Field-scale preferential flow effect in landfill in-situ gas injection aerobic stabilization project

Landfill in-situ aerobic stabilization is a crucial technology for accelerating the stabilization of landfills. Existing evaluation methods focus on assessing the stabilization process but lack estimation and evaluation of the spatial distribution of gas injection flow rate. By analyzing the on-site monitoring data of oxygen, methane, and carbon dioxide from an aerobic stabilization project at a basic landfill in Wenzhou, Zhejiang Province, uneven spatial and temporal distributions of gas concentrations within the landfill pile during the operation period were revealed. A method to estimate the gas flow distribution using real-time gas concentration data was proposed to uncover the field-scale preferential flow effect of landfill aerobic stabilization. The results showed: (1) Spatial heterogeneity was observed in the distribution of oxygen, methane, and carbon dioxide within the landfill pile. Oxygen levels were significantly negatively correlated with methane and carbon dioxide levels. (2) During the landfill aerobic stabilization process, 23% of the total area with the lowest flow rate had a flow rate accounting for merely 1.3% of the total flow, whereas 90% of the area contributed to 47% of the total flow. The remaining 10% of the area accounted for 53% of the total flow, resulting in an unevenness represented by a Gini coefficient of 0.594, indicating a severe field-scale preferential flow effect. The study suggested that differences in the permeability properties of the landfill body were the cause of this issue. Uneven aeration could lead to a reduction in aeration efficiency and an increase in greenhouse gas emissions and energy consumption. Measures and suggestions were proposed for the pre-operation, operation, and monitoring and maintenance phases of the stabilization project, recommending zonal and temporal gas injection based on the gas permeability coefficient.