Study of Ultraviolet Disinfection of Water and Factors in Treatment Efficiency

• Published in: Public health reports (1896) 1965-08, Vol.80 (8), p.695-705
• Main Authors: C. B. Huff, Smith, H. F., W. D. Boring, N. A. Clarke
• Format: Article
• Language: English
• Subjects: Bacteria; Disinfection; Flow velocity; Lamps; Old Medline; Poliovirus; Potable water; Public health; Sewage effluent; Sterilization; Turbidity; Ultraviolet Rays; Viruses; Wastewater treatment; Water; Water Microbiology; Water treatment
• ISSN: 0094-6214
• DOI: 10.2307/4592510

An evaluation of a commercially manufactured ultraviolet disinfecting system for water, designed primarily for shipboard use, indicated that the system will give satisfactory results if factors affecting transmission do not lower the intensity of ultraviolet energy below 15 on a special ultraviolet recording meter, and if the designed flow rate is not exceeded. The safety factor for the designed minimum total dosage is 1.6 to 1.7 for Escherichia coli at initial densities of 1 million per 100 ml., as determined by breakdown in treatment efficiency at two flow rates. Color, at a maximum level of 5 units, or iron, up to 3.7 ppm, as interfering factors in ultraviolet transmission did not decrease efficiency of treatment. Turbidity levels of 15 to 20 units may cause a decrease in intensity below the designed minimum. Turbidity levels up to 5 units did not decrease treatment efficiency below acceptable limits. Generally, units of color and units of turbidity are not adequate measures of the decrease that may occur in ultraviolet transmission. The organic nature of materials present in water can give rise to significant transmission difficulties. Waters relatively low in turbidity, color, iron content, and organic composition were adequately treated by the unit; however, most river waters, sewage, and other sources of high turbidity and organic and iron content usually did not result in a potable product at designed capacity. The apparatus also effectively inactivated certain enteric viruses when operated at the recommended intensity and flow rate, when virus levels were kept at approximately 1,000 plaque-forming units per milliliter. When the virus titer was raised above this level or when color material (instant tea) was added, live virus was detected in the treated water. The use of an accurate meter to record minimum intensity at 2,537 A. was a reliable means, along with flow-control valves, of monitoring the minimum dosage applied. These two controls incorporated in the continuous operation of a unit should provide an adequate checking system for treatment efficiency.