Occurrence and fate of pathogenic parasites in an overland flow and percolation wastewater treatment system under arid climate

Pathogenic enteric parasites are the major health concern associated with sewage reuse in irrigation. Therefore, reduction of these agents is recommended to prevent any risks for human health. The present study was designed to evaluate the occurrence and persistence of pathogenic parasite eggs and cysts in a constructed overland flow and percolation plant. The pilot was operated at a flow rate of 0.02 m³ s⁻¹ with a hydraulic loading of 0.21 m³ m⁻² d⁻¹. The found results demonstrated that the process was effective in the removal of eggs and cysts from treated wastewater with rates up to 100%. During the treatment process cysts and eggs concentrate in soil with mean numbers of 2.8 × 10⁴ cysts/100 g d.w (dry weight) and 37.5 eggs/100 g d.w, respectively, with decreasing levels from the system's inlet toward the outlet. Also, eggs and cysts were found to percolate in soil but not greater than 12 cm of depth. Crops grown on soil were contaminated with averages of 1.7 × 10³ cysts/kg and 0.9 eggs/kg. Ascaris and Trichuris eggs developed in soil, mainly during the hot period, and 19.8% attained the infective stage. Helminth eggs persisted for longer periods in soil reaching over 3 months versus few days for protozoan cysts. Relatively shorter persistence periods were seen on crops with 9 days for eggs versus 6 days for cysts.