Impact of UV intensity, water temperature, and turbidity on solar disinfection efficiency: insights from moderated mediation analysis using the Johnson–Neyman technique†

This study investigated the bacterial inactivation effects of solar disinfection (SODIS) by separating direct UV inactivation from temperature-mediated mechanisms using moderated mediation analysis. The influence of turbidity and interactions between these inactivation pathways were examined with the Johnson–Neyman (J–N) technique. Analysis of data from five months of SODIS experiments, including the E. coli inactivation rate constant, 5 hour average midday UV intensity, maximum water temperature, and turbidity, revealed that within the synergistic temperature range, temperature-mediated inactivation accounts for 62% of total bacterial reduction, while UV contributes 38%. The lowest significant synergistic temperature was identified to be 48 °C at 5 NTU, with the synergistic effect ceasing beyond 56 °C as inactivation becomes independent of UV. Inactivation was optimized at 17 NTU, beyond which the role of turbidity became unclear. The implications of the findings on the choice of enhancement technology were discussed. The findings also highlight the limitations of multivariate regression in assessing parameter interactions, emphasizing the need for the J–N technique to accurately identify interaction ranges and parameter significance.