PB 389 Integrated Solid Waste Management Numfon Eaktasang, Ph. D. Thammasat University
Solid Waste Management Waste generation Waste reduction and separation at the source Collection Separation, processing & transformation Transportation Disposal
Target of this chapter Commingled wastes Material Recovery Facility (MRF) Reuse Processing for recycle Separated wastes Source separation Thermal treatment Biological treatment Landfill disposal 3
Waste minimization & the waste hierarchy Prevent the creation of waste or reduce the amount generated Reduce the toxicity or negative impact of the waste that is generated Reuse in their current forms the materials recovered from the waste stream Recycle, compost, or recover materials for use as direct or indirect inputs to new products Recovery energy by incineration, anaerobic digestion or similar processes Dispose of waste in an environmentally sound manner, generally in sanitary landfills 4
Waste minimization & the waste hierarchy Past Present 5
Terms in recycling ² Reuse Products are recovered as they are and are reused for the same purpose without much treatment or change to the product. For example: bottles, containers, plastic bags. ² Recycle The recovered waste material is treated and reprocessed to a new product whereby a new purpose could also result. For example: plastics, organic waste ² Energy recovery The product is processed and thereby resulting energy is used. For example: incineration 6
Refuse-derived fuel: RDF 7
Animal feed Large dealers Industry Waste Recycling Recyclers Household 1. Inorganic fraction 2. Organic fraction Collection Composting Transfer point Collection Agriculture 8 Disposal
What is recycled ? Anything that has value! Inorganics Metal Glass Paper Plastics Aluminium Organics Food waste Sometimes also batteries, oils etc. ) 9
Who are the actors in recycling? ² Household members u separating at source ² Individuals u collection from house to house u on the road, at transfer stations (collection points) u on the disposal site u as employees in primary or secondary collection ² Municipality/Government u if some recycling schemes are implemented ² Small enterprises and dealers u as waste pickers or middle men, sometimes with treatment and/or processing steps ² Large dealers u as middle men, often with storage, treatment, and/or processing steps ² Industry u as buyer and final processing
The advantages of recycling Advantages for solid waste management u u Reduction of waste volume (example of Jakarta, Japan) Cost savings for collection, transport and disposal Longer life span for landfills Less environmental impact of landfills Advantages for the economy u u u Reducing imports for fertilizers or soil amendments (less foreign currency needed) Job opportunities and income for the people Cheap products (made from recycled materials) for the poor Advantages for the environment u Sustainable use of natural resources (e. g. less energy consumption aluminium (-96%) and paper (-60%)
The main problems of informal recycling Working conditions u u u Health risk due to contact with the waste (cuts, infections) Inhaling of toxic gases (burning) and direct contact with infectious or toxic wastes Contact with vermin or other vectors carrying diseases Environmental aspects u u u Containers with paint residues or solvents are often burnt, polluting the air Insulation plastics around wiring are burnt. Cleaning of the products in open waters Strongly fluctuating prices for the products u u This makes it difficult to plan (business plan) Imported cheap wastes undermine the local market 12
How can the situation be improved ? It needs commitment of national and local governments u u u Recognise the importance of the informal sector. Integrate them into the solid waste management system. Give opportunities to recycle on household level or at transfer stations. Promote and support the use of recycled products Support programmes for social integration of ECO-HELPERS (refrain using terms like scavengers or waste pickers). Support and try organising alternative organisation structure (partly formalised), e. g. co-operatives, if possible as close to the waste generation source as possible. 13
Planning a resource recovery center ? Centralised "Economy of scale" controlled work conditions high transport costs, as you need to transport your materials to the site and then transport the products back to the buyers. Strong tendency to mechanize, making the center capital and maintenance intensive. Decentralised Community-scale Products are nearer to the buyers Less transport costs As mostly small scale, then often adapted technology based on manual labour. Problems of space in densely populated areas. 14
Recycling organic material As animal feed As soil amendment or fertilizer Composting (aerobic) Vermicomposting Co-Composting (solid waste together with faecal matter) Digestion (anaerobic) As fuel Digestion (using the methane produced) Pelletisation 15
Recycle and reuse opportunities ² Important points in recycle and reuse Available options for separation and processing u Economics of materials recovery u Materials specification u 16
Use of materials recovered from MSW ² Direct reuse u Furniture, bicycle, electrical appliance, bottle to bottle, … ² Raw materials for remanufacturing and reprocessing u Aluminum, Paper and cardboard, Plastics, Glass, Ferrous metals, non ferrous metals, rubber, textile ² Feedstock for production of biological and chemical conversion products u Compost (Aerobic), methane production (Anaerobic) 17
Use of materials recovered from MSW ² Fuel Source u Combustion of wastes and recovering heat l u Sometimes used for electricity generation Converting some type of fuel that can be stored and used locally or transported distant energy market. (RDF = Refuse Derived Fuel) ² Land Reclamation u Clean or processed demolition wastes 18
Typical materials specification ² To consider quantity, shipment means, storage, and delivery point is important for all type of material recovery. ² Direct reuse Must be usable for original or related function. u Degree of cleanliness u ² Raw materials for remanufacturing and reprocessing Aluminum: particle size, degree of cleanliness, and density u Paper and cardboard: grade, no magazines, no adhesives, and moisture content u 19
