Gaseous and liquid effluents treatment in bubble column reactors by advanced oxidation processes: A review

This review aims to provide insight and highlight recent research trends about the treatment of gaseous and liquid effluents by advanced oxidation processes (AOPs) in bubble column reactors (BCRs), which has become an important technology to ensure efficient degradation of different types of pollutants. UV/H2O2, Fenton, and photo-Fenton processes have been applied in BCRs for pollutants removal from gas streams, namely containing NO, Hg0, SO2, and VOCs. In such a case, degradation is carried out in the liquid phase, while bubbling promotes an efficient mass transfer of the contaminants from the gas to the liquid before oxidation. This reactor configuration was however also used to remove pollutants present in liquid effluents by Fenton, electro-Fenton, as well as ozonation, which has been extensively studied; for that reason, only a summary view of BCRs application in ozonation is presented. In this case, a good mass transfer of the oxidant (O3), present in the gas stream, is required before oxidation in the polluted liquid phase. In this review, the main features that should be taken into account in the application of different homogeneous AOPs in BCRs are addressed. The effects of determining factors like temperature, pH, oxidant, and catalyst dose or radiation power are also analyzed, with some relevant illustrative examples.