Horizontal Flow Constructed Wetlands Research Articles

Constructed wetland as a low cost and sustainable solution for wastewater treatment adapted to rural settlements: the Chorfech wastewater treatment pilot plant

The paper presents the detailed design and some preliminary results obtained from a study regarding a wastewater treatment pilot plant (WWTPP), serving as a multistage constructed wetland (CW) located at the rural settlement of 'Chorfech 24' (Tunisia). The WWTPP implemented at Chorfech 24 is mainly designed as a demonstration of sustainable water management solutions (low-cost wastewater treatment), in order to prove the efficiency of these solutions working under real Tunisian conditions and ultimately allow the further spreading of the demonstrated techniques. The pilot activity also aims to help gain experience with the implemented techniques and to improve them when necessary to be recommended for wide application in rural settlements in Tunisia and similar situations worldwide. The selected WWTPP at Chorfech 24 (rural settlement of 50 houses counting 350 inhabitants) consists of one Imhoff tank for pre-treatment, and three stages in series: as first stage a horizontal subsurface flow CW system, as second stage a subsurface vertical flow CW system, and a third horizontal flow CW. The sludge of the Imhoff tank is treated in a sludge composting bed. The performances of the different components as well as the whole treatment system were presented based on 3 months monitoring. The results shown in this paper are related to carbon, nitrogen and phosphorus removal as well as to reduction of micro-organisms. The mean overall removal rates of the Chorfech WWTPP during the monitored period have been, respectively, equal to 97% for total suspended solids and biochemical oxygen demand (BOD5), 95% for chemical oxygen demand, 71% for total nitrogen and 82% for P-PO4. The removal of E. coli by the whole system is 2.5 log units.

A new empirical law to accurately predict solute retention capacity within horizontal flow constructed wetlands

Constructed wetlands are being considered a sustainable and promising option whose performance, cost and resources utilization can complement or replace conventional water treatment. The literature reported the fact that an insufficient residence time of pollutants in soils induces an incomplete and unfinished biodegradation process. In this work, engineering solutions are proposed with the objective of significantly increasing the solute retention capacity in the horizontal flow constructed wetland (HFCW). Using several numerical tracers experiments with different operating scenarios, such as the HFCW physical configuration, the flow rate, the boundary conditions, the adsorption layer thickness, practical methods and a new empirical law are suggested in order to substantially increase the adsorption ability in the HFCW, and hence the pollutant removal. Furthermore, it appears that there is no impact of the adsorbent layer thickness on the solute mean residence time with high values of adsorption coefficient ( k d). For smaller k d values, the deeper the adsorption layer thickness, the higher the retention time.

Treatment of fishpond water by recirculating horizontal and vertical flow constructed wetlands in the tropics

Common practice of aquaculture in Vietnam and other countries in South East Asia involves frequent discharge of polluted water into rivers which results in eutrophication and degradation of receiving water bodies. There is therefore a need to develop improved aquaculture systems which have a more efficient use of water and less environmental impact. The aim of this study was to assess the suitability of using constructed wetlands (CWs) for the treatment of fishpond water in a recirculating aquaculture system in the Mekong Delta of Vietnam. Water from a fishpond stocked with Nile tilapia ( Oreochromis niloticus) and common carp ( Cyprinus carpio) was recirculated through horizontal and vertical flow CWs. The CWs were able to keep a good water quality with DO (> 1 mg/l − 1 ), BOD (< 30 mg l − 1 ), TAN (< 1 mg l − 1 ) and NO 2 − (< 0.07 mg l − 1 ) at acceptable concentrations for growth of the fish. There was a good removal of organic matter measured as oxygen demand with up to 50% removal of BOD and COD in both types of CWs despite the high loading rates and low concentration levels. However, the vertical flow CWs performed better than the horizontal flow CWs as they had higher nitrification rates and higher DO concentrations in the outlets. The ornamental Canna × generalis planted in the CWs grew faster and took up more N and P in the vertical flow CWs. The aquaculture fish had a feed conversion ratio of 1.53 based on feed dry weight, and 31% and 34% of N and P input, respectively, were incorporated into fish biomass. Only minor quantities of phytoplankton algae were removed in the CWs but abundance of toxic algae such as Microcystis was low. It is concluded that particularly vertical flow CWs have great potential for treatment of fishpond water in recirculating aquaculture systems in the tropics as the discharge of polluted water and the associated environmental impact can be significantly reduced.

