Mechanism of the Degradation of 1,4-Dioxane in Dilute Aqueous Solution Using the UV/Hydrogen Peroxide Process

Abstract

Dioxane is an EPA priority pollutant often found in contaminated groundwaters and industrial effluents. The common techniques used for water purification are not applicable to 1,4-dioxane, and the currently used method (distillation) is laborious and expensive. This study aims to understand the degradation mechanism of 1,4-dioxane and its byproducts in dilute aqueous solution toward complete mineralization, by using the UV/H 2 O 2 process in a UV semibatch reactor. The decay of 1,4-dioxane generated several intermediates identified and quantified as aldehydes (formaldehyde, acetaldehyde, and glyoxal), organic acids (formic, methoxyacetic, acetic, glycolic, glyoxylic, and oxalic) and the mono-and diformate esters of 1,2-ethanediol. Measurement of the total organic carbon (TOC) during the treatment indicated a good agreement between the experimentally determined TOC values and those calculated from the quantified reaction intermediates, ending in complete mineralization. A reaction mechanism, which accounts for the observed intermediate products and their time profiles during the treatment, is proposed. Considering the efficacy of the 1,4-dioxane removal from dilute aqueous solutions, as shown in this work, the present study can be regarded as a model for industrially affordable Advanced Oxidation Technologies.

Removal of 1,4-dioxane from industrial wastewaters: Routes of decomposition under different operational conditions to determine the ozone oxidation capacity

“…Likewise, while generated in the beginning, the concentration of EGDF decreases during the experiment, as the amount of several decomposition products increases along the reaction ( Figure 7A). According to the chromatography, the further oxidation of EGDF leads mainly to the formation of glycolic acid, in accordance with Maurino et al and Stefan and Bolton [31,32]. In the relative absorbance profiles, glyoxylic acid appears concurrently with glycolic acid, most likely as a decomposition product of the latter [32], and when its concentration decreases, more oxalic acid appears ( Figure 7A).…”

“…According to the chromatography, the further oxidation of EGDF leads mainly to the formation of glycolic acid, in accordance with Maurino et al and Stefan and Bolton [31,32]. In the relative absorbance profiles, glyoxylic acid appears concurrently with glycolic acid, most likely as a decomposition product of the latter [32], and when its concentration decreases, more oxalic acid appears ( Figure 7A). Oxalic acid could be generated from both the degradation of glycolic and glyoxylic acids [31,32].…”

“…Considering these results and taking into account the literature, the decomposition of 1,4-dioxane by molecular O3 in acidic conditions ( Figure 7A) follows a pathway of EGDF formation as a primary intermediate, similarly to several UV assisted AOPs [31,32,[56][57][58]. EGDF is generated by an oxidative ring opening mechanism through peroxyl radical [32,35].…”

“…EGDF is generated by an oxidative ring opening mechanism through peroxyl radical [32,35]. In addition, a parallel route occurs through the formation of methoxyacetic acid [32], but in a lesser extent, since the chromatography analysis detected metoxyacetic acid only in the first quarter of the experiment. Likewise, while generated in the beginning, the concentration of EGDF decreases during the experiment, as the amount of several decomposition products increases along the reaction ( Figure 7A).…”

“…No reports have been published on the decomposition pathways of 1,4-dioxane by classical ozonation process, although the understanding of the degradation mechanism could play a great role in the process optimization. So far, the intermediates and by-products of 1,4-dioxane degradation have been studied based on chromatography analyses for UVbased AOPs [31,32].…”