Attenuation of Organic Matter in Landfill Leachate: Seasonal Characterization and Soil Column Evaluation

andfill leachate (LL) from landfills and open dumpsites poses significant risks to surrounding soils and water bodies. This study investigated seasonal variations in physicochemical and heavy metal characteristics of LL at the newly operational Bancharedada landfill site in Nepal using the Leachate Pollution Index (LPI). It also evaluated the attenuation of organic content, measured as chemical oxygen demand (COD), across different soil textures using fixed-bed column tests. Kinetics analyses employed the Yoon-Nelson model (YNM), Thomas model (TM), and Adam and Bohart model (ABM). The biological oxygen demand (BOD5)/COD ratio ranged from 0.44 to 0.51, with higher values in the dry seasons and lower values during the monsoon, indicating rainfall-induced dilution of organic pollutants. The bed saturation time for COD removal was longest in clayey soil (35 days) and shortest in sandy soil (4 days). YNM provided the best model fit and was therefore applied for COD breakthrough prediction across soil textures. YNM rate constants (KYN) were lower in clayey soils and higher in sandy soils, thereby increase in breakthrough times (τ) and adsorption capacities (Qo) in clayey soils whereas the sandy soils shows the opposite trend, highlighting the strong influence of soil texture on COD attenuation potential.