Free Water Surface Wetland Research Articles

Design and Season Influence Nitrogen Dynamics in Two Surface Flow Constructed Wetlands Treating Nursery Irrigation Runoff

Constructed wetlands (CWs) are used to remediate runoff from a variety of agricultural, industrial, and urban sources. CW remediation performance is often evaluated at the laboratory scale over durations less than one year. The purpose of this study was to characterize the effect of CW design (cell depth) and residence time on nitrogen (N) speciation and fate across season and years in two free water surface wetlands receiving runoff from irrigated plant production areas at an ornamental plant nursery. Water quality (mg·L−1 of nitrate, nitrite, and ammonium, dissolved oxygen and oxidation reduction potential) was monitored at five sites within each of two CWs each month over four years. Nitrate-N was the dominant form of ionic N present in both CWs. Within CW1, a deep cell to shallow cell design, nitrate comprised 86% of ionic N in effluent. Within CW2, designed with three sequential deep cells, nitrate comprised only 66% of total N and ammonium comprised 27% of total N in CW2 effluent. Differences in ionic N removal efficacies and shifts in N speciation in CW1 and CW2 were controlled by constructed wetland design (depth and hydraulic retention time), the concentration of nutrients entering the CW, and plant species richness.

Two variable residence time-based models for removal of total phosphorus and ammonium in free-water surface wetlands

This paper presents two powerful and productive models, called VART-TP model and VART-NH4 model, for simulating the removal processes of total phosphorus (TP) and ammonium (NH4+), respectively, in constructed wetlands with free water surface (FWS). A distinctive feature of the models is the incorporation of a dynamic diffusion-dominated root-zone. The VART-TP model was tested with data collected from four small test cells of constructed wetlands (TCW) planted with submerged aquatic vegetations in south Florida, USA. The test cells were divided into two groups with the north test cells (N1 & N15) receiving an average phosphorus (TP) concentration of 71μg/l and the south test cells receiving an average TP concentration of 27μg/l. Testing results showed that root mean square error (RMSE) of the VART-TP model varied in the range of 4.45-17.50μg TP/l., respectively, for north test cells while the RMSE ranged between 3.58-7.63μg TP/l for south test cells. The result suggested that (1) the N1 and N15 test cells receiving high TP concentrations are capable of removing TP with high efficiency and (2) the VART-TP model is capable of simulating the removal processes of TP. The VART-NH4 model was tested with data collected from Lake Manzala Engineered Wetland (LMEW), Egypt, which generally received the influent of high ammonia concentration (average=2.26mg NH4/l). The testing results showed that the NH4+ concentrations simulated with the VART-NH4 model were in reasonable agreement with those monitored at the wetland outlet, as indicated with the RMSE of 0.06mg/l. The results demonstrated that the VART-TP and VART-NH4 models are reliable and efficient modeling tools for designing constructed wetlands.

BTEX removal in a modified free water surface wetland

A pilot scale free water surface (FWS) wetland with provision of additional intermediate berms composed of gravel material was tested for assessing its potential to remediate hydrocarbons present in produced water from a gas field. The average influent BTEX values were as follows: benzene (1.57mg/L), toluene (0.14mg/L), ethyl benzene (0.29mg/L), m and p-xylene (2.01mg/L) and o-xylene (0.13mg/L). The FWS wetland removed all monitored hydrocarbons with very good removal efficiencies during the monitoring period: benzene (92.6%), toluene (93.4%), ethyl benzene (98.3%), m and p-xylene (91.3%) and o-xylene (87.4%). Biodegradation was considered to be the main pathway for benzene removal in the studied system. Reaction kinetics were studied and the first-order area based rate coefficient for benzene was 0.13m/d while for BTEX it was 0.12m/d. Metagenomic analysis of bacterial community retrieved from the wetland showed majority of sequences were related to phylum proteobacteria.

