Oxidative degradation of AOX and COD by different advanced oxidation processes: A comparative study with two samples of a pharmaceutical wastewater

Using two samples of a pharmaceutical wastewater, the efficiency of three advanced oxidation processes (AOPs) (H2O2/UV, O-3/UV and H2O2/Fe(II)) for the removal of adsorbable organic halogen (AOX) and chemical oxygen demand (COD) were compared on a laboratory scale. The AOX contents of these samples ranged from 3 to 5 mg/L. Generally the results showed that all three methods are suitable for the degradation of AOX and COD. UV irradiation involved a high selectivity for the degradation of AOX compared to COD. On the other hand, processes based on hydroxyl radicals were less selective but considerably more effective in COD degradation. This explains why the combined methods H2O2/UV and O-3/UV lead both to a complete destruction of AOX and a large removal of COD. During ozone treatment - without UV radiation a decrease of AOX was also observed, although to a lower degree. Using Fenton's reagent both AOX and COD could be removed almost completely. The reaction time needed for this kind of treatment was very low compared to the other two AOPs. O-3/UV treatment showed the largest consumption of ''activated'' oxygen (AO) during COD degradation. H2O2/Fe(II) treatment required almost the same amount of AO as H2O2/UV. (C) 1997 IAWQ. Published by Elsevier Science Ltd.