Horizontal Subsurface Flow Constructed Wetlands Research Articles

Removal Efficiencies of Constructed Wetland Planted with Phragmites and Vetiver in Treating Synthetic Wastewater Contaminated with High Concentration of PAHs

This study aimed to evaluate the capability of horizontal subsurface flow constructed wetlands (HSFCWs) in treating contaminated wastewater with a high concentration of polycyclic aromatic hydrocarbons (PAHs) (Phenanthrene, Pyrene, and Benzo[a]Pyrene), using two plants, namely Phragmites and Vetiver. The investigated parameters were (1) PAHs uptake by the plants, (2) PAHs removal efficiencies, (3) accumulated PAHs in the soil of CWs, (4) shoot/root concentration factor, (5) translocation factor, and (6) PAHs correlation to lipid contains in the plants. During the treatment period, the results showed that the highest concentration of Phenanthrene in the shoot and the root systems of Phragmites, was 229.3 and 192 μg/g; Pyrene was 69.1 and 59.2 µg/g; and Benzo[a]Pyrene 25.1 and 20.2 µg/g, respectively. Meanwhile, in the Vetiver shoot and root systems were Phenanthrene 87.5 and 64.1 µg/g; Pyrene 63.2 and 42.1 µg/g; and Benzo[a]Pyrene 21.3 and 27.3 µg/g, respectively. The removal rates of Phenanthrene, Pyrene, and Benzo[a]Pyrene (PAHs compounds) by the CW planted with Phragmites were found to be 83%, 71%, and 81%, respectively, while the removal rates by CW planted with Vetiver were found to be 67%, 66%, and 73%, respectively. Moreover, the removal rates by unplanted CW were found to be 62%, 58%, and 55%, respectively. The results indicated that the HSFCW planted with Phragmites has an effective pathway to remove high concentrations of PAHs.

Performance of organic substrate amended constructed wetland treating acid mine drainage (AMD) of North-Eastern India

A horizontal subsurface flow constructed wetland (HSSF-CW) was evaluated for the remediation of synthetic acid mine drainage (AMD) using an organic-rich substrate (cow manure and bamboo chips) planted with common cattail. The synthetic AMD simulated the source AMD generated in North Eastern Coalfield of Assam, India. The synthetic AMD was highly acidic (pH < 2.5) and contained heavy metals (Fe, Mn, Al, Co, Ni and Cr) and sulfate (900–1500 mg L–1). HSSF-CW was operated under varying levels of AMD concentration (10, 25, 40, 70 and 100%) during the acclimatization and thereafter continued to operate at full strength AMD at hydraulic retention time of 7 days. After the 6-month experiment, the results suggested the potential application of HSSF-CW due to its ability to raise the pH from 2.1 to 6.4 with the simultaneous removal of metals (except for manganese) and microbial sulfate reduction (44–75%). Metal removal efficiency in the order: chromium (99.7%) > nickel (97.8%) > cobalt (93.7%) > iron (91.6%) > aluminium (59.7%). Toxicity Characteristic Leaching Procedure test (TCLP) study suggested very negligible leachability of chromium for safe disposal. Common cattails exhibited poor bioaccumulation and translocation for all heavy metals except for manganese and cobalt.

Purification Effect of Sequential Constructed Wetland for the Polluted Water in Urban River

Constructed wetlands can play an active role in improving the water quality of urban rivers. In this study, a sequential series system of the floating-bed constructed wetland (FBCW), horizontal subsurface flow constructed wetland (HSFCW), and surface flow constructed wetland (SFCW) were constructed for the urban river treatment in the cold regions of North China, which gave full play to the combined advantages. In the Yitong River, the designed capacity and the hydraulic loading of the system was 100 m3/d and 0.10 m3/m2d, respectively. The hydraulic retention time was approximately 72 h. The monitoring results, from April to October in 2016, showed the multiple wetland ecosystem could effectively remove chemical oxygen demand (COD), ammonia nitrogen (NH4+-N), total nitrogen (TN), total phosphate (TP), and suspended solids (SS) at average removal rates of 74.79%, 80.90%, 71.12%, 78.44%, and 91.90%, respectively. The removal rate of SS in floating-bed wetland was the largest among all the indicators (80.24%), which could prevent the block of sub-surface flow wetland effectively. The sub-surface flow wetland could remove the NH4-N, TN, and TP effectively, and the contribution rates were 79.20%, 64.64%, and 81.71%, respectively. The surface flow wetland could further purify the TN and the removal rate of TN could reach 23%. The total investment of this ecological engineering was $12,000. The construction cost and the operation cost were $120 and $0.02 per ton of polluted water, which was about 1/3 to 1/5 and 1/6 to 1/3 of the conventional sewage treatment, respectively. The results of this study provide a technical demonstration of the restoration of polluted water in urban rivers in northern China.