Removal of organic carbon, nitrogen, emerging contaminants and fluorescing organic matter in different constructed wetland configurations

The elimination of organic carbon, nitrogen, five emerging organic contaminants (EOCs) and fluorescence signature was evaluated in two treatment lines comprising different constructed wetland (CW) configurations: (i) partially saturated vertical subsurface flow (SVF) wetland (treatment line 1) and (ii) unsaturated vertical subsurface flow (UVF), horizontal subsurface flow (HF) and free water surface (FWS) wetlands in series (treatment line 2). Results showed important differences between the different CW configurations. The highest removal of BOD5 (81%), COD (67%), TOC (72%) and fluorescing organic matter were observed in the UVF wetland, whereas the HF and FWS wetlands were the most efficient units for total nitrogen removal (60 and 69%, respectively). The SVF wetland showed a greater performance in the reduction of total nitrogen than the UVF bed (52 vs. 35%). In addition, the SVF wetland exhibited a higher removal of the EOCs caffeine (95 vs. 90%), trimethoprim (99 vs. 87%) and sulfamethoxazole (64 vs. 4%), as opposed to DEET (34 vs. 63%), whose removal was superior in the UVF unit. Sucralose was negligibly removed in all the CWs. PARAFAC analysis of fluorescence measurements revealed that the proteinaceous tryptophan-like fluorescent component was the most highly removed one in all the investigated CWs (>28%) and, particularly, in the UVF wetland (66%), whereas humic and fulvic-like components resulted recalcitrant to decomposition. Increases of fluorescence intensities were often observed for fulvic-like substances in CWs operating with saturation of the bed, and these were particularly relevant in the SVF unit. Finally, important correlations (r>0.7) between the tryptophan-like fluorescent component and the wastewater quality parameters COD and BOD5 suggest fluorescence spectroscopy asan useful monitoring tool for water treatment efficiency in CW systems.

Enhancement of total nitrogen removal through effluent recirculation and fate of PPCPs in a hybrid constructed wetland system treating urban wastewater.

The effect of effluent recirculation on the removal of total nitrogen (TN) and eight pharmaceuticals and personal care products (PPCPs) was evaluated during 9months in an experimental hybrid constructed wetland (CW) system applied in the treatment of urban wastewater. An Imhoff tank was followed by three stages of CWs (two 1.5-m2 vertical subsurface flow (VF) beds alternating feed-rest cycles, a 2-m2 horizontal (HF) and a 2-m2 free water surface (FWS) wetland in series). A fraction of the final effluent was recycled back to the Imhoff tank with a recirculation rate of 50% (hydraulic loading rate=0.37md-1). The system's performance varied throughout the study. In Period I (summer) consistently high load removal efficiencies of TN (89±5%) and a removal rate of 6.6±1.4gTNm-2d-1 were exhibited. In Period II (fall), the poor performance of the FWS during the senescence of macrophytes caused a large increase in organic matter, solids and nutrient concentrations, drastically deteriorating water quality. The determination of PPCPs was conducted during this period. Recalcitrant compounds, namely sulfamethoxazole, carbamazapine, TCEP and sucralose were negligibly removed in all CWs. However, noteworthy was the ≈30% removal of sucralose in the VF wetland. Caffeine (80%) and fluoxetine (27%) showed similar elimination rates in both VF and HF units, whereas trimethoprim and DEET were significantly better removed in the VF than in the HF. The concentration of the four latter compounds showed a severe increase in the FWS, indicating possible desorption from the sediment/biomass during adverse conditions. Harvesting of the aboveground biomass in this unit returned the system's performance back to normality (Period III), achieving 77±7% TN removal despite the winter season, proving effluent recirculation as an effective strategy for TN removal in hybrid CW systems when stringent restrictions are in place.

Variable residence time-based model for BOD removal in free-water surface wetlands

Constructed wetlands have been increasingly used for treatment of secondary wastewater containing various contaminants. This paper presents a Variable Residence Time (VART)-based model, called VART-BOD model, for simulation of BOD removal processes in constructed wetlands with free water surface (FWS). Mathematically, the VART-BOD model describes a free water surface wetland with three vertical layers, including vegetated water column layer, advection-dominated upper root layer, and diffusion-dominated lower root layer. Biogeochemically, the VART-BOD model simulates various BOD removal processses and mechanisms, including monod kinetics of bacterial growth, mass exchange between water column and root layers, advection, dispersion, and diffusion. A unique feature of the VART-BOD model is the incorporation of a dynamic diffusion-dominated root-zone. The VART-BOD model was tested with data collected from two distinct FWS wetlands: Gustine Wetland, USA and Manzala Wetland, Egypt. Testing results showed that the coefficient of determination (r2) and root mean square error (RMSE) values vary in the ranges of 0.73–0.99 and 0.41–8.70mg/L, respectively, for Gustine Wetland cells while r2=0.98 and RMSE=0.72mg/L for Manzala Wetland. The VART-BOD model is a reliable and efficient tool for designing constructed wetlands and for understanding effects of various processes and mechanisms on the treatment efficiency of wastewater in constructed wetlands.

