The effects of hydrogen peroxide (H2O2) dose on treatment performance during ozone (O3)/H2O2 process in a continuous countercurrent reactor was investigated. Waters after sedimentation at two water purification plants were used as target waters. P-Chlorobenzoic acid (pCBA) was selected as a target compound because pCBA is not reactive with O3 molecule and degraded only by hydroxyl radicals. When H2O2 doses were set to be optimal for reduction of bromate formation, the H2O2 doses were also optimal for pCBA degradation. In case that H2O2 doses were expressed by molar ratios of H2O2 dose to O3 dose ([H2O2]/[O3]), the optimal values of [H2O2]/[O3] were not affected by O3 dose and types of waters after sedimentation. However, the optimal values were affected by water temperature, which was higher at lower temperature. The optimal treatment performance of O3/H2O2 process was achieved when residual ozone at an outlet of the reactor was not detected.

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