Water balance and pollutant removal efficiency when considering evapotranspiration in a pilot-scale horizontal subsurface flow constructed wetland in Western Sicily (Italy)

Abstract

tIn constructed wetland systems (CWs) for wastewater treatment, the performance of the system isaffected by evapotranspiration (ET). This study shows the results of a series of water balance andpollutant removal efficiency analyses taken from a pilot horizontal-subsurface flow system (HSSFs)in the West of Sicily (Italy). The system comprised three separate units, one planted with Cyperusalternifolius L., one planted with Typha latifolia L. and an unplanted unit. The system was fed withurban wastewater from an activated-sludge wastewater treatment plant. The aims of the study wereto determine water balance and pollutant removal rates when considering evapotranspiration in tworoot emergent macrophytes in typically Mediterranean climate conditions. ET values were calculatedby determining three components of a simplified water balance model without taking subsurface andsurface water into consideration. Crop coefficient values were estimated using the FAO 56 method.Removal efficiency (RE) of a pilot HSSFs was calculated using both inflow and outflow pollutant con-centrations and mass loads. Biochemical oxygen demand (BOD5) and chemical oxygen demand (COD)were the main pollutants examined. The T. latifolia-unit was found to have higher cumulative evapo-transpiration rates (3579 mm) than the C. alternifolius-unit (3142 mm). Water-use efficiency (WUE)for C. alternifolius (0.66 g/L) and T. latifolia (0.75 g/L) was somewhat low on average compared to tra-ditional open-field crops. Percent removal was calculated using mass loads was on average higherthan that determined using concentrations for both the planted and unplanted units. Further knowl-edge on water losses could provide useful information when designing CWs. The estimate of ET ishighly important for arid areas, especially where the water at the outflow of the CWs is required forreuse.