Two Year Survey of Indicator Bacteria and Enteroviruses during the Preparation of Drinking Water from Three Water Treatment Plants in Paris Suburbs

Three conventional drinking water treatment plants were sampled monthly during a two year period for the removal of indicator bacteria and enteroviruses. Most 20 ℓ samples of raw river water were positive for viruses (principally Coxsackievirus B4 and B6, and echoviruses) with average virus concentrations varying from 0-3.5 PFU/ℓ for the less polluted river water (10³-10⁴ fecal coliforms/100 mℓ) to 0.1-20 PFU/ℓ for the highly polluted source (10⁴-10⁵ fecal coliforms/100 mℓ). In spite of these high levels of bacterial contamination, no viruses were detected from the 72 samples of 1 000 ℓ finished water. These results are discussed in regard to the virus removal efficiency of each treatment step previously evaluated by both pilot plant and full-scale water treatment plant studies. The mean virus removal was found to be 0-85% for storage (3 day period) of river water, 64-98% for preozonation (0.8 mg/ℓ/2-3 minutes), 31-90% for clarification by coagulation, flocculation and decantation, and 77-99% for sand filtration (5m/h). Total coliform counts were found to be good indicators of treatment for the presence of viruses in postozonated (1.5 mg/ℓ/10 min) water.