PB389 Integrated Solid Waste Management

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1 PB389 Integrated Solid Waste Management Numfon Eaktasang, Ph.D. Thammasat University

2 Solid Waste Management Waste generation Waste reduction and separation at the source Collection Transportation Separation, processing & transformation Disposal

3 Target of this chapter Commingled wastes Material Recovery Facility (MRF) Separation, Processing for recycle, Transformation Landfill disposal 3

4 Waste separation at MRFs MRF (Material recovery facility) Function as a centralized facility for the separation, cleaning, packaging, and shipping of large volumes of materials recovered from MSW. Further processing of source-separated wastes Separation and Recovery of reusable and recyclable materials from commingled MSW Improvements in the quality (specifications) of the recovered waste materials. 4

5 Manual and mechanical separation Manual separation Flexible Need more labors Easy at source Mechanical separation Not flexible: need frequent maintenance Less labors Current trend Integration of manual and mechanical separation 5

6 Unit operation in MRFs Unit operations in MRFs are designed To modify the physical characteristics of the waste To remove specific components and contaminants from the waste stream To process and prepare the separated materials for subsequent use Category of operations in MRFs Size reduction Size separation Density separation Electric and magnetic field separation Densification (compaction) 6

7 Size Reduction type of equipment Hammer-mill effective with brittle materials Shear shredders: two opposing counter-rotating blades Cut ductile materials Tub grinder Widely used for yard wastes processing 7

8 Hammer-mill shredder Inner shaft is rotated at high speed, rev/min Solid waste can not adhere to the hammer Cutting action continues to until the material falls out of the bottom. Either horizontal-shaft or vertical-shaft configuration Horizontal-shaft is more reliable 8

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10 Shear shredder Scissor-like action With two counterrotating knives or blades Low-speed devices rev/min Need reversed action in the event of jam 10

11 Tub Grinder Essentially mobile hammermill shredder Used for wide variety of materials It consists of tub with grinder for shredding Engine for grinder Loading equipment Discharging equipment 11

12 Size reduction selection of equipment Factors to be considered Materials to be shredded: Mechanical characteristics: shear strength and ductility Size requirements: uniform or non-uniform Method of feeding: capacity Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, reliability, noise, air and water pollution control requirements Site considerations: floor space and height, access Materials storage and conveyance requirements: for shredded materials Safety issues: Explosion and fire Potentially explosive: VOCs, spray cans Explosive atmosphere: dust, high-speed impact of metal 12

13 Size separation Size separation = screening Can be accomplished dry or wet. Reciprocating screen Vibrating screen Trommel screen Rotary drum screen Disc screen 13

14 Vibrating screen Application Dry materials such as glass or metals Wood chip for composting Solid Waste Management: Chapter 5 14

15 Trommel screen Versatile type of screen Large-diameter screen Rotating on a horizontal axis Application Protect shredder in RDF production (removing oversized materials) Separate cardboard and paper Solid Waste Management: Chapter 5 15

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17 Disc screen An alternative to reciprocating screen Advantages Self-cleaning Capability of adjustment by varying the spacing of the discs on the drive shafts 17

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19 Size separation Selection of equipment Factors to be considered Waste characteristics: particle size, shape, bulk specific weight, moisture content, particle size distribution, clumping tendency, rheological properties Materials specifications for screened components Design parameters: size of opening, percentage of open space, total surface area, oscillation rate for reciprocating screens, rotational speed for trommel, elevation angle for trommel, loading rates and length Separation efficiency: recovery, purity and efficiency Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, reliability, noise, air and water pollution control requirements Site considerations: floor space and height, access 19

20 Density separation type of equipment Separated based on the density and aero dynamic characteristics Applied to the separation of shredded MSW into Light fraction; paper, plastics and organics Heavy fraction; metals, wood, etc.. Type Air classification Stoner Flotation Heavy media separation 20

21 Air classifier (1) Lighter materials transport to the top of chute by the upward airflow Control of the percentage split is accomplished by varying the waste loading, airflow rate, and the crosssectional area of chute 21

