Disinfection of roof harvested rainwater inoculated with E. coli and Enterococcus and post-treatment bacterial regrowth: Conventional vs solar driven advanced oxidation processes

Solar driven advanced oxidation processes (AOPs) (an alternative solar photo Fenton like process (SPF), sunlight/H2O2 (SHP) and sunlight/chlorine (SCL)) and respective dark conditions, were compared for the first time to conventional (chlorination and UV-C radiation) disinfection processes, in the inactivation of E. coli and Entero strains inoculated in real roof-harvested rainwater (RHRW), to evaluate their possible safe use for crop irrigation. In this regard, bacterial regrowth was also evaluated 6, 12, 24 and 48 h after disinfection treatment. The SPF, using iminodisuccinic acid (IDS)-Cu complex as catalyst, was optimized (H2O2/IDS-Cu 55/1 best molar ratio) under mild conditions (spontaneous pH) and sunlight. The faster inactivation kinetics were observed for the SCL process (k = 1.473 min−1, t1/2 = 0.47 min for E. coli and k = 1.193 min−1, t1/2 = 0.57 min for Entero), while the most effective processes in controlling bacterial regrowth were SPF and SCL. Although UV-C radiation (0–1.3 × 104 μW s cm−2 dose range) was the second faster disinfection process (k = 1.242 min−1, t1/2 = 0.55 min for E. coli and k = 1.150 min−1, t1/2 = 0.60 min for Entero), it was the less effective process in controlling bacterial regrowth (>10 CFU 100 mL−1 already after 6 h post-treatment incubation). According to the bacterial inactivation and regrowth tests carried out in this work, SPF and SCL are interesting options for RHRW disinfection, in case of effluent use for crop irrigation.