14 Physical, Chemical, and biological properties of municipal solid Waste 14- 1 Physical Properties of MSW Important physical characteristics of MSW include specific weight. moisture content, particle size and size distribution, field capacity, and compacted waste porosity. The discussion is limited to an analysis of residential. commercial and some industrial solid wastes. Note. however. that the fundamentals of analysis presented in this and the following chapter are applicable to all types of solid wastes dditional details on the various physical, chemical, and microbiological methods of testing for solid wastes may be found in the various publications of the American Society for Testing and Materials (ASTM Specific Weight Specific weight is defined as the weight of a material per unit volume. (It should be noted that specific weight expressed as lb/yd is commonly referred to in the solid waste literature incorrectly as density In U.S. customary units density is expressed correctly as slug/f t) Because the specific weight of basis used for the reported values should al ways be noted. Specific weight data are often needed to assess the total mass and volume of waste that must be managed. Unfortunately, there is little or no uniformity in the way solid waste specific weights have been reported in the literature. Frequently,no distinction has been made between uncompacted or compacted specific weights Because the specific weights of solid wastes vary markedly with geographic location, season of the year, and length of time in storage, great care should be used in selecting typical values. Municip solid wastes as delivered in compaction vehicles have been found to vary from 300 to 700 lb/yd;a Moisture content The moisture content of solid wastes usually is expressed in one of two ways. In the wet-weight method of measurement, the moisture in a sample is expressed as a percentage of the wet weight of the material; in the dry-weight method, it is expressed as a percentage of the dry weight of the material The wet-weight method is used most commonly in the field of solid waste management. In equation form, the wet-weight moisture content is expressed as follows d\100 (14-1) where M= moisture content. w=initial weight of sample as delivered, Ib(kg) d= weight of sample after drying at 105 C, Ib(kg) For most MSw in the United States, the moisture content will vary from 15 to 40 percent, depending on the composition of the wastes, the season of the year, and the humidity and weather conditions, Particle Size and Size distribution The size and size distribution of the component materials in solid wastes are an important consideration in the recovery of materials, especially with mechanical means such as trommel screens and magnetic separators. The size of a waste component may be denned by one of the following measures (142) (143) S where Sc l h
14-1 14 Physical, Chemical, and Biological Properties of Municipal Solid Waste 14- 1 Physical Properties of MSW Important physical characteristics of MSW include specific weight, moisture content, particle size and size distribution, field capacity, and compacted waste porosity. The discussion is limited to an analysis of residential, commercial, and some industrial solid wastes. Note, however, that the fundamentals of analysis presented in this and the following chapter are applicable to all types of solid wastes. Additional details on the various physical, chemical, and microbiological methods of testing for solid wastes may be found in the various publications of the American Society for Testing and Materials (ASTM). Specific Weight Specific weight is defined as the weight of a material per unit volume. (It should be noted that specific weight expressed as lb/yd3 is commonly referred to in the solid waste literature incorrectly as density. In U.S. customary units density is expressed correctly as slug/f t3 .) Because the specific weight of MSW is often reported as loose, as found in containers, uncompacted, compacted, and the like, the basis used for the reported values should always be noted. Specific weight data are often needed to assess the total mass and volume of waste that must be managed. Unfortunately, there is little or no uniformity in the way solid waste specific weights have been reported in the literature. Frequently, no distinction has been made between uncompacted or compacted specific weights. Because the specific weights of solid wastes vary markedly with geographic location, season of the year, and length of time in storage, great care should be used in selecting typical values. Municipal solid wastes as delivered in compaction vehicles have been found to vary from 300 to 700 lb/yd3 ; a typical value is about 500lb/yd3 . Moisture Content The moisture content of solid wastes usually is expressed in one of two ways. In the wet-weight method of measurement, the