Descriptive study on the presence of protozoan cysts and bacterial indicators in a drinking water treatment plant in Maracaibo, Venezuela

This study evaluates the occurrence of the protozoan parasites Giardia and Cryptosporidium in raw and finished water samples collected from a drinking water treatment plant that serves a large community in Maracaibo, Venezuela. The cartridge filtration method was used for detection of the two protozoa. In addition, two clarification techniques [the Percoll-sucrose flotation (P/S) and the immunomagnetic separation technique (IMS)] were applied. Water quality indicator bacteria as well as physicochemical parameters were studied. Both protozoa were detected in raw and finished water samples with no significant improvements in recovery provided by the two clarification techniques. Giardia cysts were found in four of 12 (33%) raw water samples with a geometric mean of 0.86/100 l. Cryptosporidium oocysts were found in 9 of 12 (75%) of the raw water samples processed with a geometric mean of 15.4/100 l. In finished water samples Giardia cysts were detected in four of 11 (36%) with a geometric mean of 1.31/100 l. Cryptosporidium oocysts were detected in 10 of 11 (90%) with a geometric mean of 4.4/100 l. There were no correlations between the concentration of water quality indicator bacteria and either protozoa. Coliforms and high turbidity (6 NTU) were also detected in the finished water indicating poor operation of the filters and the subsequent interference with disinfection. The levels of protozoan cysts detected may involve significant public health risks and recommendations were made to the utility for improvements.