Presentation Outline

Presentation Outline • Physical Properties of MSW • Chemical Properties of MSW • Biological Properties of MSW • Physical, Chemical and Biological Transformation of MSW • Importance of Waste Transformations in Solid Waste Management

Physical Properties • Physical Properties of MSW • Specific Weight • Moisture Content • Particle Size • Size Distribution • Field Capacity • Compacted Waste Properties

Physical Properties :Specific Weight • Specific Weight is the weight of material per unit volume (e.g., lb/ft3, lb/yd3). It is usually reported as loose, as found in container, un-compacted, compacted and the like. • Specific Weight data are often needed to assess the total mass and volume of waste that must be managed • Frequently, no distinction has been made between un-compacted or compacted specific weight • Specific Weight of solid waste vary with: • geographic location • season of the year • length time of storage

Physical Properties :Specific Weight Typical Specific Weight and Moisture Content Data for Residential, Commercial wastes

Physical Properties :Moisture Content • The moisture content of solid wastes usually is expressed in one of two ways • percentage of the wet-weight of the material ( when wet-weight method is used) • Percentage of the dry-weight of the material ( when dry-weight method is used) • The wet – weight method is used most commonly in the field of solid waste management . • The moisture content of MSW depends on the composition, the season of the year, humidity and weather conditions, particularly rain. • M= (w-d)/w * 100 • where: • M= moisture content , % • w= initial weight of sample as delivered, Ib (kg) • d= weight of sample after drying at 105 C, Ib(kg)

Physical Properties :Moisture Content

Physical Properties: Particle Size and 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 magnetic separators. • The size of a waste component may be defined by one or more of the following measures • Sc = L • Sc= (I+W)/2 • Sc = (L+W+h)/3 • Where • Sc : size of the component (mm) • l : Length (mm) • W : Width (mm) • h : height (mm)

Physical Properties: 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 relesed as leachate • The field capacity varies with the degree of • applied pressure • the state of decomposition of the waste

Permeability of Compacted Waste • The hydraulic conductivity of compacted wastes is an important physical properties that governs the movement of liquids and gases in a landfill. • The coefficient of permeability is normally written as K= k (γ/µ) • The intrinsic permeability depends solely on the properties of the solid material inculding • Pore size distribution • Tortuosity • Specifc surface • Porosity

Chemical Properties • Information on the chemical composition of the components that constitute MSW is important in evaluating alternative processing and recovery options. • Example: the feasibility of combustion depends on the chemical composition of the solid wastes. • Typically, waste can be thought of as a combination of semimoist combustible and noncombustible materials. Combustible materials are substances that can be burned to provide heat or power. • If solid wastes are to be used as fuel, the four most important properties to be known are: • Proximate analysis • Fusing point of ash • Ultimate analysis (major elements) • Energy content

Chemical Properties: Proximate Analysis • Proximate analysis for the combustible components of MSW includes the following test • Moisture (loss of moisture when heated to 105 C for 1 h) • Volatile combustible matter ( additional loss of weight on ignition at 950 C in a covered crucible) • Fixed carbon ( combustible residue left after volatile matter is removed) • Ash ( weight of residue after combustion in an open crucible) • It is important to note that the test used to determine volatile combustible matter in a proximate analysis is different from the volatile test used in biological determinations

Chemical Properties: Proximate Analysis

Chemical Properties: Fusing Point of Ash • The fusing point of ash is defined as that temperature at which the ash resulting from the burning of waste will from a solid (clinker) by fusion and agglomeration. • Typical fusing temperatures for the formation of clinker from solid waste range from 1100 to 1200 C

Chemical Properties: Ultimate Analysis • The ultimate analysis of a waste component typically involves the determination of the percent of • Carbon • Hydrogen • Oxygen • Nitrogen • Sulfur • Ash • Chlorinated compounds ( emission concerns) • The results of the ultimate analysis are used to • characterize the chemical composition of organic matter in MSW. • define the proper mix of waste materials to achieve suitable C/N ratios for biological conversion procesess

Chemical Properties: Ultimate Analysis

Chemical Properties: Energy Content • The energy content of the organic components in MSW can be determined by: • Full scale boiler as a calorimeter • laboratory bomb calorimeter • Calculation, if the elemental composition is known • because of the difficulty in instrumenting a full-scale boiler, most of the data on energy content of the organic components of MSW are based on the results of bomb calorimeter tests. • Approximate BTU values for the individual waste materials can be determined by Dulong formula • Btu/lb = 145C + 610 (H2-0.125O2)+40S+10N