Life cycle assessment of vertical and horizontal flow constructed wetlands for wastewater treatment considering nitrogen and carbon greenhouse gas emissions

Life cycle assessment (LCA) is used to compare the environmental impacts of vertical flow constructed wetlands (VFCW) and horizontal flow constructed wetlands (HFCW). The LCAs include greenhouse gas (N 2O, CO 2 and CH 4) emissions. Baseline constructed wetland designs are compared to different treatment performance scenarios and to conventional wastewater treatment at the materials acquisition, assembly and operation life stages. The LCAs suggest that constructed wetlands have less environmental impact, in terms of resource consumption and greenhouse gas emissions. The VFCW is a less impactful configuration for removing total nitrogen from domestic wastewater. Both wetland designs have negligible impacts on respiratory organics, radiation and ozone. Gaseous emissions, often not included in wastewater LCAs because of lack of data or lack of agreement on impacts, have the largest impact on climate change. Nitrous oxide accounts for the increase in impact on respiratory inorganic, and the combined acidification/eutrophication category. The LCAs were used to assess the importance of nitrogen removal and recycling, and the potential for optimizing nitrogen removal in constructed wetlands.

Winery wastewater treatment in a hybrid constructed wetland

A full-scale hybrid constructed wetland (CW) was built to treat mixed effluent derived from a winery and tourist establishment. The treatment system consisted of a hydrolytic upflow sludge bed (HUSB) digester for suspended-solids removal, a vertical-flow (VF) constructed wetland and three parallel subsurface horizontal-flow (HF) constructed wetlands. The HUSB reduced TSS loads to 72–172 mg L −1, helping to prevent clogging, while organic loads for the wastewater entering the VF ranged from 422 to 2178 mg COD L −1 and from 216 to 1379 mg BOD 5 L −1. At an average hydraulic loading rate (HLR) of 19.5 mm d −1 and average surface loading rates (SLR) of 30.4 g COD m −2 d −1 and 18.4 g BOD 5 m −2 d −1, the overall VF + HF CW system reached average removal efficiencies of 86.8% of TSS, 73.3% of COD, and 74.2% of BOD 5. The system also removed 52.4% of total Kjeldhal nitrogen (TKN), 55.4% of NH 3-N and 17.4% of phosphates. While the VF unit showed high removal rates, the HF unit operated at lower removal rates than those previously reported. The CW units showed rapid adaptation to low pH values. A linear-regression analysis indicated that the independent variables SLR and temperature determined more than 95% of the variation in performance and efficiency of the CW system and offered simple mathematical models for design and system-description purposes.

Comprehensive assessment of the design configuration of constructed wetlands for the removal of pharmaceuticals and personal care products from urban wastewaters

Seven mesocosm-scale constructed wetlands (CWs) of different configurations were operated outdoors for nine months to assess their ability to remove pharmaceuticals and personal care products (PPCPs) from urban wastewaters. CWs differed in some design parameters, namely the presence of plants, the species chosen (i.e., Typha angustifolia vs Phragmites australis), flow configuration (i.e., surface flow vs subsurface flow) and the presence of a gravel bed. A nearby conventional activated-sludge wastewater treatment plant (WWTP) fed with the same sewage was simultaneously monitored for comparison. The PPCPs ketoprofen, naproxen, ibuprofen, diclofenac, salicylic acid, carbamazepine, caffeine, galaxolide, tonalide and methyl dihydrojasmonate were monitored. The presence of plants favoured the removal of some PPCPs. The performance of the mesocosm studied was compound-dependant, soilless CWs showing the highest removal efficiency for ketoprofen, ibuprofen and carbamazepine, while free-water CWs with effluent leaving through the bottom of the tank performed well for the degradation of ketoprofen, salicylic acid, galaxolide and tonalide. Finally, subsurface horizontal flow CWs were efficient for the removal of caffeine. Significant linear correlations were observed between the removal of some PPCPs and temperature or redox potential. Hence, microbiological pathways appear to be the most probable degradation route for PPCPs in the CWs studied.

