Evaluating the Performance of Horizontal Subsurface Flow Constructed Wetlands Using the Plant Cynodon dactylon in an Arid Climate.

Abstract

     The target of this study is to show the potential of Cynodon dactylon in the purification of wastewater with a horizontal flow system under a dry and hot climate. This subject involves a comparison between a planted station and an unplanted bed (used as witness) focusing on the plant's ability to treat wastewater. The study was carried out through an experimental pilot station in the urban area of wastewater treatment (ONA EL Oued, Algeria). The process consists of circular beds with a capacity of 130 L filled with superimposed layers of gravel (25/15) mm and sand, 45cm and 15cm deep respectively. The first bed was planted with freshly collected stems of the plant Cynodon dactylon (40 stems/m²) and an unplanted bed taken as a witness. The procedure consists of providing the bed with urban wastewater (feed) after primary treatment (physical treatment) with a flow rate of 30 L per day over regular intervals once every week. The water obtained after staying 5 days in the bed is collected in a vase. After analysis the results revealed important removal fractions of the main pollutants namely : chemical oxygen demand (COD) 82.21%, biochemical oxygen demand (BOD₅) 85%, total suspended solids (TSS) 94.41% ,amnium(NH₄⁺) 99 ,68, nitrit( NO₂ ^–) 85,49% natarat( NO₃^-) 82.92%, orthophosphate (PO₄^2-) 80,64% ,E. coli 99.41%, coliformes fecaux 99.97 % and total streptococcus 99.90 %. The presence of the plant stems in the unplanted bed leads to the creation a crossing water channel so as to avoid plugging.The considerable decrease of pollutants content and harmful organisms enables the reuse of the treated water in agriculture and industry.