Devenir des œufs et kystes de parasites au cours d'un cycle d'épuration de la station Cherguia à Tunis

Fate of parasites eggs and cysts in the course of waste water treatment cycle of the Cherguia station in Tunis

Laboratoire de parasitologie des eaux usées, Institut National de Recherche en Génie rural, Eaux et Forêts

Abstract

In Tunisia particular attention is accorded to the sanitation aspects, when treated waste water is reused for agriculturaI purposes. The current water quality standard requires an average number inferior or equal to one intestinal helminth egg per litre of treated waste water. Information concerning parasitic risk is however rather limited in Tunisia. ln this context researches for protozoa cysts and helminth eggs were conducted on raw waste water, water after primary decantation, treated waste water, primary and secondary sewage sludge from the biological treatment plant in Cherguia.

The identified protozoa include Amebae and Flagellates. Among the Amebae, Entamoeba coli and Entamoeba histolytica cysts are detected, among the Flagellates, Giardia spp cysts are found. As a general rule, this later predominates. Among the helminths, Nematods and cestods are observed. The average number of helminth eggs is markedly lower.

For in inlet water, aIl analysed samples contained protozoa cysts particulary Giardia cysts in mean concentration of 2.1. 10² cysts t^-1. In lower frequency we found helminth eggs in mean concentration from 4 to 2.6. 10¹ eggs t^-1.

Through the treatment chain the greater part of eggs were eliminated during the primary decantation. The efficiency of elimination is about 30% for cysts and 63% for eggs.

In treated waste water the efficiency of the cysts elimination is about 97% and 100% of the samples were exempt from helminth eggs. The use of activated sludge is thus demonstrated, as very efficient for removal of parasitic elements.