Enhanced HO[rad] production from ozonation activated by EDTA

Abstract

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 production from ozone at acidic pHs by EDTA. EDTA significantly accelerated the degradation of benzoic acid (BA), an HO probe, by ozonation in the pH range of 2.3–5.5, with higher efficiency than the O3/H2O2 process. Such enhancement was less dependent on temperature compared to the O3 or O3/H2O2 processes. The O3 decay and BA degradation kinetics were both highly dependent on the EDTA concentration. At an O3 dosage of 1.0mg/L and pH 2.3, Rct(∫OHdt/∫O3dt) was significantly increased by 8–50times with increasing the EDTA concentration from 1.0 to 40μM. The enhanced HO production was further confirmed by electron paramagnetic resonance, with the HO yield at ∼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 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.