Study On Gas Permeability Of Compacted MSW And Landfill Gas Migration Process

Presently, sanitary landfill is the predominant method of municipal solid waste (MSW) treatment, so does it in the long time of future. Landfill gas(LFG) is principal contamination produced from sanitary landfill. It is combustible, explosive and greenhouse gas, which will be harmful to environment and human beings. However, It is a kind of renewable energy. If it is reused, it can eliminate pollution and change harm into availability. In order to control pollution and recover LFG, it is necessary to study and master the LFG permeability and migration law of compacted MSW. Presently, the reports in the field are still few, so the extraction system of landfill is designed based on the experiences of abroad or the tests on-site. Though many experiences and results can be used for reference, there are many insufficiencies in these studies, which are unsatisfied in our country. Because the tests on-site are limited by many conditions, they are not satisfied the actual demands. So the study in the field is necessary to provide the theoretic basis and technical references for designing the extraction system and environmental impact assessment of landfill site.The gas permeability and LFG migration process in compacted MSW were studied based on the simulation experiments carried out in the laboratory. The main conclusions are as follows:① The gas permeability of compacted MSW;1) The simulated experiment equipment and method to test the different direction gas permeability coefficient of compacted MSW was established. And based on which, the value of gas permeability coefficient of Chongqing MSW was tested(horizontal permeability coefficient Kh and vertical permeability coefficient Kv);2) The gas permeability coefficient of Chongqing MSW was determined in the condition of different density of compacted MSW, different water content, and different humic degree, which was systemic analyzed, and the conclusions were in the follow:a. The permeability coefficient K was descending obeying the rule of index with increasing of the density of compacted MSW;b. The permeability coefficient K was descending obeying the rule of linearity withincreasing of the water content of compacted MSW;c. During the different overrotten degree, the value of the permeability coefficient of semi-overrotten MSW is close to the originality MSW, and which of the overrotten MSW is more than the former;3) The value of horizontal permeability coefficient Kh of compacted MSW is greater than that of vertical permeability coefficient Kv, and the average of Kh/Kv varies from 9.1 to 20.1, which shows that the anisotropy characteristics of compacted MSW are obvious, so it is more advantageous to collect LFG for vertical extraction well than horizontal extraction well.② The mathematical model of LFG migration for vertical extraction system was put up, and the solution was obtained. The influences of the production of LFG, extraction quantity, gas permeability coefficient of compacted MSW, buried depth of extraction well and thickness and characteristics of covered layer in compacted MSW were all reflected in the model.③ On the base of the model in the paper, the pressure distribution of gas in a landfill vertical extraction system was forecasted. According to the pressure distribution, the radius of influence of extraction well was confirmed. The analysis showed that the optimal value of the radius of influence of extraction well was 35.0～40.0m...