Application of constructed wetlands for domestic wastewater treatment in an arid climate

The present study consists in assessing the efficiency of a constructed reed bed for domestic wastewater purification under an arid climate. The experimental system is made up of four beds differing in length ( 20, 30, 40 and 50 m) and planted with Phragmites australis. Raw domestic wastewater inflow through these beds is horizontal with a flow of 10 litres per second. Hydraulic application rate varies between 0,86 to 2,16 m(3).m(-2).day(-1). The frequency of irrigation is weekly. The studied parameters are : the organic load (COD and TSS), nutrients (total Kjeldhal nitrogen : TKN, NH4, total phosphorus : TP, PO4) and the parasitical load (helminth eggs). Results shows that the constructed reed beds are efficient in reducing organic load (TSS: 58% to 67%; COD:48% to 62%) and parasitical load (Helminth eggs: 71% to 95%) in arid climates even with high hydraulic application rate. However, reduction of nutrient concentrations by the four beds is slight (TKN : 23 to 43% ; NH4 : 18 to 41% ; TP: 5 to 17% ; PO4 : -9 to 13%). At the hot period (March to August), the reed beds seem to be more efficient in reducing organic load, nutrients and parasitical load. This period coincides with the reed's exponential growth phase. Moreover, the largest bed (50m in length) showed the best efficiency in the removal of nutrients (TKN: 53% ; NH4: 61% ; TP: 30% ; PO4: 14%) and parasitical load (helminth eggs : 99%). This is due to its lowest application rate (0,86 m(3).m(-2).day(-1)). (C) 1998 Published by Elsevier Science Ltd. All rights reserved