Surface Flow Treatment Wetland Research Articles

High methane emissions as trade-off for phosphorus removal in surface flow treatment wetlands

Constructed wetlands (CW) treating runoff from agricultural catchments reduce the nutrient load of water, however, they can also be significant sources of greenhouse gases, especially methane (CH4). We simultaneously assessed CH4 emission potentials and phosphorus (P) removal efficiency in a 0.45 ha in-stream surface flow CW to determine the main drivers of CH4 emissions, and to analyze the temporal dynamics of CH4 emissions and P removal during an almost 4-year period. The TP (total phosphorus) removal efficiency had a clear seasonal dynamic, with the highest removal occurring during summer and early autumn (monthly average 60.5%), when the flow rate was lowest and water residence time longest. Due to increasing sedimentation and related anaerobic conditions, the mean hourly CH4 emissions for each year demonstrated an increasing trend over the years: from 88 µg CH4-C m−2 h−1 in 2018–2505 µg CH4-C m−2 h−1 in 2021. There was a clear seasonality in CH4 emissions: up to 90% of CH4 fluxes occurred during the warm period (from May to October). We assume that maintenance of treatment wetlands is essential and predominantly regular removal of aboveground vegetation at the second half of the growing season would decrease CH4 emissions. Nevertheless, due to the P saturation in sediments, regular sediment removal in the long term is also necessary.

The fate of microplastics from municipal wastewater in a surface flow treatment wetland

Microplastics (MPs) are an anthropogenic pollutant of emerging concern prominent in both raw and treated municipal wastewater as well as urban and agricultural run-off. There is a critical need for the mitigation of both point- and diffuse sources, with treatment wetlands a possible sustainable nature-based solution. In this study, the possible retention of MPs in treatment wetlands of the widely used surface flow (SF) type was investigated. In- and outflow water, as well as atmospheric deposition, at a full-scale reed-based SF wetland (operating as a polishing phase of municipal wastewater treatment) was analyzed for MPs in a size range of 25–1000 μm. FPA-based μFT-IR spectroscopic imaging was used in combination with automated data analysis software, allowing for an unbiased assessment of MP numbers, polymer types and size distribution.Inflow water samples (secondary treated wastewater) contained 104 MPs m−3 and 56 MPs m−3 in sampling campaigns 1 and 2, respectively. Passage through the SF wetland increased the MP concentration in the water by 92 % during a rain intense period (campaign 1) and by 43 % during a low precipitation period (campaign 2). The MP particle numbers, size and polymer type distribution varied between the two sampling campaigns, making conclusions around the fate of specific types of MPs in SF wetlands difficult.Atmospheric deposition was measured to be 590 MPs m−2 week−1 during the rain-intense period. Our findings point towards atmospheric deposited MPs as an important factor in the fate of MPs in SF wetlands, causing an increase of MP concentrations, and potentially explaining the variations observed in MP concentrations in wetland effluent and removal efficiency. Furthermore, atmospheric deposition might also be a reason for the considerable inter-study variation regarding MPs removal efficiency in SF wetlands found in the available literature.

Treatment of naphthenic acids in oil sands process-affected waters with a surface flow treatment wetland: mass removal, half-life, and toxicity-reduction

This study is the first to investigate the removal of naphthenic acids in a full-scale constructed wetland within the Alberta Oil Sands region. The average mass-removal efficiency for all O2-naphthenic acids measured in three separate deployments in the wetland ranged from 7.5% to 68.9% and appeared sensitive to physicochemical properties of the naphthenic acids, environmental conditions, and water quality. Treatment efficiency of individual naphthenic acids was found to increase with increasing carbon number and decreasing number of double bond equivalents in the molecule. Treatment efficiency was also found to increase with both higher initial turbidity in OSPW entering the wetland, and warmer average OSPW temperatures during wetland operation. Half-life times of naphthenic acids in the treatment wetland ranged between 8.9 and 39 days and were substantially lower than those in tailings ponds (i.e., 12.9–13.6 years) and laboratory studies focussed on bench-scale aerobic microbial biodegradation (i.e., 44–315 days). Using published dose-response data, biomimetic extraction measurements using solid phase microextraction fibers indicate that 14 days of wetland treatment resulted in a reduction in (4 d) deformity of Danio rerio from 50 to 16%, while exhibiting less than 1% toxic response for less sensitive toxic endpoints. The study concludes that wetland treatment is a feasible and productive treatment method for naphthenic acids in oil sands process-affected water due to a combination of sorption and biodegradation.

