Horizontal Subsurface Flow Constructed Wetlands Research Articles

Biological mechanisms associated with triazophos (TAP) removal by horizontal subsurface flow constructed wetlands (HSFCW)

Triazophos (TAP) is a widely used pesticide that is easily accumulated in the environment due to its relatively high stability: this accumulation from agricultural runoff results in potential hazards to aquatic ecosystems. Constructed wetlands are generally considered to be an effective technology for treating TAP polluted surface water. However, knowledge about the biological mechanisms of TAP removal is still lacking. This study investigates the responses of a wetland plant (Canna indica), substrate enzymes and microbial communities in bench-scale horizontal subsurface-flow constructed wetlands (HSCWs) loaded with different TAP concentrations (0, 0.1, 0.5 and 5mg·L−1). The results indicate that TAP stimulated the activities of superoxide dismutase (SOD) and peroxidase (POD) in the roots of C. indica. The highest TAP concentrations significantly inhibited photosynthetic activities, as shown by a reduced effective quantum yield of PS II (ΦPS II) and lower electron transport rates (ETR). However, interestingly, the lower TAP loadings exhibited some favorable effects on these two variables, suggesting that C. indica is a suitable species for use in wetlands designed for treatment of low TAP concentrations. Urease and alkaline phosphatase (ALP) in the wetland substrate were activated by TAP. Two-way ANOVA demonstrated that urease activity was influenced by both the TAP concentrations and season, while acidphosphatase (ACP) only responded to seasonal variations. Analysis of high throughput sequencing of 16S rRNA revealed seasonal variations in the microbial community structure of the wetland substrate at the phylum and family levels. In addition, urease activity had a greater correlation with the relative abundance of some functional microbial groups, such as the Bacillaceae family, and the ALP and ACP may be influenced by the plant more than substrate microbial communities.

BPA and NP removal from municipal wastewater by tropical horizontal subsurface constructed wetlands

It has been recognized that numerous synthetic compounds like Bisphenol A (BPA) and nonylphenols (NP) are present in effluents from wastewater treatment plants (WWTP) at levels of parts per billion (μgL−1) or even parts per trillion (ngL−1) with a high potential to cause endocrine disruption in the aquatic environment. Constructed wetlands (CW) are a cost-effective wastewater treatment alternative with promising performance to treat these afore mentioned compounds. This research was aimed to evaluate the efficacy of CW treatment of WWTP effluent for mitigating the effects endocrine disrupting compounds (EDCs). This research goal was accomplished by (1) quantifying the removal of BPA and NP in CWs; (2) isolating CW fungal strains and testing for laccase production; and (3) performing endocrine disruption (reproduction) bioassays using the fruit fly Drosophila melanogaster. Three pilot scale horizontal subsurface flow constructed wetlands (HSSF-CW) were operated for eight weeks: one planted with Phragmites australis; one planted with Heliconia psitacorum; and one unplanted. The Heliconia CW showed a removal efficiency of 73.3(±19%) and 62.8(±20.1%) for BPA and NP, respectively; while the Phragmites CW demonstrated a similar removal for BPA (70.2±27%) and lower removal efficiency for NP 52.1(±37.1%).The unplanted CW achieved 62.2 (±33%) removal for BPA and 25.3(±37%) removal for NP. Four of the eleven fungal strains isolated from the Heliconia-CW showed the capacity to produce laccase. Even though complete removal of EDCs was not achieved by the CWs, the bioassay confirmed a significant improvement (p<0.05) in fly viability for all CWs, with Heliconia sp. being the most effective at mitigating adverse effects on first and second generational reproduction. This study showed that a CW planted with a native Heliconia sp. CW demonstrated a higher removal of endocrine disrupting compounds and better mitigation of reproductive disruption in the bioassay.