Effects of different substrates in the mitigation of algae-induced high pH wastewaters in a pilot-scale free water surface wetland system.

Waste stabilization ponds (WSPs), as part of municipal wastewater treatment strategies, can exhibit variability in performance due to climatic conditions. Under elevated temperature and strong solar radiation, algal blooms and subsequent high pH effluents have often been observed. In this study, four substrates (gravel, peat, organic mulch, and topsoil) were evaluated for their ability to attenuate high pH effluents from a WSP. Synthetic wastewater with pH > 9.5, and low organic and nutrient loadings, was used to mimic algal-induced high pH effluents in 72 L rectangular bench-scale superficial constructed wetland configuration reactors. Peat exhibited the highest attenuation ability, where the effluent pH decreased substantially from 10.3 to 7.7, primarily due to its high organic contents. Peat also removed 53.7% of the influent total phosphorus, which could effectively limit algal growth. No statistically significant differences were discovered among gravel, topsoil, and organic mulch in terms of pH attenuation. Topsoil and organic mulch both have a relatively high alkalinity, making them ideal to maintain consistent pH levels. However, naturally high chemical oxygen demand levels in organic mulch raised concerns in the leaching of these compounds into the treated wastewater, making it less appealing for systems with low organic loading.

Long-term performance of two free-water surface wetlands for metallurgical effluent treatment

The aim of this study was to evaluate the efficiency of two constructed wetlands (CW1 and CW2) for the wastewater treatment of metallurgical industries and determine if contaminants are retained by the sediment or the plants, key knowledge for suitable wetland management. Both systems are free water surface CWs and were designed to treat industrial wastewater (with high pH and salinity containing Cr, Ni and Zn) and sewage together. Wastewaters receive a primary treatment before reaching the wetlands. CW1 and CW2 have been operating for 14 and 7 years, respectively. Wastewater, sediment and plants were sampled monthly in the inlet and outlet zones of both CWs. In both CWs, removal efficiencies were satisfactory. T. domingensis, the dominant species, is tolerant to metallurgical wastewaters and efficient in metal accumulation. Metals and P were efficiently removed in both CWs, being metals retained mainly in sediment, and P was retained in sediment and plants of the inlet zone. Metal concentration in macrophyte tissues is related to influent concentration while metal concentration in sediment depends not only on influent concentration but also on the time of operation of the CWs. Metals are bound to sediment fractions that can be considered steady under chemical and environmental conditions of the wetlands. Since the conditions for metal removal are largely provided by the influents (high pH, alkalinity, Fe, Ca and ionic concentrations), the sediment will continue retaining metals as far as the composition of the influents remain the same.

An integrated sewage treatment pond-wetland challenges conventional process treatment performance

This paper presents a case example showing how integrating a constructed free water surface (FWS) wetland with sewage treatment ponds system can deliver effluent quality results that rival conventional sewage treatment plants (STP). Treatment ponds, commonly used in regional and remote communities, provide low cost and operationally simple wastewater treatment. Despite the benefits of sewage ponds, many systems struggle to achieve modern environmental standards. This paper focuses on the treatment performance of a pond-wetland STP throughout the initial 15-month establishment period of a 2,000 sqm FWS wetland at Helidon Queensland, Australia. The pre-existing STP comprised a two-stage pond with chlorination. In 2013, a two-cell FWS wetland was built to achieve long-term licence compliance at the STP for biological oxygen demand (BOD), total suspended solids (TSS) and pH. Post establishment, the effluent quality out of the wetlands was BOD <10 mg/L; SS < 20 mg/L; pH of 7–8 despite the influent BOD and TSS levels being well above the values used for the system's design. This paper demonstrates that FWS wetlands can easily integrate into existing or new sewage pond systems to deliver high quality and reliable treatment outcomes.