Treatment of Naphthenic Acids in Oil Sands Process-Affected Waters with a Surface Flow Treatment Wetland: Mass Removal, Half-Life, and Toxicity-Reduction

Treatment of Naphthenic Acids in Oil Sands Process-Affected Waters with a Surface Flow Treatment Wetland: Mass Removal, Half-Life, and Toxicity-Reduction

A radial basis function neural network based multi-objective optimization for simultaneously enhanced nitrogen and phosphorus removal in a full-scale integrated surface flow treatment wetland–pond system

In this study, a radial basis function neural network (RBFNN) model was developed and implemented in a multi-objective optimization procedure to determine the optimal hydraulic loading rate (HLR), hydraulic retention time (HRT), and mass loading rates (MLR) for enhanced removal of nitrogen and phosphorus by an integrated surface flow treatment wetland–pond system treating drinking source water in Yancheng, China. Prior to modelling, the system’s 6-year nitrogen and phosphorus removal efficiencies were found to trend downwards as effluent concentrations trended positively. Meanwhile, operating parameter interaction effects impacted final effluent quality. Thus, total nitrogen and total phosphorus removal were simulated by an RBFNN model with satisfactory R2 of 0.99 and 0.98 respectively. Optimal average HLR, HRT and MLR for 80% simultaneous removal efficiencies were subsequently determined to be 0.10860 ± 0.03 md-1, 30.43 ± 9.96 d and 306.416 ± 89.54 mgm-2d-1 respectively. The results highlight the feasibility of the RBFNN modelling based optimization procedure for treatment wetlands.

Distribution and degradation trend of micropollutants in a surface flow treatment wetland revealed by 3D numerical modelling combined with LC-MS/MS

Conventional wastewater treatment plants are not designed to treat micropollutants; thus, for 20 years, several complementary treatment systems, such as surface flow wetlands have been used to address this issue. Previous studies demonstrate that higher residence time and low global velocities promote nutrient removal rates or micropollutant photodegradation. Nevertheless, these studies were restricted to the system limits (inlet/outlet). Therefore, detailed knowledge of water flow is crucial for identifying areas that promote degradation and optimise surface flow wetlands. The present study combines 3D water flow numerical modelling and liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS/MS). Using this numerical model, validated by tracer experimental data, several velocity areas were distinguished in the wetland. Four areas were selected to investigate the waterflow influence and led to the following results: on the one hand, the number and concentration of micropollutants are independent of the waterflow, which could be due to several assumptions, such as the chronic exposure associated with a low Reynolds number; on the other hand, the potential degradation products (metabolites) were also assessed in the sludge to investigate the micropollutant biodegradation processes occurring in the wetland; micropollutant metabolites or degradation products were detected in higher proportions (both number and concentration) in lower flow rate areas. The relation to higher levels of plant and microorganism metabolites suggests higher biological activity that promotes degradation.

