Iranian Journal of

Backgrounds and Objectives:Today, due to health, environmental and economical problems, of chlorine application, UV radiation is better option than chlorine for disinfection of effluent. The aim of this study was disinfection of secondary effluent with UV radiation.
Materials and Methods: Two types of UV disinfection system including low pressure (LP) and medium pressure (MP) was used to disinfection of Isfahan North Wastewater Treatment Plant (INWWTP) effluent without pretreatment. Single and combined lamps were operated to evaluate the removal of total and fecal coliforms (TC and FC), and fecal streptococcus (FS). TSS, iron, hardness, UV absorption and transmittance were analyzed in order to observe the fouling of the quartz sleeves.
Results: After using LP lamp with dose of 161 mws/cm2, TC and FC content was declined to standard level (1000 TC, and 400 FC/100ml). In addition, disinfection with MP lamp was led to FS content of 400 MPN/100 mL. Combination of LP and MP, with dose of 460 mws/cm2 could be met the environmental requirements of TC & FC, and the FS count was reached to 400 MPN/100 mL with dose of 237 mws/cm2. Maximum photo-reactivation percentage of coliforms after LP and MP lamps were appeared 15 and 3 percent respectively, while it was not observed for FS.
Conclusion: High fluctuation in secondary effluent quality of INWWTP mainly TSS concentration was caused to decline of the UVT value. Therefore, disinfection of effluent by LP, MP and even combined both systems are not applicable in conventional UV dose. Hence, using advanced process unit before UV disinfection system is necessary for removal of TSS.