CLOSTRIDIUM-PERFRINGENS AND SOMATIC COLIPHAGES AS INDICATORS OF THE EFFICIENCY OF DRINKING-WATER TREATMENT FOR VIRUSES AND PROTOZOAN CYSTS

To find the most suitable indicator of viral and parasitic contaminati on of drinking water, large-volume samples were collected and analyzed for the presence of pathogens (cultivable human enteric viruses, Giar dia lamblia cysts, and Cryptosporidium oocysts) and potential indicato rs (somatic and male-specific coliphages, Clostridium perfringens). Th e samples were obtained from three water treatment plants by using con ventional or better treatments (ozonation, biological filtration). All samples of river water contained the microorganisms sought, and only C. perfringens counts were correlated with human enteric viruses, cyst s, or oocysts. For settled and filtered water samples, all indicators were statistically correlated with human enteric viruses but not with cysts or oocysts. By using multiple regression, the somatic coliphage counts were the only explanatory variable for the human enteric virus counts in settled water, while in filtered water samples it was C. per fringens counts. Finished water samples of 1,000 liters each were free of all microorganisms, except for a single sample that contained low levels of cysts and oocysts of undetermined viability. Three of nine f inished water samples of 20,000 liters each revealed residual levels o f somatic coliphages at 0.03, 0.10, and 0.26 per 100 liters. Measured virus removal was more than 4 to 5 log10, and cyst removal was more th an 4 log10. Coliphage and C. perfringens counts suggested that the tot al removal and inactivation was more than 7 log10 viable microorganism s. C. perfringens counts appear to be the most suitable indicator for the inactivation and removal of viruses in drinking water treatment. T hey also appear to have a relationship to cysts and oocysts and could be used as indicators of their inactivation and removal. We propose th eir use as surrogates for virus and parasite testing of drinking water .