Studies on disappearance and inactivation of viruses in sewage, 2

Methods of inactivating viruses in wastewater were studied. Polio visuses were added to the distilled water until the number of viruses reached 10sup(6.8) TCID50/ml, and liquid layer was 2 mm. The inactivation rate of viruses was determined at each time of ultraviolet (U.V.) irradiation (from 0.425 x 104μw/cm2 to 10.0 x 104μw/cm2). A linear correlation was seen between the inactivation rate of viruses and the time of U.V. irradiation obtained from logarithmic transformation. The irradiation time required for inactivation of 99.9% viruses was 15 sec when U.V. intensity was 10.0 x 104μw/cm2 and 9.6 min when it was 0.423 x 104μw/cm2. When the U.V. intensity was 0.425 x 104μw/cm2, the time required for inactivation was dependent on the number of viruses (120 sec in cases of 10sup(3.8) TCID50/ml of viruses and 720 sec in cases of 10sup(7.8) TCID50/ml of viruses). When viruses were added to the distilled water until the number reached 10sup(5.8) TCID50/ml, and the depth of water was designated as 2 mm, 10 cm, and 15 cm, the U.V. permeability was more than 89% at any depth of water, and a sixteen-min U.V. irradiation inactivated more than 99.99% of viruses. When polio viruses were added to triple step-treated water until the number reached 10sup(5.3) TCID50/ml, the irradiation time required for inactivation of more than 99.99% was one min when the U.V. intensity was 10.0 x 104μw/cm2 and 20 min when it was 0.425 x 104μw/cm2. (Namekawa, K.)