Institute of Geoscience and Georesources-CNR, 56124, Pisa, Italy.
Environ Sci Pollut Res Int. 2010 Jul;17(6):1197-206. doi: 10.1007/s11356-010-0294-2. Epub 2010 Feb 24.
BACKGROUND, AIM AND SCOPE: Landfill gas (LFG) tends to escape from the landfill surface even when LFG collecting systems are installed. Since LFG leaks are generally a noticeable percentage of the total production of LFG, the optimisation of the collection system is a fundamental step for both energy recovery and environmental impact mitigation. In this work, we suggest to take into account the results of direct measurements of gas fluxes at the air-cover interface to achieve this goal.
During the last 5 years (2004-2009), 11 soil gas emission surveys have been carried out at the Municipal Solid Waste landfill of Legoli (Peccioli municipality, Pisa Province, Italy) by means of the accumulation chamber method. Direct and simultaneous measurements of CH(4) and CO(2) fluxes from the landfill cover (about 140,000 m(2)) have been performed to estimate the total output of both gases discharged into the atmosphere. Three different data processing have been applied and compared: Arithmetic mean of raw data (AMRD), sequential Gaussian conditional simulations (SGCS) and turning bands conditional simulations (TBCS). The total amount of LFG (captured and not captured) obtained from processing of direct measurements has been compared with the corresponding outcomes of three different numerical models (LandGEM, IPCC waste model and GasSim).
Measured fluxes vary from undetectable values (<0.05 mol m(-2) day(-1) for CH(4) and <0.02 mol m(-2) day(-1) for CO(2)) to 246 mol m(-2) day(-1) for CH(4) and 275 mol m(-2) day(-1) for CO(2). The specific CH(4) and CO(2) fluxes (flux per surface unit) vary from 1.8 to 7.9 mol m(-2) day(-1) and from 2.4 to 7.8 mol m(-2) day(-1), respectively.
The three different estimation methodologies (AMRD, SGCS and TBCS) used to evaluate the total output of diffused CO(2) and CH(4) fluxes from soil provide similar estimations, whereas there are some mismatches between these results and those of numerical LFG production models. Isoflux maps show a non-uniform spatial distribution, with high-flux zones not always corresponding with high-temperature areas shown by thermographic images.
The average value estimated over the 5-year period for the Legoli landfill is 245 mol min(-1) for CH(4) and 379 mol min(-1) for CO(2), whereas the volume percentage of CH(4) in the total gas discharged into the atmosphere varies from 29% to 51%, with a mean value of 39%. The estimated yearly emissions from the landfill cover is about 1.29 x 10(8) mol annum(-1) (2,100 t year(-1)) of CH(4) and 1.99 x 10(8) mol annum(-1) (8,800 t year(-1)) of CO(2). Considering that the CH(4) global warming potential is 63 times greater than that of CO(2) (20 a time horizon, Lashof and Ahuja 1990), the emission of methane corresponds to 130,000 t annum(-1) of CO(2).
The importance of these studies is to provide data for the worldwide inventory of CH(4) and CO(2) emissions from landfills, with the ultimate aim of determining the contribution of waste disposal to global warming. This kind of studies could be extended to other gas species, like the volatile organic compounds.
背景、目的和范围：即使安装了垃圾填埋气（LFG）收集系统，LFG 也往往会从填埋场表面逸出。由于 LFG 泄漏通常是 LFG 总产量的一个显著比例，因此优化收集系统是能源回收和减轻环境影响的基本步骤。在这项工作中，我们建议考虑直接测量在空气覆盖界面上的气体通量的结果，以达到这个目的。
在过去的 5 年（2004-2009 年），通过积累室法，在意大利比萨省佩奇奥利市的城市固体废物填埋场对 11 个土壤气体排放进行了测量。对垃圾填埋场覆盖层（约 140000 m2）的 CH4 和 CO2 通量进行了直接和同步测量，以估算排入大气的两种气体的总排放量。应用并比较了三种不同的数据处理方法：原始数据的算术平均值（AMRD）、序贯高斯条件模拟（SGCS）和转向带条件模拟（TBCS）。从直接测量处理中获得的 LFG（捕获和未捕获）总量与三种不同数值模型（LandGEM、IPCC 废物模型和 GasSim）的相应结果进行了比较。
测量的通量从不可检测值（CH4 为<0.05 mol m-2 day-1，CO2 为<0.02 mol m-2 day-1）到 CH4 为 246 mol m-2 day-1，CO2 为 275 mol m-2 day-1。特定的 CH4 和 CO2 通量（单位表面积的通量）分别为 1.8 至 7.9 mol m-2 day-1 和 2.4 至 7.8 mol m-2 day-1。
用于评估土壤中扩散的 CO2 和 CH4 通量的总输出的三种不同估计方法（AMRD、SGCS 和 TBCS）提供了相似的估计值，而这些结果与数值 LFG 生产模型的结果存在一些差异。等通量图显示出非均匀的空间分布，高通量区并不总是与热像图所示的高温区相对应。
在 Legoli 垃圾填埋场的 5 年期间，CH4 的平均估计值为 245 mol min-1，CO2 的平均估计值为 379 mol min-1，而排入大气中的总气体中 CH4 的体积百分比从 29%到 51%，平均值为 39%。从垃圾填埋场覆盖层估计的年排放量约为 1.29 x 10（8）mol 年-1（2100 t 年-1）的 CH4 和 1.99 x 10（8）mol 年-1（8800 t 年-1）的 CO2。考虑到 CH4 的全球变暖潜能是 CO2 的 63 倍（20 年时间范围，Lashof 和 Ahuja 1990），甲烷的排放相当于 130000 t 年-1 的 CO2。
这些研究的重要性在于为全球垃圾填埋场 CH4 和 CO2 排放清单提供数据，最终目的是确定废物处理对全球变暖的贡献。这种研究可以扩展到其他气体物种，如挥发性有机化合物。
