Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4482534 | Water Research | 2013 | 9 Pages |
Reverse osmosis concentrate from wastewater reclamation contains biorefractory trace organic contaminants that may pose environmental or health hazard. Due to its high conductivity, electrochemical oxidation of brine requires low voltage which is energetically favourable. However, the presence of chloride ions may lead to the formation of chlorinated by-products, which are likely to exert an increased toxicity and persistence to further oxidation than their non-chlorinated analogues. Here, the performance of Ti/Pt–IrO2, Ti/SnO2–Sb and Si/BDD anodes was evaluated for the electrochemical oxidation of ROC in the presence of chloride, nitrate or sulfate ions (0.05 M sodium salts). In order to investigate the electrooxidation of ROC with nitrate and sulfate ions as dominant ion mediators, chloride ion concentration was decreased 10 times by electrodialytic pretreatment. The highest Coulombic efficiency for chemical oxygen demand (COD) removal was observed in the presence of high chloride ions concentration for all anodes tested (8.3–15.9%). Electrooxidation of the electrodialysed concentrate at Ti/SnO2–Sb and Ti/Pt–IrO2 electrodes exhibited low dissolved organic carbon (DOC) (i.e. 23 and 12%, respectively) and COD removal (i.e. 37–43 and 6–22%, respectively), indicating that for these electrodes chlorine-mediated oxidation was the main oxidation mechanism, particularly in the latter case. In contrast, DOC removal for the electrodialysed concentrate stream was enhanced at Si/BDD anode in the presence of SO42− (i.e. 51%) compared to NO32− electrolyte (i.e. 41%), likely due to the contribution of SO4·− and S2O82− species to the oxidative degradation. Furthermore, decreased concentration of chloride ions lead to a lower formation of haloacetic acids and trihalomethanes at all three electrodes tested.
Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (120 K)Download as PowerPoint slideHighlights► Electrodialysis was applied to decrease chloride concentration prior to oxidation. ► Anodic oxidation in the presence of chloride, nitrate or sulfate was investigated. ► The highest COD removal was achieved when high chloride concentration was present. ► Decreased concentration of chloride ions lead to a lower formation of by-products.