22 Air classifier (2) Type of classfier Straight: Zigzag: creates turbulence and allows bunched materials to be broken up. Pulsed air: can achieve a greater discrimination Straight zigzag Passive pulsed 22

23 Stoner (1) Consists of a vibrating porous deck through which air is blown Solid Waste Management: Chapter 5 23

24 Stoner (2) Initially designed to remove stones and other heavy rejects Separate heavy grit from organic material in trommel underflow streams Called inert separator Actual separating criterion is terminal velocity, not density or weight. Important operation variables are deck slope and air volumes 24

25 Flotation Employs a fluid to separate two components of different densities. Using water Sink to bottom: glass chips, rocks, bricks Float: light organics, plastics, Change the liquid, we can separate in a different density. 25

26 Heavy Media Separation Shredded feedstock is dumped into a liquid stream that has a high specific gravity. Aluminum separation (floating in a liquid) After ferrous metal and glass have been removed. Disadvantage Optimum-size requirement: ton/d of feedstock Increase success of source separation 26

27 Density separation Selection of equipment Factors to be considered Characteristics of material produced by the shredder or other separation device: particle size, shape, bulk specific weight, moisture content, particle size distribution, clumping tendency, fiber content Materials specifications for light fraction: particle size and its distribution Air classifier design parameters: air/solids ratio, fluidizing velocity, unit capacity, total air flow Stoner design parameters: bet slope, fluidizing air, exhaust air Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, noise, air emission Site considerations: floor space and height, access 27

28 Magnetic and Electric field separation Magnetic separation Based on magnetic permeability Separate ferrous from nonferrous metals Electrostatic separation Based on differing surface charge characteristics Separate plastics from paper Eddy current separation Varying magnetic fields are used to induce eddy currents in nonferrous metals such as aluminum 28

29 Magnetic separation Permanent magnets or electromagnets can be used 29

30 Electrostatic separation Use high-voltage electrostatic field to separate Nonconductors of electricity such as glass, plastic and papers from conductors (metal) Nonconductors from each other based on differences in their electrical pemittivity or ability to retain electrical charge Separate paper from plastics Different types of plastics from each other Not widely used now, but promising technology Plastic recycling 30

31 Electrostatic separation 31

32 Eddy current separation Mechanism Time-varying magnetic field Voltage (eddy current) are generated in conductors Magnetic force is produced. Widely used Aluminum separation from shredded waste Non-metals Nonferrous metals Waste 32

33 Eddy current separation 33

34 Magnetic and Electric field separation performance characteristics Performance criteria Recover, Purity, Efficiency Magnetic separation devices Generally, very high efficiency (>95%) Design criteria Based on mass loading and power consumption Permanent magnets, comparing with electromagnets Reduce operating cost, but need more capital costs 34

35 Magnetic and Electric field separation Selection of equipment Factors to be considered Characteristics of material to be separated: particle size, shape, moisture content, material composition Materials specifications for separated materials: purity, recovery and efficiency requirements Device design parameters: unit capacity, power requirements (voltage and amperage), magnet strength, electrostatic field strength Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, noise, air emission Site considerations: floor space and height, access 35

36 Densification (compaction) Unit operation which increases the density of waste materials Reduction of storage requirements of recyclables Reduction of volume for shipping Preparation of densified refuse-derived fuels (RDF) Type of equipment Stationary compactor Prior to landfilling or combustion to reduce haul costs Baling machine (Baler) Processing recovered materials prior to sale Cubing and pelleting equipment Preparation of densified RDF 36

37 Stationary compactor Compactor is categorized into stationary or movable. Mechanism is same as a collection vehicle. Usage of stationary compactor Light duty Commercial and light industry Heavy industry Transfer station Low-pressure (<100lb/inch 2 ) High-pressure (>100lb/inch 2 ) 37

38 Baling equipment Operating under high pressure Typically, 100 to 200 lb/inch 2 Target materials Cardboard, newsprint, plastic,pet bottles, aluminum can Baled materials Easy to load with forklifts and economically shipped 38

