Air Injection Tests Via Single Wells and Multiple Wells in a Municipal Solid Waste Landfill

Aeration is an effective in situ remediation technique to accelerate the stabilization process and reduce the odor's concentration of municipal solid waste (MSW) landfills. The distribution of oxygen in a landfill is crucial to the effective operation and performance of a landfill aeration project. In this study, field-scale tests of air injection via vertical wells were conducted at an MSW landfill in Shanghai, China. The spatial and temporal distributions of oxygen during single- and multiple-well injections were measured and compared. The results showed that the methane volume fraction decreased from 60% to less than 10%, and the oxygen volume fraction increased to approximately 15% only after 2 h of air injection. The rapid change in gas concentration over time could potentially be attributed to the preferential flow that occurred in the heterogeneous MSW. Further, a dual-porosity model was proposed to simulate the rapid advection and diffusion of air in the macropores, thus reflecting the fast increase in the oxygen concentration in the total pore space. During multiple-well injection, a "competitive injection" phenomenon was observed; specifically, the air injection volume of different vertical wells greatly varied even under the same injection pressure due to the large difference in the gas permeability of waste in different areas, and different degrees of aerobic degradation of waste would occur in different areas. Electrical resistivity tomography images showed that only part of the leachate was driven away by the air, leading to an uneven increase in waste resistivity.