Abstract

The growing water scarcity has promoted the search for alternative water sources, including the harvesting and use of rainwater (RW). However, the microbiological quality of water collected from roofs poses health risks and requires effective treatment. This study evaluated the disinfection efficiency of advanced oxidation processes (AOPs) using UV-C irradiation, the application of O3 and their combination (UV-C/O3), when applied to simulated harvested rainwater (SHRW). Physicochemical and microbiological parameters, as well as the formation of disinfection byproducts, were analyzed. Furthermore, a bioassay using human fibroblast cells was conducted to establish the cytotoxicity of the generated byproducts. The UV-C/O3 combination achieved the highest bacterial Log reduction (3.9 in 60 min), significantly outperforming UV-C (1.6) and O3 (1.0) applied alone, with a 99.98% removal of faecal coliforms, indicators of waterborne disease risk. In addition, no byproducts were detected in the AOP treatments, whereas hypochlorite generated high levels of trihalomethanes and other regulated substances. The bioassay shows that SHRW treated with UV-C/O3 maintains significantly higher cell viability than hypochlorite-disinfected SHRW. Consequently, UV-C/O3-treated SHRW exhibits no detrimental effects on the cells, while hypochlorite-disinfected SHRW displays a cytotoxic behavior. Although the UV-C/O3 process showed higher energy consumption (EEO: 5.2 kWh/m3) than UV-C alone (EEO: 3.2 kWh/m3), both were considerably more efficient than O3 alone (EEO: 6.1 kWh/m3). The results show a synergistic effect between UV-C and O3, suggesting a safe and effective alternative for treating RW intended for human consumption or non-potable uses in rural and arid regions worldwide, and could be part of a water management plan.