Wastewater disinfection applying solar energy

Solar Water Disinfection Process (SODIS) is a simple technology using solar UV-A radiation (wavelength 320-400 nm) and elevated water temperature to inactivate pathogens. In the present survey, the effect of solar radiation on the disinfection of domestic secondary treated wastewater from the Wastewater Treatment Plant (WWTP) of the Municipality of Chania (Crete, Greece) was investigated during the day hours in summer. The used secondary treated wastewater samples had initial turbidity of 6 ΝΤU, BOD5 of 23 mgO2/L, and concentration of 4.6 × 104 and 2.6 × 104 CFU/100ml for the total heterotrophic bacteria cultivated at 37οC and at 22οC respectively, 5.5 × 105 CFU/100ml for the total coliforms, 1.5 × 105 CFU/100ml for the fecal coliforms, and 2 × 104 CFU/100ml for the fecal Enterococcus. The experiments were carried out in transparent Polyethylene Terephthalate plastic bottles during the months July, August and September. An average reduction of 97-99% of the concentration of the total heterotrophic bacteria, and of 99.5-99.9% of the total and fecal coliforms, as well as of the fecal Enterococcus was obtained after 6 hours of exposition in solar radiation with intensity ranging from 500 to 1,280 W/m2 and temperature from 33οC to 49οC in the wastewater. The results showed that solar disinfection of secondary treated domestic wastewater with turbidity less than 6 ΝΤU could be applied during the period of sunlight in WWTPs of settlements ≤15,000 equivalent population, of at least 6 hours in tanks with deepness of 10cm or tubes with a diameter of 10cm.