AVALIAÇÃO DO EMPREGO DA RADIAÇÃO ULTRAVIOLETA NA DESINFECÇÃO DE ÁGUA DE LAVAGEM DE FILTRO DE ESTAÇÃO DE TRATAMENTO DE ÁGUA

Abstract

The backwash water in a conventional water treatment plant (WTP) can represent 3 to 10% of the total production of treated water. As this volume is high, there is potential interest in the recirculation of this waste. However, there are some precautions that should be taken, as this wastewater may contain metals, organic matter, solids, trihalomethanes precursors, cysts and oocysts protozoan, indicators of fecal contamination, or other impurities that remain in the filtration process. This research aimed to investigate the process of coagulation, flocculation, and decantation with and without the use of chemical coagulant aluminum sulfate applied to the filter backwash water of a conventional WTP and its subsequent disinfection with ultraviolet radiation. During the tests, the equipment used was a jar-test and a bench-scale UV reactor. Without using a chemical coagulant (0 mg.L−1) and with 30 minutes of decantation, the average turbidity value was reduced to 4.92 uT, promoting the best removal value. The evaluation of microorganisms E. coli, total coliforms and spores of aerobic bacteria were performed after the preliminary treatment of the washing water in jar-test equipment with three assays and a liquid depth of 2 cm, the statistical treatment of the data was performed using the Tukey test. For the tests with UV radiation, after the application of doses that varied from 200.42 mWs.cm−2 to 721.53 mWs.cm−2, it was observed that the average removal from E. coli was 1.5 logs, and after analysis of variance, it was observed that there was no significant difference between the means, with increasing doses of UV radiation used in all tests. For total coliforms, there were significant decreases in removal, reaching an average removal of 3.21 logs of inactivation. The aerobic bacteria spores group did not show greater resistance to UV radiation in all tests, and there was no significant difference between the means, reaching an average inactivation efficiency of 3.92 logs. In this way, the study allows the consolidation of the good perspective of the application of coagulation, flocculation, and decantation, followed by UV radiation as an alternative in the treatment of filter backwash water, allowing for better water quality waste and recirculation more safely.