Assessment of Catalytic Performance of Fe2+ , Fe3+ and Fe2+:Cu2+ In Fenton and Photo-Fenton Treatment of Pulp Bleaching Wastewaterr

- Fenton process has been widely studied for the abatement of recalcitrant pollutants, such as adsorbable organic halides (AOX), from industrial wastewaters. In this work, Fenton and photo-Fenton processes were applied to remove AOX from real pulp bleaching wastewater. The catalytic performance of different oxidation states of iron (Fe 2+ and Fe 3+ ) and a combination of Fe 2+ :Cu 2+ were studied. Advantages, limitations, and operating cost of the different solutions studied were discussed. At the optimum operating condition adopted for AOX removal, side effect on organic load (COD and BOD 5 ) was also assessed. Iron catalysts Fe 2+ and Fe 3+ were firstly compared. For that purpose, response surface methodology (RSM) was applied to find the operating conditions yielding maximum AOX removal at minimum cost, for both iron species. After defining the most suitable iron catalyst load, a second round of experiments were conducted, to study Cu 2+ as Fenton (co)catalyst. In those experiments, the optimum load of catalyst previously found was maintained, and different Fe:Cu ratios were studied, namely: 0:100; 25:75, 50:50, 75:25 and 100:0 % (mol/mol). Fe 2+ proved to be a more cost-effective iron catalyst than Fe 3+ , with photo-Fenton process allowing for better performance with lower chemical, and lower operating cost. Fe 2+ showed superior catalytic performance than Cu 2+ , yielding around twice the AOX removal. In Fenton process, up to 50 % Cu 2+ was successfully included in the catalyst mixture, with no significant loss of catalytic activity neither increase in operating cost. On the other hand, no synergetic effect between metals was registered. The photolytic regeneration of Cu 2+ was not effective, which may have hindered ● OH production in photo-Fenton process, leading to a decrease efficacy with a decrease in the Fe:Cu molar ratio.