Treatment of Polycyclic Aromatic Hydrocarbons in Oil Sands Process-Affected Water with a Surface Flow Treatment Wetland

This study applied a passive sampling approach using low-density polyethylene passive samplers to determine the treatment efficiency of the Kearl surface flow treatment wetland for polycyclic aromatic hydrocarbons (PAHs) in Oil Sands Process-affected Waters (OSPW). Treatment efficiency was measured as concentration-reduction and mass-removal from the OSPW. The results show that the wetland’s ability to remove individual PAHs from the influent varied substantially among the PAHs investigated. Treatment efficiencies of individual PAHs ranged between essentially 0% for certain methylated PAHs (e.g., 2,6-dimethylnaphthalene) to 95% for fluoranthene. Treatment in the Kearl wetland reduced the combined total mass of all detected PAHs by 54 to 83%. This corresponded to a reduction in the concentration of total PAHs in OSPW of 56 to 82% with inflow concentrations of total PAHs ranging from 7.5 to 19.4 ng/L. The concentration of pyrene in water fell below water quality targets in the Muskeg River Interim Management Framework as a result of wetland treatment. The application of the passive samplers for toxicity assessment showed that in this study PAHs in both the influent and effluent were not expected to cause acute toxicity. Passive sampling appeared to be a useful and cost-effective method for monitoring contaminants and for determining the treatment efficiency of contaminants in the treatment wetland.

Seasonal and ageing effect on the behaviour of 86 drugs in a full-scale surface treatment wetland: Removal efficiencies and distribution in plants and sediments

The presence of human drugs in the aquatic environment is partly due to an incomplete and insufficient removal process of wastewater treatment plants (WWTPs). Thus, drug traces are observed at different concentrations in water bodies, sediments and aquatic plants all over the world. At the same time, Surface Flow Treatment Wetlands (SFTWs) at the outlet of WWTPs are commonly observed in small municipalities as complementary treatment. However, little is known regarding the role of SFTWs in the complementary mitigation of emerging contaminants, such as drugs, and the interactions between drugs, plants and sediment throughout the seasons. For that reason, we conducted sampling sessions over a period of two years on a full-scale SFTW downstream of a vertical-flow constructed wetland. At each session, the SFTW influent and effluent, as well as five different plant species and one composite sediment sample, were sampled. We detected more than fifty pharmaceutical compounds in the inflow and outflow water. The compounds most frequently detected were bisoprolol and ketoprofen. We emphasized that the SFTW removal ability was better in the summer than in the winter, due to the impact of weather on physicochemical parameters. Large variations of removal efficiencies were also observed when considering all of the detected compounds. Large seasonal variations were also observed for each compound. In addition, the study of the five plants showed their ability to uptake drugs from water and soil to the leaves in a species-specific manner. The pharmaceutical composition of the sediment was also correlated with the season: the maximum occurrence was reached in summer, and the minimum was reached in winter. Finally, the continuous decrease in removal efficiencies highlights the ageing effect on SFTW removal ability.

Seasonal and ageing effects on SFTW hydrodynamics study by full-scale tracer experiments and dynamic time warping algorithms

Surface flow treatment wetlands (SFTW) are considered as ecological engineering treatment wetlands used for wastewater and stormwater treatment. In France SFTW are commonly located between the wastewater treatment plant (WWTP) and the receiving aquatic environment. Furthermore, they are not considered as a regulatory treatment step but as a complementary element to WWTP. In this regard, there is currently no established design and sizing rule since (i) they are built on the remaining space after WWTP construction, (ii) it is a nature-based system, subject to high variability and complex interactions and (iii) feedback on ageing effects is lacking. This study permitted to qualify and to quantify seasonal and ageing effects on the SFTW hydraulic behavior which is a pond. The combination of fluorescent dye tracer application in a real system and data analysis by dynamic time warping (DTW) allowed to perform efficiency comparisons between all campaigns. Similar behaviors of dimensionless retention time distributions were observed for all campaigns. They were eventually linked with the SFTW shape. The analysis of these curves highlighted that the measured mean residence time was always lower than the nominal hydraulic residence time, due to preferential flow and dead-zones. A statistical approach suggested that the winter hydraulic behavior was characterized by the highest short-cutting index and strongest convective flow regime in comparison to others campaigns. A lower vegetation density, especially subaquatic plants, and presence of important preferential flow could explain this observation. DTW processing on RTD curves shed light on the ageing effect that has a much bigger impact than seasonal effect. This is mainly due to sediments accumulation, sludge and vegetation development.

