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.

Acetone is a significant pollutant in contaminated groundwaters and industrial effluents. It can be treated by the UV/H2O2 process but only slowly. This study aims to understand the degradation mechanism and hence the reasons for slow treatment. The degradation of acetone was carried out in a UV reactor in the presence of ∼16 mM H2O2 such that most of the UV was absorbed by H2O2. The decay of acetone was followed by gas chromatography, and the generation of intermediates (identified as acetic, formic, and oxalic acids) was followed by ion chromatography. Measurement of the total organic carbon indicated a complete carbon balance throughout the reaction ending in mineralization. A kinetic model, based on an assumed mechanism, was developed that generated a profile of reactants and intermediates in agreement with the experimental data, including the pH profile. The initial concentrations of acetone and hydrogen peroxide strongly affect the initial rate of acetone degradation, but no pH effect was observed in the range of 2−7. It is concluded that acetone treats slowly because intermediates build up to such a concentration that they compete significantly for hydroxyl radicals and also because the mechanism appears to involve some degree of acetone recycling.

The application of the UV/H 2 O 2 process to the degradation of methyl tert-butyl ether (MTBE) in dilute aqueous solution resulted in the generation of tert-butyl formate (TBF), 2-methoxy-2-methyl propionaldehyde (MMP), formaldehyde, acetone, tert-butyl alcohol (TBA), and methyl acetate as primary byproducts. Other intermediates, such as carbonyl compounds (hydroxy-iso-butyraldehyde, hydroxyacetone, pyruvaldehyde) and organic acids (hydroxy-iso-butyric, formic, pyruvic, acetic, oxalic) were also detected and quantified during the irradiation. A good organic carbon balance is obtained throughout the treatment, indicating that almost all of the intermediates have been detected. The TOC pattern shows that eventually all the organic compounds are mineralized. Various analytical techniques, such as GC/MS, GC, IC, HPLC, and TOC analysis, were employed in order to identify and quantify the organic products. The detailed reaction mechanism proposed in this study for the degradation of MTBE by • OHdriven oxidation processes accounts for all observed intermediates and the high oxygen demand required for their complete mineralization.

A reinvestigation of the UV/H2O2 treatment of acetone has revealed previously undetected intermediates (pyruvic acid, pyruvic aldehyde, and hydroxyacetone). The time profiles of the concentrations of all intermediates have been determined, and a detailed mechanism for the degradation steps accounting for all detected intermediates is proposed. A kinetic model was developed on the basis of the proposed mechanism, and the predicted patterns of the reactants and intermediates are in good agreement with the experimental data. The application of the UV/H2O2 process to the degradation of acetone results in the eventual mineralization of all organic compounds, as demonstrated by TOC measurements.

Dedicated to Professor Andre¬ M. Braun on the occasion of his 60th birthdayThe ultraviolet (UV) direct photolysis of N-nitrosodimethylamine (NDMA) in aqueous solutions at pH 3 and 7 leads to dimethylamine, and nitrite and nitrate ions as the major degradation products. In addition, small amounts of formaldehyde, formic acid, and methylamine are formed. When the initial concentration of NDMA was 1 mm, only a 13% decrease in the total organic carbon (TOC) was measured at pH 7, whereas no significant change in the TOC was observed at pH 3. In the concentration range 0.01 ± 1 mm NDMA, zero-order kinetics is obeyed, whereas first-order kinetics is followed at concentrations below 0.01 mm. The photolysis occurs much faster at pH 3 than at pH 7, which is explained by the difference in the quantum yields of the process at these two pH values. UV Direct photolysis is an efficient process for the removal of NDMA from contaminated waters, and electrical energy per order (E EO ) values as low as 0.3 ± 0.5 kWh/order/m 3 were calculated for treatment of low concentrations of NDMA (0.001 mm).