Multi-point ozone dissolution for enhanced bromate control with hydrogen peroxide in potable reuse

Abstract

In the present study, a novel pilot ozone contactor configuration was employed using hydrogen peroxide (H₂O₂) and multiple ozone diffusion zones in an over-under contactor for testing three wastewater effluents. With a 1 : 1 molar H₂O₂ : O₃ dose, splitting the ozone dose between three diffusers reduced bromate formation by as much as 93% compared to the traditional single diffuser control condition. The required H₂O₂ dose for similar bromate levels was decreased by more than 90%. 1,4-Dioxane was used as a representative contaminant and hydroxyl radical (·OH) probe compound. H₂O₂ addition significantly improved 1,4-dioxane removal, and removal was similar between different diffuser conditions for the same total ozone dose. Detailed ozone residual and ozone exposure measurements showed that, with H₂O₂, similar ozone exposure was provided between the single and multi-diffuser H₂O₂ experiments. This indicates that minimization of local ozone concentration, rather than exposure, is vital for preventing the O₃–Br· reaction which controls bromate formation and may be beneficial for removal of ozone reactive contaminants and disinfection. Ozone decay, both with and without H₂O₂, was extremely sensitive to pH. Bromate formation increased by a factor of nearly two from pH 6 to 8 in the control condition, while the effect was less pronounced with H₂O₂. 1,4-Dioxane removal was unaffected by pH or temperature, while bromate formation decreased with increasing temperature.