ULTRAVIOLET DISINFECTION OF WASTE-WATER - EFFECT OF DOSE ON SUBSEQUENT PHOTOREACTIVATION

The objective of this research was to examine the significance of photoreactivation of total coliform for u.v. disinfected secondary effluent. An appropriate methodology for quantifying photoreactivation was identified. Photoreactivation was evaluated in relation to u.v. dose, exposure to photoreactivating light and various water quality parameters. An increase in u.v. dose is extremely valuable in minimizing photoreactivation events. A significant inverse relationship was found between average u.v. dose and photoreactivation of coliform in wastewater at both low and high u.v. doses. Increased levels of suspended solids had the effect of reducing the true u.v. dose reaching targeted organisms, thus reducing DNA damage and increasing subsequent photoreactivation. The dose of photoreactivating light was also observed to be an important parameter in the reactivating process.