Low-cost mineral packing materials improve DOM and micropollutants removal from landfill leachate in ozonation bubble columns: Insights into the enhancement mechanisms and applicability of surrogate-based monitoring

To intensify O3 mass transfer and increase removal of micropollutants in bio-treated landfill leachate, this study applied two minerals (lava rock and expanded clay aggregate (ECA)) to build mineral-packed bubble columns (named as LBC and EBC, respectively). The O3 gas–liquid mass transfer coefficient kLa of EBC (0.58 min−1) and LBC (0.62 min−1) was 2.4–2.5 times that of a non-packed bubble column (BC, 0.24 min−1). The O3 decomposition coefficient kd was also increased to 0.066 min−1 in EBC and 0.050 min−1 in LBC, as ECA and lava rock could work as stable catalysts to promote the O3 decomposition and generation of •OH. LBC and EBC had a comparable beneficial effect towards micropollutants removal and their intermediates’ degradation. At O3 dose of 0.08–1.46 g O3/g COD, minerals increased the removal of O3-recalcitrant compounds (atrazine and alachlor) by 20–40 % and the UV254 reduction (ΔUV254) by over 20 %. The enhancement of LBC and EBC resulted from the improved O3 mass transfer and the catalytic function of the minerals. Besides, a two-stage linear correlation between the O3-recalcitrant compounds removal and ΔUV254 was observed. The first and second stage are dominated by the direct O3 reaction and •OH oxidation process, respectively. For the packed columns, removal mainly occurred at the second stage probably due to the improved •OH production by the packing materials. Based on such correlation model, ΔUV254 can be used as a surrogate for predicting the removal of micropollutants in packed columns. Overall, this study provides novel insights into the enhanced micropollutants abatement in landfill leachate by using mineral-packed ozone bubble columns.