Migrating characteristics of pollutants from landfill leachate in cold regions and impact on hydrothermal conditions

Economic development, unique tourism resources, and lifestyle changes of herdsmen in the Qinghai-Tibet Plateau (QTP) have resulted in an increasing waste disposal problem and most of the domestic waste was dumped into garbage pits for open burning and simple landfills in the rural and pastoral areas of Tibet. However, knowledge about heat transfer, water, and pollutant transport from landfill leachate in cold regions is currently limited. A series of migration tests were carried out under freeze-thaw cycles (FTCs), analyzing the distribution of temperature, water, and pollutants from the landfill leachate (main components include ammonia nitrogen (AN), chemical oxygen demand (COD), and cadmium (Cd)). The results show that the distribution of temperature, water, and pollutants in frozen soil is closely related to FTCs, water migration, boundary temperature, and the polluted degree of soil. The response degree to the top temperature is largest, secondary, and smallest for the unpolluted, polluted, and polluting soil, respectively. In the polluting soil, with the increasing FTCs, the content of AN, Cd, and COD also increases, and the water content mainly increases in the first 5 cycles. AN and COD are mainly adsorbed in the shallow layer, and Cd is enriched in the bottom where the temperature is close to the initial freezing one. The higher the boundary temperature, the greater the adsorption capacity for AN and COD, and the smaller the enriched content of Cd in the measured depth. AN and Cd are more easily adsorbed or removed than COD.