[Use of UV rays for the disinfection of water. II. Microbiological studies of surface water].

Untreated surface water of a total bacterial count of approximately 10(4) cfu/ml was contaminated additionally with suspensions of E. coli and S. faecium, which contained about 10(6) cfu/ml. At flow rates of 7.2 m3/h, 4.0 m3/h and 2.0 m3/h the survival of bacteria as a function of exposure to radiation was measured with two different U.V.-disinfection units. In surface water, -without an additional contamination -minimum doses of radiation up to 74 mWs/cm2 were necessary to cause a reduction of 99.99% for total bacterial counts and counts of lactose-positive colonies. When suspensions of E. coli or S. faecium were added, a reduction of 99.99% for total bacterial count was attainable with minimum doses up to 71 mWs/cm2. To reduce the number of lactose-positive colonies or the number of D-streptococci to 99.99% a minimum dose up 56 mWs/cm2 or 18 mWs/cm2 was necessary.