OCCURRENCE OF GIARDIA SP CYSTS DURING A WASTE-WATER TREATMENT BY A STABILIZATION POND IN THE SOUTH OF FRANCE

This study was conducted to determine Giardia sp, cysts concentration in wastewater influents and effluents of a stabilization pond system l ocated in Meze (03 degrees 35'06''E, 43 degrees 25'10''N), South of Fr ance. In raw sewage mean concentrations ranging from 0.23-25.10(3) cys ts 1(-1) were found from February 92 to July 93. Prior to November 92, large volume filtration combined with brightfield microscopy served a s the method for cyst recovery and detection in pond effluents. From N ovember 92, the detection of Giardia sp. cysts was performed by an ind irect immunofluorescent antibody test. No cysts could be detected in t he final effluents during summer 92 by brightfield microscopy, whereas cysts were recovered in effluents from the first basin. Cysts were de tected in final effluents during wintertime by the fluorescent antibod y-technique (0.1 to 2.5 cysts 1(-1)). However, no cysts were detected during spring/summer 93 in final effluents. We conclude that alum coag ulation in conjunction with immunofluorescent antibody techniques for the concentration and detection of Giardia sp. in stabilization pond e ffluents increases the recovery efficiency and identification of water borne cysts. The results of this study indicate a good removal efficie ncy of cysts in a stabilization pond during spring/summertime but a po tential risk of cyst discharge during wintertime.