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Author      Title/Abstract      


Design Considerations for Ultraviolet Disinfection
Author: David S. Murray, Rob Baur
Date:
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The Hillsboro and Forest Grove Facilities treat wastewater for discharge to the Tualatin River to meet a 200 fecal coliform per 100 milliliters (mL) standard during wet weather and for Level II reuse during dry weather periods. Level II reuse under Oregon regulations is defined as disinfection to meet a 23 total coliform weekly median, with no more than two consecutive samples exceeding 140 total coliforms per 100 mL. The treatment facilities are undergoing major plant upgrades that include improvements to the disinfection processes. The continued use of sodium hypochlorite followed by a new dechlorination system at each plant was considered. Sodium hypochlorite disinfection/dechlorination was also compared to low pressure and medium pressure ultraviolet (UV) disinfection. Medium pressure UV disinfection was determined to be the most cost-effective processes at both plants. New medium pressure UV disinfection systems are currently under construction that will eliminate the use and presence of chlorine-based disinfectants at both facilities.