Canadian Journal of Chemical Engineering, Vol.97, No.1, 67-73, 2019
Heterogeneous catalytic ozonation of naphthenic acids in water
A major challenge the oil sands industries are facing is the urgent need to treat large amounts of oil sands process-affected water (OSPW). OSPW is toxic to many species mainly due to the presence of naphthenic acids (NAs). Ozonation can significantly reduce both concentration and toxicity of the NAs. Unfortunately, this method suffers from its relatively high cost. To enhance NAs removal, we initiated heterogeneous catalytic ozonation of synthetic OSPW. Two types of catalysts were investigated: i) alumina supported metal oxides, and ii) unsupported catalysts. The alumina supported oxides included MnO2, MnO2/Co3O4, and MnO2/Li2O, while the unsupported catalysts were alumina and activated carbon (AC). All tested catalysts enhanced the ozone removal of NAs. Specifically, AC was found to be a very effective catalyst in addition to its adsorbability. AC significantly enhanced the removal of NAs and COD, the detoxification of the OSPW, and the biodegradability of NAs. For 85 % removal of NAs, the AC catalyzed ozonation needed 15 min whereas over 45 min were required by its non-catalyzed counterpart. By using AC catalyzed ozonation, the efficiencies of detoxification and COD removal were both over four times and the biodegradability of the synthetic OSPW was over five times of those treated by non-catalyzed ozonation. The mechanism study confirmed that due to the presence of AC the hydroxyl radical concentration increased 31 %, resulting in 26.4 % reduction in ozone consumption compared to non-catalyzed ozonation. The removal of NAs was enhanced because of the higher oxidation power of hydroxyl radicals than molecular ozone.