Pilot-Scale Studies of Combined Clarification, Filtration,and Ultraviolet Radiation Systems for Disinfection ofSecondary Municipal Wastewater Effluent

Disinfection of municipal wastewater effluent was evaluated using three alternatives, including:1) low-pressure (LP) + medium-pressure (MP) UV lamps; (2) clarifier + LP + MP; and (3)pressurized sand filter + LP + MP. Total coliform (TC), fecal coliform (FC), fecal Streptococcus (FS), TSS, several physicochemical parameters, absorbtivity and UV- ransmittance (UVT; %) were tested. The UVT% for secondary, clarified and filtered effluents were 3.5, 34 and 50,respectively. It was observed a 15 percent photoreactivation in secondary effluent disinfected by LP lamp, while it was limited to 0.03 percent by the MP lamp after filtration. Filtration to a surface overflow rate (SOR) of 1,050 L/m2·hr, followed by MP irradiation at a dose of 230 mW·s/cm2 was an effective alternative to reduce the TC, FC, and FS in the disinfected secondary effluent. Filtration + MP lamp met the standards of 1,000 TC and 400 FC/100 mL for effluentdischarge to receiving waters. This process can also inactivate FS, effecting a 6-log reduction. Among the evaluated alternatives, none of the other treatment systems performed as well as the pressurized sand filter + MP lamp, making this the best combination for post-treatment and disinfection of secondary effluent from a well-run wastewater treatment plant

Keywords:

Combined Processes , Clarification , Effluent , Pressurized sand Filtration , Ultraviolet Radiation