Efficiency of horizontal subsurface flow-constructed wetlands considering different support materials and the cultivation positions of plant species

The present work evaluated the influence of filling substrate material (crushed PET bottles or fine gravel) on the efficiency of pollutant removal in horizontal subsurface flow constructed wetlands (HSSF-CWs). They were cultivated with a consortium of elephant grass cv. Napier (Pennisetum purpureum Schum) and Tifton 85 (Cynodon spp.) to treat wastewater from a common milk cooling tank (WWMT). For this, six HSSF-CWs were used which had dimensions of 0.6 m tall x 1.0 m wide x 2.5 m long. In order to investigate possible efficiency loss in the removal of pollutants from the system, operation was divided into two periods: Period I (from April to December 2015) and Period II (April to December 2016). Thus, the removal efficiencies of BOD5, solids and total nitrogen (TN), total phosphorus (TP), potassium (K) and sodium (Na) from WWMT were statistically compared. Results indicated that the efficiency of the HSSF-CWs for removing pollutants increased or remained similar after one year and nine months of their operation; and PET bottles were a viable alternative substrate in HSSF-CWs based on the efficient removal of pollutants from WWMT during the one year and nine months of monitoring. Crushed PET bottles constitute a viable substrate for filling HSSF-CWs. Altering the cultivation positions of the plant species did not change pollutant removal efficiencies, but indicates the importance of species arrangement to maximize system performance.

Principal component analysis as a criterion for monitoring variable organic load of swine wastewater in integrated biological reactors UASB, SABF and HSSF-CW

The multivariate analysis to optimize the parameters of wastewater is essential to reduce costs. The aim of this study was to evaluate the use of multivariate and conventional analysis in biological system composed by upflow anaerobic sludge blanket (UASB), submerged aerated biological filters (SABF) and horizontal subsurface flow constructed wetland (HSSF-CW) reactors in the organic stabilization of swine wastewater (SW). Four loads were used in the system with alteration by COD concentration of untreated SW, and the data were evaluated by principal components (PCA). The average efficiency of COD and BOD removal increased from 45% in phase I to 67% in phase IV in the UASB, SABF and HSSF-CW reactors. The principal component analysis promoted the reduction of 13 original variables to 5, 8 and 5 principal components in the UASB, SABF and HSSF-CW reactors, respectively, optimizing the dynamics of interpretation of the data that influenced the most the stability of the wastewater system across the four phases. There was a strong negative effect of oxygen concentrations in the SABF reactor in relation to organic variables, optimizing the biological mechanisms of the HSSF-CW and, therefore, enabling better decision making and cost reduction with analysis at treatment plants.

Evapotranspiration of the Vetiver and Tifton 85 grasses grown in horizontal subsurface flow constructed wetlands

Estimation of the Crop Evapotranspiration (ETC) in Horizontal Subsurface Flow Constructed Wetlands (HSSF-CWs) is of great importance for hydrological modeling of these systems. The objective of this work was to obtain the Crop Coefficient (KC) values of Vetiver (Chrysopogon zizanioides) and Tifton 85 (Cynodon spp.) grasses when grown in HSSF-CWs whose porous medium was saturated with solutions containing different nutrients concentrations. The water balance was performed every day in order to determine the KC of the grasses. It was verified that the KC values of the Vetiver grass were independent of the nutrient availability, expressed in terms of Electrical Conductivity (EC) of the nutrient solution. The KC value in the initial growth phase (Phase I) was 0.99, independent of the seasons. In Phase II, the KC were 0.95 and 1.36 for autumn and spring, respectively, and for Phase III were 1.12 in autumn and 1.60 in spring. In relation to the Tifton 85 grass, the KC values showed a quadratic behavior as a function of the EC, where the KC estimation models were obtained by the cluster analysis in Phase II and III. For Phase I, the KC value was 1.17, independent of the EC and the time of year.

