| The concentration of pathogenic protozoan (Cryptosporidium and Giardia) in water samples of different units in a full-scale wastewater treatment plant in Beijing was investigated periodically. The average concentrations of Cryptosporidium detected in untreated wastewater, primary sedimentation, secondary sedimentation, flocculation-sedimentation and sand-filtration effluent were 238, 179, 6, 1, 0.3 oocysts/L respectively, and the average concentrations of Giardia were 1 568, 1 048, 22, 4, 0.6 cysts/L respectively. The total removal efficiencies of Cryptosporidium and Giardia in this treatment process were 2.98 and 3.46 log respectively. Very little protozoan in wastewater could be removed by preli minary treatment process, the removal efficiencies were only 0.13 and 0.18 log respectively. Biological treatment unit had the highest removal efficiency, up to 1.50 and 1.67 log respectively. Advanced treatment process could enhance the removal of the protozoan effectively. The results also showed that the pollution level of pathogenic protozoan in the influent of wastewater treatment and reclamation plant was various according to the climate, high in dry seasons and low in rainy season. |
