Ultraviolet disinfection of secondary effluent

Abstract

The elimination of pathogenic microorganisms in wastewater discharged to receiving waters that may be used for human or livestock purposes is of utmost importance. In North America, wastewater is disinfected almost exclusively with chlorine. An increasing body of research1-4 reveals that chlorine residuals in receiving waters are deleterious to the aquatic biota. Chlorination also produces chlorinated compounds that may be toxic to hu mans and animals.4 An alternative to chlorination is ultraviolet (UV) disinfection.5 To date, studies involving UV disinfection of wastewater have involved the assessment of disinfection efficiency, factors that affect efficiency, and problems with the application of UV ir radiation. Laboratory studies with UV light have demonstrated an adequate reduction in indicator bacteria from secondary effluents.68 UV-irradiated effluent exhibited no toxicity to fish when compared to undisinfected wastewater.3,8 Jolley et al.9 showed that UV irradiation of nonvolatile organics in secondary effluent produced only slight chemical changes in the nonvolatile organics while in one effluent mutagenic constituents were elim inated. Pilot-1014 and full-scale15 studies of UV disinfection of waste water have demonstrated that the process can consistently achieve the objective of 200 fecal coliforms per 100 mL of effluent. UV devices designed for disinfection of potable water were used in most of these studies.