Effects of interspecific competition on the growth of macrophytes and nutrient removal in constructed wetlands: A comparative assessment of free water surface and horizontal subsurface flow systems

The outcome of competition between adjoining interspecific colonies of Phragmites and Typha in two large field pilot-scale free water surface (FWS) and subsurface flow (SSF) CWs is evaluated. According to findings, the effect of interspecific competition was notable for Phragmites australis, whereby it showed the highest growth performance in both FWS and SSF wetland. In a mixed-culture, P. australis demonstrates superiority in terms of competitive interactions for space between plants. Furthermore, the interspecific competition among planted species seemed to cause different ecological responses of plant species in the two CWs. For example, while relatively high density and shoot height determined the high aboveground dry weight of P. australis in the FWS wetland, this association was not evident in the SSF. Additionally, while plants nutrients uptake accounts for a higher proportion of the nitrogen removal in FWS, that in the SSF accounts for a higher proportion of the phosphorous removal.

An investigation into the relationship between water quality volume (design storage volume) and stormwater wetland performance.

An investigation on free water surface wetland, which has an area of 0.23 ha and is employed to control the non-point source pollution from a watershed of 7.4 ha, was carried out to examine how the WQvr (the ratio of stormwater inflow volume to water quality volume (WQv)) affects the wetland treatment performance. As stormwater went through the wetland, TSS (total suspended solids), TCOD (total chemical oxygen demand), TN (total nitrogen) and TP (total phosphorus) were reduced by 85%, 57%, 6% and 68%, on average, respectively. Increase in the WQvr resulted in a decrease in the reduction efficiencies of TSS, TCOD and TP, but a slight increase in TN removal. WQv was identified as a useful parameter for the design of stormwater wetlands, as this volumetric design approach overcomes the variation in flow rate and pollutant concentrations with respect to time and rainfall conditions. However, the design goal of 80% TSS reduction was not accomplished as inflow water volume equal to designed WQv. On the other hand, it was found that TCOD and TP reduction could also be considered as wetland design goals together with TSS. However, TN reduction did not show any significant relationship with the WQv.

Soil and phosphorus accretion rates in sub-tropical wetlands: Everglades Stormwater Treatment Areas as a case example

Wetlands are known to serve as sinks for particulate matter and associated nutrients and contaminants. Consequently rate of soil accretion is critical for continued performance of wetlands to provide ecosystem services including water quality improvement and reduce excess contaminant loads into downstream waters. Here we demonstrate a new technique to determine rate of soil accretion in selected subtropical treatment wetlands located in southern USA. We also report changes in soil accretion rates and subsequent phosphorus (P) removal efficiency with increasing operational history of these treatment wetlands.Utilizing discernible signatures preserved within the soil depth profiles, ‘change points’ (CP) that corresponded to specific events in the life history of a wetland were determined. The CP was observed as an abrupt transition in the physico-chemical properties of soil as a manifestation of prevailing historical conditions (e.g. startup of treatment wetlands in this case). Vertical depth of CP from the soil surface was equivalent to the depth of recently accreted soil (RAS) and used for soil accretion rate calculations. Annual soil and P accretion rates determined using CP technique (CPT) in studied wetlands ranged from 1.0±0.3 to 1.7±0.8cmyr−1 and 1.3±0.6 to 3.3±2gm−2yr−1, respectively. There was no difference in RAS depth between emergent and submerged aquatic vegetation communities found at the study location. Our results showed that soil and P accretion rates leveled off after 10yr of treatment wetlands' operation. On comparison, soil accretion rates and RAS depth determined by CPT were commensurate with that measured by other techniques. CPT can be easily used where a reliable record of wetland establishment date or some significant alteration/perturbation is available. This technique offers a relatively simple alternative to determine vertical accretion rates in free-water surface wetlands.