moisture in a sample is expressed as a percentage of the wet weight of the material; in the dry-weight method, it is expressed as a percentage of the dry weight of the material. The wet-weight method is used most commonly in the field of solid waste management. In equation form, the wet-weight moisture content is expressed as follows: 100 − = w w d M (14- 1) where M = moisture content, % w = initial weight of sample as delivered, lb (kg) d = weight of sample after drying at 105℃, lb (kg) For most MSW in the United States, the moisture content will vary from 15 to 40 percent, depending on the composition of the wastes, the season of the year, and the humidity and weather conditions, particularly rain. Particle Size and Size Distribution The size and size distribution of the component materials in solid wastes are an important consideration in the recovery of materials, especially with mechanical means such as trommel screens and magnetic separators. The size of a waste component may be denned by one or more of the following measures: (14- 2) (14- 3) (14- 4) (14- 5) (14- 6)
Field Capacity The field capacity of solid waste is the total amount of moisture that can be retained in a waste sample sIs or cr formation hate in landfills. Water in excess of the field capacity will be eleased as leachate. The field capacity varies with the degree of applied pressure and the state of decomposition of the waste. A field capacity of 30 percent by volume corresponds to 30 in/100 in. The field capacity of uncompacted commingled wastes from residential and commercial sources is in the range of 50 to 60 percent 4- 2 Chemical properties of MSW Information on the chemical composition of the components that constitute MSw portant in evaluating alternative processing and recovery options. For example, the feasibility bustion depends on the chemical cor ition of the solid wastes. Typically, wastes can be thought of as a combination of semimoist combustible and noncombustible materials. If solid wastes are to be used as fuel, the four most important properties to be known are I Proximate analysis Fusing point of ash 3. Ultimate analysis(major elements) 4. Energy content Where the organic fraction of MSW is to be composted or is to be used as feedstock for the production of other biological conversion products, not only will information on the major elements(ultimate analysis) that compose the waste be important, but also information will be required on the trace elements in the waste materials Proximate Analysis Proximate analysis for the combustible components of MSw includes the following tests 1. Moisture(loss of moisture when heated to 105C for 1 h) 2. Volatile combustible matter(additional loss of weight on ignition at 950%C in a covered crucible) 3. Fixed carbon(combustible residue left after volatile matter is removed) 4. Ash(weight of residue after combustion in an open crucible Fusing point fash waste wilT form a solid(clinker) by fusion and agglomeration Typical fusing temperatures for,of The fusing point of ash is denned as that temperature at which the ash resulting from the burr formation of clinker from solid waste range from 2000 to 2200.F(1100 to 1200C) Tab 14-I Typical proximate analysis and energy data for materials found in residential, commercial, and industrial solid Proximate analysis, % by weight Energy content, Btu/b Type of waste Moisture matter Dry ash-free Food wastes(mixed) Fruit wastes 1,707 Meat wastes 56.4 23 7428 Waxed cartons 909 45 2.0 2222 11204 Polyvinyl chloride Textiles. rubber leather 18:21.2 14-2
14-2 Field Capacity The field capacity of solid waste is the total amount of moisture that can be retained in a waste sample subject to the downward pull of gravity. The field capacity of waste materials is of critical importance in determining the formation of leachate in landfills. Water in excess of the field capacity will be released as leachate. The field capacity varies with the degree of applied pressure and the state of decomposition of the waste. A field capacity of 30 percent by volume corresponds to 30 in/100 in. The field capacity of uncompacted commingled wastes from residential and commercial sources is in the range of 50 to 60 percent. 