Landfills gas from

Economics for generating electricity from biogas can be favorable. Landfill gas from municipal solid waste can supply about 4 percent of the energy consumed in the United States. In 1997, a total of 90 trillion Btus were generated by landfill gas, about 3 percent of total biomass energy consumption. 

An analysis of landfill gas from 20 Class II (municipal) landfills revealed a maximum concentration of 32 ppm for benzene (Wood and Porter 1987). Benzene was measured in the vicinity of the BKK landfill, a hazardous waste landfill in California, at a maximum concentration of 3.8 pg/m3 (1.2 ppb) (Bennett 1987). Maximum estimated levels of benzene in air near uncontrolled (Superfund) hazardous waste sites were 190 pg/m3 (59.5 ppb) at the Kin-Buc Landfill (Edison, New Jersey) and 520 pg/m3 (162.8 ppb) in Love Canal basements (Niagara Falls, New York) (Bennett 1987 Pellizzari 1982). 

City of Los Angeles, Bureau of Sanitation, Research and Planning Division, "Estimation of the Quantity and Quality of Landfill Gas from the Sheldon-Arleta Sanitary Landfill" Jan. 2, 1976. 

Table 9. Compounds detected in landfill gas from UK sites which exceed OEL...

Landfill gas from the decomposition of waste in landfills is also mostly methane and CO2, again at low pressnre. 

Although explosions caused by groxmd gas are by no means a common occurrence, incidents where death or serious injury has resulted from suspected ground gas explosions have been documented. A selection of these incidents is listed below. All are associated with migration of landfill gas from landfill sites. The explosions were caused by the methane within the landfill gas. Detailed information about the background to the incidents can be obtained from the specific references. 

Kim, K-H., Baek, S.O., Choi, Y.J., Sunwoo, Y, Jeon, E.C., Hong, J.H. 2006. The emissions of major aromatic VOC as landfill gas from urban landfill sites in Korea, Environ. Monit. Assess. 118 407-422. 

The initial biogas recovered is an MHV gas and is often upgraded to high heat value (HHV) gas when used for blending with natural gas suppHes. The aimual production of HHV gas ia 1987, produced by 11 HHV gasification facihties, was 116 x 10 m of pipehne-quaUty gas, ie, 0.004 EJ (121). This is an iacrease from the 1980 production of 11.3 X 10 m . Another 38 landfill gas recovery plants produced an estimated 218 x 10 m of MHV gas, ie, 0.005 EJ. Additions to production can be expected because of landfill recovery sites that have been identified as suitable for methane recovery. In 1988, there were 51 sites ia preliminary evaluation and 42 sites were proposed as potential sites (121). 

Landfill G as Recovery. This process has emerged from the need to better manage landfill operations. Landfill gas is produced naturally anaerobic bacteria convert the disposed organic matter into methane, carbon monoxide, and other gases. The quantity of methane gas is substantial and could be utilized as fuel, but generally is not. Most of the methane simply leaks into the surrounding atmosphere. 

Not all of the gas is wasted. About 300 MW of electricity is generated from landfills. A variety of electric generation systems have been employed by a small number of developers. Most projects use simple technology and are small (2—10 MW). However, an EPRI study has estimated that landfill gas resources in the United States could support 6,000 MW of generation if utilized in 2-MW-sized carbonate fuel cells. Constmction on the world s first utihty-scale direct carbonate fuel cell demonstration was begun in California. If successful, EPRI estimates that precommercial 3-MW plants based on this design could become available by the end of this decade at an installed cost of 17,000/kW. 

Recovery of Riologieal Conversion Products Biological conversion produces that can be derived from solid wastes include compost, methane, various proteins and alcohols, and a variety of other intermediate organic compounds. The principal processes that have been used are reported in Table 25-64. Composting and anaerobic digestion, the two most highly developed processes, are considered further. The recovery of gas from landfills is discussed in the portion of this sec tion dealing with ultimate disposal. 