Systemic models of full-scale Surface Flow Treatment Wetlands: Determination by application of fluorescent tracers

In Rhin-Meuse hydrological basin (North-East of France), local authorities have encouraged the setup of Surface Flow Treatment Wetlands (SFTW) at the outlet of several small communities wastewater treatment plants. These systems are devoted to effluent polishing by providing potential pollutant mitigation effects. However, such systems are designed mainly empirically and resulting surfaces and shapes may not be optimal. In the present study, the hydrodynamic behavior of three full-scale SFTWs used for sewage tertiary treatment was assessed by means of multi-tracer experiments involving two fluorescent dyes: uranine and sulforhodamine B. Residence Time Distribution analysis shows that the three investigated wetlands displayed very different hydrodynamic properties. Mean residence times were lower in the ditches (1–3h) than in the pond (mainly 20h). The effective volume ratio was very low for all investigated wetlands. Sediment deposition as well as vegetation cover development may explain this result. Ditches behaved as Plug-Flow Reactors with dispersion whereas the pond underwent strong internal recirculation. The influence of vegetation cover on hydrodynamic dispersion was evidenced as it induced long tails in the tracer breakthrough curves. Three systemic model structures are proposed to describe wetlands hydrodynamics: combination of ideal reactors (Plug Flow and/or Continuous Stirred Tank Reactors) with varying degrees of complexity were able to reproduce accurately the experimental Residence Time Distributions. Combination with a first-order kinetic model allowed photochemical decay of uranine to be described. In the future, combination of the proposed hydrodynamic models with more complex kinetics models will constitute a valuable tool for process understanding and optimization.

Reducing phosphorus flux from organic soils in surface flow treatment wetlands

Treatment wetlands have a finite period of effective nutrient removal after which treatment efficiency declines. This is due to the accumulation of organic matter which decreases the capacity and hydraulic retention time of the wetland. We investigated four potential solutions to improve the soluble reactive P (SRP) removal of a municipal wastewater treatment wetland soil including; dry down, surface additions of alum or calcium carbonate and physical removal of the accreted organic soil under both aerobic and anaerobic water column conditions. The flux of SRP from the soil to the water column under aerobic conditions was higher for the continuously flooded controls (1.1 ± 0.4 mg P m −2 d −1), dry down (1.5 ± 0.9 mg P m −2 d −1) and CaCO 3 (0.8 ± 0.7 mg P m −2 d −1) treatments while the soil removal and alum treatments were significantly lower at 0.02 ± 0.10 and −0.07 ± 0.02 mg P m −2 d −1, respectively. These results demonstrate that the two most effective management strategies at sequestering SRP were organic soil removal and alum additions. There are difficulties and costs associated with removal and disposal of soils from a treatment wetland. Therefore our findings suggest that alum addition may be the most cost effective and efficient means of increasing the sequestering of P in aging treatment wetlands experiencing reduced P removal rates. However, more research is needed to determine the longer term effects of alum buildup in the organic soil on the wetland biota, in particular, on the macrophytes and invertebrates. Since alum effectiveness is time limited, a longer term solution to P flux may favor the organic soil removal.

Integrated stream and wetland restoration: A watershed approach to improved water quality on the landscape