Intensified nitrogen removal in constructed wetlands by novel spray aeration system and different influent COD/N ratios

The degradation performance of organic matters and microorganism abundance variations of two horizontal subsurface flow constructed wetlands (HSSFCWs) with different influent COD/N ratios and a spray aeration system were investigated. Oxygen-enriched influent water was beneficial to enhance the abilities of nitrification and biodegradation of organic matters. Due to the sufficient carbon source supply under influent COD/N ratio of 8.0, the high removal performances of COD (93%), NH4-N (85%) and total nitrogen (78%) were simultaneously obtained in HSSFCWs with a spray aeration system. The increase in nitrite and nitrate bacteria was beneficial to complete nitrification and improve NH4-N removal. The increase in denitrifying bacteria contributed to complete denitrification and guaranteed the high removal efficiency of NO3-N. The results suggested that the spray aeration combined with high influent COD/N ratios could achieve the high nitrogen removal in HSSFCWs.

Treatment of WASTEWATER from the Tannery Industry in a Constructed Wetland Planted with Phragmites australis

Constructed wetlands (CWs) can remove a high amount of pollutants from wastewater, and therefore play an important role in water purification. In this study, a pilot system to improve the traditional treatment of industrial wastewater from the tannery industry was tested. The main objective of this research was to remove nitrogen, phosphorus, boron, and chromium from a tannery’s industrial wastewater using a horizontal subsurface flow constructed wetland (HSSFCW) formed from three cells, planted with Phragmites australis and operated in batch mode as an ecofriendly system. P. australis was selected due to its ability to adapt to climatic conditions, its wetland and management characteristics, and its high capacity for pollutant absorption. The concentrations of total Kjeldahl nitrogen (TKN), total phosphorus (TP), boron (B), and chromium (Cr) were analyzed in both wastewater and purified water, and the removal efficiencies were calculated. In addition, both the absorption capacity of P. australis in the aerial and root parts and the adsorption capacity of substrates (gravel and washed sand) were analyzed. Results showed that the concentrations of TP and Cr decreased in the wastewater at both hydraulic retention times (HRTs) tested (3 and 7 days), with 3 days being the most effective, showing removal efficiency values of 78% and 48% for TP and Cr, respectively. However, concentrations of TKN and B were not statistically reduced at either HRTs. Regarding the absorption capacity of P. australis, the highest absorption efficiencies for TKN and TP were reported at 7 days in the aerial part of the plants. In contrast, B was retained in roots at HRT of 3 days. Finally, Cr was more significantly absorbed at 3 days by P. australis. Moreover, the substrates also played important roles in the adsorption of nitrogen and boron. Therefore, CWs planted with P. australis could be used as an ecofriendly technique to the reduce pollution load of the wastewater from tannery industry, especially for P and Cr, although in order to increase the removal efficiency of B and N, the combination with other plant species and different retention times should be tested.

A novel pilot and full-scale constructed wetland study for glass industry wastewater treatment

Industrial wastewaters represent a serious threat to the environment due to their variable and complex composition. Though mostly mechanical systems are used for treatment of such wastewater, there is growing need for sustainable and cost-effective solutions, especially in low-income regions. In this study, a horizontal sub-surface flow Constructed Wetland (HSFCW) system was used for the first time to treat wastewater from a glass manufacturing industry in Iran. In order to de-risk the treatment approach, a pilot system consisting of a settling tank and a HSFCW was first tested for 4 months. The results of the pilot study were then used to build the full-scale CW system treating 10 m³/day. In general, the tested design proved to be very effective reaching high removal rates of BOD5, COD, and TSS (90, 90, and 99, respectively), as also for TN and TP (>90%). The high efficiency of the tested system allowed for the recycle and reuse of the treated effluent in the glass manufacturing processes, reducing this way the fresh water consumption in the glass industry and the related operational costs.

