Upstream Ozone or Downstream UVAOP: Where to Manage 1,4-Dioxane and Other Trace Contaminants in High-Bromide Applications of Carbon-Based Advanced Water Treatment

Alternatives for the removal of 1,4-dioxane in the context of a carbon-based advanced treatment were considered in this study. In ozonation, monochloramine used for bromate control limited 1,4-dioxane removal by scavenging hydroxyl radicals; however, most other ozone-reactive trace contaminants were well removed. Hydrogen peroxide (H2O2) addition enhanced 1,4-dioxane removal but could not control bromate formation when using a traditional ozone contactor, and CT credit could not be achieved. UV advanced oxidation (UVAOP) tests were conducted with H2O2 in the downstream UV disinfection system. Up to 75% removal was achieved. Pilot experiments showed that bromate could be controlled using multiple smaller ozone doses with H2O2. Analyses of chemical and energy costs were performed for the demonstration-scale and full-scale designs. O3–H2O2 using the multipoint dissolution approach of O3–H2O2 was significantly less expensive than UVAOP under most operating conditions for similar levels of 1,4-dioxane removal and was the preferred method for 1,4-dioxane removal. However, UVAOP was cost-competitive with O3–H2O2 at low GAC effluent TOC (≤2 mg/L) and if H2O2 was not quenched with free chlorine, which was a major cost of UVAOP. Early GAC regeneration to improve UVAOP performance was not cost-effective but may be necessitated by other treatment objectives.