Gas and Leachate Movement and Control Under ideal conditions, the gases generated from a landfill should be either vented to the atmosphere or, in larger landfills, collected for the production of energy. Landfills with >2.5 miUion cubic meters of waste or >50 Mg/y NMOC (nonmethane organic compounds) emissions may require landfill-gas collection and flare systems, per EPA support WWW, CFR 60 Regulations. The leachate should be either contained within the landfill or removed for treatment. 

Landfill leachate or gas condensate derived from listed waste. Landfill leachate and landfill gas condensate derived from previously disposed wastes that now meet the listing description of one or more of the petroleum refinery listed wastes would be regulated as a listed hazardous waste. However, U.S. EPA temporarily excluded such landfill leachate and gas condensate from the definition of hazardous waste provided their discharge is regulated under the CWA. The exclusion will remain effective while U.S. EPA studies how the landfill leachate and landfill gas condensate are currently managed, and the effect of future CWA effluent limitation guidelines for landfill wastewaters. 

Anaerobic. Moisture is added to the waste mass in the form of recirculated leachate and from other sources to obtain optimal moisture levels. Biodegradation occurs in the absence of oxygen (anaerobically) and produces landfill gas. Landfill gas, primarily methane, can be captured to minimize greenhouse gas emissions and for energy projects. 

Hybrid (aerobic-anaerobic). The hybrid bioreactor landfill accelerates waste degradation by employing a sequential aerobic-anaerobic treatment to rapidly degrade organics in the upper sections of the landfill and collect gas from lower sections. Operation as a hybrid results in an earlier onset of methanogenesis compared to aerobic landfills. 

Control layers, such as those used to minimize animal intrusion, promote drainage, and control and collect landfill gas, are often included for conventional cover systems and may also be incorporated into ET cover system designs. For example, a proposed monolithic ET cover at Sandia National Laboratories in New Mexico will have a biointrusion fence with 1/4-in. squares between the topsoil layer and the native soil layer to prevent animals from creating preferential pathways, potentially resulting in percolation. The biointrusion layer, however, will not inhibit root growth to allow for transpiration. At another site, Monticello Uranium Mill Tailings Site in Utah, a capillary barrier ET design has a 12-in. soil/rock admixture as an animal intrusion layer located 44 in. below the surface, directly above the capillary barrier layer. 

Degradation of solid waste materials in a landfill proceeds from aerobic to anaerobic decomposition very quickly, thereby generating gases that collect beneath the closure FML. Almost 98% of the gas produced is either carbon dioxide (CO2) or methane (CH4). Because C02 is heavier than air, it will move downward and be removed with the leachate. However, CH4, representing about 50% of the generated gas, is lighter than air and, therefore, will move upward and collect at the bottom of the facility s impermeable FML. If the gas is not removed, it will produce a buildup of pressure on the LML from beneath. 

Kryosol An adsorptive process for purifying methane from landfill gas. Operated at high pressure. The overall methane recovery is 90 to 95 percent. 

Renewable electricity (RES-E) Electricity generated from renewable non-fossil energy sources, i.e., wind, solar, geothermal, wave, tidal, hydropower, biomass, landfill gas, sewage treatment plant gas and biogas (this corresponds to the definition in Directive 2001/77/EC on renewables, Article 2). 

Wave power, tidal power, municipal solid waste, gas from animal wastes (biogas), landfill, peat energy and ocean thermal energy conversion (OTEC) are the other renewable energy sources (RES). Water energy sources are hydropower, tidal and wave technologies. 

Alternative fuels can be used to power a fuel cell such as hydrogen, methane, natural gas, methanol, ethanol, liquehed petroleum gas and landfill gas, which can be produced from renewable energy sources such as biomass and wind. 

This traditional system is still the disposal method most widely used in the EU. In landfills, biodegradable waste decomposes to produce landfill gas and leachate. The landfill gas consists mainly of methane and, if not captured, contributes considerably to the greenhouse effect. For this reason, the move away from landfill is an important part of the European Waste Framework Directive. 

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