Identification of benzene-degrading Proteobacteria in a constructed wetland by employing in situ microcosms and RNA-stable isotope probing.

Constructed wetlands (CWs) are effective ecological remediation technologies for various contaminated water bodies. Here, we queried for benzene-degrading microbes in a horizontal subsurface flow CW with reducing conditions in the pore water and fed with benzene-contaminated groundwater. For identification of relevant microbes, we employed in situ microcosms (BACTRAPs, which are made from granulated activated carbon) coupled with 13C-stable isotope probing and Illumina sequencing of 16S rRNA amplicons. A significant incorporation of 13C was detected in RNA isolated from BACTRAPs loaded with 13C-benzene and exposed in the CW for 28days. A shorter incubation time did not result in detectable 13C incorporation. After 28days, members from four genera, namely Dechloromonas, Hydrogenophaga, and Zoogloea from the Betaproteobacteria and Arcobacter from the Epsilonproteobacteria were significantly labeled with 13C and were abundant in the bacterial community on the BACTRAPs. Sequences affiliated to Geobacter were also numerous on the BACTRAPs but apparently those microbes did not metabolize benzene as no 13C label incorporation was detected. Instead, they may have metabolized plant-derived organic compounds while using the BACTRAPs as electron sink. In representative wetland samples, sequences affiliated with Dechloromonas, Zoogloea, and Hydrogenophaga were present at relative proportions of up to a few percent. Sequences affiliated with Arcobacter were present at < 0.01% in wetland samples. In conclusion, we identified microbes of likely significance for benzene degradation in a CW used for remediation of contaminated water.

Application of an innovative front aeration and internal recirculation strategy to improve the removal of pollutants in subsurface flow constructed wetlands

The pollutant removal performance of traditional horizontal subsurface flow (HSSF) constructed wetlands (CWs) is limited because of the dissolved oxygen (DO) supply is insufficient. The aeration of HSSF CWs usually improves their pollutant removal performance, but a high DO induces the accumulation of nitrate-nitrogen (NO3−-N) and suppresses the improvement of total nitrogen (TN) removal. In this study, an integrated solution that involved in-tank front aeration and internal recirculation (FAIR) was used to improve the pollutant removal performance of HSSF CWs. Based on the experimental results, the FAIR system significantly increased the removal efficiencies of biochemical oxygen demand (BOD) from 53.8–76.0% to 82.0–91.7% and reduced the BOD concentration in the effluent to below 10 mg L−1. The removal efficiency of ammonia-nitrogen (NH3–N) increased from 15.1–78.3% to 98.5–98.6% while the removal efficiencies of the total Kjeldahl nitrogen (TKN) of the control and FAIR HSSF CWs were 18.2–77.1% and 93.5–94.3%, respectively. HSSF CWs with FAIR outperformed aerated HSSF CWs in the removal of NH3–N and TKN. The effects of two recirculation flow ratios (Rr = recirculation flow rate/influent flow rate), 14.3 and 3.0, on the improvement of pollutant removal performance were investigated. The lower Rr did not significantly affect the improvement of BOD, NH3–N, and TKN, but a higher Rr resulted in more severe accumulation of NO3−-N. The removal efficiency of TN in control HSSF CWs ranged from 20.4% to 75.5%, and in the FAIR HSSF CW was 71.6% for Rr = 14.3 and 81.3% for Rr = 3.0. However, the FAIR system did not enhance the removal performance of total phosphorus, suggesting that the DO level and internal recirculation were not dominant mechanisms for the removal of phosphorous. The easy maintenance of the FAIR system made it a superior modification for improving the pollutant removal performance of HSSF CWs.

