Adsorbable organic halogens formed during treatment of Cl--containing wastewater by sulfate and hydroxyl radical-based advanced oxidation processes

The formation of adsorbable organic halogens (AOX) in two typical advanced oxidation processes (AOPs), (OH)-O-center dot-based (UV/H2O2) and SO4 center dot--based (UV/potassium persulfate (PDS)) processes, was investigated during the treatment of Cl--containing wastewater. Compared with the original AOX concentration (0.08 mg/L), a significant increase in the AOX concentration was observed in both AOPs under the condition that TOC concentration was minimized. Higher concentration of AOX was formed in the UV/PDS process than that in the UV/H2O2 process under all experimental conditions, although the former showed a better performance on TOC removal. An increase of effluent AOX concentration from 0.4 mg/L to 1.1 mg/L in the UV/H2O2 process and from 1.9 mg/L to 3.4 mg/L in the UV/PDS process was observed, respectively, when the Cl- concentration increased from 1800 mg/L to 10000 mg/L. This enhancement of high Cl- concentration on the AOX formation was attributed to the reactive halogen species generated in the AOP treatment. The term AOX(MFP) was created to determine the AOX formation potential of wastewater and AOPs system. The results showed that organic matters with a molecular weight (MW) between 1 k similar to 100 k Da tend to form AOX more easily than those with a MW lower than 1 k Da and higher than 100 k Da. In addition, eight and fourteen kinds of formed organic halogens were identified in UV/H2O2 and UV/PDS treated wastewater, respectively. Five kinds of them have been proved to be toxic, which partially contributed to the increase of acute toxicity of effluent. The results of this work provides a new perspective to evaluate, in terms of eco-safety and efficiency, the application of AOPs to wastewater containing high concentration of Cl-.