Feasibility of using tuberose (P. tuberosa L.) in horizontal subsurface flow constructed wetland for heavy metal removal from domestic wastewater

Constructed wetlands (CW) are well known for removal of organics, suspended solids, nutrients, and bacteria. However, the information on removal of heavy metals and their sequestration in plants especially, the ornamental plants is very limited. In this experimental study, efficiency of horizontal subsurface‐flow constructed wetland (HSCW) planted with an ornamental species Polianthus tuberosa L. was evaluated for heavy metal sequestration in the phytomass. The plants were harvested during the peak standing crop in early September, divided into leaves, inflorescence, roots, and rhizomes, and analyzed for six trace elements (Cu, Zn, Ni, Al, Pb, and Fe). Metal concentrations decreased in the order of roots &gt; rhizomes &gt; leaves &gt; inflorescence. The highest concentration in aboveground biomass were recorded for Al (3.66 mg kg−1) and Fe (1.35 mg kg−1), while the lowest concentration was recorded for Pb (0.06 mg kg−1). Belowground biomass also followed the same decreasing trend, the highest concentrations being recorded for Al (6.28 mg kg−1) with 5.78 mg kg−1 and 6.09 mg kg−1 concentration in rhizomes and roots, respectively. The lowest concentration in belowground biomass was recorded for Ni (0.28 mg kg−1) and Pb (0.17 mg kg−1). The belowground/aboveground concentration ratio ranged between 1.19 and 5.13 with an average value of 2.50. Due to average belowground/aboveground biomass ratio &lt; 1, the belowground/aboveground standing stock ratios for all the metals were &gt; 1 except Fe (0.79). The maximum values for bioconcentration factor (BCF) were found for Al and Zn 81.5 and 16.3, respectively. Biological accumulation factor (BAF) and transfer factor (TF) values were &gt; 1 and &lt;1, respectively for most of the heavy metals, which suggests their immobilization in the roots/rhizosphere and therefore, the species can be best suited for phytostabilization. The results of this study therefore provide the comprehensive information on sequestration of Cu, Zn, Ni, Al, Pb, and Fe in vegetation during domestic wastewater treatment in CW with horizontal subsurface flow. © 2015 American Institute of Chemical Engineers Environ Prog, 35: 125–132, 2016

Nitrobenzene degradation pathways and their interaction with sulfur and nitrogen transformations in horizontal subsurface flow constructed wetlands

Nitrobenzene (NB) degradation pathways and their interaction with sulfur and nitrogen transformations in constructed wetlands are not fully understood. This study investigates the effectiveness of horizontal subsurface flow constructed wetlands (HSSFCWs) in NB biodegradation including the biodegradation pathways and microbial interactions. The investigation was based on two laboratory-scale wetlands planted with Juncus effusus. One wetland was intermittently aerated while the other was not. Data about NB degradation were collected at varying influent loading rates [35 and 140mg/L] for 120-day period. From the results, both wetlands exhibited an overall performance of 99% NB removal. More so, intermittent aeration did not significantly improve overall performance but rather it enhanced the buffer capacity of NB degradation to shock influent loading. The result also demonstrates that NB mineralization account for about 96% and 4% for volatilization. Formation of ammonium from NB degradation increased the ammonium concentration in the pore water. In unaerated wetland, 84mg/L of sulfide accumulated from complex microbial reaction involving sulfate as electron acceptor and NB as electron donor.

Constructed wetlands as a potential management practice for cold climate dairy effluent treatment — VT, USA

Four horizontal subsurface flow constructed wetlands (HSSF-CW) were monitored to determine their efficiency at reducing the concentrations of five-day biological oxygen demand (BOD5) and total suspended solids (TSS) from dairy farm effluents in cold climate in Vermont during the four year study period (between 2004 and 2007). This study evaluates effects of seasonal variations, wetland age, supplemental aeration and design connected in-series on BOD5 and TSS treatment performances of CWs. Aerated CWs achieved higher BOD5 and TSS treatment efficiencies by 8% and 5% respectively, compared with non-aerated ones. The performances of the CWs increased with increasing age, and in the best growing seasons (between April and September) of the plants. The utilization of in-series design increased BOD5 and TSS removal efficiencies by 12% and 16%, respectively. In conclusions, the high treatment efficiency achieved by average 83% for BOD5 and 90% for TSS presented that the CWs had a high potential as an appropriate technology for dairy farm effluents in cold climates.