Organophosphorus and Organochlorine Pesticides Bioaccumulation by Eichhornia crassipes in Irrigation Canals in an Urban Agricultural System

A natural wetland in Mexico City Metropolitan Area is one of the main suppliers of crops and flowers, and in consequence its canals hold a high concentration of organochlorine (OC) and organophosphorus (OP) pesticides. There is also an extensive population of water hyacinth (Eichhornia crassipes), which is considered a plague; but literature suggests water hyacinth may be used as a phytoremediator. This study demonstrates bioaccumulation difference for the OC in vivo suggesting their bioaccumulation is ruled by their log Kow, while all the OP showed bioaccumulation regardless of their log Kow. The higher bioaccumulation factors (BAF) of the accumulated OC pesticides cannot be explained by their log Kow, suggesting that the OC pesticides may also be transported passively into the plant. Translocation ratios showed that water hyacinth is an accumulating plant with phytoremediation potential for all organophosphorus pesticides studied and some organochlorine pesticides. An equation for free water surface wetlands with floating macrophytes, commonly used for the construction of water-cleaning wetlands, showed removal of the pesticides by the wetland with room for improvement with appropriate management.

Comparative Analysis of Greenhouse Gas Emission from Three Types of Constructed Wetlands

Copyright: © 2015 Tao W. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Wastewater treatment processes can produce anthropogenic greenhouse gases, including carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). Wastewater treatment in the U.S. emitted 17.8 Tg CO2equivalent (CO2-eq) in 2012, accounting for 0.27% of the U.S. total greenhouse gas emission and 14.3% of the total greenhouse gas emission from waste management and treatment activities (U.S. EPA, 2014). Constructed wetlands are green infrastructure for treatment of various types of wastewater. As ecologically engineered treatment systems, constructed wetlands mimic the appearance of natural wetlands (Figure 1). Constructed wetlands utilize natural processes involving macrophytes, soils or other porous media, and the associated microbial assemblages for water quality improvement. There are mainly three types of constructed wetlands [1]. Free water surface (FWS) wetlands typically consist of cells with aquatic plants, relatively impermeable rooting substrate, and shallow water. Treatment in FWS constructed wetlands occurs as water flows slowly above ground through the leaves and stems of aquatic plants. Horizontal subsurface flow (HSSF) wetlands contain beds of porous media that may have been planted with aquatic plants. Wastewater flows horizontally beneath the surface of the medium beds. Vertical flow (VF) wetlands contain beds of media that may have been planted with aquatic plants. Water is distributed over the ground surface or from the base, and flows downward or upward through the medium beds. When designing a constructed wetland treatment system, wetland type is first selected in regards to several factors such as land availability, local climate, and wastewater characteristics. Sustainability has become an important consideration in wastewater treatment. Correspondingly, greenhouse gas emission from constructed wetlands has been measured in full-scale constructed wetlands in the last decade. Mander et al. [2] compared the three types of constructed wetlands in terms of CO2-C, CH4-C, and N2O-Nemission rates separately. Actually, the same mass emission rates of CO2, CH4, and N2O contribute very differently to global warming. To compare the overall effect of greenhouse gas emissions amongst different types of constructed wetlands, it is necessary to calculate CO2-eq emissions [3,4]. With inclusion of climate-carbon feedbacks in response to emissions of non-CO2 gases, the 100-year global warming potential (GWP100) is 1 for CO2, 34 for CH4, and 268 for N2O (IPCC, 2013). CO2-eq emission rate in the three types of constructed wetlands were then obtained by multiplying the emission rate of a greenhouse gas reviewed by (2) by its GWP100 as given in Equations 1-3: CO2-eq of CO2, mg/m /h=(CO2, mg C/m 2/h) × (44/12) × 1 (1) CO2-eq of CH4, mg/m /h=(CH4, mg C/m 2/h) × (16/12) × 34 (2) CO2-eq of N2O, mg/m /h=(N2O, mg N/m 2/h) × (44/28) × 268 (3) Based on emission rates of individual greenhouse gases, Mander et al., [2] concluded that CO2 emission was significantly lower in FWS constructed wetlands than in HSSF and VF constructed wetlands, CH4emission was significantly lower in VF constructed wetlands than HSSF constructed wetlands, and that there were no significant differences in N2O emission in various wetland types. Based on the CO2-eq emission rates (Table 1), we found that: 1. CO2-eq emission rate in constructed wetlands is in the order of HSSF>VF>FWS, either in terms of total or individual greenhouse gases except for CH4 that FWS>VF; 2. CO2-eq emitted from constructed wetlands is in the order of CO2>CH4>N2O for all the three types of constructed wetlands. 3. CO2 accounted for 76% of the total CO2-eq emitted from VF constructed wetlands; 4. Both CO2 and CH4 are the primary greenhouse gases emitted from FWS constructed wetlands; and 5. CO2 and CH4 accounted for 51% and 41% of total CO2-eq emitted, respectively, from HSSF constructed wetlands.

