Modeling the Effect of Plants and Peat on Evapotranspiration in Constructed Wetlands (original) (raw)
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The presence of plants (reed, rush, cattail, willow, etc) in constructed wetlands (CW) for wastewater treatment brings several benefits, including enhanced removal of pollutants (N, P, heavy metals) from treated wastewater, creating micro-aerobic conditions and providing carbon compounds in the rhizosphere, hence supporting a diverse subsurface microbial community. Aquatic macrophytes are also of great importance in evapotranspiration (ET), especially during hot periods, in both natural and constructed wetlands. ET increases the concentration of dissolved compounds due to decreasing water volume in a CW. This may result in zero-discharge from the system. Where ET is high, removal efficiency (calculated as the difference between influent and effluent concentrations) is lower than expected from mass balance (based on pollutant loadings). Case studies from Poland (lab scale) and Portugal (field scale) illustrate the influence of ET on volume reduction and on the calculation of pollutant removal efficiencies. Evapotranspiration can cause substantial reduction in volume of an effluent stream in a well vegetated constructed wetland, leading to reduced flow and increase in hydraulic retention time. This may lead to problems estimating pollutant loads and removal rates in field systems. Pollutant removal efficiency values calculated from pollutant concentrations may be unreliable in conditions of high evapotranspiration due to water loss within the constructed wetland system. Where evapotranspiration is high (warm dry climate, high macrophyte biomass), removal efficiency values based on concentrations may be greatly underestimated. Hence, inflow and outflow rates (hydraulic flux), should be measured so that pollutant mass loads can be used as the basis for calculating removal efficiency. In warm dry climates it may be feasible to increase the hydraulic loading rate of vegetated constructed wetlands , relying on enhanced water loss by evapotranspiration, but without reducing treatment performance. 94 surfaces and that in the overlying air. The water flux is affected by factors including wind speed, air and leaf surface temperatures and air humidity. Hence ET varies with season, typically being highest in summer. ET rate (E) is described by Eq. (1) .
COMPARISON OF TREATMENT PERFORMANCE BETWEEN CONSTRUCTED WETLANDS WITH DIFFERENT PLANTS
Constructed wetlands have gained much importance for treating domestic, industrial and agricultural wastes and are considered as an effective secondary or tertiary treatment method. The main characteristics affect the removal efficiency of constructed wetland are the vegetation type, hydraulic residence time and substrate. The aim of the present study is to examine effect of vegetation type on organic and nutrient removal under varying hydraulic residence time in constructed wetlands. With this in mind, we have designed, constructed and operated two pilot-scale horizontal subsurface flow constructed wetlands having two different wetland vegetation plants in our open-air laboratory receiving pre-treated domestic wastewater by varying hydraulic residence time as 2, 4, 6 and 8 days. The influent wastewater is rich in orgnic matter with high variability presence of nutrients. In the first unit, the removal efficiency of COD, BOD, TN, and TP was increased from 39 to 69%, 29 to 56%, 23 to 45% and 25 to 75% when there was an increase in HRT from 2 days to 8 days respectively. In the second unit, the removal efficiency of COD, BOD, TN, and TP was increased from 31 to 68%, 25 to 52%, 26 to 36% and 40 to 77% when there was an increase in HRT from 2 days to 8 days respectively. It was found that vegetation type influenced concentration reduction. A 6-day hydraulic residence time is suggested for an acceptable level of treatment in these systems.
