CW design process is proposed based on prediction models and virtual samples. This integrated forward prediction and reverse design tool can efficiently support CW design when sample sizes are limited, ultimately leading to more accurate and cost-effective design solutions.

Hydrologic and water quality performance of a subsurface gravel wetland treating stormwater runoff

Subsurface gravel wetlands are an emerging type of green infrastructure that can be used to manage stormwater through the capture and slow release of runoff. They are unique to other types of green infrastructure in that they have a distinct fully saturated gravel layer below an occasionally saturated soil layer that influences pollutant removal processes. While they have been widely applied to treat wastewater, our understanding of their efficiency in treating stormwater with variable pollutant inputs is limited. To fill this gap, this study monitored the flow and water quality (total suspended solids, total nitrogen, total phosphorus, and chloride) in a subsurface gravel wetland in Oshkosh, Wisconsin at the influent, effluent, and in an observation well. Results from nine storm events indicated that the wetland had a median volume reduction of 74% and a median peak flow reduction of 89%. The reduction in pollutant concentrations where highly dependent upon the influent concentration. Average reductions of total suspended solids, total nitrogen, and total phosphorus were 49%, -21% and -0.2%, respectively, indicating an increase in nutrients; however, where influent concentrations were above irreducible levels, total phosphorus was reduced by 45% (influent ≥0.25 mg/L) and total nitrogen was reduced by 38% (influent ≥2.5 mg/L). Overall, this study shows that the subsurface gravel wetland performed similar to other types of green infrastructure and could be a good management practice to mitigate the harmful effects of stormwater runoff.

Nutrient Removal by Floating Treatment Wetlands Under Different Spatial Arrangement Modes: a Field Study

Floating treatment wetlands (FTWs) are a management method to improve urban rivers, but most studies have been carried out at laboratory, micro, and meso levels, so it is necessary to study full-scale FTWs as a method to improve urban water bodies. In this experiment, the purification effects of water temperature (WT), dissolved oxygen (DO), ammonia nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), total phosphorus (TP), chemical oxygen demand (COD_Mn), and chlorophyll-a (Chl-a) under staggered arrangement (SA) and centered arrangement (CA) were evaluated. It was found that the DO concentration and removal rate of COD_Mn, Chl-a, and TP in the SA were significantly higher than those in the CA in months with heavy rainfall. However, interestingly, for TP, August showed the opposite trend. The removal rates of NH₄⁺-N and NO₃^--N were significantly different throughout the test period. The biomass growth values of shoots and roots of plants in the FTWs were 0.40 ± 0.03 kg/m² and 1.38 ± 0.07 kg/m² in the SA and 0.32 ± 0.07 kg/m² and 1.26 ± 0.30 kg/m² in the CA. The increments of N absorbed by plants in the SA and CA were 7.08 ± 0.49 g/kg and 6.83 ± 0.07 g/kg, respectively, and the increments of P were 0.57 ± 0.02 g/kg and 0.32 ± 0.07 g/kg, respectively, which indicated that the growth status of plants in the FTWs in the SA was slightly better than that in the CA. In summary, the hybrid-constructed FTWs of both arrangements can effectively improve the water quality of urban rivers, and the effect of the SA was greater than that of the CA. The purification effect of in situ tests under different arrangement modes of hybrid-constructed FTWs was evaluated, which provides guidance and support for the field layout of FTWs in rivers in the future.

Effects of Recycled Sponge Iron on Phosphorus Recovery from Polluted Water

Phosphorus in water not only degrades water quality but also leads to a waste of resources. In this study, adsorption thermodynamics and kinetics were used to study the effect of sponge iron on phosphorus removal, and a filtration bed was used to simulate the phosphorus removal in polluted water. The results showed that the maximum theoretical adsorption capacity of the modified sponge iron was increased from 4.17 mg/g to 18.18 mg/g. After desorption with 18.18 mol/L of sodium hydroxide and reactivation with 6% (w%) sulfuric acid, the activation rate of modified sponge iron can reach 98%. In a continuous operation experiment run for approximately 200 days, the sponge iron phosphorus removal percolation bed showed a good phosphorus removal ability. Under the condition of TP = 10 mg/L, HRT = 1 H, the comprehensive phosphorus removal rate was 30–89%, and the accumulated phosphorus adsorption per unit volume was 6.95 kg/m3. Wastewater from the regeneration of the sponge iron base can be used to recover guano stone. The optimum conditions were pH = 10, n (Mg2+):n (PO43−):n (NH4+) = 1.3:1:1.1. Under the optimum conditions, the phosphorus recovery rate could reach 97.8%. The method provided in this study has theoretical and practical significance for the removal and recycling of phosphorus in polluted water.

