Comparative study of the UV/chlorine and UV/H2O2 advanced oxidation processes
The comparative study of the photodecomposition rates of chlorine (0.05-50 mM; pH = 4.5-11.5; 25°C) and of hydrogen peroxide (0.1-100 mM; pH &lt; 8.5) in pure water has shown that the values of the overall quantum yield of photodecomposition of HOCl and ClO‐ at 254 nm are almost identical (Φ = 1.0 ± 0.1) to that for H2O2 (Φ = 1.0) and do not vary with the initial concentration of chlorine or bicarbonate ions (0-10 mM; pH 8.5). The decomposition of chlorine is accompanied by a production of oxygen and chlorate. The study of the oxidation of benzoic acid (pH ≈ 8) showed that the degradation rates decrease in the following order: UV/chlorine &gt; UV/H2O2 &gt;&gt; UV alone &gt;&gt; chlorination alone. High pressure liquid chromatography (HPLC) analyses have shown that oxidation of benzoic acid by the UV/chlorine advanced oxidation process (AOP) leads to more degradation by-products than by the UV/H2O2 AOP, because of the formation of chlorinated by-products by reactions involving chlorine and Cl•.