14-3 Biological Properties of MSW Excluding plastic, rubber, and leather components, the organic fraction of most MSw can be classified as follows. 1. Water-soluble constituents, such as sugars, starches, amino acids, and various organic acids 2. Hemicellulose, a condensation product of five-and six-carbon sugars, 3. Cellulose, a condensation product of the Six-carbon sugar glucose 4. Fats, oils, and waxes, which are esters of alcohols and long-chain fatty acids, 5. Lignin, a polymeric material containing aromatic rings with methoxyl groups(-OCH3, the exact chemical nature of which is still not known(present in some paper products such as newsprint and fiberboard 6. Lignocellulose, a combination of lignin and cellulose, 7. Proteins, which are composed of chains of amino acids Perhaps the most important biological characteristic of the organic fraction of Ms w is that almost all of the organic components can be converted biologically to gases and relatively inert organic and inorganic solids. The production of odors and the generation of flies are also related to the putrescible nature of the organic materials found in MSW(e.g, food wastes Biodegradability of organic Waste Components Volatile solids(VS) content, determined by ignition at 550C, is often used sure of the biodegradability of the organic fraction of msw. The use of vS in describing the adability of the organic fraction of MSW is misleading, as some of the organic constituents of MSw are highly volatile but low in biodegradability (e.g, newsprint and certain plant trimmings). Alternatively, the lignin content of a waste can be used to estimate the biodegradable fraction, using the following BF=0.814-0.028LC Where BF= biodegradable fraction expressed on a volatile solids(vS)basis 0.83 irical constan 0. 028=empirical constant Wase. lc= lignin content of the VS expressed as a percent of dry weight adable organic wastes found in MSW.The rate at which the various components can be degraded varies markedly. For practical purposes, the principal organic waste components in MSW are often classified as rapidly and slowly decomposable Production of odors Odors can develop when solid wastes are stored for long periods of time on-site between collections in transfer stations, and in landfills. The development of odors in on-site storage facilities is more significant in warm climates. Typically, the formation of odors results from the anaerobic decomposition of the readily decomposable organic components found in MSw. For example, under anaerobic(reducing) conditions, sulfate can be reduced to sulfide(S), which subsequently combines with hydrogen to form H2S. The formation of H2S can be illustrated by the following two series of reacto 2CH3 CHOHCOOH +SO4 2CH3 COOH +S+2H20+2C02 S2-+4H2O (14-9) HS The sulfide ion can also combine with metal salts that may be present, such as iron, to form metal FeS (14-11) The black color of solid wastes that have undergone anaerobic decomposition in a landfill is primarily due to the formation of metal sulfides. If it were not for the formation of a variety of sulfides, od problems at landfills could be quite significant The biochemical reduction of an organic compound containing a sulfur radical can lead to the formation of malodorous compounds such as methyl mercaptan and aminobutyric acid. The reduction of methionine, an amino acid serves as an example14-5 14- 3 Biological Properties of MSW Excluding plastic, rubber, and leather components, the organic fraction of most MSW can be classified as follows: 1. Water-soluble constituents, such as sugars, starches, amino acids, and various organic acids, 2. Hemicellulose, a condensation product of five- and six-carbon sugars, 3. Cellulose, a condensation product of the six-carbon sugar glucose, 4. Fats, oils, and waxes, which are esters of alcohols and long-chain fatty acids, 5. Lignin, a polymeric material containing aromatic rings with methoxyl groups (-OCH3, the exact chemical nature of which is still not known (present in some paper products such as newsprint and fiberboard), 6. Lignocellulose, a combination of lignin and cellulose, 7. Proteins, which are composed of chains of amino acids. Perhaps the most important biological characteristic of the organic fraction of MSW is that almost all of the organic components can be converted biologically to gases and relatively inert organic and inorganic solids. The production of odors and the generation of flies are also related to the putrescible nature of the organic materials found in MSW (e.g., food wastes). Biodegradability of Organic Waste Components Volatile solids (VS) content, determined by ignition at 550°C, is often used as a measure of the biodegradability of the organic fraction of MSW. The use of VS in describing the biodegradability of the organic fraction of MSW is misleading, as some of the organic constituents of MSW are highly volatile but low in biodegradability (e.g., newsprint and certain plant trimmings). Alternatively, the lignin content of a waste can be used to estimate the biodegradable fraction, using the following relationship : BF = 0.814- 0.028LC (14- 7) Where BF = biodegradable fraction expressed on a volatile solids (VS) basis 0.83 = empirical constant 0.028 = empirical constant LC = lignin content of the VS expressed as a percent of dry weight Wastes with high lignin contents, such as newsprint, are significantly less biodegradable than the other organic wastes found in MSW. The rate at which the various components can be degraded varies markedly. For practical purposes, the principal organic waste components in MSW are often classified as rapidly and slowly decomposable. Production of Odors Odors can develop when solid wastes are stored for long periods of time on-site between collections, in transfer stations, and in landfills. The development of odors in on-site storage facilities is more significant in warm climates. Typically, the formation of odors results from the anaerobic decomposition of the readily decomposable organic components found in MSW. For example, under anaerobic (reducing) conditions, sulfate can be reduced to sulfide (S2- ), which subsequently combines with hydrogen to form H2S. The formation of H2S can be illustrated by the following two series of reactions. 2CH3CHOHCOOH + SO4 2- → 2CH3COOH + S2- + 2H2O + 2CO2 (14- 8) 4H2 + SO4 2- → S 2- + 4H2O (14- 9) S 2- + 2H+ → H2S (14- 10) The sulfide ion can also combine with metal salts that may be present, such as iron, to form metal sulfides. S 2- + Fe2+ → FeS (14- 11) The black color of solid wastes that have undergone anaerobic decomposition in a landfill is primarily due to the formation of metal sulfides. If it were not for the formation of a variety of sulfides, odor problems at landfills could be quite significant. The biochemical reduction of an organic compound containing a sulfur radical can lead to the formation of malodorous compounds such as methyl mercaptan and aminobutyric acid. The reduction of methionine, an amino acid, serves as an example