Leachate and landfill gas are the main contaminants produced by modern sanitary landfills. The leachate easily leads to clogging in the leachate transportation pipe, and the landfill gas can be used as renewable energy after the removal of CO₂. The study aims to investigate the removal of the major scale forming ion of Ca²⁺ in leachate using raw landfill gas before pipe transportation. The research demonstrated that, under the given experimental conditions, the removal rate of Ca²⁺ in the leachate was positively correlated with the pH value of the leachate, and negatively correlated with the intake flow rate of the landfill gas; the highest removal rate of Ca²⁺ was achieved when the intake flow rate and volume were 0.05 L/min and 2.0 L, respectively, and the highest removal rate of Ca²⁺ from the leachate was about 90%. The maximum removal rate of CO₂ from landfill gas could reach 95%, and the CO₂ content of the post-reaction gas was as low as 1.74% (volume percentage). The scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis showed that the precipitate was spherical and mainly contained inorganic substances such as CaCO₃, MgCO₃, Ca(OH)₂, Mg(OH)₂, and SiO₂. The study showed that, before the leachate was piped, the Ca²⁺ could be removed using the raw landfill gas, thereby reducing the potential for the formation of precipitation clogging in the pipeline. This study also provides new ideas for upgrading landfill gas to achieve a renewable-energy utilization plan, and reduces greenhouse gas emissions by reducing CO₂ emissions from landfills.

The preferential flow of leachate in landfill is unavoidable. Therefore, the mixed leachate formed by mixing young leachate and old leachate is the form of leachate mainly present in the gravel layer. In this study, static anaerobic culture experiments were used to investigate the changes in the properties of the mixed leachate. During the experiment, the chemical oxygen demand (COD) content of the three mixed leachates decreased greatly; CODs of 10%, 20%, and 30% were reduced by 12%, 38%, and 24%, respectively. The concentrations of Ca2+ and Mg2+ also decreased; Ca2+ was significantly reduced after a short time. The pH also dropped. The oxidation-reduction potential (ORP) of the three mixed leachates increased, indicating that the reducing organic matter in the leachate was gradually decomposed by microbial oxidation. Analysis by X-ray diffraction (XRD) showed that the main inorganic precipitate is magnesium-containing calcite, an isomorphous crystal. Studies have shown that if there is a mixed leachate in the gravel layer, severe clogging occurs therein. The clogging material is mainly a magnesium-containing calcite precipitate formed by the metabolic activity of organic matter in the microbial degradation of mixed leachate. Some suggestions were made for the operation and management of landfills.