Water quality in Upper Sandy Creek, a headwater stream for the Cape Fear River in the North Carolina Piedmont, is impaired due to high N and P concentrations, sediment load, and coliform bacteria. The creek and floodplain ecosystem had become dysfunctional due to the effects of altered storm water delivery following urban watershed development where the impervious surface reached nearly 30% in some sub-watersheds. At Duke University, an 8-ha Stream and Wetland Assessment Management Park (SWAMP) was created in the lower portion of the watershed to assess the cumulative effect of restoring multiple portions of stream and former adjacent wetlands, with specific goals of quantifying water quality improvements. To accomplish these goals, a three-phase stream/riparian floodplain restoration (600 m), storm water reservoir/wetland complex (1.6 ha) along with a surface flow treatment wetland (0.5 ha) was ecologically designed to increase the stream wetland connection, and restore groundwater wetland hydrology. The multi-phased restoration of Sandy Creek and adjacent wetlands resulted in functioning riparian hydrology, which reduced downstream water pulses, nutrients, coliform bacteria, sediment, and stream erosion. Storm water event nutrient budgets indicated a substantial attenuation of N and P within the SWAMP project. Most notably, (NO 2 − + NO 3 −)–N loads were reduced by 64% and P loads were reduced by 28%. Sediment retention in the stormwater reservoir and riparian wetlands showed accretion rates of 1.8 cm year −1 and 1.1 cm year −1, respectively. Sediment retention totaled nearly 500 MT year −1.

Evaluation of a Diffused Air Aeration System for a Constructed Wetland Receiving Dairy Wastewater

Treatment systems that utilize natural processes, such as constructed wetlands, offer a sustainable and economical alternative to conventional wastewater treatment. Dairy farm wastewater was loaded into two similar (~100 m2 each) surface flow treatment wetlands in Bible Hill, Nova Scotia, Canada, at an average rate of 65 kg BOD5 ha-1 d-1. A diffused air aeration system was installed in one of the wetlands based on a design oxygen requirement of 3.52 kg O2 d-1. Wetland treatment performance was evaluated over 20 months (September 2002 to April 2004), during which time the aeration system operated for 13 months. The wetlands were monitored intensively for dissolved oxygen (DO), five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), total Kjeldahl nitrogen (TKN), ammonia-nitrogen (NH3-N), nitrate-nitrogen (NO3--N), total phosphorus (TP), and Escherichia coli. Both the aerated and non-aerated wetlands provided effective year-round wastewater treatment. Artificial aeration significantly increased TKN and NH3-N mass reductions (P < 0.001). Aeration did not significantly affect the removal of BOD5, TSS, NO3--N, TP, and E. coli. The data suggest that the benefits of wetland aeration are not great enough to warrant its widespread adoption for small-scale agricultural systems.

A modeling approach for mixing and reaction in wetlands with continuously varying flow

Prior investigations have examined steady-state flow in surface flow treatment wetlands, with mixing modeled as advection-dominated, and reaction calculated using flow-weighted averages over collections of stream tubes with different velocities. This work extends these concepts to non-steady flow conditions and temporally varying inlet concentrations. The essential construct that makes the approach feasible is definition of a set of reference (steady) state conditions under which the residence time distribution (RTD) and stream-tube specific rate constants are defined. Residence time in any stream tube under non-steady flow is treated as a linear function of its reference-condition residence time, and the overall wetland retention time under both mean and varying flow regimes. Outlet concentration is found by convolution of the reaction term with a varying inlet concentration function. For real-world flow and concentration data collected at discrete points in time, integration for outlet concentration is approximated using linear interpolation to generate inlet concentrations and velocities at intermediate points in time. The approach is examined using data from the literature. Vegetation density and depth distributions are seen as central in determining mixing and treatment performance.

English

Several new passive treatment systems have been constructed to treat acid mine drainage (AMD) in the Mid-Continent Region. This poster discusses the construction and preliminary results of one new site—LeBosquet 064 2004 Clean Streams Reclamation Project. As a part of ongoing technical assistance with the Oklahoma Conservation Commission’s (OCC) Abandoned Mine Lands Program, the Office of Surface Mining (OSM), Mid-Continent Region (MCR) assisted in the design and evaluation of the treatment system. The project site was an artesian seep located 4 miles (5 km) west of the town of Fanshawe, in LeFlore County, Oklahoma. Preliminary water quality results indicated that the combination of an anoxic limestone drain system and a surface flow treatment wetland has been effective at mitigating the adverse impact associated with the AMD. Additional

