固体废弃物全过程管理.ppt

1、CHAPTER 4PHYSICAL, CHEMICAL,AND BIOLOGICAL PROPERTIES OF MUNICIPAL SOLID WASTE,4-1 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.,Specific Weight,Specif

2、ic Weight is defined as the weight of a material per unit volume. 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 asses

3、s 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.,Moisture Content,The mo

4、isture 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 w

5、et-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:,Particle Size and size Distribution,The size and size distribution of the component materials in solid wastes are an important consideration in th

6、e recovery of materials, especially with mechanical means such as trommel screens magnetic separators.,The size of a waste component may be defined by one or more of the following measures:,Field Capacity,Definition: The field capacity(场地持水量) of solid waste is the total amount of moisture that can b

7、e 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 o

8、f 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.,Permeability of Compacted Waste,The h

9、ydraulic conductivity of compacted wastes is an important physical property that, to a large extent, governs the movement of liquids and gases in a landfill. The coefficient of permeability is normally written as,固有渗透性,水的动力黏度,渗透系数,4-2 CHEMICAL PROPERTIES OF MSW,Information on the chemical compositio

10、n 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 noncom

11、bustible 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

12、the production of other biological conversion products, the information we must know: 1）the major elements (ultimate analysis) that compose the waste, 2）the trace elements in the waste materials.,Proximate Analysis,Proximate analysis for the combustible components of MSW includes the following tests

13、: 1. Moisture (loss of moisture when heated to 105 for 1 h) 2. Volatile combustible matter (additional loss of weight on ignition at 950 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),

14、Fusing Point of Ash,definition The fusing point of ash is defined as that temperature at which the ash resulting from the burning of waste will form a solid (clinker) by fusion and agglomeration. Notation: Typical fusing temperatures for the formation of clinker from solid waste range from 2000 to 2

15、200 (1100 to 1200).,Ultimate Analysis of Solid Waste Components,Ultimate Analysis of Solid Waste Components typically involves the determination of the percent C,H,O,N, S and ash (sometimes halogen). The purpose: To characterize the chemical composition of organic matters in MSW.,Energy Content of S

16、olid Waste Components,The energy content of the organic components in MSW can be determined (1) by using a full scale boiler as a calorimeter, (2) by using a laboratory bomb calorimeter (3) by calculation, if the elemental composition is known. Because of the difficulty in instrumenting a full-scale

17、 boiler, most of the data on the energy content of the organic components of MSW are based on the results of bomb calorimeter tests.,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 compos

18、t, 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 element

19、s found in the principal materials that compose the organic fraction of MSW are reported in Table 4-6.,4-3 BIOLOGICAL PROPERTIES OF MSW,the organic fraction of most MSW can be classified as follows（ Excluding plastic, rubber, and leather components ）: 1. Water-soluble constituents, such as sugars, s

20、tarches, 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(蜡), which are esters of alcohols and long-chain fatty acids, 5. Lignin, a polymeric

21、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

22、.,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 put

23、rescible 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, is often used as a measure of the biodegradability of the organic fraction of MSW. The use of VS in describing the biod

24、egradability 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

25、 the following relationship:,The biodegradability of several of the organic compounds found in MSW, based on lignin content, is reported in Table 4-7. As shown in Table 4-7, wastes with high lignin contents, such as newsprint, are significantly less biodegradable than the other organic wastes found

26、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

27、 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.,B

28、reeding of Flies,In the summertime and during all seasons in warm climates, fly breeding is an important consideration in the on-site storage of wastes. Flies can develop in less than two weeks after the eggs are laid. The life history of the common house fly from egg to adult can be described as fo

29、llows:,The extent to which flies develop from the larval (maggot) stage in on-site storage containers depends on the following facts: If maggots develop, they are difficult to remove when the containers are emptied. Those remaining may develop into flies. Maggots can also crawl from uncovered cans a

30、nd develop into flies in the surrounding environment.,4-4 PHYSICAL, CHEMICAL,AND BIOLOGICAL TRANSFORMATIONS OF SOLID WASTE,The purpose of this section is to introduce the reader to the principal transformation processes that can be used for the management of MSW. These transformations can occur eith

