AWWA ACE56144

In Germany and Austria ultraviolet (UV) disinfection was used in the '80s for small water systems as a simple chemical free technology, and for large water systems as a disinfection technique without chlorination byproducts. But at that time, nothing was known about how much UV dose was needed to insure sufficient disinfection, and how sufficient UV dose could be monitored. The usual assumption was: detention time (flow rate divided by reactor volume) times assumed UV intensity at the end of lamp life time (calculated for some 2 inch distance from lamp) should lie between 150 and 250 J/m^2 (i.e. 15 and 25 mJ/cm^2). End of lamp life was determined either by an assumption of 10,000 hours or 1 year, or, if a light intensity monitor was installed, when reaching 50 to 60% of the initial intensity that was adjusted to 100% after mounting the new lamps. This practice kept most health authorities from allowing UV-disinfection in public water supply. To overcome this situation two German joint research projects on prerequisites to use ultraviolet radiation for drinking water disinfection were carried out from 1987 to 1994. Advised by a panel of 25 experts from health authorities, university institutes on hygiene, chemistry and technology, and major water suppliers, the project resulted in the findings, that disinfection performance of UV-systems: must insure a fluence of 400 J/m^2 (= 40 mJ/cm^2) based on radiation of 253,7 nm to inactivate all relevant waterborne micro-organisms and viruses to more than 4 logs (reproducible determination of UV susceptibility requires a homogeneous parallel beam irradiation in Petri dishes); depends on water quality, components and design; needs full scale challenge tests under worst case operation conditions with seeding microorganisms of specific UV susceptibility, (calculation can only model but not detect insufficiently irradiated volume parts); requires reproducible physical monitoring that insures challenge test conditions are maintained during use (removable standardized online UV sensors in sensor ports, that allow checking for proper reading by comparison to portable reference UV-sensors). To make UV disinfection acceptable for water suppliers and health authorities, it was necessary to establish: a national standard on properties and performance testing for UV systems; an online monitoring concept that allows verification of proper operation (comparable to the determination of residual chlorine with conventional disinfection); a testing facility to certify performance and monitoring; and, a certification body to keep track of quality of certified systems. According to these requirements, the German DVGW Standard W 294 was released in 1997 and the DVGW Test Facility for UV Disinfection Systems was established at the Wahnbach Reservoir Association near Bonn. The test facility is able to run full scale biodosimetric challenge tests of UV-systems with up to 20 mgd (3000 m^3/h) capacity. Furthermore, a standardized monitoring sensor was developed and adopted as industry standard. Includes 6 references, tables, figures.