OCCURRENCE AND REMOVAL OF GIARDIA SP CYSTS BY KENYAN AND FRENCH WASTESTABILIZATION POND SYSTEMS

A study was conducted to determine the occurrence and removal of Giard ia sp. cysts in municipal wastewater by two waste stabilisation pond s ystems; one at Eldoret, Kenya and one at Mete, France. A total of 71 a nd 26 grab raw wastewater samples from Eldoret and Mete, respectively, were examined for the presence of cysts. Cysts were detected in 37% ( 26) and 100% (26) raw wastewater samples, respectively. Cyst concentra tions detected in raw wastewater samples ranged from 1 x 10(3) to 2.5 x 10(4) cysts/l at Eldoret and 230 to 2.5 x 10(4) cysts/l at Mete, At Eldoret, all anaerobic (8/8), secondary facultative (5/5) and primary maturation (5/5) pond effluent samples examined were positive for Giar dia. Cyst concentrations ranged from 1.25 to 483 cysts/l (anaerobic), 23.5 to 192.5 cysts/l (secondary Facultative) and 17.2 to 118.5 cysts/ l (primary maturation), respectively. At Mete, cysts were detected in 12 of 12 primary facultative (range 4.4 to 48 cysts/l) and 9 of 11 (82 %) primary maturation pond effluents (range 0.2 to 16 cysts/l). In fi nal maturation pond effluent, Giardia cysts were detected in 100% of f inal pond effluents discharged from Eldoret (n=10; range 21 to 90 cyst s/l) and 7 of 16 (44%; range 0.1 to 2.5 cysts/l) from Mete. The occurr ence of cysts in final pond effluents examined would indicate that cum ulative retention periods of up to 25.3 days at Eldoret and 40 days at Mete would be sufficient to remove between 99.1% and 99.7% of cysts, respectively, but that such retention periods are insufficient to ensu re the complete removal of Giardia sp. cysts. Copyright (C) 1996 IAWQ. Published by Elsevier Science Ltd.