MICROBICIDAL EFFECT OF REFLECTED UV-RADIATION IN DEVICES FOR WATER DISINFECTION

A standardised biodosimetric method was used to quantify the influence of reflection on the reduction equivalent UV doses (RED) in two comme rcially available water disinfection systems. One device, possessing a reflector made of aluminium, showed a decrease of RED of about 40% af ter removing the reflector. In the other plant, made of stainless stee l, the inner surface of the irradiation chamber served as a reflector by itself. After eliminating the reflectance by black lacquering the i nner surface of the irradiation chamber a distinctive decrease of RED was measured. This effect depended on the transmittance of the water ( 253.7 nm). With increasing water transmittance an increasing relative loss of RED was observed. The results showed that the relative extent of the RED caused by reflection may even exceed the reflectance of the material due to multiple reflection, especially in water with high tr ansmittance. However, in UV disinfection plants with inner surfaces ma de of reflecting material the reflectance may decrease during the oper ating life. Therefore, measuring the extent of reflection influencing the RED by using a suitable biodosimetric method is essential in UV de vices for water disinfection. Copyright (C) 1996 IAWQ.