Functions of slags and gravels as substrates in large-scale demonstration constructed wetland systems for polluted river water treatment.

The choice of substrates with high adsorption capacity, yet readily available and economical is vital for sustainable pollutants removal in constructed wetlands (CWs). Two identical large-scale demonstration horizontal subsurface flow (HSSF) CWs (surface area, 340m(2); depth, 0.6m; HLR, 0.2m/day) with gravel or slag substrates were evaluated for their potential use in remediating polluted urban river water in the prevailing climate of northwest China. Batch experiments to elucidate phosphorus adsorption mechanisms indicated a higher adsorption capacity of slag (3.15g/kg) than gravel (0.81g/kg), whereby circa 20% more total phosphorus (TP) removal was recorded in HSSF-slag than HSSF-gravel. TP removal occurred predominantly via CaO-slag dissolution followed by Ca phosphate precipitation. Moreover, average removals of chemical oxygen demand and biochemical oxygen demand were approximately 10% higher in HSSF-slag than HSSF-gravel. Nevertheless, TP adsorption by slag seemed to get quickly saturated over the monitoring period, and the removal efficiency of the HSSF-slag approached that of the HSSF-gravel after 1-year continuous operation. In contrast, the two CWs achieved similar nitrogen removal during the 2-year monitoring period. Findings also indicated that gravel provided better support for the development of other wetland components such as biomass, whereby the biomass production and the amount of total nitrogen (TN;43.1-59.0g/m(2)) and TP (4.15-5.75g/m(2)) assimilated by local Phragmites australis in HSSF-gravel were higher than that in HSSF-slag (41.2-52.0g/m(2) and 3.96-4.07g/m(2), respectively). Overall, comparable pollutant removal rates could be achieved in large-scale HSSF CWs with either gravel or slag as substrate and provide a possible solution for polluted urban river remediation in northern China.

Modeling total phosphorus removal in an aquatic environment restoring horizontal subsurface flow constructed wetland based on artificial neural networks.

A horizontal subsurface flow constructed wetland (HSSF-CW) was designed to improve the water quality of an artificial lake in Beijing Wildlife Rescue and Rehabilitation Center, Beijing, China. Artificial neural networks (ANNs), including multilayer perceptron (MLP) and radial basis function (RBF), were used to model the removal of total phosphorus (TP). Four variables were selected as the input parameters based on the principal component analysis: the influent TP concentration, water temperature, flow rate, and porosity. In order to improve model accuracy, alternative ANNs were developed by incorporating meteorological variables, including precipitation, air humidity, evapotranspiration, solar heat flux, and barometric pressure. A genetic algorithm and cross-validation were used to find the optimal network architectures for the ANNs. Comparison of the observed data and the model predictions indicated that, with careful variable selection, ANNs appeared to be an efficient and robust tool for predicting TP removal in the HSSF-CW. Comparison of the accuracy and efficiency of MLP and RBF for predicting TP removal showed that the RBF with additional meteorological variables produced the most accurate results, indicating a high potentiality for modeling TP removal in the HSSF-CW.

Full-scale hybrid constructed wetlands incorporated with an initial anaerobic stage for domestic wastewater treatment in a drinking water catchment area

This study involves sequential treatment of domestic wastewater by anaerobic reactors followed by horizontal (HSSF-CW) and vertical (VSSF-CW) subsurface flow-constructed wetlands. Two full-scale systems constructed in two villages were operated in order to treat domestic wastewaters of about 2,000 and 500 inhabitants. Anaerobic treatment of domestic wastewater served as a pretreatment step before the constructed wetland (CW) systems. Anaerobic pretreatment was performed by an upflow anaerobic sludge bed reactor or an anaerobic baffled reactor. Anaerobically pretreated wastewater was first introduced into parallel HSSF-CWs and then parallel VSSF-CWs before being discharged. Efficient treatment of wastewaters of the two villages was particularly important since they are located in the watershed of a drinking water reservoir. The treatment efficiencies of systems were 88 and 83% for chemical oxygen demand, 89 and 81% for BOD5, 57 and 39% for total nitrogen, 55 and 53% for total phosphorus, 94 and 90% for total suspended solids removal on average, respectively, in Balcik and Orucoglu villages. The effluent concentrations met the discharge limits. The study showed that hybrid CW system with anaerobic pretreatment is an effective method to treat domestic wastewaters of small communities with populations below 2,000.

