Domestic Wastewater Disinfection Using Solar Radiation for Agricultural Reuse

A study was performed in Vicosa, Minas Gerais, Brazil, to determine the feasibility of using solar radiation to disinfect treated domestic wastewater (TDWW). The effluent from a residential development, after passing through a pre-treatment unit (bar screen and grit channel) and a septic tank, was used as supply. After the septic tank, the TDWW had mean values of 286 mg L -1 COD, 54 mg L -1 TSS, and 65 NTU turbidity. A square cement block reactor was constructed (located at 20° 45' 14" S, 42° ° 52 ' 53 " W) and used to disinfect the reclaimed TDWW Fixed depths of water (0.05, 0.10, 0.15, and 0.20 m) were tested at different exposure times from November 2004 to May 2005. Solar UV disinfection (SODIS) was effective in reducing mean concentration of indicator microorganisms, i.e., total coliform (TC) and Escherichia coli (E. coli), after 8 h of exposure to direct sunlight. Statistical analysis showed that the inactivation rates of E. coli did not significantly vary due to turbidity or dissolved oxygen. A model was developed to estimate the surviving E. coli population after SODIS from its initial population, depth of water treated, and solar energy received. The model indicated that, for a fluence accumulated of 32.91 MJ m -2 , a 4 log reduction of E. coli population was achieved with a wastewater depth of 0.05 m in the SODIS reactor.