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 h14-1 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)