Ultraviolet Disinfection for Small Treatment Plants

The increasing concerns regarding disinfection byproducts (e.g. THMs) and the safety of disinfection practices have led to an increasing popularity in the use of ultraviolet light (UV) disinfection in wastewater treatment facilities, particularly in wastewater reuse facilities where filtration (e.g. membrane) technologies are used to produce high quality effluent. UV disinfection has been evaluated and recommended as the low cost option for disinfection in comparison to chlorination (either with gaseous or liquid chlorine) for new facilities, mainly because no dechlorination facility will be required with UV disinfection. Existing facilities with chlorine disinfection are under the regulatory pressure to consider disinfection alternatives. Many existing facilities practicing chlorination disinfection have switched to UV.The key issues we faced and solutions we developed while selecting disinfection technologies for wastewater reuse applications are presented. Considerations for design of a UV system, particularly in wastewater reuse facilities to ensure that the UV system is compatible with the site-specific conditions are also addressed. Subjects to be presented include: 1) Know what you want: select a suitable UV disinfection technology for your wastewater treatment plant; 2) Get what you want: design-bid-build or equipment procurement. Case studies of recent UV system designs, installations and startup at four northern California coastal and central valley wastewater treatment plants are presented to illustrate the effectiveness of the overall selection and design processes.