Calculation Of Leachate Generation And Analysis Of Horizontal Trench In MSW Landfills

High moisture content,large leachate yield and high leachate mounds are very common in municipal solid waste(MSW)landfills of China,which may cause several problems including instability of landfill structure,environmental pollution.Based on systematic tests of initial moisture content,components and filed capacity,the research works in this paper focused on the analysis of leachate production and the design of horizontal trench.The analytical solution of saturation line and the relationship between design spacing of horizontal trench and warning water level are deduced through a new seepage model of horizontal trench.The influences of drainage effect of horizontal trench are demonstrated by numerical analysis.The main research works and conclusions are as follows:(1)Based on available testing results in and abroad,the average initial moisture content of landfilled wastes in Chinese was found to be about 53%,and the content of organic matters in fresh wastes was about 52.6%.However,the average initial moisture content of landfilled wastes in western countries was found to be about 27%,and the content of organic matters in fresh wastes was about 22.7%.After landfilling,leachate is gradually generated during the compression and biodegradation processes of wastes.(2)Field capacity tests were carried out on drilled MSW samples with different ages in Shenzhen.The results showed that field capacity is related to the age and stress level of landfilled wastes.Field capacity decreases with the increase of stress level within the same sample.Under the same stress level,field capacity decreases with the increase of waste age,it also influenced by sampling method and depth.Soil waste characteristic curve(SWCC)of the drilled MSW samples was summarized.(3)A modified model of leachate conduction calculation which considerated the loss of quality of waste was proposed for the leachate generation rate calculation based on the model in the standard of leachate treatment.The monitored leachate production data were simulated through the modified model.A secure tendency of the simulated results indicated that the model is fit for the design of leachate treatment in Chinese landfills.(4)Based on Dupuit assumption,a new seepage model of horizontal trench was proposed.The analytical solution of saturation line and the relationship between design spacing of horizontal trench and warning water level can be deduced.Considerated the same infiltration and steady control condition,spacing of horizontal trench was proportional to the coefficient of permeability of waste.When km is greater than 10-3cm/s,the curve that Dmax/L with s/k is steady and can be used in design.(5)The major influences of drainage effect of horizontal trench in landfills are permeability of filtration and insulation layer,backfiling aggregate and pipe.They were demonstrated by numerical analysis.The obtained results showed that the water level control of horizontal trench would be affected greatly when the permeability of filtration and insulation layer,backfiling aggregate and drain droped respectively to 1×10-4cm/s,1×10-4cm/s and 5×10-5cm/s under the basis of a rainfall of 5 mm.(6)Clogging of horizontal trench will reduce the ability of drainage and may cause high leachate mound in the landfills.The monitoring data including groundwater level,discharge of horizontal trench and clogging of drainage pipe showed that the proposed "optimization structure" of horizontal trench was very high efficiency.(7)The modified model of leachate conduction calculation was applied to the project of leachate conduction prediction in a south China landfill.It was accepted by the manager while the prediction was reliable.The measures of water level control proposed in this article were also accepted by the treatment program,which are under construction now.