Controlling landfill gas migration with various cover systems
Başlık çevirisi mevcut değil.
- Tez No: 601929
- Danışmanlar: DR. JAMES M. TINJUM
- Tez Türü: Doktora
- Konular: Çevre Mühendisliği, Şehircilik ve Bölge Planlama, Environmental Engineering, Urban and Regional Planning
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2018
- Dil: İngilizce
- Üniversite: University of Wisconsin-Madison
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 168
Özet
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Özet (Çeviri)
A solid waste landfill is designed and operated to safely contain and dispose of municipal solid waste and other waste materials such as demolition debris and recycling residuals by encapsulating and isolating the waste from the environment with a low-permeability liner at the base and a multi-purpose cover system. Cover systems provide physical protection by retarding the migration of contaminations such as greenhouse gasses (GHG) including CH4 and CO2, volatile organic compounds (VOCs) such as methylene chloride (MC) and trichloroethylene (TCE), and odiferous gases (e.g., hydrogen sulfide, H2S) towards the atmosphere. Cover systems typically consist of a lightly compacted, finer-grained (e.g., clay, or silty clay) soil and/or geomembranes (GM). This study evaluates landfill gas transport mechanisms through various temporary covers (e.g., soil, geomembrane, and composite soil-geomembrane) that are widely used in waste industry. Limited fundamental, mechanistic-based research has been conducted to determine the physical-chemical properties of polymers that affect the diffusive transport of gases (e.g., H2S, VOCs, CH4, and CO2) through GM barriers. A multilayer GM produced with a layer of ethylenevinyl alcohol (EVOH) has the potential to substantially reduce the diffusion of landfill gasses (LFG), such as CH4 and CO2. Eun et al. (2016 and 2017b) demonstrated that co-extruded EVOH GM is decidedly effective at reducing transport of CH4 and odiferous H2S from bench-scale laboratory testing when a GM is used within an interim cover. However, there are still latent and critical issues such as the applicability and validation of the effectiveness of using co-extruded EVOH GM for an interim cover at field-scale with dual consideration of boundary effects and in situ environmental conditions. This applicability and validation of the effectiveness of coextruded EVOH GM within a composite interim cover should be resolved prior to fuller acceptance by multiple stakeholders (landfill owners and managers, regulators and local/county/district governments, impacted communities proximate to landfills, and nongovernmental organizations (NGO) associated with landfill siting and operations). Thus, a convincing demonstration of the full suite of benefits and multi-ranging value of co-extruded EVOH GM product based on field study is, ultimately, warranted. Furthermore, limited tests have been conducted with odiferous compounds such as H2S. These compounds are particularly important to landfill operators as strong landfill odors may disenfranchise landfill neighbors, resulting in strained relationships with the community, potential regulatory actions, and costly litigation in some cases. The first chapter of this study presents an outline and background to introduce basic physical and chemical mechanisms of LFG transport through landfill cover systems. The second and third chapters of this study focus on bench-scale column tests that were conducted to evaluate H2S and CO2 transport in simulated interim covers comprised of a GM overlain by a thin layer of silt. The tests were conducted with a co-extruded GM comprised of a thin (0.04 mm) layer of EVOH sandwiched between an outer jacket of LLDPE as well as a thin PE sheet and conventional LLDPE and PVC GMs. Comparisons were made between the covers with different GMs in terms of H2S and CO2 breakthrough times and relative concentrations. Lower relative concentrations and less rapid increases in concentration of H2S and CO2 were obtained for the simulated interim cover with the EVOH GM compared to other GMs. The H2S diffusion coefficient for the extruded EVOH GM was approximately 100 times lower than the H2S diffusion coefficient for the PE geofilm, conventional LLDPE and PVC GMs. Likewise, the CO2 diffusion coefficient for EVOH was approximately two orders of magnitude lower than the CO2 diffusion coefficient of PE geofilm. The hierarchies of CO2 and H2S transmissions in terms of highest relative concentration to lowest were PE > LLDPE > PVC > EVOH and PE > PVC > LLDPE > EVOH, respectively. The findings suggest that EVOH GMs may be much more effective in controlling emission of odiferous H2S and CO2 from municipal solid waste (MSW) landfills than conventional PE, LLDPE, and PVC GMs. In the fourth chapter of this study, CH4, CO2, and H2S emission rates from cover soil at three different locations (with 200-, 300-, 450-mm-thick cover soils) were evaluated within an MSW landfill in the Midwest of the US. LFG emission and diffusion mechanisms were monitored using a static flux chamber technique. CH4, CO2 and H2S emissions varied temporally and spatially. These variations might be related with the physical-chemical properties of soil (e.g., soil cover thickness, moisture content, grain size distribution, etc.), buried waste age and organic material content, uneven distribution of gas collection wells, and seasonal environmental changes (e.g., temperature and barometric pressure). Long-term generated LFG was predicted using US EPA LandGEM v3.02 LFG emission model based on first-order decomposition rate equation and compared with the field emission measurements. Further, LFG diffusion coefficients were calculated using a bench-scale diffusion column test and compared with a three-parameter relative diffusion model. Depending on the location and permeant gas type, slightly different results were observed between predicted and measured diffusion coefficients. Additionally, the LFG emission rate changed depending the number of the in-service gas collection well at different locations. Further, uncaptured CH4 emission, by gas collection system, can be reduced to one fourth through an appropriate cover soil (300-mm to 400-mm, CL). In Chapter 5, a preliminary field study plan is proposed to monitor and evaluate odiferous compounds and VOCs (e.g., H2S, aromatic hydrocarbons, fatty acids, ketones, aldehydes etc.) through polymeric GMs including LLDPE and EVOH.
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