Constructed wetland with a polyculture of ornamental plants for wastewater treatment at a rural tourism facility

Sewage management in remote rural and mountain areas constitutes a challenge because of the lack of adequate infrastructure and economic capability. Tourism facilities, in particular, possess a special challenge because of huge variability in sewage production and composition as a consequence of variations in number of guests and their activities. Constructed wetlands (CWs) are recognized as a robust and economical ecotechnology capable of meeting these challenges.A horizontal subsurface flow CW system was established at a guest house located in a rural and mountain area of Portugal. The substrate of the bed was an expanded clay substrate, and the system was planted with a polyculture of ornamental flowering plants (Canna flaccida, Zantedeschia aethiopica, Canna indica, Agapanthus africanus and Watsonia borbonica). The load and composition of sewage varied significantly seasonally (17–579kg CODha−1d−1), but removal efficiencies of BOD and COD were generally high (>90%) and independent of the loading conditions. The system also reduced PO43− (up to 92%), NH4+ (up to 84%) and total coliform bacteria (up to 99%). The ornamental polyculture provided an aesthetic pleasing system with different appearance during the seasons. Of the five species tested, four grew well (C. flaccida, C. indica, Z. aethiopica and W. borbonica), whereas A. africanus was outcompeted. The system owner cut flowers from the CW system and used them for decorations at the guest house. It was demonstrated that CW systems planted with a polyculture of ornamental plant species, besides the water treatment function, possess several additional benefits including aesthetics and biodiversity enhancement.

The evaluation of potential purification of a horizontal subsurface flow constructed wetland treating greywater in semi-arid environment

The potential purification of an horizontal subsurface flow constructed wetlands (HSSFCW) treating greywater in a Moroccan primary school was investigated according to the monitoring of water quality parameters over a period of 100 days through two simultaneous stages: first, an internal three dimensional grid of sampling ports; secondly, an entry and exit. The calibration of the relaxed TIS concentration model based on tank in series hydraulic assumption with experimental data gave the frequency distribution profiles of K-rate constant values for the three parameters: BOD5, COD and TN, whose maximum values are respectively 50m/yr, 70m/yr, and 42m/yr. The HSSFCW system has higher K-rate coefficient for all the three parameters at the bottom layer compared with the surface layer, with increasing K-rates over length. The analysis of bacteriological and chemical results has shown that the HSSFCW could not completely remove all pollutants (especially TN and TP), but it could be used successfully to upgrade the quality of greywater to an acceptable level. However, we predict that there will be an increase in removal efficiencies with time bearing in mind that the system is newly implemented.

Removal of nutrients from septic tank effluent with baffle subsurface-flow constructed wetlands

Three new baffle flow constructed wetlands (CWs), namely the baffle horizontal flow CW (Z1), baffle vertical flow CW (Z2) and baffle hybrid flow CW (Z3), along with one traditional horizontal subsurface flow CW (Z4) were designed to test the removal efficiency of nitrogen (N) and phosphorus (P) from the septic tank effluent under varying hydraulic retention times (HRTs). Results showed that the optimal HRT was two days for maximal removal of N and P from the septic tank effluent among the four CWs. At this HRT, the Z1, Z2, Z3 and Z4 CWs removed, respectively, 49.93, 58.50, 46.01 and 44.44% of TN as well as 87.82, 93.23, 95.97 and 91.30% of TP. Our study further revealed that the Z3 CW was the best design for overall removal of N and P from the septic tank effluent due to its hybrid flow directions with better oxygen supply inside the CW system.

