APPENDIX A BASICS OF LANDFILL GAS mass gov

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Basics of Landfill Gas Methane Carbon Dioxide Hydrogen Sulfide and Sulfides. Landfill gas is produced through bacterial decomposition volatilization and chemical reactions Most. landfill gas is produced by bacterial decomposition that occurs when organic waste solids food i e. meats vegetables garden waste i e leaf and yardwaste wood and paper products are broken down by. bacteria naturally present in the waste and in soils Volatilization generates landfill gas when certain. wastes change from a liquid or solid into a vapor Chemical reactions occur when different waste. materials are mixed together during disposal operations Additionally moisture plays a large roll in the. speed of decomposition Generally the more moisture the more landfill gas is generated both during the. aerobic and anaerobic conditions,Landfill Gas Production and Composition. In general during anaerobic conditions the composition of landfill gas is approximately 50 percent. methane and 50 percent carbon dioxide with trace amounts 1 percent of nitrogen oxygen hydrogen. sulfide hydrogen and nonmethane organic compounds NMOCs The more organic waste and moisture. present in a landfill the more landfill gas is produced by the bacteria during decomposition The more. chemicals disposed in a landfill the more likely volatile organic compounds and other gasses will be. The Four Phases of Bacterial Decomposition, Bacteria decompose landfill waste in four phases The composition of the gas produced changes with. each of the four phases of decomposition Landfills often accept waste over a 20 to 30 year period so. waste in a landfill may be undergoing several phases of decomposition at once This means that waste in. one area might be in a different phase of decomposition than more recently buried waste in another area. During the first phase of decomposition aerobic bacteria bacteria that live only in the presence of. oxygen consume oxygen while breaking down the long molecular chains of complex carbohydrates. proteins and lipids that comprise organic waste The primary byproduct of this process is carbon. dioxide Nitrogen content is high at the beginning of this phase but declines as the landfill moves through. the four phases Phase I continues until available oxygen is depleted Phase I decomposition could last. for days or months depending on how much oxygen is present when the waste is disposed of in the. landfill Oxygen levels will vary according to factors such as how loose or compressed the waste was. when it was buried, Phase II decomposition starts after the oxygen in the landfill has been used up Using an anaerobic. process a process that does not require oxygen bacteria convert compounds created by aerobic bacteria. into acetic lactic and formic acids and alcohols such as methanol and ethanol The landfill becomes. highly acidic As the acids mix with the moisture present in the landfill they cause certain nutrients to. dissolve making nitrogen and phosphorus available to the increasingly diverse species of bacteria in the. landfill The gaseous byproducts of these processes are carbon dioxide and hydrogen If the landfill is. disturbed or if oxygen is somehow introduced into the landfill microbial processes will return to Phase I. Phase III decomposition starts when certain kinds of anaerobic bacteria consume organic acids produced. in the Phase II and form acetate an organic acid This process causes the landfill to become a more. neutral environment in which methane producing bacteria begin to establish themselves Methane and. acid producing bacteria have a symbiotic or mutual beneficial relationship Acid producing bacteria. create compounds for the methanogenic bacteria to consume Methanogenic bacteria consume the. carbon dioxide and acetate too much of which would be toxic to the acid producing bacteria. Phase IV decomposition begins when both the composition and production rates of landfill gas remain. relatively constant Phase IV landfill gas usually contains approximately 45 percent to 60 percent. methane by volume 40 percent to 60 percent carbon dioxide and 2 percent to 9 percent other gasses such. as sulfide Gas is produced at a stable rate in Phase IV typically for about 20 years however gas will. continue to be emitted for 50 or more years after the waste is placed in the landfill Crawford and Smith. 1985 Gas production might last longer for example if greater amounts organics are present in the. waste such as at a landfill receiving higher than average amounts of domestic animal waste ATSDR. Due to the fact that refuse is placed in a landfill at different times and consists of different types of solid. waste at different moisture content all four phases of degradation may be occurring simultaneously within. the landfill,Factors Affecting Landfill Gas Production. Gas production rates depend on the rate of decomposition which in turn is affected by moisture content of. the waste temperature soil cover permeability amount of precipitation composition of the waste refuse. particle size compaction and landfilling practices. Moisture is essential for bacterial survival Ideal moisture content for decomposition is one that. approaches saturation Biological reactions can be retarded if moisture content drops below 40 percent. and essentially stops when moisture content is below 20 percent Thus in very dry climates. methanogenic methane producing decomposition will have a very small possibility of occurring. Methane will be produced only when oxygen O2 is no longer present in the landfill. Capping of a landfill with a low permeability layer reduces the available moisture thus retarding landfill. gas production Smaller particles decompose more quickly due to the high surface area to mass ratio. Thus shredded waste produces gas more quickly than non shredded waste For additional information on. landfill gas production and composition refer to Chapter 7 of MassDEP s Landfill Technical Guidance. http www mass gov dep recycle laws policies htm, Figure 1 Production Phases of Typical Landfill Gas.
