This study was conducted to determine Giardia sp. cysts concentration in wastewater influents and effluents of a stabilization pond system located in Mèze (03°35′06″E, 43°25′10″N), South of France.

In raw sewage mean concentrations ranging from 0.23-25.103 cysts 1-1 were found from February 92 to July 93.

Prior to November 92, large volume filtration combined with brightfield microscopy served as the method for cyst recovery and detection in pond effluents. From November 92, the detection of Giardia sp. cysts was performed by an indirect immunofluorescent antibody test.

No cysts could be detected in the final effluents during summer 92 by brightfield microscopy, whereas cysts were recovered in effluents from the first basin. Cysts were detected in final effluents during wintertime by the fluorescent antibody-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 coagulation in conjunction with immunofluorescent antibody techniques for the concentration and detection of Giardia sp. in stabilization pond effluents increases the recovery efficiency and identification of waterborne cysts.

The results of this study indicate a good removal efficiency of cysts in a stabilization pond during spring/summertime but a potential risk of cyst discharge during wintertime.

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