14- 2 Chemical properties of MSW Information on the chemical composition of the components that constitute MSW is important in evaluating alternative processing and recovery options. For example, the feasibility of combustion depends on the chemical composition of the solid wastes. Typically, wastes can be thought of as a combination of semimoist combustible and noncombustible materials. If solid wastes are to be used as fuel, the four most important properties to be known are: 1. Proximate analysis 2. Fusing point of ash 3. Ultimate analysis (major elements) 4. Energy content Where the organic fraction of MSW is to be composted or is to be used as feedstock for the production of other biological conversion products, not only will information on the major elements (ultimate analysis) that compose the waste be important, but also information will be required on the trace elements in the waste materials. Proximate Analysis Proximate analysis for the combustible components of MSW includes the following tests : 1. Moisture (loss of moisture when heated to 105°C for 1 h) 2. Volatile combustible matter (additional loss of weight on ignition at 950°C in a covered crucible) 3. Fixed carbon (combustible residue left after volatile matter is removed) 4. Ash (weight of residue after combustion in an open crucible) Fusing Point of Ash The fusing point of ash is denned as that temperature at which the ash resulting from the burning of waste will form a solid (clinker) by fusion and agglomeration. Typical fusing temperatures for the formation of clinker from solid waste range from 2000 to 2200°F (1100 to 1200°C). Tab 14-1
6585 Glass, Metals Glass and mineral 9699+ Metal, tin ca 301b Metal, ferrous 20 9699+ Metal, nonferrous 94-99+ 3,869 3791 6,250 (1030) MSW 20.0 00 5750 Adapted in part from Refs. 6-8. Energy content is om coatings, label, and attached materials N;跏x10551=k Ultimate Analysis of Solid Waste Components The ultimate analysis of a wasen Nio nent typically involves the determination of the percent C emission of chlorinated compounds during combustion, the determination of halogens is often included in an ultimate analysis. The results of the ultimate analysis are used to characterize the chemical composition of the organic matter in mSW. They are also used to define the proper mix of waste materials to achieve suitable C/n ratios for biological conversion processes. Data on the ultimate analysis of individual combustible materials are resented in Table 14-2 Tab 14-3 Elemental analysis of the organic materials used as the feedstock for biological conversion processes nstituent Unit Newsprint Office paper Yard waste Food was NHa-N 3500 2210 3200 82 57 4.0
14-3 Ultimate Analysis of Solid Waste Components The ultimate analysis of a waste component typically involves the determination of the percent C (carbon), H (hydrogen), 0 (oxygen), N (nitrogen), S (sulfur), and ash. Because of the concern over the emission of chlorinated compounds during combustion, the determination of halogens is often included in an ultimate analysis. The results of the ultimate analysis are used to characterize the chemical composition of the organic matter in MSW. They are also used to define the proper mix of waste materials to achieve suitable C/N ratios for biological conversion processes. Data on the ultimate analysis of individual combustible materials are resented in Table 14- 2. Tab 14-3
Tab 14-2 Typical data on the ultimate analysis of the combustible materials found in residential, commercial, and industrial solid wastes Percent by weight (dry basis) Type of waste Carbon Hydrogen Oxygen Nitrogen Sulfur Ash Food and food products 14.8 0. 48.0 6.4 37.6 2.6 .0 Fruit wastes 48.5 2 Meat wastes 0.2 4.9 aper products Cardboard 43.0 448 03 02 50 Magazines 329 0 386 23.3 Newsprint 49.1 43.0 15 Paper(mixed) 58 44.3 0.3 0.2 60 Waxed cartons 9.3 Plastics Plastics(mixed) 228 852 14.2 0.4 Polystyrene 87,1 8.4 2 Polyurethane 176 60 4.3 Polyvinyl chloride 2.0 Textiles, rubber, leather Textiles 48.0 64 40.0 Rubber 69.7 60.0 8.0 11.6 10.0 Wood, trees, etc Yard wastes 46.0 60 3.4 03 63 Wood (green timber) 6.4 49.6 43.2 <0.1 09 Wood(mixed) 49.5 60 42.7 <0.1 Wood chips(mixed 8 0.1 <0.1 0.4 Glass and minera° <0.1 989 0.6 4.3 <0.1 90 Miscellaneous Office sweepings 243 4.0 0.5 0268.0 Oils, paints Refuse-derived fuel( RDF) 44.7 384 99 Essential Nutrients and other elements Where the organic fraction of msw is to be used as feedstock for the production of biological ne and ethanol. information on the elements in the waste materials is of importance with respect to the microbial nutrient balance and in assessing what final uses can be made of the materials remaining after biological conversion The essential nutrients and elements found in the principal materials that compose the organic fraction of ted in Table 14-3
14-4 Essential Nutrients and Other Elements Where the organic fraction of MSW is to be used as feedstock for the production of biological conversion products such as compost, methane, and ethanol, information on the essential nutrients and elements in the waste materials is of importance with respect to the microbial nutrient balance and in assessing what final uses can be made of the materials remaining after biological conversion. The essential nutrients and elements found in the principal materials that compose the organic fraction of MSW are reported in Table 14- 3. Tab 14-2
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 example
14-5 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