Hydrogen Sulfide and Sulfides, Sulfides are naturally occurring gasses that often give a landfill gas mixture its rotten egg smell Sulfides. can cause unpleasant odors even at very low concentrations Hydrogen sulfide is a colorless flammable. gas and is one of the most common sulfides responsible for landfill odors Some people can smell. hydrogen sulfide individual s odor threshold at concentrations as low as 0 5 parts per billion ppb. However the odor threshold can vary significantly among individuals based on the olfactory sensitivity of. the person For many compounds including hydrogen sulfide there is a wide variability in published odor. thresholds refer to Table 1 Odors alone cannot be relied upon as providing an early warning for. elevated concentrations of hydrogen sulfide At concentrations around 100 ppm parts per million. no odor is detected due to a loss of olfactory sensation resulting in loss of warning properties at lethal. levels Integrated Risk Information System IRIS Hydrogen sulfide is more dense than air and. therefore more likely to pool at lower elevations under still conditions depending upon topography. Hydrogen sulfide is found naturally in the environment and is also produced from man made processes. Hydrogen sulfide occurs naturally in crude petroleum natural gas volcanic gasses hot springs and tidal. flats and can also be produced from bacterial breakdown of organic matter Hydrogen sulfide is produced. by human and animal waste and landfilling of solid waste and can result from industrial activities such as. food processing coke ovens paper mills tanneries and petroleum refineries to name a few. Dimethyl sulfide and mercaptans are sulfides that can also cause odors but typically are not emitted from a. landfill at the high concentrations or at production rates associated with hydrogen sulfide. The concentration of hydrogen sulfide detected in landfill gas samples at solid waste landfills that receive. construction and demolition C D waste is usually much higher than at landfills that do not accept C D. The higher concentrations of hydrogen sulfide are believed to be associated with the gypsum board. component e g wallboard present in C D material The combination of gypsum organic material. moisture and anaerobic conditions present in C D landfills is believed to provide a favorable mixture and. environment for bacteria to produce hydrogen sulfide gas Concentrations of hydrogen sulfide detected in. raw landfill gas samples collected from within a landfill waste mass have ranged from 50 000 ppb to. 15 000 000 ppb 50 ppm 15 000 ppm for those landfills that accepted C D solid waste Landfills. which do not accept C D typically have much lower concentrations of hydrogen sulfide in the raw gas. usually less than 100 000 ppb 100 ppm, Hydrogen sulfide is generated as a result of a series of reactions that biologically reduce sulfate leached. from gypsum contained in the C D In general wallboard consists of the gypsum core CaSO4 x 2H2O. with facing and backing consisting of paper The microorganisms responsible for generating hydrogen. sulfide include sulfate reducing bacteria and sulfur reducing bacteria Florida 2002 Sulfate reducing. bacteria require the following to produce hydrogen sulfide a sulfate source gypsum a carbon source. organic material anaerobic conditions and moisture. Laboratory studies have indicated that under anaerobic conditions decaying drywall even alone. leached enough sulfide ions and organic matter for sulfate reducing bacteria to generate large hydrogen. sulfide concentrations Florida 2002 Factors contributing to hydrogen sulfide production are. anaerobic conditions pH moisture organic matter content in the presence of sulfate Florida 2002. Additional information on factors affecting hydrogen sulfide production is available from the State. University System of Florida, Hydrogen sulfide production from various mixtures of municipal solid waste MSW and C D waste. has been measured under laboratory conditions Laboratory experiments have documented higher sulfide. production from wastes with wallboard than in those without. Table 1 Chemical and Physical Properties of H2S,Characteristic Property Data Reference. Common Name hydrogen sulfide ATSDR 1999, Synonyms hydrosulfuric acid stink damp sulfur ATSDR 1999.
