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

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

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

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 cross-sectional area of chute

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

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

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

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.

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: 2000-3000 ton/d of feedstock Increase success of source separation

Density separation – performance characteristics (2) Solid Waste Management: Chapter 5

Density separation – design criteria (1) Design based on Air/solid ration (kg-air/kg-waste): 2 to 7 Required fluidizing velocity Fluidizing velocity for pulsed air classifiers

Solid Waste Management: Chapter 5 Density separation Solid Waste Management: Chapter 5

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

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

Magnetic separation Permanent magnets or electromagnets can be used

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

Electrostatic separation

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 Waste Non-metals Nonferrous metals

Eddy current separation

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

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

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

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/inch2) High-pressure (>100lb/inch2)

Baling equipment Operating under high pressure Target materials Typically, 100 to 200 lb/inch2 Target materials Cardboard, newsprint, plastic,PET bottles, aluminum can Baled materials Easy to load with forklifts and economically shipped

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.

Densification – design criteria (1)

Densification

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

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

Functions of MRF (1) Depend on For source-separated wastes 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.

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.

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.

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

Development of separation process flow diagrams Assemble of unit operations Important factors Characteristics of the waste materials to be processed Specifications for recovered materials now and future Available types of equipment and facilities

Flow diagrams for source-separated waste (1) Paper and cardboard Plastics and glass Aluminum and tin cans Process for mixed paper 

Materials balances and loading rate Design of MRF Appropriate design loading rate Loading rate (ton/h) = total loading (ton/yr or ton/d) / operating hours (h/yr or h/d) Total loading is estimated based on mass balance. Quantities of materials that can be recovered is essential to consider mass balance.

Material recovery rates for source-separated materials Materials recovery rates For input of MRFs Indicate the effectiveness or performance of the recycling program Material recovery rate 　　　　　= composition factor * recovery factor * participation factor Composition factor= fraction of waste component in total Recovery factor= fraction of material recovered Participation factor= fraction of the public that participates

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

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

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