Disinfection methods in urban wastewater reuse: Process performance, chemical stability impact, and end-use...

Growing water stress compels the search for alternative water sources, such as reuse of treated urban wastewater. This study compares three disinfection methods, namely chlorination, ozonation, and UV irradiation, for urban wastewater reclamation. While the effectiveness of disinfection processes in terms of bacterial inactivation has been widely addressed in the literature, little attention has been paid to how different disinfection methods affect the chemical stability of reclaimed water. A comprehensive comparative analysis of disinfection methods (chlorination, ozonation, UV irradiation) was conducted, covering (i) microbial inactivation of E. coli, total coliforms, fecal enterococci, and Clostridium perfringens; (ii) impacts on chemical stability assessed using LSI, RSI, PSI, LR, and SI indices, and (iii) end-use suitability in relation to recognized industrial and agricultural standards. It was documented that across most indices (RSI, PSI, SI, LR), ozonation and UV did not intensify corrosive tendencies relative to the pre-disinfection state, and in some cases (RSI) even reduced them, with ozonation showing a clear stabilizing effect. By contrast, chlorination led to more corrosive conditions due to chloride addition, as indicated by LR. All tested methods achieved complete E. coli inactivation. Ozonation uniquely resulted in complete removal of total coliforms and C. perfringens, whereas UV achieved high but incomplete reductions, and chlorination produced near-complete coliform removal but limited C. perfringens inactivation. Reclaimed water from all disinfection methods applied met EU Class A irrigation criteria (Reg. 2020/741). For industrial uses, microbial targets were met, though pH adjustment, decarbonization and monitoring of TSS, Fe, Mn, and Salmonella are recommended.