Pilot study on bromate reduction in ozonation of water with low carbonate alkalinities by carbon dioxide

A pilot study was carried out to explore the application of carbon dioxide for pH depression in a bubble column and its ability to inhibit bromate formation for water with a low alkalinity. Results showed that in the absence of ammonia, CO₂ was capable of reducing bromate 38.0%–65.4% with one-unit pH depression. CO₂ caused a slightly lower bromate reduction (4.2%) than did H₂SO₄ when the pH was depressed to 7.4, and a more a pronounced lower reduction (8.8%) when the pH was depressed to 6.9. In the presence of 0.20 mg/L-N ammonia, bromate was largely inhibited with 73.9% reduction. When the pH was depressed to 7.4, CO₂ and H₂SO₄ showed an 11.3% and 23.5% bromate reduction respectively, demonstrating that the joint use of CO₂ and ammonia might be a plausible strategy of blocking all three bromate formation pathways. CO₂ could be applied through the aeration diifuser together with ozone gas, resulting in a similar bromate reduction compared with the premixing method through Venturi mixer.