Effect of different plant species in pilot constructed wetlands for wastewater reuse in agriculture
Journal of Agricultural Engineering, 2013
In this paper the first results of an experiment carried out in Southern Italy (Sicily) on the evapotranspiration (ET) and removal in constructed wetlands with five plant species are presented. The pilot plant used for this study is made of twelve horizontal sub-surface flow constructed wetlands (each with a surface area of 4.5 m 2) functioning in parallel, and it is used for tertiary treatment of part of the effluents from a conventional municipal wastewater treatment plant (trickling filter). Two beds are unplanted (control) while ten beds are planted with five different macrophyte species: Cyperus papyrus, Vetiveria zizanoides, Miscanthus x giganteus, Arundo donax and Phragmites australis (i.e., every specie is planted in two beds to have a replication). The influent flow rate is measured in continuous by an electronic flow meter. The effluent is evaluated by an automatic system that measure the discharged volume for each bed. Physical, chemical and microbiological analyses were carried out on wastewater samples collected at the inlet of CW plant and at the outlet of the twelve beds. An automatic weather station is installed close to the experimental plant, measuring air temperature, wind speed and direction, rainfall, global radiation, relative humidity. This allows to calculate the reference Evapotranspiration (ET0) with the Penman-Monteith formula, while the ET of different plant species is measured through the water balance of the beds. The first results show no great differences in the mean removal performances of the different plant species for TSS, COD and E.coli, ranged from, respectively, 82% to 88%, 60% to 64% and 2.7 to 3.1 Ulog. The average removal efficiency of nutrient (64% for TN; 61 for NH4-N, 31% for PO4-P) in the P.australis beds was higher than that other beds. From April to November 2012 ET measured for plant species were completely different from ET0 and ETcontrol, underlining the strong effect of vegetation. The cumulative evapotranspiration highest value was measured in the CWs vegetated with P.australis (4,318 mm), followed by A.donax (2,706 mm), V.zizanoides (1,904), M.giganteus (1,804 mm), C.papyrus (1,421 mm).
Microcosm Wetlands for Wastewater Treatment with Different Hydraulic Loading Rates and Macrophytes
Journal of Environment Quality, 2002
Constructed wetlands (CW) usually require large land areas for ties. Applying any traditional wastewater treatment treating wastewater. This study evaluated the feasibility of applying system to purify these reservoirs would be expensive. CW with less land requirement by operating a group of microcosm wetlands at a hydraulic retention time (HRT) of less than 4 d in In addition, the annual water temperature in southern southern Taiwan. An artificial wastewater, simulating municipal waste-Taiwan ranges from 20 to 32ЊC and under such warm water containing 200 mg L Ϫ1 of chemical oxygen demand (COD), weather conditions treating the polluted water with a 20 mg L Ϫ1 of NH ؉ 4-N (AN), and 20 mg L Ϫ1 of PO 3Ϫ 4-P (OP), was the wetland system becomes a reasonable option. inflow source. Three emergent plants [reed, Phragmites australis In our initial study, we found that a CW system effec-(Cav.) Trin. ex Steud.; water primrose, Ludwigia octovalvis (Jacq.) tively removed nutrients from highly polluted river wa-P.H. Raven; and dayflower, Commelina communis L.] and two floatter (Jing et al., 2001). Removal efficiencies for organics, ing plants [water spinach, Ipomoea aquatica Forssk.; and water letammonia nitrogen (AN), and orthophosphate (OP) tuce, Pistia stratiotes L.] plants were tested. The planted systems were influenced by the health and growth rate of the showed more nutrient removal than unplanted systems; however, macrophytes. The presence of the macrophytes enthe type of macrophytes in CW did not make a major difference in treatment. At the HRTs of 2 to 4 d, the planted system maintained hances several functions in the CW system: assisting greater than 72, 80, and 46% removal for COD, AN, and OP, respecsolids sedimentation, reducing algae production, providtively. For AN and OP removal, the highest efficiencies occurred at ing surface area for microbial growth, improving nutrithe HRT of 3 d, whereas maximum removal rates for AN and OP ent uptake, and releasing oxygen (Brix, 1997). Comoccurred at the HRT of 2 d. Both removal rates and efficiencies were monly used macrophytes in CW systems in the United reduced drastically at the HRT of 1 d. Removals of COD, OP, and States are bulrushes (Scirpus spp.), cattails (Typha spp.), AN followed first-order reactions within the HRTs of 1 to 4 d. The and water hyacinth [Eichhornia crassipes (Mart.) Solms] efficient removals of these constituents obtained with HRT between (Brown and Reed, 1994). However, it was necessary to 2 and 4 d indicated the possibility of using a CW system for wasteidentify domestic macrophytes for potential use in our water treatment with less land requirement. CW system. The treatment efficiency of pollutants in a CW system is usually improved by decreasing the hydraulic loading: Abbreviations: AN, ammonia nitrogen; CCE, surface-covered control experimental system; COD, chemical oxygen demand; CW, constructed wetlands; CW-Co, constructed wetlands planted with day-Shuh-Ren Jing, Ying-Feng Lin, and Der-Yuan Lee, Department of flower; CW-Ip, constructed wetlands planted with water spinach; CW-Environmental Engineering and Health, and Tze-Wen Wang, Depart-Lu, constructed wetlands planted with water primrose; CW-Ph, conment of Pharmacy, Chia
