Bacterial inactivation kinetics, regrowth and synergistic competition in a photocatalytic disinfection system using anatase titanate nanofiber catalyst

This work studied the inactivation kinetics, bacterial regrowth and synergistic competition in the photocatalytic disinfection of a sewage isolated Escherichia coli (ATCC 11775) in an annular slurry photoreactor (ASP) system using anatase titanate nanofibers catalyst (TNC). The inactivation performance and disinfection kinetics of the TNC-ASP system were investigated with respect to operation conditions: TNC loading, pH, aeration rate and inoculums size. At the optimum conditions, a 99.999% inactivation of 7 × 10⁶ CFU mL^-1 E. coli was achieved in 60 min. The modified Hom model was used to perfectly-fit the sigmoid-shaped disinfection kinetic profile. The residual disinfecting effect was evaluated by post-irradiation Fenton reaction. It was found that the 1.0 mg L^-1 Fe²⁺ in conjunction with low chemical oxygen demand (COD) was able to initiate the post-photocatalytic Fenton reaction, where substantial bacterial regrowth was suppressed after 24 h treatment. Studies on the synergistic effect of COD concentration on the inactivation and the bacterial regrowth potential revealed that the E. coli could regrowth at a COD concentration over 16 mg L^-1. Thus, significant removal of COD has to be ensured in a photocatalytic disinfection process to successfully maintain the biostability of the treated water.