Escherichia coli control in a surface flow treatment wetland

A field experiment showed that numbers of Escherichia coli declined significantly when floating Lemna spp. plants were removed to create open water areas in a typical newly constructed surface flow treatment wetland in southern Ontario. It is suggested that E. coli declined immediately after Lemna removal because the Lemna was shading the water column from penetration by natural UV radiation, it was providing favourable attachment sites for the E. coli, and it was not allowing effective free exchange of oxygen from surface winds to the water column to maintain high enough dissolved oxygen supplies for predator zooplankton populations. Operators of wetland systems must have the specialized skills required to recognize the cause and the appropriate maintenance requirements to maintain efficient operation of such unconventional systems should E. coli numbers increase during the course of operation.

Pathogen Removal by Agricultural Constructed Wetlands in Cold Climates

Constructed treatment wetlands have been found to remove fecal coliform (FC) through a variety of mechanisms. This research evaluated the removal of FC in both warm and cold seasons from surface flow treatment wetlands in Bible Hill, Nova Scotia. Two wetlands (100 m2), of differing depths were monitored over a 17 month period. The wetlands were loaded with dairy wastewater (average inlet FC concentration of 7438 CFU) at a rate of 2.2A—10^7 CFU ha-1d-1. Weekly samples were collected at the wetland inlet and outlet for FC using the MPN method. Removal rates and mass reductions ranged from 96.8 to 99.7% over the entire monitoring period. Fecal coliform discharge levels were below guidelines for recreation (< 200 CFU 100 mL-1) and irrigation (< 100 CFU 100 mL-1) purposes the majority of the time, indicating that removal of FC in these systems was sufficient in both warm and cold seasons, even when ice conditions existed.

2차처리장 방류수 정화 부들습지셀의 초기운영단계 질산성질소 제거

Nitrate removal was examined from May to October 2003 of a surface flow treatment wetland cell, which was a part of a treatment wetland system composed of four wetland cells and a distribution pond The system was established on rice paddy near the Kohung Estuarine Lake located in the southern part of the Korean Peninsula. Effluent from a secondary-level night soil treatment plant was funneled into the system. The investigated cell, 87 m in length and 14 m in width, was created in April 2003. An open water was designed at its center, which was equivalent to 10 percent of its total area. Cattails (Typha angustifolia) were transplanted from natural wetlands into the cell and their stems were cut at about 40cm height from their bottom ends. Average of effluent from the treatment plant was funneled into the cell by gravity flow and average of its treated effluent was discharged into the Sinyang Stream flowing into the lake. Its water depth was maintained about 0.2 m and its hydraulic detention time averaged 5.2 days. Average height of the cattail stems was 42.5 cm in May 2M3 and 117.7 cm in September 2003. The number of stems averaged in May 2003 and in September 2003. The growth of cattails was good. Temperature of influent and effluent averaged 25.9 and , respectively. -N loading rate of influent and effluent averaged 176.67 and , respectively. Removal of rf03-N averaged and its removal rate by mass was about 50%. Considering its initial operating stage in which cattail rhizomes and litter layer on the bottom were not Idly established, the -N removal rate of the cell was rather good.

Overview: Surface flow constructed wetlands

Several hundreds of marshes have now been built primarily for the purposes of water quality improvement. This paper reviews statistics on the types and numbers and character of these low-tech water treatment wetlands. The operational processes are discussed, including sedimentation, plant uptake, sorption, nutrient cycling, and chemical and microbial conversion. Performance has been good for reduction of suspended solids, biological oxygen demand, phosphorus, nitrogen, metals and some anthropogenic chemicals. Design procedures are evaluated, showing that the overly simplistic techniques used in the infancy of the technology may now be replaced by rational procedures based on the large and rapidly growing information base for constructed surface flow treatment wetlands. Ancillary wildlife and human use is an important part of this type of wetland, and should be acknowledged in design. Capital costs are low, but the principal financial advantage is the extremely low base cost of operation.