Formation and minimization of bromate ions within non-thermal-plasma advanced oxidation

The formation and minimization of bromate ions as a by-product of the operation of a non-thermal plasma reactor for the removal of refractory organic species from drinking water was investigated. BrO3− formation kinetics was found to be 1st order with respect to the Br− concentration. BrO3− formation increased when the organic pollutant concentration fell below a threshold value, intrinsic to each organic species. Formation also increased when dissolved ozone concentration was elevated by injection of O3-rich air, generated inside the reactor, back to the water, although measured O3 concentrations were low (~0.1 mg/l). BrO3− formation significantly decreased at high temperatures (>35 °C) and low pH (~pH6.0) values and was found insensitive to the carbonate alkalinity concentration. Dosage of hypochlorite followed by ammonia to the inlet water was found to be more effective in minimizing bromate formation than ammonia dosage alone. A general method was developed for assessing the relative importance of the various possible bromate formation pathways within plasma reactors, and a probable dominant BrO3− formation reaction sequence was suggested for the particular conditions prevailing in non-thermal plasma systems.

► Potential formation of BrO3− and minimization thereof were quantified for the 1st time within non-thermal plasma operation.
► BrO3− formation was evaluated in presence of a few organic species under various water quality and operational parameters.
► A dominant pathway for bromate formation in non-thermal-plasma reactors was suggested.
► Stepwise addition of low Cl2 and NH4+ concentrations is an effective method for minimizing bromate formation to <10 μg/l.