Tertiary treatment of abattoir wastewater in a horizontal subsurface flow-constructed wetland under tropical conditions

A horizontal subsurface flow-constructed wetland (HSSF-CW) system planted with Cyperus papyrus was used to polish abattoir wastewater pre-treated in anaerobic and aerobic sequencing batch reactors at City Abattoir, Kampala. The HSSF-CW was 13 m long, 5 m wide, and was filled with gravel up to a depth of 0.6 m, of which 0.55 m was saturated with wastewater at hydraulic retention time (HRT) of 1.16 days. The percentage removals for turbidity, ammonium-nitrogen (NH4-N), total nitrogen (TN), orthophosphate (o-PO4-P), total phosphorus (TP), chemical oxygen demand (COD) and faecal coliform were 76, 48, 46, 74, 63, 60, and 100, respectively. Among different plant tissues investigated (roots, culm, sheath and umbel), nitrogen concentration was highest in the sheath. The different parts of plants also had different concentrations of phosphorus, with the culm having the highest concentration. Compared to literature, the percentage removals for organic matter, nutrients and faecal coliforms reported in this paper were high. Therefore, C. papyrus based constructed wetlands could potentially be used for tertiary treatment of abattoir effluents.

WASTEWATER TREATMENT IN A CONSTRUCTED WETLAND FOLLOWED BY AN OXIDATION POND IN A RURAL AREA OF CHINA

The aim of this study was to examine the pollutant removal performance of a combined process using horizontal subsurface flow constructed wetland (HFCW) and an oxidation pond (OP) in the treatment of a decentralized domestic wastewater. Waters along the water flow and at different depths of the wetland substrate were sampled and analyzed during continuous operation. It was found that the HFCW-OP combined system presented good organic matter and phosphorus removal capacity. In the first year, COD and TP outputs were 30.0 and 0.5 mg/L, respectively. The concentrations of NH3-N and TN decreased notably from 6.3 and16.5 mg/L to approximately 0.2 and 5.0 mg/L after 120 days of operation. This decrease was mainly achieved due to the formation of an anoxic environment in the wetland substrate. After 3 years of operation, however, the wetland showed different degrees of substrate clogging and pollutant accumulation. Although the removal of NH3-N and TN were 88% and 90%, respectively, COD removal decreased from 90% to 78%. By replacing the substrate and vegetation in the last two stages of the wetland and increasing the depth of the oxidation pond from 1.2 to 1.5 m could improve the COD and TP removal capacity of the HFCW-OP system effectively.

Performance Evaluation of the Horizontal Subsurface Flow Constructed Wetland with Ipomoea Aquatica Plant for Rural Domestic Wastewater Treatment

In this study, the performance treatment of horizontal subsurface flow constructed wetland (HSFCW) was evaluated. The HSFCW built as a tertiary treatment process after the biological reactors to improve the effluent quality. The HSFCW system was operated with different hydraulic loading rates (HLRs) ranged from 0.15 to 0.333 m3/ (m2.d) to assess their influence on removal efficiency. During the system operation time, the average temperature was ranged of 22.3 to 31.2 °C and pH ranges was 7.3 – 8.1. The Ipomoea aquatica (Chinese spinach) planted into HSFCW system and the growth parameters during the experimental operation observed. The Ipomoea aquatica growth parameters such as the plant height, a fresh and dry weights were monitored and measured. The influent and effluent of chemical oxygen demand (COD), ammonium nitrogen (NH4-N), total nitrogen (TN) and total phosphorus (TP) were examined. The removal efficiency for all parameters showed decreased with an increase in HLR from 0.15 to 0.333 m3/ (m2.day). The results demonstrated that the average removal efficiency of the COD, NH4-N, TN and TP during system operation is 52.9%, 64.6%, 58.2% and 72.8% respectively. These results confirm that the HSFCW has a good efficient in treatment and can be used for the nutrients and organic matter removal from the domestic wastewater.