Strengthening Effect of Different Cattail Pretreatment Methods on the Denitrification of Horizontal Subsurface Flow in a Constructed Wetland

Nitrogen removal in constructed wetlands (CWs) is highly affected by the supply of organic carbon. Thus, to enhance nitrogen removal in the horizontal subsurface flow of CWs, plant carbon sources were added during the downstream portion of the wetland. Moreover, the characteristics of static release and the denitrification potential of Typha were evaluated using three different pretreatment methods (i.e., minced, acid-heated, and alkali-heated). The average concentrations of COD released and the nitrate removal rate with the alkali-heated, acid-heated, and minced Typha were 89.57 mg·L-1 and 75.2%, 67.27 mg·L-1 and 67.2%, and 54.45 mg·L-1 and 23.5%, respectively. The results showed that different pretreatment methods resulted in the release of different amounts of acetic acid, and the alkali-heated Typha performed much better than the other pretreatments. Therefore, the alkali-heated Typha was selected and added to the middle of the horizontal subsurface flow CW, which improved the nitrogen-removal rate significantly; the average removal rate of TN and TP was higher than that of a control CW by 30.3% and 33.9%, respectively. However, the COD concentration of the CW with the alkali-heated Typha was not significantly increased.

EXTRACTION CAPACITY OF GRASSES GROWN IN CONSTRUCTED WETLAND SYSTEMS USING DIFFERENT ARRANGEMENTS AND SUBSTRATES

ABSTRACT Constructed wetland systems have been used to treat different wastewater; among their essential components are the cultivated plant species and type of substrate used to fill them. The choice of plant species and type of substrate are important for the good system performance in wastewater treatment. This study aimed to evaluate the extraction capacity of Napier and Tifton 85 grasses when cultivated at different positions in horizontal subsurface flow constructed wetlands (HSSF-CWs) filled with different substrates in wastewater treatment from a bulk milk-cooling tank (MTWW). The experimental unit consisted of four HSSF-CWs, in which an average surface organic loading rate of 318 kg ha−1 d−1 of BOD5,20 was imposed and a hydraulic holding time of 1.8 and 3.0 d, respectively, in units filled with gravel or crushed PET bottles. Tifton 85 grass presented the highest Na extraction capacity, with better results obtained in HSSF-CWs filled with crushed PET bottles, while Napier grass was more effective in extracting N, K, and P from MTWW. When cultivated in the second half of gravel-filled HSSF-CWs, both grasses provided higher average N extractions when compared to those filled with crushed PET bottles, which had higher extractions in the first half of HSSF-CWs.

Relationship between microbial community and environmental conditions in a constructed wetland system treating greywater

Knowledge of the diversity of microbial communities and their relationship with biogeochemical cycles is a key factor in understanding and improving the performance of constructed wetland (CW) systems, allowing improvements in design and operation methods to reach the desired effluent quality. Assemblies of microbial groups in CWs are driven by several factors, including the environmental conditions of the mesocosm and substrate availability. This study combined physicochemical analyses, high-throughput DNA sequencing, and statistical methods to gain an insight into the influence of operational conditions on the bacteria and archaea communities in a modified constructed wetland system treating raw-light greywater. The EvaTAC system is composed of an upflow evapotranspiration and treatment tank (CEvaT) which has an inbuilt anaerobic chamber (AnC), followed by a horizontal subsurface flow constructed wetland (HSSF-CW). Samples were collected after five years of system operation in both units: sludge from the AnC, coarse gravel from the CEvaT, and fine gravel from the CW. The results showed that the system operated predominantly in anaerobic conditions, with redox potential (Eh) increasing from the inlet (−364.1 mV) to the outlet (−240.4 mV) zone. The Eh was the environmental condition that most influenced the microbial community diversity and richness, and, as well as Eh, increased along the light greywater (LGW) flow. Conversely, the chemical oxygen demand (COD) decreased, thus suggesting a negative correlation among these factors. The clustering analyses of microbial community showed that, besides environmental conditions, the media filter and related depth could also be drivers of microbial community composition. The bottom layer of CEvaT was assigned to the Proteobacteria and Synergistetes phyla indicating the accomplishment of the first steps of anaerobic digestion. The next layer was characterised by the presence of Desulfovibrio, Syntrophobacter, and Methanobacterium, microorganisms responsible for the sulfidogenesis and methanogenesis processes. Finally, in the CW zone, the community composition was dominated by microorganisms involved in the methane oxidation, such as Methylosinus, Bradyrhizobium, and Candidatus Koribacter. This study explored the universe of bacteria and archaea communities, and is an initial step in elucidating microbial diversity conversions in CW systems treating greywater, which is important knowledge to steer the conversion pathway and establish the ideal environmental conditions for the development of desired microbial communities in these systems.

