Comparison of macro and micro-pollutants abatement from biotreated landfill leachate by single ozonation, O3/H2O2, and catalytic ozonation processes

Micropollutants (MPs) in landfill leachate have attracted increasing attention because they pose a potential threat to the aquatic environment and ecosystems once discharged into nearby aquifers without proper treatment. Although ozone-based oxidative techniques perform well for the removal of MPs in low-strength water streams, their role in leachate containing high dissolved organic matter (DOM) concentration requires further exploration. Moreover, it is unclear the mechanism of different ozone-based processes in advanced treatment for biotreated landfill leachate. This study compared the single ozonation and two ozone-based advanced oxidation processes (AOPs, heterogeneous catalytic ozonation and O3/H2O2 process) for polishing biotreated leachate. The mechanism of different ozone-based processes during leachate treatment was explored, which facilitates selecting of the appropriate process based on leachate quality and target treatment requirements. The removal efficiency and energy requirements of the macro and micro-pollutants were evaluated. The results revealed that the role of catalytic ozonation is mainly to enhance the direct ozone oxidation, whereas the O3/H2O2 process is to promote the indirect oxidation. The strengthening effect was most visible in the early stage (specific transferred ozone dose (STOD) < 2 gO3/gDOC) for catalytic ozonation, whereas it was more pronounced in the later stage for the O3/H2O2 process. The removal of UV-quenching substances correlated well with the elimination of MPs (R2 > 0.95), which provides a surrogate-based predictive model for the removal of MPs from high-strength leachate. Catalytic ozonation consumed the least amount of energy when the desired chemical oxygen demand (COD) removal was ≤ 35 %, otherwise, the O3/H2O2 process was the most energy-efficient. In any process, MPs with O3 or OH reactivity could achieve more than 90 % elimination when the COD removal exceeded 30 %.