Sanitary sewage disinfection with ultraviolet radiation and ultrasound

Currently, the world is facing a horrible situation due to SARS-CoV-2. Though its RNA was found in wastewater, there are still no studies on RNA contamination detected in sewage. Hence, a possible treatment of sewage is suggested in this work. The disinfection stage is extremely important in the treatment of effluents, minimizing the impacts on the receiving body of water and promoting public health. In this context, the sequential use of ultrasound and ultraviolet radiation, on a bench scale, was investigated as a way to improve the disinfection of anaerobically treated effluents. Two types of treated effluents were tested, by septic tank and anaerobic filter, for which, two ultrasound frequencies, 25 and 40 kHz, and four doses of UV, 3.6; 9.0; 18 and 36 mJ cm−2 were applied. Physicochemical and microbiological parameters were observed for individual and sequential assays. The better quality of the anaerobic filter effluent influenced the performance of both processes, decreasing the concentration of organic load and turbidity, even though a concentration of total coliforms and Escherichia coli occurred in the lowest quality effluent (septic tank). The application of ultrasound has a positive effect on the inactivation of total coliforms and E. coli up to 1.0 log and provides better conditions for ultraviolet radiation to be sequentially applied. The UV radiation applied for the septic tank and the anaerobic filter inactivates 2.5 log for total coliforms and 3.5 log for E. coli, respectively. It is suggested that the disinfection methods applied in this work to inactivate gram-negative bacteria (E. coli) can also be applied to secondary treatment effluents, as well as being better tested for viruses, protozoa, and helminths.