Deep Insight into the Effect of Bicarbonate on Pollutant Abatement in the Uv/Chlorine Process

Abstract

The UV/chlorine process has gained significant attention from researchers and practitioners and is considered as a viable alternative to the UV/H2O2 process. HCO3–, widely spread in natural water, was traditionally perceived to act as a quencher in advanced oxidation processes (AOPs). It transformed less selective radicals to the much more selective CO3•–. Different with other radical precursors (e.g., persulfate, H2O2), HOCl swiftly reacts with CO3•–, giving rise to ClO•. Consequently, HCO3– introduces complexity to the radical chemistry in UV/chlorine process. This study comprehensively investigated the roles of HCO3– in the UV/chlorine process on pollutants degradation, and 1,4-dimethoxybenzene (DMOB) was selected as the target contaminate. Adding HCO3− in the UV/chlorine system significantly amplifies the generation of ClO• by ~2 times, thereby markedly expediting the degradation of DMOB. The reaction rate constant of CO3•− with free chlorine was measured to be 8.82×107 M−1 s−1 at pH 7.0. The influence of HCO3− on radical distribution in the UV/chlorine process is also contingent upon other solution conditions, including pH and chlorine concentration. Furthermore, this study demonstrated that the HCO3−-mediated radical conversion remains relatively unaffected by background constituents. The experimental data on pollutant degradation via UV/chlorine process in pure water can be leveraged to estimate the treatment efficiency in actual water scenarios. These findings enhance our comprehension of the intricacies of UV/chlorine chemistry in real water, thereby advancing the potential of this emerging AOP for niche application in water treatment.

Keywords: chlorine, bicarbonate, Oxychloride radical, DMOB