Study On Daily Variation Of Methane Emission At Senescence Phase From Landfill

The daily variation characteristics of methane emission from landfill at senescence phase are analyzed, by combining site observation with laboratory experiment, using regression analysis and biogas production model. The effects of different temperature and water content on the gas production process in different stages of fermentation were discussed, and the effects of different compaction degree on permeability coefficient were also discussed. The landfill biogas production rate at senescence phase was estimated by biogas production model, and the pressure in landfill was estimated by combining biogas production model with Darcy law. The reasons for the uncertainty of the daily variation of methane emission from landfill at senescence phase can be revealed by the results. The results are summarized as follows.The emission of methane from the landfill at senescence phase was intermittent emission, was not continuous emission. The methane concentration was changed between 1.9 and 119.7mg/m3. And the methane flux was changed between -20.6 and 52.6mg/(m2·h). There was a significant difference in methane flux at each sampling point, and it was hard to discover the law of the methane flux change.The effects of temperature on the different stages of waste fermentation were different. The temperature would not only affect the activity of the main strains, but also affect the proportion of each stage in the whole fermentation process. At 25?,the cumulative gas production and gas production time at acrophase was much less than the other three experimental groups, the cumulative gas production at acrophase was 287.6mL, and the proportion of gas production time to the whole fermentation process was 13%. And At 25?, the cumulative gas production and gas production time at stationary phase was much more than the other three experimental groups,the cumulative gas production at stationary phase was 405.6mL, and the proportion of gas production time to the whole fermentation process was 40%. These means lower temperature inhibits hydrolysis and acid production process, but it can promote the production of methane, it would also affect the proportion of two stage in the whole fermentation process. And the results showed that the cumulative gas production at stationary phase would be the most at 31?, The biogas production at acrophase was related to temperature, but the relationship need to further explore through experiments. The effect of water content on the fermentation was mainly on the influence of cumulative gas production. Under the condition of different water content, there were significant differences in the cumulative gas production at acrophase and stationary phase. At 49% water content,the cumulative gas production at acrophase was 676.8mL, much less than the 60%, 70% and 80%experimental groups, but the cumulative gas production at stationary phase was 311.5mL, much more than the 60%, 70% and 80% experimental groups. And at 90%water content,the cumulative gas production at each stage was lower than that of the other groups. The results show that the increase of water content is beneficial to the hydrolysis and acid production,but at the same time,it can inhibit the production of methane, and the high water content was not conducive to the whole fermentation process.The permeability coefficient was affected by the change of compaction degree.The permeability coefficient decreases exponentially with the increase of compaction, and the relationship was K=0.139e-10.211p. And under the same compaction, the permeability coefficient could be different. This indicated that the waste has a greater heterogeneity. Therefore, in estimating the methane emission from landfill, the impact of the inhomogeneity of the waste on landfill should be fully considered.The biogas production rate in landfill at senescence phase changed at different temperature, the variation range was between 0.12·10-9 and 1466.67·10-9m3·kg-1·s-1.Under the assumption, pressure in landfill would also change at different temperature; the variation range was between 0.0926 and 50490.0789Pa. So landfill gas in landfill would move lateral first, when the lateral movement was prevented ,landfill gas could move up to the surface of landfill.