Geoderma, 2014
ABSTRACT Peat extraction for energy purposes causes major changes in the aquatic and terrestrial environment. According to national strategies for extracting peat in Finland, new peat extraction areas should be established on previously drained peatlands. On such areas it is difficult to find the natural, intact peatland required for treatment wetlands or so-called overland flow areas, which are considered the best available technology for runoff water purification. Therefore treatment wetlands must be constructed on drained peatland. It is known that drainage causes physical, biogeochemical and hydraulic changes in the peat layer, as well as changes in vegetation. It is probable that these changes affect the purification efficiency of wetland treatment systems in many ways. This study evaluated the function and characteristics of drained peatland areas for purification of peat extraction runoff water. Study sites were established on 11 drained wetlands and their purification efficiency was evaluated. Detailed measurements of peat physical properties and hydraulic conductivity, as well as studies on vegetation, were also made in the study areas. The results showed that wetlands constructed on drained peatland areas can purify peat extraction runoff. However, leaching of phosphorus (P) and iron (Fe) was observed in some areas. Leaching is influenced e.g. by pH and the soil P pool. The chemical oxygen demand was also observed to increase in runoff water from the wetland. The results indicated that low (Fe + aluminium (Al) + manganese (Mn))/P ratio (≤ 25) and quite high P content (> 1200 mg/kg) in the surface peat characterised those areas where P leaching was observed. The presence of a dense tree stand in a drained peatland area also seemed to indicate release of nutrients from the area after its rewetting and use as a treatment wetland. Thus, potential nutrient release from a drained peatland area intended for use as a treatment wetland can be assessed by studying the characteristics of the peatland area, especially the peat mineral content, and the vegetation, especially tree stand density in the area. Using the findings obtained, a conceptual decision tree was drawn up in order to help to establish and design wetlands in previously drained peatland areas.
Ecological Engineering, 2013
The aim of this study was to conduct a comparative evaluation of evapotranspiration (ET) rates for eight different mesocosm constructed wetlands (CWs), and the relationship with redox potential (E H). Inflow, outflow and E H were measured over 4 years in winter and summer campaigns as well as over 24 h on selected days in summer. Vegetation was the main design parameter which affected water loss in the wetlands (on average, ET in planted wetlands was 4 times higher than in unplanted ones), and Typha angustifolia was more active than Phragmites australis (mean daily ET-expressed as the average of ET rate measured every 2 h in selected days in summer-was 36.8 ± 2.3 mm d −1 and 23.0 ± 1.9 mm d −1 for hydroponic wetlands planted with cattail and common reed, respectively), although P. australis water use efficiency was lower. Positive relationships were found between ET and E H for planted wetlands. Cattail presented a stronger linear regression than common reed, demonstrating that ET and consequently redox conditions are plant species-dependent.
The influence of evapotranspiration on vertical flow subsurface constructed wetland performance
Ecological Engineering, 67, 89–94, 2014
This paper presents an example of the importance of evapotranspiration in constructed wetlands, with vertical subsurface flow, comparing different methods of treatment efficiency calculations and discussing the influence of evapotranspiration on removal rates. The application of reed, marked by high transpiration ability, is a cheap and effective method of landfill leachate disposal. A 2-year study examined the effectiveness of leachate treatment in constructed wetlands with reed. Two kinds of vertical subsurface flow systems: first with sand, and second with combined two layers of sewage sludge and sand has been tested. 1, 3, and 5 mm d−1 hydraulic loading rates of landfill leachate have been applied. Daily evapotranspiration was in the range from 0.98 to 2.99 mm d−1 in the first year of research and from 2.56 to 4.61 mm d−1 in the second year. The influence of evapotranspiration rate on chemical oxygen demand (COD) removal rate was examined. Two methods of removal efficiency calculation have been used: first based on inlet and outlet COD concentrations, second on mass balance determination. Research showed that the removal efficiency calculated as a comparison between initial and final concentration is significantly lower, than expected from mass balance, especially, when higher hydraulic loading rates were applied.