Reductive Electrochemical Activation of Hydrogen Peroxide as an Advanced Oxidation Process for Treatment of Reverse Osmosis Permeate during Potable Reuse

Abstract

The UV/hydrogen peroxide (H₂O₂) advanced oxidation process (AOP) frequently employed to generate hydroxyl radical (^•OH) to treat reverse osmosis permeate (ROP) in potable reuse treatment trains is inefficient, using only 10% of the H₂O₂. This study evaluated ^·OH generation by electron transfer from a low-cost stainless steel cathode. In deionized water, the electrochemical system achieved 0.5 log removal of 1,4-dioxane, a benchmark for AOP validation for potable reuse, within 4 min using only 1.25 mg/L H₂O₂. Hydrogen peroxide and 1,4-dioxane degradations were maximized near -0.18 and + 0.02 V versus standard hydrogen electrode, respectively. Degradations of positively and negatively charged compounds were comparable to neutral 1,4-dioxane, indicating that degradation occurs by ^·OH generation from neutral H₂O₂ and that electrostatic repulsion of contaminants from the electrode is not problematic. For ROP without chloramines, 0.5 log 1,4-dioxane removal was achieved in 6.7 min with 7 mM salts for ionic strength and 2.5 mg/L H₂O₂. For ROP with 1.4 mg/L as Cl₂ chloramines, 0.5 log 1,4-dioxane removal was achieved in 13.2 min with 7 mM salts and 4.5 mg/L total H₂O₂ dosed in three separate injections in 5 min intervals. Initial estimates based on lab-scale electrochemical AOP treatment indicated that, except for the cost of salts, the electrochemical AOP featured lower reagent costs than the UV/H₂O₂ AOP but higher electricity costs that could be reduced by optimization of the electrochemical design.