Numerical Simulation Study On Drainage Clogging And Parameters Optimization Of Leachate Recirculation In MSW Landfill

Leachate recirculation is of great significance for accelerating the landfill stabilization and purifying the leachate,but the effects of which are greatly influenced by operation parameters.In addition,it is prone to drainage clogging during the process of recirculation,thus resulting in leachate mound in the landfill and further causing some environmental problems,such as leachate leakage,methane explosion and landfill instability.In this paper,related problems about parameters optimization of leachate recirculation and drainage clogging are studied by numerical simulation,in order to provide a theoretical basis for parameters design of leachate recirculation as well as the prevention and control of drainage clogging.First of all,a 2-D biological-hydro-thermo coupled model about leachate recirculation is established based on the kinetics of organic degradation,percolation theory and heat transfer theory,and it is also verified using COMSOL Multiphysics5.2;Based on this model and clogging dynamics,a coupled model of leachate recirculation and drainage clogging is also established.Then,the influence of different parameters（recirculation intensity,recirculation cycles,recirculation ratios）on leachate recirculation efficiency and drainage clogging are respectively investigated through single-factor test and orthogonal test.Finally,selecting the optimal parameters considering its comprehensive influence on both landfill stabilization and drainage clogging,and discussing the temporal and spatial variability of drainage clogging taking 3 typical cases as examples.The results are as follows:The optimum parameters for landfill stabilization are recirculation intensity of 6.6×10^-6 m/s,recirculation cycle of 3d/times,and recirculation ratio of 5.3%;The optimum parameters for leachate purifying are recirculation intensity of 6.6×10^-6 m/s,recirculation cycle of 3d/times,and recirculation ratio of 2.7%;Drainage is most seriously clogged when the recirculation intensity is of 6.6×10^-6 m/s,recirculation cycle of 5d/times,and recirculation ratio of 5.3%;Based on the dual objective of rapid landfill stabilization and preventing high leachate mounds,the optimum parameters are recirculation intensity of 6.6×10^-6 m/s,recirculation cycle of 3d/times and recirculation ratio of 2.7%;The speed of drainage clogging is from slow to fast,then slow down again at last.And the area near entrance and exit of drainage are more prone to be clogged.