Design and configuration criteria for wetland systems treating greywater

Design and configuration for wetlands treating greywater are usually based on literature data obtained from domestic wastewater operating wetlands. It is very important to determine proper criteria for design and configuration to provide efficiency and minimum maintenance, avoiding bad odour and clogging amongst others, ensuring the acceptance of householders. The aim of this work was to design a wetland system treating greywater for a household and determine whether the chosen criteria were appropriate. Some of the criteria taken into consideration for design and configuration were: quantitative and qualitative characteristics, desired removal of biochemical oxygen demand (BOD) and suspended solids (TSS), substrate and ornamental aspect of the system. The system was composed of a grease trap (kitchen), sedimentation tank, a horizontal flow constructed wetland (HF-CW), intermittent feeding system, and a vertical flow constructed wetland (VF-CW). The results showed that the suggested design and configuration were in accordance with the expected efficiency. Being a compact system, it was susceptible to peak flows, temporarily deteriorating the performance of the HF-CW. The hybrid system, however, showed to cope well with influent fluctuations. The overall performance of the system shows that the removal of turbidity, TSS, COD and BOD were over 88%, reaching 95% removal for both BOD and turbidity.

Adsorption distribution impact on preferential transport within horizontal flow constructed wetland (HFCW)

Predicting preferential water flow and solute transport in soils is in the interest of scientists and engineers in the fields of agricultural soil, forest hydrology, soil physics and wastewater treatment by constructed wetland. In artificial wetlands, any preferential pathway induces an insufficient residence time of pollutants in the soil, making an incomplete and unfinished biodegradation process, a wrong evaluation of the hydraulic residence time of the system which would hinder its management in a complete system with several entities of treatment and a non-homogeneous growth of the biofilm in the solid filter mass. This paper is a contribution in tracer experiment data analysis within a horizontal flow constructed wetland built in a storm water basin. A two-dimensional numerical model was used to simulate flow and reactive solute transport. The flow model was successfully calibrated in very dry soil conditions. The adsorption profiles used in the reactive transport modeling are those of five molecules: metolachlor, atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (HA). We show that the adsorption distribution is an internal factor of soil which is responsible to the “preferential” pathway transport in a homogeneous gravel texture. The mean residence time of pollutants within the filter is strongly correlated with the average value of the adsorption coefficient. Moreover, we note a lack of significant impact of the heterogeneity of the medium on the statistical moments of breakthrough curve. It appears that a uni-modal breakthrough curve is not significant to the absence of preferential flow in the medium and at least a two-dimensional display can provide sufficient evidence on the presence or absence of preferential pathways. Finally, using a PLS regression, it is possible to perfectly discriminate the number of peaks of concentration and the asymmetry of the breakthrough curve.

Enhancement of nitrogen removal in towery hybrid constructed wetland to treat domestic wastewater for small rural communities

Efforts to protect watercourses, especially sources of drinking water, particularly in rural areas, are now underway in China. Nitrogen present in wastewater, due to its role in eutrophication and potential toxicity to aquatic species, is a focus of primary concern. Constructed wetlands (CWs), a simpler, less costly treatment alternative, have been used to treat domestic wastewater for small communities. Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been successful in removing nitrogen mainly due to lack of dissolved oxygen (DO). To enhance nitrogen removal, a novel CW configuration with three stages, towery hybrid constructed wetland (THCW), was designed. The first and third stages were rectangle subsurface horizontal flow CWs, and the second stage was a circular three-layer free-water flow CW. Increased DO by passive aeration of a tower type cascade overflow from the upper layer into the lower layer in the second stage of the wetland enhanced nitrification rates. Denitrification rates were also improved by additional organic matter supplied as a result of bypass influent directly into the second stage. Evergreen tree Pond Cypress ( Taxodium ascendens), industrial plants Mat Rush ( Schoenoplectus trigueter) and Wild Rice shoots ( Zizania aquatica), ornamental floriferous plants Pygmy Waterlily ( Nymphaea tetragona) and Narrow-leaved Cattail ( Typha angustifolia) were planted in the wetland. The average percentage of removal was 89%, 85%, 83%, 83% and 64% for total suspended solid, chemical oxygen demand, ammonia nitrogen, total nitrogen and total phosphorus, respectively. There was no significant difference ( p < 0.05) at low and high hydraulic loads (16 cm/d and 32 cm/d) for performance of THCW. Nitrifying and denitrifying bacteria as well as potential nitrification activity and potential denitrification rates measured have shown that nitrification–denitrification is the main mechanism for nitrogen removal in the wetland. THCW also provided additional aesthetic benefits.

