Bromate Formation and Control During Ozonation in Advanced Wastewater Purification for Potable Reuse

ABSTRACT

The formation of bromate, a possible human carcinogen, remains a critical challenge in ozone‐based advanced water purification facilities (AWPF), particularly in potable reuse applications. This study investigates bromate formation and reduction dynamics within a pilot‐scale ozone‐biological activated carbon (ozone/BAC) treatment system at two water reclamation facilities (WRFs) in Reno, Nevada, USA. Ozone was transferred by a Venturi injection configuration followed by two ozone contactors, an intermediate break tank, and parallel BAC filters. Results demonstrated that increasing ozone doses significantly elevated bromate concentrations, with levels peaking at 3.8 μg/L (South Truckee Meadows WRF, STMWRF) and 5.2 μg/L (Reno Stead WRF, RSWRF) in the ozone effluent at ozone‐to‐TOC (ozone/TOC) ratios of 1.5 and 1.2, respectively. BAC filtration effectively reduced bromate levels, particularly at extended Empty Bed Contact Times (EBCTs) of 20 min, achieving bromate reductions to 2.4 ± 1.2 μg/L at STMWRF and to 3.0 ± 1.2 μg/L at RSWRF. Apparent bromide‐to‐bromate molar conversion was low relative to several wastewater ozonation studies, consistent with low measured ozone residuals/CT and strong matrix ozone demand. A bromide spiking study further highlighted the direct correlation between elevated bromide concentrations (up to 340 μg/L), ozone dose, and bromate formation, with bromate levels reaching 14 μg/L at higher ozone/TOC ratios, and then completely removed after BAC filtration. BAC filtration reduced bromate in several sampling campaigns, particularly at longer EBCTs; however, this is a site‐specific investigation and potentially linked to mature biofilms and carbon‐bed microenvironments. These findings emphasize the importance of optimizing ozone doses and EBCTs to balance contaminant removal, disinfection efficacy, and bromate mitigation, ensuring compliance with current and anticipated regulatory standards for potable water reuse.