Activation of ozone for water treatment in acidic solution is challenging due to the lack of efficient initiators (e.g., HO-). Here, we report a marked enhancement of HO center dot production from ozone at acidic pHs by EDTA. EDTA significantly accelerated the degradation of benzoic acid (BA), an HO center dot probe, by ozonation in the pH range of 2.3-5.5, with higher efficiency than the O-3/H2O2 process. Such enhancement was less dependent on temperature compared to the O-3 or O-3/H2O2 processes. The O-3 decay and BA degradation kinetics were both highly dependent on the EDTA concentration. At an O-3 dosage of 1.0 mg/L and pH 2.3, R-ct (integral (OH)-O-center dot dt/ integral O-3 dt) was significantly increased by 8-50 times with increasing the EDTA concentration from 1.0 to 40 mu M. The enhanced HO center dot production was further confirmed by electron paramagnetic resonance, with the HO center dot yield at similar to 14.4%. Continuous batch runs were performed with the initial addition of EDTA only, and a similar enhancement effect was observed during cyclic runs. A plausible mechanism involving the formation of organonitrogen intermediates and nitrogen- or carbon- centered radicals is proposed to interpret the HO center dot generation in the system. This study sheds new light on the activation of ozone at acidic pHs, and is believed to broaden the scope of ozonation in water treatment. (C) 2015 Elsevier B.V. All rights reserved.