Mechanism and dynamic evolution of leachate collection system clogging in MSW landfills in China.

When the leachate collection system (LCS) clogged, the accumulated leachate mound within the landfill will rise both the disposal operation safety and groundwater contamination risks, which is a common phenomenon in China. In our previous studies, geotextile filtration tests and a set of simulated column experiments were conducted to investigate the physical and biochemical clogging mechanisms, respectively. To evaluate the LCS failure development in the long term, in this study, based on the field investigations and above experiments, a comprehensive finite element numerical model was developed to predict the LCS clogging and leachate accumulation. Results showed that the LCS in China was facing serious clogging challenges. Due to the larger size and higher concentration of particle matter in raw leachate, the pores of the nonwoven geotextile were clogged by it over a shorter period than designed. Meanwhile, under the assistance of biological and biochemical clogging, the hydraulic conductivity of the geotextile layer decreased to 10-8-10-9 (m/s) over 1-2 years and resulted in leachate accumulation within the waste layer. In contrast, the gravel layer clogging was dominated by biochemical reactions, which were relatively slow but continuously. When the gravel layer was completely clogged after 17 years of simulated operation, the stagnated leachate mound inside the landfill body and the leachate head on the bottom liner would both rise to the unacceptable height. Therefore, the LCS clogging should be fully considered in municipal solid waste (MSW) landfill design and operation in China.