31、er by the intervention of people or by natural phenomena.,Solid waste can be transformed by physical, chemical, and biological means. One must understand the transformation processes that are possible and the products that may result because they will affect directly the development of integrated so

32、lid waste management plans.,Physical Transformations,The principal physical transformations that may occur in the operation of solid waste management systems include (1) component separation, (2) mechanical volume reduction, (3) mechanical size reduction. comment:Physical transformations do not invo

33、lve a change in phase (e.g., solid to gas), unlike chemical and biological transformation processes.,Component Separation.,Component separation is the term used to describe the process of separating, by manual and/or mechanical means, identifiable components from commingled MSW. Component separation

34、 is used to transform a heterogeneous waste into a number of more-or-less homogeneous components.,Mechanical Volume Reduction.,Volume reduction (sometimes known as densification) is the term used to describe the process whereby the initial volume occupied by a waste is reduced, usually by the applic

35、ation of force or pressure. In most cities, the vehicles used for the collection of solid wastes are equipped with compaction mechanisms to increase the amount of waste collected per trip.,Mechanical Size Reduction.,Size reduction is the term applied to the transformation processes used to reduce th

36、e size of the waste materials. The objective of size reduction is to obtain a final product that is reasonably uniform and consider- ably reduced in size in comparison with its original form. In practice, the terms shredding, grinding, and milling are used to describe mechanical size-reduction opera

37、tions.,Chemical Transformations,Chemical transformations of solid waste typically involve a change of phase . To reduce the volume and/or to recover conversion products, the principal chemical processes used to transform MSW include (I) combustion (chemical oxidation), (2) pyrolysis, (3) gasificatio

38、n. All three of these processes are often classified as thermal processes.,Combustion (Chemical Oxidation).,Combustion is defined as the chemical reaction of oxygen with organic materials, to produce oxidized compounds ac- companied by the emission of light and rapid generation of heat. In the prese

39、nce of excess air and under ideal conditions, the combustion of the organic fraction of MSW can be represented by the following equation:,Pyrolysis.,Pyrolysis is the term used to describe the process. In contrast with the combustion process, which is highly exothermic, the pyrolytic process is highl

40、y endothermic. For this reason, destructive distillation is often used as an alternative term for pyrolysis.,Gasification.,The gasification process involves partial combustion of a carbonaceous fuel so as to generate a combustible fuel gas rich in carbon monoxide, hydrogen, and some saturated hydroc

41、arbons, principally methane. The combustible fuel gas can then be combusted in an internal combustion engine or boiler.,When a gasifier is operated at atmospheric pressure with air as the oxidant, the end products of the gasification process are,(1) a low-Btu gas typically containing carbon dioxide

42、(CO2), carbon monoxide (CO), hydrogen (H2), methane (CH4), nitrogen (N2); (2) a char containing carbon and the inerts originally in the fuel, (3) condensible liquids resembling pyrolytic oil.,Other Chemical Transformation Processes.,Example: The hydrolytic conversion of cellulose to glucose, followe

43、d by the fermentation of glucose to ethyl alcohol.,Biological Transformations,The biological transformations of the organic fraction of MSW may be used to reduce the volume and weight of the material; to produce compost, a humus-like material that can be used as a soil conditioner; to produce methan

44、e. The principal organisms involved in the biological transformations of organic wastes are bacteria, fungi(真菌), yeasts, and actinomycetes（放线菌）. These transformations may be accomplished either aerobically or anaerobically, depending on the availability of oxygen.,Aerobic Composting.,Left unattended

45、, the organic fraction of MSW will undergo biological decomposition. The extent and the period of time over which the decomposition occurs will depend on the nature of the waste, the moisture content, the available nutrients, other environmental factors. Under controlled conditions, yard wastes and

46、the organic fraction of MSW can be converted to a stable organic residue known as compost in a reasonably short period of time (four to six weeks).,Composting the organic fraction of MSW under aerobic conditions can be represented by the following equation:,Anaerobic Digestion.,The biodegradable por

47、tion of the organic fraction of MSW can be converted biologically under anaerobic conditions to a gas containing carbon dioxide and methane (CH4). This conversion can be represented by the following equation:,Other Biological Transformation Processes.,In addition to the aerobic composting and anaerobic digestion processes, a variety of other