Typical materials specification ² Raw materials for remanufacturing and reprocessing Plastics: type (PETE, PVC, PP, PS, and so on…), degree of cleanliness, and moisture content u Glass: color, no labels or metal, degree of cleanliness, free from metallic contamination, no broken crockery u Ferrous metals: source, specific weight, degree of cleanliness, degree of contamination with tin, aluminum and lead u Non ferrous metals: vary with local needs and markets u 20
Typical materials specification ² Raw materials for remanufacturing and reprocessing Rubber (cf. waste tires): recapping standard u Textile: type of materials, and degree of cleanliness u ² Feedstock for bioconversion product Yard wastes: composition of material, particle size distribution, degree of contamination u Organic fraction of MSW: composition of material, degree of contamination u 21
Typical materials specification ² Fuel source u u u Yard wastes: composition of material, particle size, moisture content Organic fraction of MSW: composition of material, calorific value, moisture content, storage limits Plastics, waste oil, tires: depends on design of combustion equipment Papers: up to local needs and markets Wood: Composition, degree of contamination ² Land reclamation u Construction and demolition wastes: composition, degree of contamination, local regulation, final land-use design 22
Important point for recycle materials ² Storage, shipment means and delivery point u Transportation issue ² Degree of cleanliness, degree of contamination u How we achieve good quality of materials for recycle. Product design: material choice to separate easily and less contamination, easiness to disassemble Design for Environment (Df. E) in ISO 14000 s l Efficiency of separation process l Residents cooperation l n n Cooperation for separation Choice of recyclable products 23
Source separation and collection ² How to separate at source Collected by different containers in a collection station u Discharge each separated waste for assigned day u ² How to collect separate wastes By collectors: Each home, curbside or collection station in residential area u By homeowner (residents and businesses): Drop-off center, buy-back center u 24
Drop-off and buy-back center ² Homeowners bring the separated material to center ² Low participation can be a problem ² Require homeowners to store the materials until sufficient material is collected ² How to encourage the participation u u Make drop-off center at convenient place: shopping center, supermarket, station Buy-back center provides a monetary incentive to participate Residents are paid directly or indirectly through a reduction of collection fee. l Deposit refund system l u Contest or lottery l Eco-station for shopping center in Japan n Lottery for discount ticket of shopping center 25
Deposit refund system Manufacturer Product with package Cleaning packages and reuse Package Retailer Product with package Manufacturer After consumption Price + deposit Consumer Retailer Package Refund Consumer 26
Eco-station activity in Iiyama, Japan Opening of eco-station Collecting and lottery machine 27
Waste separation at MRFs ² MRF (Material recovery facility) u 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 l Separation and Recovery of reusable and recyclable materials from commingled MSW l Improvements in the quality (specifications) of the recovered waste materials. l 28
Manual and mechanical separation ² Manual separation Flexible u Need more labors u Easy at source u ² Mechanical separation Not flexible: need frequent maintenance u Less labors u ² Current trend u Integration of manual and mechanical separation 29
Unit operation in MRFs ² Unit operations in MRFs are designed To modify the physical characteristics of the waste u To remove specific components and contaminants from the waste stream u To process and prepare the separated materials for subsequent use u ² Category of operations in MRFs Size reduction u Size separation u Density separation u Electric and magnetic field separation u Densification (compaction) u 30
Size Reduction – type of equipment ² Hammer-mill u effective with brittle materials ² Shear shredders: two opposing counter-rotating blades u Cut ductile materials u ² Tub grinder u Widely used for yard wastes processing 31
Hammer-mill shredder ² Inner shaft is rotated at high speed, 7001200 rev/min u Solid waste can not adhere to the hammer ² Cutting action continues to until the material falls out of the bottom. ² Either horizontal-shaft or vertical-shaft configuration u. Horizontal-shaft is more reliable 32
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Shear shredder ² Scissor-like action u With two counterrotating knives or blades ² Low-speed devices u 60 -190 rev/min ² Need reversed action in the event of jam 34
Tub Grinder ² Essentially mobile hammermill shredder ² Used for wide variety of materials ²It consists of utub with grinder for shredding u. Engine for grinder u. Loading equipment u. Discharging equipment 35
Size reduction – selection of equipment ² Factors to be considered u u u 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 ² Safety issues: Explosion and fire u u Potentially explosive: VOCs, spray cans Explosive atmosphere: dust, high-speed impact of metal 36
Size separation ² Size separation = screening u Can be accomplished dry or wet. ² Reciprocating screen u Vibrating screen ² Trommel screen u Rotary drum screen ² Disc screen 37
Vibrating screen ² Application u u Dry materials such as glass or metals Wood chip for composting Solid Waste Management: Chapter 5 38
Trommel screen ² Versatile type of screen ² Large-diameter screen ² Rotating on a horizontal axis ² Application u u Protect shredder in RDF production (removing oversized materials) Separate cardboard and paper Solid Waste Management: Chapter 5 39
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Disc screen ² An alternative to reciprocating screen ² Advantages u u Self-cleaning Capability of adjustment by varying the spacing of the discs on the drive shafts 41
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Size separation – Selection of equipment ² Factors to be considered u u u 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 43
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