자연형 도로 비점오염저감시설의 저감효율 및 적용성 연구

PURPOSES : The purpose of this study is to assess removal efficiency of non-point pollutants and applicability for non-point pollutant reduction facilities by conducting the demonstration project operation. METHODS : In order to analyze removal efficiency of non-point pollutants for facilities such as a grassed swale, a small constructed wetland, a free water surface wetland, a horizontal sub-surface flow wetland, and a sand filtration, the field data including specifications of facilities, rainfall, inflow and runoff rainfall effluent etc. was acquired after occurring rainfall events, and the acquired data was analyzed for removal efficiency rate to assess road non-point pollutants facilities using event mean concentration (EMC) and summation of load (SOL) methods. RESULTS : The results of analyzing rainfall effluent, non-point pollutant sources showed that total suspended solid (TSS), chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen (TN), total phosphorus (TP), chrome (Cr), zinc (Zn), and lead (Pb) can be removed through non-point pollutant reduction facilities by 60.3% ~ 100%. Especially removal efficiency of TSS, COD and BOD is relatively higher than removal efficiency of other non-point pollutant sources in all kind of non-point pollutant facilities. CONCLUSIONS : Based on the result of this study, even though natural type of non-point pollutant reduction facilities for roads occupy small areas comparing with drainage basin areas, most of non-point pollutant sources would be removed through the facilities.

Emerging organic contaminant removal in a full-scale hybrid constructed wetland system for wastewater treatment and reuse

A full-scale hybrid constructed wetland (CW) system based on three stages of different wetlands configurations showed to be a very robust ecotechnology for domestic wastewater treatment and reuse in small communities. It consisted of a 317-m2 vertical subsurface flow (VF), a 229-m2 horizontal subsurface flow (HF), and a 240-m2 free water surface (FWS) CWs operating in series. VF and HF wetlands were planted with Phragmites australis and the FWS contained a mixture of plant species. An excellent overall treatment performance was exhibited on the elimination of conventional water quality parameters (98–99% average removal efficiency for TSS, BOD5 and NH4–N; n=8), and its final effluent proved to comply with existing Spanish regulations for various reuse applications. The removal of studied emerging contaminants, which included various pharmaceuticals, personal care products and endocrine disruptors, was also very high (above 80% for all compounds), being compound dependent (n=8). The high rates were achieved due to high temperatures as well as the differing existing physico-chemical conditions occurring at different CW configurations, which would allow for the combination and synergy of various abiotic/biotic removal mechanisms to occur (e.g. biodegradation, sorption, volatilization, hydrolysis, photodegradation). While aerobic metabolic pathways and solids retention are enhanced in the VF bed, other removal mechanisms such as anaerobic biodegradation and sorption would predominate in the HF bed. At last, photodegradation through direct sunlight exposure, and less importantly, sorption onto organic matter, seem to take an active part in organic contaminant removal in the FWS wetland.

A correction coefficient for pollutant removal in free water surface wetlands using first-order modeling

Pollutant removal in free water surface wetlands (FWS) for practical purposes is calculated using the simplified hydraulic retention time (HRT) of the first-order model. Although the residence time distribution (RTD) represents the hydraulic conditions seen in natural wetlands better when compared to the HRT, the RTD is more difficult to calculate. It is crucial to determine the situations that the first-order model would have good performance and quantify the difference between HRT and RTD. In this study, the correction coefficient for the first-order model is presented and examined through 28 numerical experiments. The relationship between the correction coefficient and the related hydraulic efficiency is also established and discussed. The refining results show that the aspect ratio has a logarithmic trend while the water depth has turned an exponential trend with the variant correction coefficients. Higher aspect ratios or lower water depths can ensure better pollutant removal estimation by the first-order model. Both water depth and aspect ratio influence correction coefficients; however, water depth is the factor that has a greater impact. It is suggested that the first-order model is employed for shallow water wetlands with water depths lower than 0.8m and narrow long wetlands with aspect ratios higher than 1.20 without modification. We also concluded that the first-order model could be more widely and adequately used for practical purposes after modification by the correction coefficients. Furthermore, increasing water depth and decreasing aspect ratio resulted in lower hydraulic efficiency. Wetland designers should avoid selecting a dysfunctional plan when designing deep water and low aspect ratio constructed wetlands.

