Soil flushing for remediation of landfill leachate-contaminated soil: A comprehensive evaluation of optimal flushing agents and influencing factors

• Published in: Waste management (Elmsford) Vol. 200; p. 114771
• Main Authors: Yu, Haitao, Liu, Zhibin, Song, Min, Liu, Luqi, Liu, Zhu
• Format: Journal Article
• Language: English
• Published: United States Elsevier Ltd 01.06.2025
• Subjects: ammonium nitrogen; Chelating Agents - chemistry; chromium; Contaminated soil; Environmental Restoration and Remediation - methods; Flushing agents; Hydrogen-Ion Concentration; Landfill leachate; landfill leachates; landfills; Metals, Heavy - analysis; Nitrogen; polysorbates; remediation; rhamnolipids; Saponin; saponins; soil; Soil - chemistry; Soil flushing; Soil Pollutants - analysis; Soil Pollutants - chemistry; Surface-Active Agents - chemistry; Temperature; total nitrogen; waste management; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry; Flushing agents; Soil flushing; Contaminated soil; Landfill leachate; Saponin
• ISSN: 0956-053X; 1879-2456; 1879-2456
• DOI: 10.1016/j.wasman.2025.114771

•Saponin has great potential for flushing landfill leachate-contaminated soil.•A higher temperature or lower solid–liquid ratio will improve the extraction yield.•Higher pH reduced the effectiveness of saponin in removing chromium.•The preferred saponin injection conditions are proposed for different contaminants.•The flushing efficiency of 8 common agents were compared in detail. Screening the appropriate agent is essential to enhancing the effectiveness of soil flushing techniques in remediating landfill leachate contaminated soil. To identify effective flushing agents for leachate-contaminated soil and determine optimal conditions for their use, this study evaluated five surfactants and three chelating agents. These agents were analyzed through batch experiments and one-dimensional column tests to assess the effects of pH, temperature, solid–liquid ratio, and injection conditions on their efficacy. The findings revealed that saponin, known for its high degradability, was most effective in extracting heavy metals (total Cr and Cr (VI)), total nitrogen, ammonia nitrogen, and organic compounds. Notably, the removal efficiency of these contaminants by saponin increased with higher concentrations. Conversely, higher pH levels reduced the effectiveness of polysorbate 80 (Tween 80), rhamnolipid (RL), and saponin in removing chromium but improved ammonia nitrogen extraction. Alternatively, the remediation outcomes are also subject to a tight control of temperature and solid–liquid ratios, which is reflected in the strengthening efficiency along with rising temperatures and the amount of flushing agents applied. The study further examined the impact of different injection methods on the remediation process. Continuous injection was most effective for soils primarily contaminated with chromium, whereas a step-gradient mode yielded better results for nitrogen compounds. For soils with a high concentration of organic pollutants, a multi-pulse injection mode was optimal. These insights provide a solid foundation for developing targeted soil flushing strategies aimed at enhancing the remediation of soils contaminated by landfill leachate.