Constructed wetlands with horizontal subsurface flow in the Czech Republic: Two long-term case studies

Constructed wetlands have been used for treatment of municipal and domestic sewage in the Czech Republic since 1989. At present, nearly 250 constructed wetlands (CWs) are in operation and all CWs have been designed with horizontal sub-surface flow. The present study describes long-term treatment performance of two systems. Constructed wetland at [Zcirc]itenice treats domestic sewage from 6 PE and was put in operation in 1993. Single bed with the surface area of 18 m2 is filled with gravel (4–32 mm) and in the beginning it was planted with Common reed (Phragmites australis). Constructed wetland at Ĉistá was built in 1994 for 800 PE and combined sewer system. Four beds with a total surface of 3,040 m2 are filled with crushed rock (4–12 mm) and planted with Common reed and Reed canarygrass (Phalaris arundinacea) The evaluation of the treatment performance presented in this paper is based on the periods 1994–2004 and 1995–2007 for [Zcirc]itenice and Ĉistá, respectively. The results represent a “typical” treatment efficiency achieved in horizontal flow CWs - high removal of organics (BOD5, COD) and suspended solids and low removal of ammonia and phosphorus. However, in both constructed wetlands BOD5 and TSS are the primary target and therefore the design was set to meet these requirements. The system at Ĉistá is a good example of the ability of HF constructed wetlands treat wastewaters with low organic load. The results presented in this paper indicate that horizontal flow constructed wetlands are a suitable alternative for treatment of wastewater from small sources of pollution when organics and suspended solids are the primary target.

Evaluation of a hybrid constructed wetland for treating domestic sewage from individual housing units surrounding agricultural villages in South Korea

The treatment efficiency of 2- and 3-stage constructed wetlands (CWs) was evaluated for treating domestic sewage from houses surrounding agricultural villages. The optimum depth of filter media was 90 cm. The optimum volume ratio of vertical flow (VF) and horizontal flow (HF) beds was 1:2, and the optimum filter medium was broken stone in the VF-HF 2-stage hybrid CWs. Based on the above optimum conditions, removal efficiency of biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), total nitrogen (T-N), and total phosphorus (T-P) were 99, 98, 99, 68, and 72%, respectively. However to utilize constructed wetlands (CWs) for treating domestic sewage for an individual house, would require downsizing of the 2-stage hybrid CWs. In addition, the low removal efficiency of T-N and T-P in 2-stage hybrid CWs would require improvements necessary to meet acceptable water quality discharge standards. Thus, to reduce the CWs' area and improve the T-N and T-P removal efficiencies, VF-HF 2-stage hybrid CW was modified into VF/HF(I)-HF(II) and VF/HF(I)-HF(III) 3-stage hybrid CW. The optimum reduced size of 3-stage hybrid CW was the VF/HF(I)-HF(II) configuration which also increased T-N removal. Using this system, removal efficiency of BOD, COD, SS, T-N, and T-P were 99, 98, 99, 83, and 75%, respectively. In VF/HF(I)-HF(II) CW, the removal velocity of BOD, COD and SS was rapid on the order of VF (1st stage) >> HF(II) (3rd stage) > or = HF(I) (2nd stage), VF (1st stage) >> HF(II) (3rd stage) > HF(I) (2nd stage) and VF (1st stage) >> HF(I) (2nd stage) > HF(II) (3rd stage), respectively. The removal velocity of T-N and T-P in VF/HF(I)-HF(II) CWs was rapid on the order of HF(I) (2nd stage) > HF(II) (3rd stage) > or = VF (1st stage) and VF (1st stage) > HF(I) (2nd stage) > HF(II) (3rd stage), respectively.

