Capacity of constructed wetlands to remove parasite eggs from wastewaters in Egypt

Abstract

The use of Gravel Bed Hydroponic (GBH) constructed wetlands for wastewater treatment and reuse in semi-arid climates has been evaluated in Egypt with respect to the removal of parasite eggs from domestic wastewaters.Influent and effluent from established 100m GBH reed beds receiving partially treated wastewater, were analysed to establish daily parasite loading rates and removal performance of the system under normal operating conditions (201/min; intermittent 12h on/off flow regime.) The system was then challenged with high numbers of parasite eggs (Ascaris sp., Hymenolepis sp. and Toxocara sp.) equivalent to an influent of 100–500 eggs/l and a daily loading rate of 1.0–7.2 × 106, representing up to a 110-fold increase over typical mean daily loading rates. Wastewater samples were collected from the inlet, at varying distances along the 100m bed profile, and the outlet. Sampling was also carried out at varying rime intervals during the flow regime to determine the spatial and temporal removal of eggs along the bed.In 100m long planted beds, there was significant removal of all selected parasite eggs with the majority being removed within the first 25m. No eggs were detected in the final effluent. These studies demonstrate that GBH wetlands have a capacity for efficient removal of parasite eggs and thus provide a reliable, low cost technology for treating effluent compliant with health related objectives for the treatment of wastewater intended for agricultural reuse.