Valuation of characteristics of water purity. I. Estimation of the usefulness of some microbiological and hydrobiological characteristics.

The titres of physiological processes in bacteria (hydrolysis of urea, nitrification), total number of bacteria and photosynthesis were found to show high correlation with standard characteristics: BOD5 and saprobic index. The classificatory values of BOD5 and saprobic index depend on the pollution of waters (with BOD5 less than 3 mg O2/l more information on the extent of pollution is given by the saprobic index whereas with higher values BOD5 is better). The content of NH3-N and titres of ammonification and H2S production depend on the type of pollution and should not be used for determination of water purity without additional studies. Of increasing importance as a measure of pollution is the BOD5/BOD2 quotient.