Abstract:

Leachate recirculation can enhance landfill stability and solve the issue of excess leachate. Predicting the migration characteristics of leachate during the recirculation process is important for determining a reasonable number of recharge wells, and their separation distances. In this study, considering the heterogeneity of municipal solid waste, a probability model was developed for hydraulic conductive changes in space. Using COMSOL Multiphysics^® software, the hydraulic conductivity and head pressure of a transverse-longitudinal homogeneous model were compared with those for a normal, single porosity distribution model. The influence of the transverse-longitudinal hydraulic conductive ratio ($a$), recirculation rate ($q$), and recirculation duration ($t$) on the moisture content and horizontal radius of the two models were investigated. The results showed that after 100 d, the moisture content and horizontal influence range increased from 0.609 to 0.68, and from 4.842 to 6.79 m, respectively, under homogeneous conditions. However, in the case of the normal distribution, the moisture content and horizontal influence range increased from 0.573 to 0.610, and from 4.097 to 4.04 m, respectively. The results indicated that the influence of $a$ on leachate moisture content and horizontal migration range under conditions of a normal distribution was significantly higher than that under conditions of a homogeneous distribution. At the same $q$ and $t$, the leachate recirculation ratio under normal distribution conditions reached saturated moisture content quickly. This was only maintained for a short time, before rapidly decreasing. In contrast, with increasing $q$ and $t$, the time required to reach saturation moisture content and peak value increased gradually.

Key words: leachate recirculation, homogeneous anisotropy, single porosity, normal distribution, moisture content, COMSOL Multiphysics^® software