Occurrence and Fate of Human Pathogenic Parasites in Constructed Reed Beds for Wastewater Treatment

Pathogenic parasites are considered as the main health risk when wastewater is reused for irrigation, and one of the most targeted agents in treatment processes. The present study assessed the occurrence and fate of pathogenic helminths and protozoa in constructed reed beds under arid climate. The studied system was made of four length different beds (20-50 m) and was operated at a flow rate of 864 m³ d^-1 with 1-4 hours retention time. The reed beds were found to be effective in the removal of pathogenic parasites from wastewater with rates up to 98.4% for protozoan cysts and 97.7% for helminth eggs. Eggs and cysts removal was length dependent and longer beds (50 m length) were the most efficient. During the treatment process eggs and cysts concentrated in soil with mean numbers of 21.9 eggs/100 g and 7.4 × 10³ cysts/100 g dry weight, respectively, with decreasing levels from the bed’s inlet towards the outlet. Furthermore, Ascaris and Trichuris eggs were found to develop in soil and 27.4% and 46% attained the infective stage, respectively; especially, during spring and summer periods. Helminth eggs persisted for longer periods in beds’ soil reaching over three months versus three days for protozoan cysts.