Dissolved ozone requires degassing for about how long before discharge?

• A. 5 minutes
• B. 30 minutes
• C. 1 hour
• D. 10 minutes

Answer: (B)

Dissolved ozone must off-gas before discharge to prevent releasing ozone gas and to meet safety and regulatory limits. Ozone in water is volatile and decays with time, but allowing a dedicated degassing period gives enough time for the dissolved ozone to escape and for residual levels to drop to safe values. About 30 minutes is the typical residence time used in practice to ensure sufficiently reduced ozone before discharge, balancing effective degassing with process efficiency. Shorter times (5 or 10 minutes) risk leaving ozone in the water, while a longer time (1 hour) isn’t usually needed and slows the process.