Chemical Properties: Energy Content

Biological Properties • Excluding plastic, rubber and leather components, the organic fraction of most MSW can be classified as follows: • Water – soluble constituents, such as sugars, starches, amino acids and various organic acids • Hemicellulose, a condensation product of five and six carbon sugars • Cellulose, a condensation product of the six carbon sugar glucose • Fata, oil and waste, which are esters of alcohols and long chain fatty acids • 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 newsprints and fiberbord) • Lignocellulose, a combination of lignin and cellulose • Proteins, which are composed of chains of amino acids

Biological Properties • Perhaps the most important biological characteristics of the orgainc 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 nature of the orgainic material found in MSW (e.g., food waste)

Biodegradability of Organic Waste Components • Volatile Solids 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 Volatile solids in describing the biodegradability of the organic fraction of MSW is misleading because some of the organic constituents of MSW are highly volatile but low in biodegradability (e.g., newsprint and certain plant trimmings). • the lignin content of a waste can be used to estimate the biodegradable fraction by • BF= 0.83 – 0.028 LC • where BF= biodegradable fraction expressed on a volatile solids • 0.83 = empirical constant • 0.028 = empirical constant • LC= Lignin content of the VS expressed as a percent of dry weight

Biodegradability of Organic Waste Components • Wastes with high lignin contents, such as newsprint, are significantly less biodegradable than the other organic waste 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 classified as rapidly and slowly decomposable.

Biological Properties: Production of Odors • Odors can develop when solid waste 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. • Under anaerobic (reducing) conditions, sulfate can be reduced to sulfide, which subsequently combines with hydrogen to form H2S. • The sulfide ion can also combine with metal salts that may be present, such as iron to form metal sulfide.

Biological Properties: Production of Odors • The black color of solid wastes that have undergone anaerobic decomposition in a landfill is primarily due to the formation of metal sulfide. • if were not for the formation of a variety of sulfides, odor problem at landfill 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 mercapten and aminobutyric acid.

Biological Properties: Breeding of Flies • fly breeding is an important consideration in the on-site storage of wastes. • flies can develop in less than 2 weeks after the eggs are laid. The life history of the common house fly from egg to adult can be described as follows

Biological Properties: Breeding of Flies • The extent to which flies develop from larval 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 and develop into flies in the surrounding environments.

Transformations of Solid Waste • The transformation of solid waste can occur either by • The intervention of the people • Natural phenomena • Solid waste can be transformed by • Physical means • chemical means, and • biological means. • One must understand the transformation processes that are possible and the products that may result because the will affect directly the development of integrated solid waste management plans.

Transformations of Solid Waste

Transformations of Solid Waste: Physical • The principal physical transformations that may occur in the operation of solid waste management systems include: • component separation • mechanical volume reduction • mechanical size reduction • Physical transformations do not involve a change in phase (e.g., solid to gas) unlike the chemical and biological transformation processes.

Physical Transformation: Component Separation • Component separation is the term used to describe the process of separating identifiable components from commingled MSW. • The transformation means are manual and/or mechanical separation • Component separation is used to transform a heterogeneous waste into a number of more –or-less homogeneous components. • Component separation is a necessary operation in: • Recovery of reusable and recyclable materials from MSW. • The removal of contaminants from separated materials to improve specifications of the separated materials • The removal of hazardous waste form MSW. • Where energy and conversion products are to be recovered from processed wastes.

Physical Transformation: Mechanical Volume Reduction • Volume reduction (known as densification) is the term used to describe the process whereby the initial volume occupied by a waste is reduced by application of force or pressure. • In most cities, the vehicles used for the collection of sold wastes are equipped with compaction mechanisms to increase the amount of waste collected per trip. • Paper, cardboard, plastics, aluminum and tin cans removed from MSW for recycling are baled to reduce storage and handling costs and shipping coasts to processing centers. • Recently, high pressure compaction system have been developed to produce materials suitable for various alternative uses such as production of fireplace logs from paper and cardboad.

Physical Transformation: Mechanical Volume Reduction • To reduce the costs associated with the transport of waste materials to landfill disposal sites, municipalities also may use transfer stations equipped with compaction facilities • To increase the useful life of landfills, wastes are usually compacted before being covered.

Physical Transformation: Mechanical Size Reduction • Size reduction is the term applied to the transformation processes used to reduce the size of the waste materials • The objective of the size reduction is to obtain a final product that is reasonably uniform and considerably reduced in size in comparison with its original form. • Size reduction does not necessarily imply volume reduction. In some situations, the total volume of the material after size reduction may be greater than of the original volume (e.g., the shredding of office paper).

Chemical Transformation • Chemical transformations of solid waste typically involve a change of phase (e.g., solid to liquid, solid to gas, etc.). • The principal chemical processes used to transform MSW include • Combustion ( Chemical Oxidation) • Pyrolysis • Gasification • All of the above processes are often classified as thermal processes

Chemical Transformation: Combustion • Combustion is defined as the chemical reaction of oxygen with organic materials, to produce oxidized compounds accompanied by the emission of light and rapid generation of heat. • The combustion of the organic fraction of MSW can be represented by the following equation: • Organic matter + excess air N2 + CO2 + H2O + O2+ Ash + Heat • Excess air is used to ensure complete combustion. • In practice, small amounts of ammonia, sulfur dioxide, nitrogen oxides, and other trace gases will also be present, depending on the nature of the waste materials.

