New production pathway of musty 2,4,6-tribromoanisole during raw water disinfection processes at a surface water treatment plant

Abstract

The City of Wichita Falls’ Cypress Environmental Laboratory developed a comprehensive taste and odor (T&O) monitoring program to identify T&O compounds, their point of origin, and how to mitigate each T&O event to lessen its impact and maintain consumer confidence. In January 2023, a T&O compound was detected in the water system using sensory analysis with a threshold odor number (TON) of 3, guiding further analytical testing to identify for musty compounds. The unknown was confirmed to be 2,4,6-tribromoanisole (2,4,6-TBA) at a maximum of 9.86 ng/L. Its point of origin for production was tracked to a raw water line using chlorine dioxide as a primary disinfectant. Jar tests were performed to confirm that the mode of production was excess free chlorine from the generation of chlorine dioxide in the presence of bromide in raw water. The event was mitigated using powdered activated carbon in clarifiers to adsorb and settle out the compound, resulting in a non-detectable level (a TON of 1 and <5.00 ng/L for 2,4,6-TBA). This paper discusses the unique generation pathway within a full-scale treatment plant and how a monitoring and response program can be used to help detect a T&O event in early stages and aid mitigation processes. HIGHLIGHTS T&O monitoring programs can identify untargeted compounds.; Sensory analyses are integral to an effective T&O monitoring program.; 2,4,6-Tribromoanisole can be produced through disinfection processes.; Powdered activated carbon is highly effective for adsorbing haloanisoles.; Excess free chlorine dosing should be minimized when generating chlorine dioxide.;

Keywords

• anisole
• bromide
• chlorine
• chlorine dioxide
• t&o