Plumbing Africa February 2018 | Page 30

28 HEALTH AND SANITATION Legionella: UV light disinfection operational conditions Ultraviolet (UV) disinfection does not produce a disinfectant residual. Also, when UV disinfection is applied to waters containing a disinfectant residual, the residual may be diminished following treatment with UV. By Environmental Protection Agency, document EPA 810-R-16-001 POTENTIAL WATER QUALITY ISSUES Water treated using only UV disinfection may, in some cases, be susceptible to contamination at downstream points. More than one type of disinfection or other control measure may be needed to protect the treated water downstream of UV disinfection, between the UV lamp and the taps and other water outlets (e.g. showerheads). At UV doses typically used in drinking water, UV disinfection does not support the formation of regulated disinfection by-products (DBPs). In addition, UV disinfection does not change the pH or treated water quality in such a way as to make it more corrosive to premise plumbing. Mercury can be released into the treated water when a UV lamp breaks. The amount of mercury that could potentially enter the water depends on the type of lamp and operation. Vapor phase mercury can dissolve into solution and be discharged downstream, whereas liquid February 2018 Volume 23 I Number 12 phase or amalgam mercury would tend to settle in the UV reactor. A mercury mitigation plan is recommended. OPERATIONAL CONDITIONS Parameter conditions indicating operational effectiveness Water quality data is needed to adequately characterise the water to be treated by a UV reactor and identify any pre-treatment or UV equipment design features t