Performance of horizontal sub-surface flow constructed wetlands with different flow patterns using dual media for low-strength municipal wastewater: a case of pilot scale experiment in a tropical climate region

The work presented in this paper is based on the pilot study that was performed to investigate the role of flow pattern in the constructed wetlands (CWs) on the treatment performance of real low-strength municipal wastewater. Four identical pilot-scale horizontal sub-surface flow constructed wetlands (HSSF-CWs) were installed, out of which three beds were planted with a common macrophyte, whereas one was kept as a control. The distinction in the hydraulic design was baffles, vertical up-down (CW2) and side slits (CW3), and the third bed (CW1) was kept horizontal plain type (without baffles). The filter media used in all the beds was dual type, coarse and fine gravel. Monitoring was carried out to determine BOD5, COD, TSS, NH4+-N, TN, and TP concentrations at different sampling points. Results show that the baffled beds performed better compared to the non-baffled in the order of CW2 > CW3 > CW1 > Control. The highest removal efficiency was measured in the CW2 with a reduction in BOD5 (86%), COD (77%), TSS (80%), NH4+-N (59%), TN (66%), and TP (64%). The statistical method used also showed that the flow pattern has an impact on the treatment performances of the CWs.

Hydraulic performance evaluation of a quasi-two dimensional constructed wetland microcosm using tracer tests and Visual MODFLOW simulation

Hydraulic conditions of constructed wetlands (CWs) are crucial to pollutant removal and are influenced by factors such as influent loading rates, influent or effluent position or porous media size. The performance evaluation of CWs in real application, however, is difficult and a visualization analysis is difficult due to the black-box effect. In this paper, a nonopaque microcosmic horizontal subsurface flow constructed wetland (HSSFCW) reactor was built in the laboratory for an efficient and intuitive assessment of the influences of such parameters on the hydraulic performance of CWs. Chloride tracer tests were carried out to obtain parameters on hydraulic performance by considering hydraulic loading rates and different flow inlet-outlet configurations, while dye tracer tests were designed for the visualization of solute transport and diffusion. In parallel, an identical design of the HSSFCW reactor was modeled using the Visual MODFLOW (VM) software in order to detect the tracer movement and solute concentration field. Results show that the inflow rate and the inlet-outlet configuration have significant impacts on the hydraulic performance of a CW influencing RTD curve shape, flow path, dead zone distribution and hydraulic efficiency. The dead zone and flow path have been visualized and analyzed by comparing the dye tracer experiments of VM solute concentration field and particulate path-line tracking. In addition, the feasibility and reliability of the VM simulation has been verified. The application of VM in this study has been robust indicating a possible application for further investigations on the influencing factors of real CWs.

Nitrogen removal in integrated anaerobic\u2013aerobic sequencing batch reactors and constructed wetland system: a field experimental study

