Effect of key design parameters on the efficiency of horizontal subsurface flow constructed wetlands

Abstract:The wastewater generated by isolated houses without access to public sewers can cause environmental problems, like the contamination of aquifers with nitrates and phosphates, as occurs in southeastern Spain. The effectiveness of a previously built horizontal subsurface flow constructed wetland (HF-CW) was studied over two years as a possible solution. This HF-CW measured 27 m 2 ; it was planted with Phragmites australis (Cav.) Trin. ex Steud ssp. altissima and the parameters studied were those required by European Union (EU) legislation and adopted by Spain. Average abatement efficiency rates, for the first and the second year of study, were: biochemical oxygen demand over five days (BOD 5 because its content in influent wastewater was very low and they appear mainly from influent NH 4 + -N, as a result of purification processes carried out in the HF-CW bed. The abatement rates make the system suitable to produce discharges into the environment in accordance with Spanish law. It is noteworthy that the HF-CW patch suffered an episode of bed drying during the summer of 2013, whereby the causes were related to system oversizing and high evapotranspiration in the area. As a consequence, the decrease in the abatement of water pollutants during the second year can be attributed to the creation of preferential water flow paths and short circuits through the constructed wetland (CW) bed. As a result of the oversizing of the CW, a theoretical resizing based on BOD 5 , TSS, TN or TP is proposed. The calculated values for the redesign were: 5.22 m 2 considering DBO 5 , 0.18 m 2 considering TSS, 10.14 m 2 considering TN and 23.83 m 2 considering TP. Considering the area where the HF-CW was located and in accordance with Spanish law for non-sensitive areas (no TN or TP requirements for wastewater discharge), BOD 5 is the most appropriate parameter for design; it is 5.2 times lower than the HF-CW initially built and without risk of bed drying.

Section: Surface System Optimizationmentioning

confidence: 99%

Domestic Wastewater Depuration Using a Horizontal Subsurface Flow Constructed Wetland and Theoretical Surface Optimization: A Case Study under Dry Mediterranean Climate

Andreo-Martínez

García-Martínez

Almela

2016

“…The beds at this site were disconnected for 5 months (December 2011-April 2012) due to mechanical maintenance of the secondary treatment during which time the flow was removed from site. The mean flow to each bed is 46 m 3 Treatment at Site B is via an integral RBC followed by a combined wetland (Figure 1). The bed was retrofitted with aeration in October 2010 to provide a failsafe for occasional ammonia peaks observed in the conventional flow sheet.…”

Section: Site Detailsmentioning

confidence: 99%

“…The beds at this site were disconnected for 5 months (December 2011-April 2012) due to mechanical maintenance of the secondary treatment during which time the flow was removed from site. The mean flow to each bed is 46 m 3 Treatment at Site A consists of a primary settling tank (PST) followed by a submerged aerated filter (SAF; Figure 1). Tertiary treatment is via two HSSF CWs with a separate combined sewer overflow (CSO) HSSF CW that receives the wastewater exceeding six times the dry weather flow.…”

Section: Site Detailsmentioning

confidence: 99%

“…This type of operation and loading rates are generally insufficient to meet future discharge targets within typically limited available land areas. Across the full spectrum of applications for constructed wetlands a number of innovative adaptations have been developed to overcome the oxygen limitation including decreasing the depth of the bed [3]; recirculation of the treated effluent [4]; batch loading including traditional vertical flow systems [5] and adaption to horizontal flow beds, i.e., tidal flow [6]; and forced (artificial) aeration of traditional vertical flow systems [7], flooded vertical flow systems [8], or horizontal flow beds [2,9]. The general efficacy of the approach towards enhancing nitrification has been demonstrated predominately at pilot scale for a range of feed water types including synthetic wastewater [10,11], heavily polluted river water [12], and municipal secondary sewage [8].…”

Section: Introductionmentioning

confidence: 99%

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Performance of Four Full-Scale Artificially Aerated Horizontal Flow Constructed Wetlands for Domestic Wastewater Treatment

Butterworth

Richards

Jones

et al. 2016

A comparison of the performance of four full-scale aerated horizontal flow constructed wetlands was conducted to determine the efficacy of the technology on sites receiving high and variable ammonia loading rates not yet reported in the literature. Performance was assessed in terms of ammonia and solids removal, hydraulic conductivity and mixing patterns. The capability of systems to produce ammonium effluent concentrations <3 mgNH 4 + -N/L was observed across all sites in systems receiving variable loadings between 0.1 and 13.0 gNH 4 + -N/m 2 /d. Potential resilience issues were observed in relation to response to spike loadings posited to be due to an insufficient nitrifying population within the beds. Hydraulic conductivity and flow mixing patterns observed suggested deterioration of the reactor effective volume over time. Overall, the study demonstrates the efficacy of the technology where ammonium removal is required on small sites receiving high and variable flow rates, with adequate removal of organics and solids, but no significant benefit to the long term hydraulics of the system.

“…Some important design parameters affecting retention time in CWs include length-to-width ratio, inlet/outlet-to-length ratio, and configuration of substrate size. According to García, et al [9], the length-to-width ratio is one of the most important factors for enhancing the hydraulic and treatment performance of CWs. A relatively high length-to-width ratio can improve hydraulic behavior by reducing the internal dispersion of the water flow, thus forcing the water to pass through the whole cross-section of the wetland bed [10].…”

Section: Introductionmentioning

confidence: 99%

Multilayer Substrate Configuration Enhances Removal Efficiency of Pollutants in Constructed Wetlands

Bai

Ding

et al. 2016

Abstract:This study aimed at optimizing horizontal subsurface flow constructed wetlands (CWs) to improve hydraulic performance and pollutant removal efficiency. A groundwater modeling package (MODFLOW) was used to optimize three design parameters (length-to-width ratio, inlet/outlet-to-length ratio, and substrate size configuration). Using the optimized parameters, three pilot-scale CWs were built to treat actual wastewater. For model validation, we used a tracer test to evaluate hydraulic performance, and investigated the pollutant spatial distributions and removal efficiencies. We conclude that MODFLOW is suitable for designing CWs, accurately predicting that increasing hydraulic conductivity from surface to bottom layers could improve performance. However, the effect of vegetation, which decreased the hydraulic conductivity of the surface layer, should be considered to improve simulation results. Multilayer substrate configuration, with increasing hydraulic conductivity from the surface to bottom layers, significantly increased pollutant removal compared with monolayer configuration. The spatial variation in pollutant transport and degradation through the filling substrate showed that the multilayer configuration was able to increase use of the available space and moderately reduced short-circuiting and dead zones. Thus, multilayer CWs had higher experimental retention times, effective volume fractions and hydraulic efficiencies, and lower short-circuiting compared with monolayer CWs operating under similar conditions.