Study of sequential disinfection for the inactivation of protozoa and indicator microorganisms in wastewater

Sewage disinfection has the primary objective of inactivating pathogenic organisms to prevent the dissemination of waterborne diseases. This study analyzed individual disinfection, with chlorine and ultraviolet radiation, and sequential disinfection (chlorine-UV radiation). The tests were conducted with anaerobic effluent in batch, in laboratory scale, with two dosages of chlorine (10 and 20 mg L-1) and UV (2.5 and 6.1 Wh m(-3)). In addition, to guarantee the presence of cysts in the tests, 104 cysts per liter of Giardia spp. were inoculated. The resistance order was as follows: E. coli = Total Coliforms < Clostridium perfringens < Giardia spp.. Furthermore, synergistic effects reached 0.06 to 1.42 log of inactivation in sequential disinfection for both the most resistant microorganisms.