A study was conducted to assess the performance of an integrated system consisting of an anaerobic digester (AD), an aerobic sequence batch reactor (ASBR), and three horizontal subsurface flow constructed wetlands (HSSFCWs) vegetated with the perennial grass Phragmites karka for removal of nitrogen in tannery wastewater. Nine grab wastewater samples were collected weekly between September and December 2016 from the influent and effluent at each unit of operation of the plant and analyzed for physicochemical parameters. The AD removed 67% of oxidized nitrogen (NOX–N); the removal was improved to 76% in the ASBR with a further aeration period in the HSSFCWs, and the NOX–N removal efficiency improved progressively to 96%. The removal efficiency for nitrate (NO3–N) was 82% and for nitrite (NO2–N) 88%; for ammonium (NH4–N) removal efficiency was 77% higher in the HSSFCWs compared to the AD and the ASBR. Despite the considerable percentage of NO3–N removed, in the effluent was above the country’s permissible limit (39.3 mg/l). The high concentration might be due to a weaker denitrification process in HSSFCWs caused by lack of carbon and external organic sources in the wastewater sufficient to carry out the process. The results suggest that the addition of supplementing carbon sources (methanol, sugars, or volatile fatty acids) to the effluent would achieve better performance. Based on these findings, the application of combined anaerobic/aerobic system connected with constructed wetlands process allows the achievement of higher efficiency in removing nitrogen compared to the use of an anaerobic, aerobic, or constructed wetland system along.

Influence of the substrate type and position of plant species on clogging and the hydrodynamics of constructed wetland systems

The present work evaluated the influence of the filling substrate material, the presence of plants and position of plant species on the saturation and hydrodynamic behavior in horizontal subsurface flow constructed wetlands (HSSF-CWs). For this, six HSSF-CWs were used which differed with regards to the type of substrate (gneiss gravel or crushed PET bottles), presence of plant species and their position (consortium between Tifton 85 grass and elephant grass). For the treatment of wastewater from a milk cooling tank (WWMT), it was observed that there was a higher solids concentration and a greater extent of runoff in HSSF-CWs cultivated and filled with gravel after one year and eight months of operation, which was due the contribution of solids, resulting from substrate wear and the presence of the root entanglement. Crushed PET bottles may be a viable alternative substrate in HSSF-CWs because they are inert, present low wear and contribute fewer to pore clogging solids. It was observed that the sequence of plant species also influenced the runoff length, having greater extent of surface flow in units with elephant grass followed by Tifton 85 grass. Despite the higher solids concentration and greater surface flow, the beds filled with gravel and cultivated with the plants showed better hydrodynamic conditions than the other treatments, which indicates the importance of analyzing the characteristics of the solids and the effect of pore space expansion by the roots.

Removal efficiency of nitrate, phosphate, fecal and total coliforms by horizontal subsurface flow-constructed wetland from domestic wastewater

Background: Constructed wetlands are systems designed based on the utilization of natural processes, including vegetation, soil, and their associated microbial assemblage to assist in treating different types of wastewater. Methods: Two local Appalachian plants (Louis latifolia and Phragmites australis) were planted into smallscale constructed wetlands to treat domestic wastewater in the North of Iran. The influent wastewater and the effluent from each wetland were sampled daily for 120 days. Experiments were conducted based on the mean ± standard deviation (SD) by analysis of variance (ANOVA). Results: It was found that nitrate, phosphate, fecal and total coliforms were reduced by 84.4%, 94.4%, 96.3%, 93.9% for P. australis and 73.3%, 64.0%, 94.4%, 92.1% for L. latifolia, respectively. Conclusion: According to the results, by using the HF-CW technology with L. latifolia and P. australis plants, the treated wastewater fully meets the wastewater discharge parameters of WHO standards.

Nutrient removal in hybrid constructed wetlands: spatial-seasonal variation and the effect of vegetation.

Constructed wetlands (CWs) are an aesthetic and sustainable form to treat wastewater, however, their performance can be increased by improving a number of factors. The pilot-scale hybrid constructed wetland (CW) system was the combination of constructed floating treatment wetlands (CFWs) and horizontal subsurface flow constructed wetlands (HSFCWs); operated for a year and covered all seasons. The research was conducted to investigate the performance of the CW system regarding water depth, spatial, and seasonal removal of pollutants. Nine economical plants species were selected and divided into four groups to grow in CW-I to CW-IV, respectively. Removal increased along the bed and most of the total phosphorus (TP) removal occurred in the second bed, whereas total nitrogen (TN) and ammonium (NH4) removal were associated with the plant root system and biomass. Optimum removal of nutrients with respect to water depth was at 35 cm. TN and NH4 removal patterns were similar in different CWs. TN and NH4 removal were higher during summer compared to winter; only CW-IV showed the opposite trend.