Effect of dissolved organic matter property on the regrowth of Escherichia coli after ultraviolet disinfection

Abstract

Ultraviolet (UV) disinfection is effective in bacterial disinfection without yielding by-products. After UV disinfection, however, bacteria can regrow depending on water quality although there is a paucity of knowledge about the relation of water quality to bacterial regrowth. Therefore, this study aimed to elucidate the effect of dissolved organic matter (DOM) property on the regrowth process of Escherichia coli (E. coli) under dark and light conditions. The changes in survival ratio of UV disinfected E. coli were observed under dark and light conditions in the presence of one of four DOMs, namely sodium pyruvate, tryptone, starch, and fulvic acid. After UV disinfection (265 nm), the survival ratio of E. coli was well described by the second-order regrowth model. Under dark condition, the maximum survival ratio (Sm) of E. coli during seven-day storage ranged from 8.6 % to 169.1 % while the maximum regrowth rate (Kmax) ranged from 0.020 % h−1 to 4.03 % h−1. In light condition, Sm ranged from 2.4 % to 348.5 %, Kmax ranged from 0.029 % h−1 to 31.1 % h−1. Two-way ANOVA indicates the significant effects of DOM type on those model parameters, which was possibly owing to their roles as a source of amino acids and as a scavenger of reactive oxygen species. Overall, DOM weakened visible light disinfection after UV disinfection while promoting bacterial dark repair and photoreactivation. This study revealed that DOM property largely influences regrowth after UV disinfection, highlighting the importance for considering such effect in UV disinfection.