The effects of substrate type, HRT and reed on the lead removal in horizontal subsurface-flow constructed wetland

In this research, between June 2013 and October 2013, the effects of three substrate types, hydraulic retention time (HRT), and Phragmites (common reed) on the removal of lead in horizontal subsurface-flow constructed wetlands (CWs) were investigated in the Islamic Republic of Iran. The results showed that the more HRT increased, the more removal efficiency (RE) increased, so that there was a significant difference between RE in sand substrate and retention times of 1, 3, and 5 d (p < 0.05), while no significant difference was observed between 5 and 10 d retention time at 5% level. Moreover, there was a significant difference between retention times of 1 and 3 d in two fine- and medium-gravel substrates (p < 0.05), but no significant difference was observed between retention times of 3, 5, and 10 d at 5% level. Therefore, the best HRT for sand, gravel, and medium-gravel substrate was recommended 5, 3, and 3 d, respectively, with the maximum efficiency of 88.51, 81.53, and 80.35%. The analysis results of substrate type also showed that sand substrate had higher efficiency than the other two substrates. Moreover, the results indicated the root of reed is highly capable of assimilating and accumulating influent lead and plays an important role on the lead removal in horizontal subsurface-flow CW.

Effects of front aeration on the purification process in horizontal subsurface flow constructed wetlands shown with 2D contour plots

Two dimensional (2D) contour plots were used to visualize the effects of front-aeration on the nutrient removal processes in ceramsite-filled horizontal subsurface flow (HSSF) constructed wetlands (CWs) over a 14 month period. Heterogeneous redox conditions (with a high-low-high tendency in the oxidation–reduction potential (ORP) values) along the water flow direction were observed in the aerated CW (ACW). In contrast, the CW without aeration (NACW) was dominated by anoxic or anaerobic conditions. Good nitrogen and phosphate removal efficiencies were obtained with the ACW configuration, which outperformed the NACW configuration. 2D contour plots are convenient for providing an improved understanding of the removal processes in HSSF CWs, which will be helpful for the optimization of CWs.

The impact of a pulsing water table on wastewater purification and greenhouse gas emission in a horizontal subsurface flow constructed wetland

Artificial pulsing of water table is often used in horizontal subsurface flow (HSSF) constructed wetlands (CW) to enhance removal of BOD, COD, NH4 and total N utilization by bacteria. In 2008–2010 and during the experimental session in October–November 2012 we studied the impact of a fluctuating water table on the water purification efficiency and GHG emissions in the 216m2 HSSF bed of a hybrid CW commissioned in 2002 in Paistu, Estonia. For comparison, water purification data from a previous study (Öövel et al., 2007) have been used. Isotopologue studies have been conducted in order to distinguish between denitrification and nitrification as source processes of N2O.Short-term (one month) and short-range (up to 35cm) fluctuations in the water table enhanced CO2 and N2O emission whereas the median values varied from 0.5 to 246μg CH4-Cm−2h−1 and 1.5 to 8.3μgN2O-Nm−2h−1, respectively. There was a significant (p<0.05) negative correlation between water table depth and CO2 (R2=0.53) and N2O (R2=0.35) emissions. Due to the plant cover disturbance in the outflow section of the HSSF bed, CH4 emission did not show any significant difference between the high and low water table phase, and the correlation between water table depth and CH4 emission was positive.The impact of pulsing water table on water purification was minor: high water table enhanced the TOC removal and inhibited the TN removal, whereas the TP concentrations showed remarkable variations but no significant differences between the inflow and outflow values. Likewise, pH and dissolved O2 values, and NH4+-N removal were not significantly influenced by water table manipulations.The value of δ15NbulkN2O, δ18O-N2O and site preference (SP) of N2O in water samples varied from −2 to 32 ‰, between 41 and 78 ‰, and from 15 to 41 ‰, respectively. There was a significant positive correlation between the δ18O-N2O vs SP N2O values (R2=0.77). This correlation, the range of isotopologue values and relatively low N2O emission corroborate that the main source of N2O fluxes in the studied HSSF CW bed is denitrification.

