Treatment of aqueous solutions of 1,4-dioxane by ozonation and catalytic ozonation with copper oxide (CuO)

In this study, treatment for the removal of 1,4-dioxane by ozone and by catalytic ozonation using CuO as the catalyst was investigated. While the removal of 1,4-dioxane was small (20%) and mineralization negligible after 6 h of ozonation treatment, the removals of 1,4-dioxane and total organic carbon increased by factors of 10.35 and 81.25, respectively, after catalytic ozonation in the presence of CuO. The mineralization during catalytic ozonation was favoured at pH 10 (94.91 min^-1), although it proceeded even at pH 3 (54.41 min^-1). The CuO catalyst decreased the equilibrium concentration of soluble ozone and favoured its decomposition to reactive oxidative species. Radical scavenging experiments demonstrated that superoxide radicals were the main species responsible for the degradation of 1,4-dioxane. Further scavenging experiments with phosphate confirmed the presence of Lewis active sites on the surface of CuO, which were responsible for the adsorption and decomposition of ozone. The reaction mechanism proceeded through the formation of ethylene glycol diformate, which quickly hydrolyzed to ethylene glycol and formic acid as intermediate products. The stability of CuO indicated weak copper leaching and high catalytic activity for five recycling cycles. The toxicity of the water, assessed by Vibrio fischeri bioluminescence assays, remained the same (low toxicity) after catalytic ozonation while it increased after treatment with ozonation alone.