Pilot-scale studies of combined clarification, filtration, and ultraviolet radiation systems for disinfection of secondary municipal wastewater effluent Original Research Article

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 transmittance (UVT; %) were tested. The UVT% for secondary, clarified and filtered effluents were 3.5, 34 and 50, respectively. A 15% photo-reactivation in secondary effluent disinfected by LP lamp was observed, while it was limited to 0.03% by the MP lamp after filtration. Filtration to a surface overflow rate (SOR) of 1050 L/m2 h, 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 1000 TC and 400 FC/100 mL for effluent discharge 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.