This study analyses post-treatment Escherichia coli regrowth in drinking water after UVC LED disinfection and proposes a kinetic model to predict it. The model integrates the effects of UVC dose (0.06–0.15 J·cm −2 ), storage temperature (15, 20, 25 and 37 °C) and water matrix (wastewater secondary effluent vs isotonic water). Regrowth was monitored for up to 7 days under dark-storage conditions, representative of covered tanks, bottles and enclosed distribution systems where photoreactivation is negligible. The model, fitted to experimental data, achieved a global NRMS Error of 9.38 % for kinetic constants and a NRMSL Error of 19.77 % for bacterial concentrations, indicating good agreement with observations. Results showed an inverse relationship between UVC dose and regrowth, identifying a threshold dose (D0) of 0.129 J·cm −2 above which no detectable increase in bacteria concentration was detected, regardless of temperature or water matrix. Temperature affected regrowth kinetics, with slower proliferation at ≤ 25 °C and rapid recovery at 37 °C, close to the optimal growth temperature for E. coli . The water matrix also influenced outcomes, with lower bacterial recovery in wastewater effluents than in isotonic water. Importantly, the model indicates that ensuring compliance with stringent standards after 7 days of storage may require UVC fluences up to four times higher than those typically recommended based solely on immediate inactivation, highlighting the need to account for regrowth in system design. Overall, the model is a useful tool to assess microbial risks and optimize UVC-based disinfection strategies. • The kinetic model predicts bacterial regrowth after UVC-LED water disinfection • Higher UV doses reduce regrowth, with a dose beyond which no regrowth occurs • Storage temperature strongly influences regrowth, with faster recovery at 37°C • Water matrix affects bacterial survival, with lower regrowth in wastewater • The model provides a predictive tool for optimizing UV based water disinfection.
Martín-Sómer et al. (Sun,) studied this question.