Occurrence of Cryptosporidium oocysts and Giardia cysts in the Nakdong River and their removal during water treatment

摘要

This study was conducted in preparation of a pending Cryptosporidium regulation in Korea. The study had two main objectives: 1) to examine the occurrence of Cryptosporidium oocysts in the Nakdong River; and 2) to evaluate their removal during water treatment. Occurrence of Giardia cysts was also examined. Average (arithmetic mean) numbers of Cryptosporidium oocysts and Giardia cysts at the treatment intake site were 2.6 l~(-1) and 4.8 l~(-1), respectively. Generally, the number of Giardia cysts was higher than that of Cryptosporidium oocysts at more sites, but the difference was minimal. Comparison of tributaries indicated that livestock wastes were more serious pollutants than sewage in terms of protozoa contamination. In general, fewer oocysts and cysts were detected during winter. No correlation was found for such water quality parameters as T-N, T-P, TOC, DO, pH and temperature with the numbers of oocysts and cysts except for suspended solids, which showed the highest correlation (R~2 = 0.55). Removal of Cryptosporidium oocysts was evaluated using a Cryptosporidium tracer, which has similar characteristics to Cryptosporidium oocysts. The tracer removal depended on turbidity removal. Coagulation followed by sedimentation resulted in 1.2-1.5 log removal of the tracer under optimal conditions. Filtration resulted in 1.3-1.5 log removal of the tracer. These treatability experiments showed that traditional water treatment processes could achieve 2.5-3.0 log removal of the oocysts.