39 Cubing and pelleting Technology that can be used to produce densified refuse-derived fuels Waste paper or shredded RDF is extruded through extrusion dies with and eccentric rotating presswheel. 39

40 Densification Selection of equipment Factors to be considered Purpose of densification: compaction, cubing and pelleting, baling Characteristics of material to be processed: particle size and its distribution, shape, moisture content, material composition, specific weight Equipment design parameters: unit capacity, power requirements (voltage, amperage, horsepower), compaction ratio, unit specific weight, bulk specific weight, bale weight, operating pressure Operational characteristics: energy requirements, maintenance requirement, simplicity of operation, noise, air emission Site considerations: floor space and height, access 40

41 Development and implementation of MRFs Engineering consideration Definition of the functions of the MRF Selection of the materials to be separated (now and future) Identification of the material specifications Development of separation process flow diagram Determination of process loading rates Layout and design of the physical facilities Selection of the equipment and facilities Environmental controls and aesthetics considerations Nonengineering implementation issues Siting Environmental emissions: traffic, noise, odor, dust, airborne debris, liquid discharge, visual unsightliness, vector control Public health and safety: workers, public access economics 41

42 Functions of MRF (1) Depend on Role of the MRF in the waste management system Types of materials to be recovered Form in which the materials to be recovered will be delivered to the MRF Containerization and storage of processed materials for the buyer For source-separated wastes Mixed paper and cardboard: Manual separation of cardboard, newspaper, high-value paper or of contaminants from commingled paper types. Baling of separated materials for shipping. Storage of baled materials. PETE and HDPE plastics: Manual separation of PETE and HDPE from commingled plastics. Baling of separated materials for shipping. Storage of baled materials. 42

43 Functions of MRF (2) For source-separated wastes Mixed plastics: Manual separation of PETE, HDPE and other plastics from commingled plastics. Baling of separated materials for shipping. Storage of baled materials. Mixed plastics and glass: Manual separation of PETE, HDPE and glass by color from commingled mixture. Baling of plastics for shipping. Storage of separated materials. Mixed glass: Manual separation of clear, green and amber glass. Storage of separated materials. Aluminum and tin cans: Magnetic separation of tin cans from commingled mixture. Baling of separated materials for shipping. Storage of separated materials. 43

44 Functions of MRF (3) For source-separated wastes Plastics, glass, aluminum and tin cans: Manual or pneumatic separation of PETE, HDPE and other plastics. Manual separation of glass by color. Magnetic separation of tin cans. Baling of plastics, aluminum and tin cans, and crushing of glass for shipping. Storage of separated materials. Yard wastes: Manual separation of plastic bags and other contaminants from commingled yard wastes. Grinding of clean yard wastes. Size separation. Storage of oversized materials for biomass facility or mulch. Composting of the undersized materials. 44

45 Functions of MRF (4) For commingled MSW Recovery of recyclable materials Preparation for use as a fuel Preparation for use as a feedstock for composting Manual separation of bulky items, cardboard, PETE, HDPE, other plastics, and large ferrous items. Mechanical or manual separation of glass by color and aluminum cans. Magnetic separation of tin cans and other ferrous materials. Baling of cardboard, plastics, aluminum and tin cans, and crushing of glass for shipping. Storage of separated materials. Fuel preparation 45

46 System layout and design Important factors Methods or means by which the wastes will be delivered to the MRF Materials delivery rates Materials loading rates Material flows and handling pattern within the MRF Performance criteria for the selection of equipment and facilities Overall MRF layout includes Sizing of the unloading and presorting area Placement of conveyor lines, screens, magnets, shredders and other unit operations. Sizing of storage and outloading areas Sizing and desing of parking areas and traffic flow patterns in and out of the MRF 46

47 Selection of Equipment and facilities Factors that should be considered Capabilities: can we improve conventional practice? Reliability Service: maintenance can be done by local trained personnel? Safety of operation, health hazard Efficiency: specific energy consumption Environmental effects Economics 47

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