Detection of parasitic particles in domestic and urban wastewaters and assessment of removal efficiency of treatment plants in Tehran, Iran

Background: In recent years, decreasing annual rainfalls in some countries and population growth have led to a shortage of freshwater resources. Thus, recycled wastewaters has been suggested for agricultural activities. Contamination of wastewaters with pathogens is a major concern for the use of these waters. This study aimed to (i) investigate the occurrence of helminth eggs and protozoan (oo)cysts in human and livestock wastewaters, and (ii) evaluate the parasite removal efficiencies of urban and slaughterhouse treatment plants in Tehran province, Iran. One hundred and eight samples were collected from five urban and domestic wastewater treatment plants in Iran. Wastewater samples were concentrated by centrifugal-concentration and filtration methods. Results: The quantity of helminths egg and protozoa (oo)cyst per liter of urban raw wastewater ranged from 1.2 × 101 to 2.9 × 101 and from 9.6 × 102 to 1.9 × 103, respectively. The number of eggs and (oo)cysts per liter of animal raw wastewater ranged from 1.6 × 103 to 4.9 × 103 and 3.1 × 104 to 6.0 × 104, respectively. The helminths and protozoa identified in urban treatment plants included hookworms, Hymenolepis and Rhabditis (or probably Strongyloides), Entamoeba, Isospora, Giardia, Chilomastix and Cryptosporidium, while in slaughterhouses Trichuris, Trichostrongylus, Moniezia, Dicrocoelium, Fasciola, Entamoeba, Cryptosporidium, Eimeria and Giardia were isolated. The overall removal efficiency of eggs and (oo)cysts in the treatment plants ranged from 94.8 to 95.7% and from 79.3 to 85.8%, respectively. Conclusion: The study results revealed that the efficacy of removal of nematode eggs, and not protozoan (oo)cysts, in urban wastewater treatment plants, is in compliance with the WHO parasitological guideline ( < 1 nematode per liter) required for unrestricted irrigation.