Ozone-based advanced oxidation of biologically treated landfill leachate: Oxidation efficiency, mechanisms, and surrogate-based monitoring for bulk organics

Abstract

Landfill leachate effluent obtained from partial nitrification-Anammox (PNA) biological treatment still contains various recalcitrant organics. In this study, ozone-based oxidation processes (O3 and O3/H2O2) were applied to treat PNA leachate effluent. The oxidation efficiency and mechanisms were investigated by measuring chemical oxygen demand (COD), biochemical oxygen demand (BOD5), molecular size, fluorescence, UV–vis absorbance, and electron-donating capacity (EDC). Given the challenge of efficient ozone dosing, a surrogate-based monitoring approach was proposed and evaluated. Results show that leachate variability caused significant variation in the ozone utilization efficiency (O3E) for COD removal. The O3E of O3 and O3/H2O2 ranged between 0.32 and 0.47 mgCOD/mgO3, and between 0.43 and 0.73 mgCOD/mgO3, respectively. Compared to O3, O3/H2O2 was more effective to remove COD, to degrade the high molecular fraction, and to enhance biodegradability. The two-stage pseudo-first-order model (R2 > 0.90) can well describe the degradation of COD, fluorophores, UVA330, UVA254, and EDC during O3 and O3/H2O2 treatment, and the degradation rate can be ordered as follows: fluorophores > UVA330 > EDC > UVA254 > COD. Particularly, COD reduction was correlated well with surrogate reductions (i.e., fluorophores, UVA330, EDC, and UVA254) in an exponential function (R2 > 0.90), while exhibiting different steepness depending on the degradation kinetics of surrogates. The increased BOD5 showed a trend from rising and decline when presented as a function as surrogate reductions. The above correlations demonstrate the potential of surrogates to replace the conventional parameters for oxidation optimization and control. Overall, this research enriches the knowledge in the oxidation of recalcitrant organics in leachate and provides a reference for efficient ozone dosing.