The abundance of Cryptosporidium and Giardia spp. in treated effluents produced by four wastewater treatment plants in the Gauteng Province of South Africa

Abstract

This study aimed at assessing the effectiveness of 4 wastewater treatment plants of the Gauteng Province, namely Zeekoegat, Baviaanspoort, Rayton and Refilwe Water Care Works (WCW), in the removal of Cryptosporidium and Giardia (oo)cysts. Wastewater influent and treated effluent samples were taken weekly between January and April 2008. Cryptosporidium and Giardia (oo)cysts were detected by immunofluorescence and immunomagnetic separation, according to a modified US EPA 1623 method. Effluent samples were subjected to a molecular study for the identification of Cryptosporidium parvum Genotype I and Giardia lamblia Assemblage A. The 18S rRNA gene for restriction digests was therefore used to characterise these (oo)cysts. Cryptosporidium oocysts were repeatedly detected in effluent samples collected from all wastewater treatments at lower concentration (range <1 to 40 oocysts/L) levels than Giardia cysts (range <1 to 175 cysts/ℓ). The mean removal efficiencies of Cryptosporidium and Giardia at the 4 wastewater treatment plants ranged from 67.40% to 98.26% and from 86.81% to 99.96%, respectively. For all effluent samples, except Zeekoegat WCW, 29% and 41% contained oocysts of Cryptosporidium parvum Genotype I and cysts of Giardia lamblia Assemblage A, respectively. Both C. Parvum and G. lamblia are human pathogens. This stresses the potential risk of discharging these parasites into receiving water bodies.

Keywords

: wastewater, removal, Cryptosporidium parvum, Giardia lamblia, genotype