Abstract

Municipal solid waste (MSW) landfilling initiates long-term physical, chemical, and biological transformations that strongly influence environmental impacts and post-closure management. This study investigates the temporal evolution of physicochemical properties of landfilled MSW under semi-arid Mediterranean conditions at the Hassi Bounif technical landfill (Oran, Algeria). Representative waste samples of 500 kg were collected from landfill cells corresponding to five waste ages (<24 h, 1 week, 1-3 months, 3-6 months, and 1-3 years) following MODECOM guidelines, and based on the corresponding error intervals for each time period, which are 3.59%, 4.28%, 4.38%, 4.38%, 4.39%, respectively. Waste was characterized through granulometric sorting, compositional analysis, and determination of density, moisture content, pH, electrical conductivity, and organic matter content. Results reveal a progressive fragmentation of waste, marked by a global fall in waste fraction 20 mm < Fraction<100 mm from 55% ± 3.59% in fresh waste to 23.07% ± 4.39% in 3 years old waste, and a global accumulation of fine fractions with increasing age, going from 8% ± 3.59% in fresh waste to 19.7% ± 4.39% in 3 years old waste. Biodegradable fractions, particularly putrescible waste, undergo rapid degradation, with organic matter decreasing from 45.6% ± 3.59% in fresh waste to 0.42% ± 4.39% after three years, accompanied by characteristic pH evolution from acidic to near-neutral conditions. In contrast, non-biodegradable materials such as plastics and textiles persist and dominate aged waste with a rate of 32.06% ± 4.39% and 26.16% ± 4.39% respectively. Electrical conductivity and moisture content decrease with stabilization, reflecting reduced biological activity. These findings demonstrate that landfills function as dynamic environmental reactors rather than static storage systems and provide essential data for landfill monitoring, stabilization assessment, landfill mining potential, and sustainable post-closure management in semi-arid regions.