A pilot system integrating a settling technique and a horizontal subsurface flow constructed wetland for the treatment of polluted lake water

An integrated system was tested at pilot-scale for treating polluted water from the Marriot Lake in Egypt, comprising a settling technique followed by three parallel horizontal subsurface flow constructed wetland (HFCWs) units operating under a continuous flow mode; one HFCW unit was planted with Typha angustifolia and contained a perforated pipes network for enhanced passive aeration (CWA), one unit was planted without the perforated pipe network (CWR) and one served as a Control unit (unplanted and without perforated pipes). Changes in physicochemical parameters, BOD₅, nutrients (nitrogen, phosphorus), microbial community, and trace metals at different hydraulic retention times (HRT; 0.5-6 h) and hydraulic loading rates (HLR; 750, 1000, 1250, and 2000 L/m²/d) were monitored. The CWA unit had an overall better performance than the CWR unit, while both planted units outperformed the Control unit. CWA showed the highest performance at HLR of 1000 L/m²/d and 4-6 h-HRT with 95.3% removal for turbidity, 83% for BOD₅, 99.3% for ammonia nitrogen (NH₄-N), 70.8% for Total Nitrogen (TN), and 66.7% for Total Phosphorus (TP), while higher NO₃-N and NO₂-N effluent concentrations were observed. Trace metals levels were significantly reduced and accumulated in plant tissues. Microbial communities' densities fluctuated in the CWA unit. The integrated system with the settling stage and the planted CWA unit was proved to achieve a high removal efficiency and reached the national discharge limits, thus representing a novel nature-based solution for the sustainable remediation of polluted lake water.

Effect of design and operational parameters on nutrients and heavy metal removal in pilot floating treatment wetlands with Eichhornia Crassipes treating polluted lake water

Though having an economic and ecological impact on Marriott Lake management in Egypt, water hyacinth (Eichhornia crassipes) is an aquatic floating macrophyte with a known phytoremediation potential. In order to assess its remediation potential, pilot floating treatment wetlands (FTWs) with E. crassipes were built in duplicates to evaluate the removal of nutrients and heavy metals from the polluted lake water. The experimental design included units with different water depths (15, 25, and 35 cm; D₁₅, D_25, and D₃₅, respectively) and plant coverage (90, 70, 50, and 0%; P₉₀, P₇₀, P_50, and P₀, respectively). The pilot FTWs were monitored over a 7-day operation cycle to identify the optimum combination of design (plant coverage, water depth) and operation (hydraulic retention time; HRT) parameters needed for maximum BOD₅, TN, NH₄-N, and TP removal. NH₄-N removal reached 97.4% in the D₂₅P₅₀ unit after 3 days, BOD₅ 75% in the D₁₅P₉₀ after 3 days, TN 82% in the D₂₅P₇₀ after 4 days, and TP 84.2% in the D₃₅P₇₀ after 4 days. The open-water evaporation rate was higher than the evapotranspiration rate in the planted units, probably due to the warm climate of the study area. Metals were also sufficiently removed through bioaccumulation in plant tissues in the order of Fe > Pb > Cu > Ni (62.5%, 88.9%, 81.7%, and 80.4% for D₂₅P₅₀, D₂₅P₇₀, D₂₅P₅₀, and D₂₅P₉₀, respectively), while most of the assimilated metal mass was translocated to the plant roots. The biochemical composition of the plant tissue was significantly different between the shoot and root parts. Overall, the FTW with 70% E. crassipes coverage, 25-cm water depth, and an HRT of 3-5 days was identified as the optimum design for effective remediation of the polluted Marriott Lake in Egypt.

Root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus over the period of plant establishment in a constructed floating wetland

Constructed floating wetlands have been employed worldwide to treat effluents and to ameliorate water quality of water resources. However, the period of macrophyte establishment into the hydroponic functioning has not been specifically addressed. This paper reports root growth and nutrient removal of Typha domingensis and Schoenoplectus californicus in a floating structure without growth substrates over the period of 11 weeks of macrophyte establishment. The experiment was conducted in mesocosm with two replicas of each specie. Weekly batches were applied with three different concentrations of a synthetic effluent. Root growth was measured to evaluate the macrophyte adaptation. Physicochemical parameters were weekly monitored, and total nitrogen, nitrate, total phosphorus, and orthophosphate were quantified to assess nutrient removal. Both species have adapted to the floating structure, but T. domingensis presented superior root growth in relation to S. californicus. No significant differences were found during the application of first two synthetic solutions. As to solution 3, significant differences between input and output values were found to total phosphorus (F = 9.948, df = 1, p = 0.008), nitrate (F = 5.990, df = 1, p = 0.031), and total nitrogen (F = 40.212, df = 1, p < 0.0001). Removal efficiency of T. domingensis ranged from 4 to 31% for total nitrogen and from 8 to 15% for total phosphorus. S. californicus, on the other hand, varied its removal efficiency from - 6 to 5% and 2 to 12% for total nitrogen and total phosphorus, respectively. Time period of macrophyte establishment varied between species, and it was an important factor that contributed to the increase of nutrient removal rates and root growth.

