Dynamic changes in dissolved organic matter during transport of landfill leachate in porous medium

The dynamic changes in dissolved organic matter (DOM) during the transport of landfill leachate (LL) in porous medium should be explored, considering the high levels of DOM in the LL of municipal solid waste. Column experiments were carried out at 25 °C at a Darcy’s flux of 0.29 cm/h for 2722 h to compare the transport of Cl⁻, ultraviolet absorbance at 254 nm (UV₂₅₄), chemical oxygen demand (COD), and dissolved organic carbon (DOC) in the simulated porous medium by using the CXTFIT2.1 code. Results showed that the convection–dispersion equation (CDE) could describe Cl⁻ transport well. The high levels of λ and D could be highly correlated with the physicochemical properties of the porous medium. The transport of the studied DOM with evident aromatic character could be described appropriately by the CDE model with the first-order reaction assumption, considering the similar variation trends of UV₂₅₄, COD, and DOC in the effluent during experiments. Specifically, the values of retardation factor (R) were in the following order: DOC > UV₂₅₄ > COD, whereas the low values of the first-order decay coefficient (k₁) for DOC and COD were still higher than that for UV₂₅₄. High contents of humic-like substances in the DOM with complex toxic components resulted in the natural low removal efficiencies of COD, DOC, and UV₂₅₄ (≤ 23%), which could be confirmed by the variations of fluorescence index (FI) and humification index (HIX) in the effluent. The results should be helpful in evaluating the environmental risk induced by the LL leakage in a landfill site.