Microbial nitrogen transformation in constructed wetlands treating contaminated groundwater

Pathways of ammonium (NH4 (+)) removal were investigated using the stable isotope approach in constructed wetlands (CWs). We investigated and compared several types of CWs: planted horizontal subsurface flow (HSSF), unplanted HSSF, and floating plant root mat (FPRM), including spatial and seasonal variations. Plant presence was the key factor influencing efficiency of NH4 (+) removal in all CWs, what was illustrated by lower NH4 (+)-N removal by the unplanted HSSF CW in comparison with planted CWs. No statistically significant differences in NH4 (+) removal efficiencies between seasons were detected. Even though plant uptake accounted for 32-100% of NH4 (+) removal during spring and summer in planted CWs, throughout the year, most of NH4 (+) was removed via simultaneous nitrification-denitrification, what was clearly shown by linear increase of δ(15)N-NH4 (+) with decrease of loads along the flow path and absence of nitrate (NO3 (-)) accumulation. Average yearly enrichment factor for nitrification was -7.9 ‰ for planted HSSF CW and -5.8 ‰ for FPRM. Lack of enrichment for δ(15)N-NO3 (-) implied that other processes, such as nitrification and mineralization were superimposed on denitrification and makes the stable isotope approach unsuitable for the estimation of denitrification in the systems obtaining NH4 (+) rich inflow water.

Removal capacity of BTEX and metals of constructed wetlands under the influence of hydraulic conductivity

Constructed wetlands are a natural alternative to technical methods of wastewater treatment. They can remove Benzene, Toluene, Ethylbenzene, Xylenes (BTEX), and metals from wastewater, which are commonly encountered pollutants. In this paper, an experimental pilot-scale Horizontal Subsurface Flow Constructed Wetland (HSFCW) located in Lecce (Apulia, South Italy) has been reported. The experiments were carried out in three constructed wetlands. Two of them were planted with two different species of macrophytes and the third was used as a control. The objectives of this study are to compare hydraulic behavior of the CWs with the trend of the model by varying the hydraulic conditions, to evaluate the effect of the clogging and then to assess the efficiency of the different species of macrophytes in removing BTEX and metals. At the beginning of the experience and after 24 months, the results show a good correlation in the hydraulic behavior between model and physical data by modifying input parameters as a consequence of the clogging. The BTEX removal planted fields is higher than the unplanted one, while the three HSFCWs have a similar capacity in removing Cr, Fe, and Pb.

Salt uptake and evapotranspiration under arid conditions in horizontal subsurface flow constructed wetland planted with halophytes

The use of halophytes in constructed wetlands (CWs) for phytodesalination has been recently suggested as a strategy for dealing with excess salt, which causes land degradation and has detrimental effects on agricultural productivity. Salinity in drylands is enhanced by strong solar radiation and increased evapotranspiration, and poses additional challenges for decentralized water-treatment systems such as CWs. We tested the potential use of a horizontal subsurface flow CW (HSSF CW) planted with the halophyte Bassia indica to polish treated municipal wastewater quality and reduce salinity, using a pilot system containing eight flow cells. The system was operated under continuous flow of synthetic, secondary level-treated wastewater at a rate of 480–660ml/h, which resulted in a retention time of approximately 2 days. Water fluxes, and nutrient and salt concentrations in the water were measured and compared to those in flow cells without plants. Plant height was measured periodically and biomass and salt concentrations were recorded at harvest. Removal of biological oxygen demand, and reduction in fecal coliforms and turbidity were evident and similar in planted and non-planted cells. Significant salt uptake was measured in the planted cells, with the amount of Na+ uptake directly related to plant biomass; however, the overall salinity of the treated wastewater increased despite salt uptake by B. indica due to enhanced evapotranspiration. This study reaffirms the notion that halophytes in CWs have the potential capacity for direct uptake of salts. Nevertheless, efficient salt phytoremediation in arid and semi-arid climates will require specific application of plants and relatively short hydraulic residence time to minimize evapotranspiration.