Three-stage hybrid constructed wetland system for wastewater treatment and reuse in warm climate regions

An experimental hybrid constructed wetland system consisting of 3 stages of different wetland configurations (i.e. two vertical flow beds (1.5m2 each) alternating feed-rest cycles followed by a horizontal subsurface flow (2m2) and a free water surface (2m2) wetlands in series) and the quality of its final effluent were evaluated for about one year. Mean overall removal rates were as 97% TSS, 78% COD, 91% BOD5, 94% NH4-N, 46% TN and 4% PO4-P. Vertical flow beds achieved high organic matter retention (77% BOD5) and great nitrification capacity (74% NH4-N removal). Although horizontal and free water surface wetlands accomplished little denitrification, they enabled water disinfection to produce an effluent suitable for various reuse applications. Authors suggest partial bypass from the Imhoff tank to the horizontal subsurface flow wetland so as to provide a carbon source to promote denitrification. The treatment system performed equally well in terms of organic matter and ammonium removal both in warm and cold seasons. However, reduced nitrate retention took place in horizontal and free water surface wetlands in the cold season, presumably due to low denitrification activity at low water temperatures. In general, the three-stage hybrid constructed wetland system has proven to constitute an appropriate ecotechnology for wastewater treatment and reuse in small communities of warm climate areas.

Phosphorus Retention in a Newly Constructed Wetland Receiving Agricultural Tile Drainage Water

One measure used in Sweden to mitigate eutrophication of waters is the construction of small wetlands (free water surface wetland for phosphorus retention [P wetlands]) to trap particulate phosphorus (PP) transported in ditches and streams. This study evaluated P retention dynamics in a newly constructed P wetland serving a 26-ha agricultural catchment with clay soil. Flow-proportional composite water samples were collected at the wetland inlet and outlet over 2 yr (2010-2011) and analyzed for total P (TP), dissolved P (DP), particulate P (PP), and total suspended solids (TSS). Both winters had unusually long periods of snow accumulation, and additional time-proportional water samples were frequently collected during snowmelt. Inflow TP and DP concentrations varied greatly (0.02-1.09 mg L) during the sampling period. During snowmelt in 2010, there was a daily oscillation in P concentration and water flow in line with air temperature variations. Outflow P concentrations were generally lower than inflow concentrations, with net P losses observed only in August and December 2010. On an annual basis, the wetland acted as a net P sink, with mean specific retention of 69 kg TP, 17 kg DP, and 30 t TSS ha yr, corresponding to a reduction in losses of 0.22 kg TP ha yr from the agricultural catchment. Relative retention was high (36% TP, 9% DP, and 36% TSS), indicating that small constructed wetlands (0.3% of catchment area) can substantially reduce P loads from agricultural clay soils with moderately undulating topography.

Nitrogen Removal in Constructed Wetlands Using Nitritation/Anammox and Nitrification/ Denitrification: Effects of Influent Nitrogen Concentration

Simultaneous nitritation/anammox and nitrification/denitrification (SNAND) is a promising method to increase nitrogen removal from ammonium- and nitrate-rich wastewater. This study examined the effects of influent nitrogen concentrations on plant assimilation and microbial nitrogen removal via SNAND in three free water surface wetlands. Anammox and denitrification contributed 78 and 22%, respectively, of microbial removal of total inorganic nitrogen (TIN). Nitrogen removal rates increased with influent concentrations in the low ranges of 17 to 105 mg N/L ammonium and 51 to 179 mg N/L TIN. However, nitrogen removal rates appeared to decrease with influent concentrations in the high ranges of 248 to 293 mg N/L ammonium and 348 to 391 mg N/L TIN. Plant growth was negatively affected when influent ammonium concentration exceeded 46 to 76 mg N/L. Plant assimilation contributed 11 to 47% toward TIN removal at low influent ammonium concentrations (42 to 76 mg N/L) and 4% at high influent ammonium concentrations (mean 264 mg N/L).