Evaluation of 2- and 3-stage combinations of vertical and horizontal flow constructed wetlands for treating greenhouse wastewater

The adsorption characteristics of various filter media and treatment efficiency of small pilot-scale constructed wetlands (CWs) were investigated in order to design optimum CWs for treating greenhouse wastewater. Calcite was the best filter medium for the adsorption of ammonium nitrogen and phosphorus under various temperature and pH conditions. However, removal efficiency of calcite for total nitrogen (T-N) removal was low due primarily to high nitrate levels. Thus, several hybrid CWs (containing calcite as filter media) consisting of combinations of vertical flow (VF) and horizontal flow (HF) beds were evaluated for improving efficiency for T-N removal. Both 2- and 3-stage combinations of the VF and HF beds were tested. The optimum hybrid CWs was demonstrated to be a 3-stage combination of horizontal flow (HF)–vertical flow (VF)–horizontal flow (HF), which provided suitable conditions for both nitrification and denitrification, which improved removal of T-N in wastewater containing nitrate. In the HF–VF–HF 3-stage hybrid CWs, the reduction in chemical oxygen demand (COD), T-N, and total phosphorus (T-P) in the effluent were 95.1, 68.4 and 94.3%, respectively. The removal of COD, T-N and T-P in 3-stage HF–VF–HF CWs was rapid in order of VF (second stage) ≫ HF (first stage) ≫ HF (third stage), VF (second stage) ≫ HF (third stage) > HF (first stage) and VF (second stage) ≫ HF (first stage) ≫ HF (third stage), respectively.

Tolerance to hydraulic and organic load fluctuations in constructed wetlands

This paper describes a two-year performance evaluation of four different constructed wetland (CW) treatment systems designed by IRIDRA Srl, located in central Italy. All four CW systems were established to treat wastewater effluent from different tourist activities: (1) one single-stage CW for secondary treatment of domestic wastewater (30 p.e.) at a holiday farm site; (2) a hybrid compact system consisting of two stages, a horizontal flow (HF) system followed by a vertical flow (VF) system for the secondary treatment of effluent from a 140 p.e. tourist resort; (3) a single-stage vertical flow (VF) CW for a 100 p.e. mountain shelter; and (4) a pair of single-stage, HF CWs for the secondary treatment of segregated grey and black water produced by an 80 p.e. camping site. These tourism facilities are located in remote areas and share some common characteristics concerning their water management: they have high variability of water consumption and wastewater flow, depending on the season, weather and weekly regularities; they have no connection to a public sewer and most sites are located in a sensitive environment. Total suspended solids (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD5), ammonium (N-NH4+), nitrate (N-NOx), total nitrogen (Ntot), total phosphorus (Ptot), total coliform (TC), faecal coliform (FC), E. coli removal efficiencies for all four CW systems are presented. The results from this study demonstrate the potential of CWs as a suitable technology for treating wastewater from tourism facilities in remote areas. A very efficient COD reduction (83-95%) and pathogen elimination (3-5 logs) have been achieved. Furthermore, the CWs are easily maintained, robust (not sensitive to peak flows), constructed with local materials, and operate with relatively low cost.

Effect of design parameters in horizontal flow constructed wetland on the behaviour of volatile fatty acids and volatile alkylsulfides

A pilot-scale horizontal flow constructed wetland (HFCW) system planted with common reed ( Phragmites sp.) was constructed to study how hydraulic loading rate (HLR), aspect ratio, water depth, and granular medium affect to the fate of several organic matter degradation intermediates namely, acetic acid (HAc), isovaleric acid (Isoval), and dimethylsulfide (DMS). ANOVA statistical analysis performed on the data set of 8 months of operation shows that the HLR and the water depth are two major factors that control the performance of HFCWs for the target analytes. A clear difference in the HFCW effluent concentrations was obtained according to water depth. Effluents of the shallow water depth contained lower DMS (1.05–1.44 μg l −1), HAc (7.91–10.9 mg l −1), and Isoval (0.11–0.15 mg l −1) concentrations than the deeper beds (DMS: 1.68–2.40 μg l −1; HAc: 9.29–14.4 mg l −1, and Isoval: 0.20–0.31 mg l −1). Such differences could be accounted to the different formation and consumption rates of the organic matter degradation intermediates, which is related with the redox potentials ( E). Indeed, it could lead to different biochemical reactions of organic matter degradation according with the E value. HLR has a statistically significant influence on the effluent HAc, Isoval, and DMS concentrations. Seasonal variability of effluent HAc concentration shows that it is independent on the HAc loading. While the loading showed no seasonal pattern, the removal efficiency was clearly higher in cold months, which suggests a predominant internal production of HAc in HFCWs in the warm season from the accumulated organic particulate matter. Similar results were also found when Isoval and DMS were considered.