AOX formation and elimination in the oxidative treatment of synthetic wastewaters in a UV-free surface reactor

The effect of chloride concentration and pH on the UV oxidation systems was examined. Phenol and methanol were used as organic substances. The treatment of these chemicals by UV oxidation using a newly developed lab scale pretest UV-Free Surface Reactor (UV-FSR) with and without Cl- addition at different pH values, is evaluated. Results of this study indicated that the Cl- concentration of the water and the chemical structure of the substances is more important than the pH of the water. There was no AOX at the beginning of the experiments, but a de-novo synthesis of AOX was observed during the batch experiments. This is caused by the high chloride content of the wastewaters. It can be supposed that OH-radicals oxidize some chloride-ions to form chlorine, which further reacts with organic compounds. During the treatment, these AOX compounds which are produced from the beginning of the reaction are destroyed again. Evaluations of these experiments were done according to TOC and AOX results. Approximately 80% and 99% TOC removal efficiencies were obtained for the treatment of Phenol and Methanol-containing wastewaters, respectively. In the literature, there are no relevant publications concerning the AOX formation of wastewater by wet oxidation-iron catalysed or by application of UV. For that reason, the main objectives of this study were: 1. to see the influence of chloride concentration and pH on the AOX(de.novo) formation with newly developed UV-Free Surface Reactor (UV-FSR), 2. to make a comparison of different AOPs, 3. to observe the effect of the chloride concentration on the TOC degradation efficiency, 4. to optimise reaction conditions. In synthetic wastewaters, Methanol (CH3OH) and Phenol (C6H5 OH) are used as pollutants. The concentration of each substance was 1000 mg/l and COD values were calculated theoretically. The H2O2 addition was calculated according to the COD with a convenient stoichiometric factor (e.g. 1). During experiments, the pH was always kept constant with the addition of either 25% H2SO4 or 33% NaOH depending on the experimental conditions. Each substance was treated with the addition of 1000 mg/l Cl-, 10000 mg/l Cl- and without Cl- addition at pH 3, pH 7 and pH 10, respectively. NaCl was used as a Cl- source. Adsorbable Organic Halogenides (AOX) were determined using a TOX analyser (European Standard EN 1485 H 14, 1996). TOC measurements were carried out using an Elementar High TOC Analyzer equipped with an auto sampler. The H2O2