A novel horizontal subsurface flow constructed wetland planted with Typha angustifolia for treatment of polluted water

Rapid population growth and urbanization has put a lot of stress on existing water bodies in most developing countries such as the Marriott Lake of Egypt. Three constructed wetland configurations including Typha angustifolia planted with enhanced atmospheric aeration by using perforated pipes networks (CWA), planted without perforated pipe network (CWR), and a control non-planted and without perforated pipes wetland (Control) were used in the study. Changes in physicochemical properties and microbial community over four seasons and hydraulic loading rate (HLR) (50, 100, 200, 300, and 400 L day^-1 m^-1) were monitored using influent from Marriott Lake in Egypt. Overall, the removal performance followed the sequence CWA>CWR>control. Turbidity removal of 98.4%; biochemical oxygen demand (BOD₅) removal of 83.3%; chemical oxygen demand (COD) removal of 95.8%; NH₃-N removal of 99.9%; total nitrogen (TN) removal of 94.7%; NO₃^--N and NO₂^--N increased; total P (TP) removal of 99.7%, Vibrio sp. of 100%, Escherichia coli 100%; total bacterial count of 92.3%; and anaerobic bacteria reduction of 97.5% were achieved by using CWA. Seasonal variation and variation in HLRs had significant effect on performance. The modified planted CWA system enhances the removal of pollutants and could present a novel route for reducing the cost associated with integrating artificial aeration into wetlands.

Water Quality Improvement and Pollutant Removal by Two Regional Detention Facilities with Constructed Wetlands in South Texas

Stormwater runoff introduces several pollutants to the receiving water bodies that may cause degradation of the water quality. Stormwater management systems such as detention facilities and wetland can improve the water quality by removing various pollutants associated with the runoff. The objective of this research project is to determine the performance and efficiency of two major regional detention facilities (RDFs) with different designs and structures in reducing pollutants based on various storm events in McAllen, Texas. The two sites are the McAuliffe RDF and the Morris RDF; each site was incorporated with a constructed wetland with a different design and structure to enhance the pollutant removal process. The McAuliffe RDF reduced the concentration and load of many stormwater constituents in comparison to the Morris RDF. The observed concentrations and pollutant loads of suspended solids were much lower in the runoff of the inlet compared to the outlet for both sites. The McAuliffe RDF showed better concentration and load reduction for nutrients, such as nitrogen and phosphorus, of different species. However, both sites did not show a significant improvement of organic material. In addition, the indicator bacteria concentration represented a fluctuation between the inlet and outlet at each site.

Nonpoint source pollution

A comprehensive review of the research papers published in 2018 focusing on nonpoint source (NPS) pollution is presented in this review article. The identification of pollution from different sources and estimation of NPS pollution using various models are summarized in this review paper. Various innovative techniques are also examined to abate NPS pollution. PRACTITIONER POINTS: The non-point source pollution in 2018 is systematically reviewed and documented. This review evaluates and summarizes the identification, quantification, reduction, and management of NPS pollution. Future perspectives of NPS pollution research are discussed.

Wetlands for wastewater treatment

This article presents an update on the research and practical demonstration of wetland treatment technologies for wastewater treatment. Applications of wetlands in wastewater treatment (as an advanced treatment unit or a decentralized system) and stormwater management or treatment for nutrient and pollutant removal (metals, industrial and emerging pollutants including pharmaceutical compounds and pathogens) are highlighted. A summary of studies involving the effects of vegetation, wetland design and operation, and configurations for efficient treatment of various municipal and industrial wastewaters is also included. PRACTITIONER POINTS: Provides an update on current research and development of wetland technologies for wastewater treatment. Effects of vegetation, pathogens removal, heavy metals and emerging pollutants removal are included. Wetland design and operation is a key factor to improve water quality of wetland effluent.

Urban stormwater characterization, control, and treatment

This review summarizes over 250 studies published in 2018 related to the characterization, control, and management of urban stormwater runoff. The review covers three broad themes: (a) quantity and quality characterization of stormwater, (b) control and treatment of stormwater runoff, and (c) implementation and assessment of watershed-scale green stormwater infrastructure (GSI). Each section provides an overview of the 2018 literature, common themes, and future work. Several themes emerged from the 2018 literature including exploration of contaminants of emerging concern within stormwater systems, characterization and incorporation of vegetation-driven dynamics in stormwater control measures, and the need for interdisciplinary perspectives on the implementation and assessment of GSI. PRACTITIONER POINTS: Over 250 studies were published in 2018 related to the characterization, control, and treatment of stormwater. Studies cover general stormwater characteristics, control and treatment systems, and watershed-scale assessments. Trends in 2018 include treatment trains, vegetation dynamics, and interdisciplinary perspectives.