hydride sulfurated hydrogen dihydrogen,monosulfide sewer gas swamp gas. rotten egg gas,CAS Registry No 7783 06 4 ATSDR 1999. Chemical Formula H2S ATSDR 1999,Molecular Weight 34 08 ATSDR 1999. Physical State colorless gas ATSDR 1999, Odor Threshold 0 0081 0 13 ppm Beauchamp et al 1984 Amoore and. Hautala 1983,0 005 ppm U S Department of Health and human.
services 1999,Vapor Pressure 220 mm Hg at 21 9 C ATSDR 1999. Density 1 5392 g L at 0 C ATSDR 1999,Specific Gravity 1 192 ATSDR 1999. Freezing Boiling Flash Point 85 49 C 60 33 C 26 C ATSDR 1999. Solubility 1 g in 242 mL water at 20 C soluble in ATSDR 1999. alcohol ether glycerol gasoline kerosene,crude oil carbon disulfide. Conversion factors in air 1 ppm 1 4 mg m3 AIHA 1991. 1 mg m3 0 7 ppm,Methane and Carbon Dioxide, Landfill gas is composed primarily of 50 percent methane and 50 percent carbon dioxide and other gases. produced at less than 1 percent Methane and carbon dioxide are generated through the biological. decomposition of waste Methane is naturally occurring flammable colorless and odorless gas and is the. principal explosive component of concern in landfill gas Carbon dioxide is naturally found at low. concentrations in the atmosphere Carbon dioxide is colorless odorless and slightly acidic. Table 2 Chemical and Physical Properties of Methane. Characteristic Property Data Reference, Common Name Methane Handbook of Chemistry and Physics.
Synonyms natural gas marsh gas fire damp methyl Sax s Dangerous Properties of. hydride Industrial Materials 2000, CAS Registry No 74 82 8 Handbook of Chemistry and Physics. Chemical Formula CH4 Handbook of Chemistry and Physics. Molecular Weight 16 04 g mol Handbook of Chemistry and Physics. Physical State colorless gas Sax s Dangerous Properties of. Industrial Materials 2000, Odor Threshold Odorless Sax s Dangerous Properties of. Industrial Materials 2000,Density 0 7168 g l Sax s Dangerous Properties of. Industrial Materials 2000, Freezing Boiling Flash Point 183 C 162 C 188 C Hawley s Condensed Chemical. Dictionary 2001, Solubility Slightly soluble in water v v at 20 C is Hawley s Condensed Chemical.
0 033 soluble in alcohol and ether Dictionary 2001. Flammability Limits in Air 5 to 15 Hawley s Condensed Chemical. Dictionary 2001, 2 1 5 Hydrogen Sulfide Gas Generation Rates Vs Methane Generation Rates. C D debris landfills do not produce the large volumes of methane gas that MSW landfills generate The. lower methane production can be a problem since one of the most effective treatment technologies for. landfill gas including hydrogen sulfide is combustion using methane as the fuel source The lower. methane production may be because the landfill may not have reached anaerobic conditions which are. necessary for significant methane and hydrogen sulfide production Additionally hydrogen sulfide is toxic. to methane producing bacteria which in turn reduces methane gas production even under anaerobic. conditions Combustion technologies such as an active landfill gas collection and landfill gas flare system. require sufficient fuel methane in order to thermally treat the hydrogen sulfide gas. APPENDIX A BASICS OF LANDFILL GAS 1 Basics of Landfill Gas Methane Carbon Dioxide Hydrogen Sulfide and Sulfides Landfill gas is produced through bacterial decomposition volatilization and chemical reactions Most landfill gas is produced by bacterial decomposition that occurs when organic waste solids food i e meats vegetables garden waste i e leaf and yardwaste wood and paper

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