Efficiency of wastewater treatment plants in removal of intestinal parasites: A review approach

Background: Wastewater treatment plants (WWTPs) in urban areas, are potentially one of the causes of the spread and entry of parasitic pathogens into the environment and water resources. Numerous studies have been conducted on the presence of parasitic agents in the entry and effluent of WWTPs in different countries. This study was conducted to review the parasite prevalence in different WWTPs and assess their removal efficiency. Methods: ScienceDirect, Scopus, Web of Science, and PubMed databases and other sites with the ability to receive a full-text related articles, were reviewed. Various keywords such as parasites, wastewater, effluent, treatment efficiency, protozoan cysts, parasitic eggs, and similar keywords were used to search articles published from 2005 to 2019. After screening the titles and abstracts of articles, 26 articles were reviewed in this study. Results: Giardia spp, Cryptosporidium spp, Entamoeba spp, Blastocystis spp, Toxocara spp, Trichostrongylus spp, A. lumbricoides, and Hymenolepis are the most prevalent parasites. Studies show that parasitic egg hatching rates are up to 5%, in aerated lagoons, up to 99.9%, in activated sludge, and up to 5%, in ponds due to high retention time and downstream artificial reefs. Conclusion: Studies show that due to the current state of treatment plants and adverse operating and maintenance conditions, it is not possible to completely remove parasitic pathogens from these systems, therefore, it should be considered by regulatory authorities and the systems need to be improved for better performance of treatment plants and optimizing them, and training of users should also be improved. This review indicated that the types of natural constructed wetland in Kermanshah (Iran) and activated sludge of wastewater treatment processes in Iran and Brazil are most effective in removal of intestinal parasites.