Chemical Transformation: Pyrolysis • Because most of the organic substances are thermally unstable, they can be split, through a combination of thermal cracking and condensation reactions in an oxygen –free atmosphere, into gaseous, liquid and solid fractions. • The pyrolysis is highly endothermic. For this reason, destructive distillation is often used as an alternative term for pyrolysis. • The characteristics of the three major component fractions resulting from the pyrolysis of the organic portion are: • A gas stream containing H2, CH4 , CO , CO2 and various other gases. • A tar and/or oil stream that is liquid at room temperature and contains chemicals such as acetone and methanol • A char consisting of almost pure carbon plus any inert material that may have entered the process.

Chemical Transformation: Pyrolysis • For cellulose (C6H10O5) the following expression has been suggested as being representative of the pyrolysis reaction • 3 (C6H10O5) ……………….. 8H2O + C6H8O + 2CO + 2CO2 + CH4 + H2 + 7C • The liquid tar and/or oil compounds normally obtained are represented by the expression C6H8O.

Chemical Transformation: Gasification • The gasiication process involves partial combustion of a carbonaceous fuel so as to generate a combustible fuel gas rich in CO and H2 and some saturated hydrocarbons. • The combustible fuel gas can then be combusted in an internal combustion engine or boiler. • The end products of the gasification process are • A low – Btu gas typically containing CO2, CO, H2, CH4, N2 • A char containing carbon and inerts originally in the fuel • Condensible liquids resembling pyrolytic oil.

Biological Transformation • The biological transformation of the organic fraction of MSW may be used to reduce the volume and weight of the material to produce • compost , • Humus – like material that can be used as a soil conditioner • Methane (CH4) • The principal organisms involved in the biological transformations of organic waste are • Bacteria • fungi • Yeasts • actinomycetes • The biological transformation may be accomplished either by aerobically or ana-erobically, depending on the availability of oxygen • The principal differences between the aerobic and ana-aerobic conversion reactions are the nature of the end products and oxygen for the aerobic reaction.

Biological Transformation: aerobic composting • 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 • Composting the organic fraction of MSW under aerobic conditions can be represented by the following equation: • Organic matter + O2+ nutrients …………new cells+ resistant organic matter • CO2 + H2O + NH3 + SO2 + heat • The resistant organic matter usually contains a high percentage of lignin which is difficult to convert biologically in a relatively short time • Lignin is the organic polymer that holds the cellulose fibers in trees and certain plants.

Biological Transformation: Anaerobic Digestion • This conversion can be represented by the following equation • Organic matter + H2O + nutrients ……………………. New cells + resistant organic • + CO2 + CH4 + NH3 + H2S + heat • In most anaerobic conversion processes CO2 and CH4 constitute over 99 percent • of the total gas produced. • The resistant organic matter (digested sludge) must be dewatered before it can be disposed of by land spreading or landfilling • Dewatered sludge is often composted aerobically to stabilize before application.

Importance of Waste Transformation in SWM • Typically, physical , chemical and biological transformations are used to: • Improve the efficiency of solid waste management operations and systems • Recover reusable and recyclable materials • Recover conversion products and energy

Improving Efficiency of Solid Waste Management Systems • To improve the efficiency of solid waste management operations and to reduce storage volume requirements at medium and high rise apartment buildings, wastes are often baled. • Mechanical size reduction (shredding) has been used to improve the efficiency of disposal sites. • In some cases, waste materials are baled to reduce haul costs to the disposal sites • At the disposal site, wastes are compacted to use the available landfill capacity effectively . • Hand separation at the point of generation is now is considered an efficient way to remove small quantities of hazardous waste from MSW, thereby making landfills safer. • Chemical and biological processes can be used to reduce the volume and weight of waste requiring disposal and to produce useful products

Recovery of material for reuse and recycling • As a practical matter, components that are most amenable to recovery are those for which markets exist and which are present in the waste in sufficient quantity to justify their separation. • Materials most often recovered from MSW inculde • Paper • Cardboard • Plastic • Garden trimming • glass • Ferrous metal • aluminum • and other nonferrous metal.

Recovery of Conversion Products and Energy • The organic fraction of MSW can be converted to usable products and ultimately to energy in a number of ways including • Combustion to produce steam and electricity • pyrolysis to produce synthetic gas, liquid or solid fuel and solids • Gasification to produce a synthetic fuel • biological conversion to produce compost • Biodigestion to generate methane and to produce a stabilized organic humus.

Presentation Outline