Feng S, Ng C W W, Leung A K, Liu H W
Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
School of Science and Engineering, University of Dundee, Fulton Building, Nethergate, Dundee, Scotland DD1 4HN, UK.
Waste Manag. 2017 Oct;68:355-368. doi: 10.1016/j.wasman.2017.04.042. Epub 2017 May 22.
Microbial aerobic methane oxidation in unsaturated landfill cover involves coupled water, gas and heat reactive transfer. The coupled process is complex and its influence on methane oxidation efficiency is not clear, especially in steep covers where spatial variations of water, gas and heat are significant. In this study, two-dimensional finite element numerical simulations were carried out to evaluate the performance of unsaturated sloping cover. The numerical model was calibrated using a set of flume model test data, and was then subsequently used for parametric study. A new method that considers transient changes of methane concentration during the estimation of the methane oxidation efficiency was proposed and compared against existing methods. It was found that a steeper cover had a lower oxidation efficiency due to enhanced downslope water flow, during which desaturation of soil promoted gas transport and hence landfill gas emission. This effect was magnified as the cover angle and landfill gas generation rate at the bottom of the cover increased. Assuming the steady-state methane concentration in a cover would result in a non-conservative overestimation of oxidation efficiency, especially when a steep cover was subjected to rainfall infiltration. By considering the transient methane concentration, the newly-modified method can give a more accurate oxidation efficiency.
非饱和填埋场覆盖层中的微生物好氧甲烷氧化涉及水、气和热的耦合反应传输。这种耦合过程很复杂，其对甲烷氧化效率的影响尚不清楚，尤其是在坡度较大的覆盖层中，水、气和热的空间变化显著。在本研究中，进行了二维有限元数值模拟以评估非饱和斜坡覆盖层的性能。该数值模型使用一组水槽模型试验数据进行了校准，随后用于参数研究。提出了一种在估算甲烷氧化效率时考虑甲烷浓度瞬态变化的新方法，并与现有方法进行了比较。研究发现，由于下坡水流增强，坡度较大的覆盖层氧化效率较低，在此过程中土壤的去饱和促进了气体传输，从而导致填埋气排放。随着覆盖层角度和覆盖层底部填埋气产生速率的增加，这种影响会放大。假设覆盖层中的甲烷浓度处于稳态会导致对氧化效率的非保守高估，尤其是当坡度较大的覆盖层受到降雨入渗影响时。通过考虑甲烷浓度的瞬态变化，新改进的方法可以给出更准确的氧化效率。
