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Chapter 6.1 Choosing appropriate technologies

Chapter 6.1 Choosing appropriate technologies. Hierarchy of preferred waste management options. Source: David C Wilson 1993, 1997, 2001. Waste avoidance and minimisation. Top of the waste hierarchy Reduces pressure on treatment and disposal facilities Reduces costs Saves resources.

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Chapter 6.1 Choosing appropriate technologies

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  1. Chapter 6.1 Choosing appropriate technologies TRP Chapter 6.1 1

  2. Hierarchy of preferred waste management options Source: David C Wilson 1993, 1997, 2001 TRP Chapter 6.1 2

  3. Waste avoidance and minimisation • Top of the waste hierarchy • Reduces pressure on treatment and disposal facilities • Reduces costs • Saves resources TRP Chapter 6.1 3

  4. Re-use and recycling options • Re-use and recycling: • divert wastes from disposal • reduce resource consumption • reduce costs • reduce environmental impacts from raw material acquisition • Re-use - no treatment except for any necessary cleaning • Recycling- materials may first require cleaning or separation TRP Chapter 6.1 4

  5. Principles of treatment • Volume reduction • Reduce the volume of waste with hazardous components by concentration • Destruction • Convert hazardous to non-hazardous substances • Containment • Isolate hazardous materials TRP Chapter 6.1 5

  6. Treatment options 1 • Physical • Chemical • Physical and chemical • Biological • All treatments are aimed at modifying physical and chemical properties of the hazardous component • Most treatments leave residues for disposal TRP Chapter 6.1 6

  7. Treatment options 2 • Thermal • Stabilisation and solidification • Combined treatment methods • All treatments are aimed at modifying physical and chemical properties of the hazardous component • Most treatments leave residues for disposal TRP Chapter 6.1 7

  8. Disposal options • Landfill and land disposal may include: • Co-disposal • Disposal in engineered hazardous waste sites or cells within sites • Other options: • Soil biodegradation • Underground injection • Deep mines Unlikely to be suitable for developing economies TRP Chapter 6.1 8

  9. Technology selection • At on-site level, to deal with a particular waste stream • At national level, to decide what off-site facilities are needed to deal with residues from individual premises • Always need to know quantities and types of waste • There will always be a need for landfill TRP Chapter 6.1 9

  10. Technology criteria for on-site treatment of wastes • Can it deal with amount and type of waste? • Will it enable compliance with regulations? • What are the likely costs? What are the implications for operation? • Are there any workplace, environmental or social concerns? • What residues will be generated that have to be removed off-site? TRP Chapter 6.1 10

  11. Selection criteria for delivering national strategy • The nature and quantity of waste • The desired characteristics of outputs from treatment • The role of a centralised landfill for stabilised wastes from individual generators • The technical adequacy of treatment alternatives • Economic and financial considerations • Workplace, environmental and social considerations TRP Chapter 6.1 11

  12. Selection criteria for particular waste stream • Can it deal with amount and type of waste? • Will it enable compliance with regulations? • What are the likely costs and possible revenues? • Are there any environmental or social concerns? TRP Chapter 6.1 12

  13. Physical treatment • Manual separation - removes selected wastes by visual inspection • Sieving and screening - removes coarse material • Sedimentation - settles solids to separate liquid • Decanting - removes water content • Centrifuging - removes water content • Filtration • Solvent extraction • Adsorption • Soil washing - extracts soluble contaminants • Sludge drying • Autoclaving - sterilises waste by heat & pressure • Microwave irradiation - sterilisation TRP Chapter 6.1 13

  14. Physical treatment - example of application Filtration - Belt filter TRP Chapter 6.1 14 Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

  15. Chemical treatment • Chemical reduction and oxidation - uses oxidising and reducing agents to transform constituents • Neutralisation - adjusts pH to neutral • Precipitation - separates hazardous constituents from solution • Dechlorination - removes chlorine from organic materials • Hydrolysis - breaks down constituents by adding water • Electrolysis - breaks down chemical compounds with electrical charge TRP Chapter 6.1 15

  16. Chemical treatment - example of application Neutralisation TRP Chapter 6.1 16 Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

  17. Physico-chemical treatment • Solvent extraction - uses immiscible solvent to dissolve organic material in aqueous solution • Flocculation & coagulation - aggregates fine constituents • Stripping / Desorption - separates volatile components from liquid by passing through gas stream • Membrane-separation - uses semi-permeable memebrane • Leaching - removes soluble components from solid material • Scrubbing - removes constituents from gas or liquid stream by contact with washing liquid/slurry or powder • UV Irradiation / Ozonolysis - breaks down hazardous constituents by ozone/energy • Ion exchange - exchange with dissolved ionic species through contact with resin TRP Chapter 6.1 17

  18. Physico-chemical treatment - example of application Precipitation Flocculation Sedimentation TRP Chapter 6.1 18 Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

  19. Biological treatmentBiodegradation of organic into simple inorganic species with suitable microbes • Activated sludge treatment - biodegrades organic species with bio-active sludge in aqueous phase • Rotating biological contactor - breaks down aqueous organic species in contact with bacterial rich filter • Aerated lagoons and stabilisation ponds - break down organic wastes in shallow pools with oxygen • Anaerobic digestion - degrades organic waste in absence of oxygen • Land application - biodegrades organic matter through action with soil microbes TRP Chapter 6.1 19

  20. Biological treatment - example of application Activated Sludge treatment TRP Chapter 6.1 20 Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

  21. Stabilisation and Solidification Converts waste into insoluble rock-like materials • Stabilisation - treats waste tominimise migration • Solidification - uses cement-based process • Encapsulation - encloses waste within casing or layer of inert substance • Recommended for inorganic hazardous wastes • A pretreatment step prior to landfill disposal TRP Chapter 6.1 21

  22. Stabilisation and solidification - example of application Drums of solidified waste Source: David C Wilson TRP Chapter 6.1 22

  23. Thermal treatment Thermal treatment of waste: • Incineration • allows energy recovery, materials recycling • Pyrolysis • Gasification • allow recovery of useful materials TRP Chapter 6.1 23

  24. Co-combustion in cement kilns • Existing lime or cement kilns can be adapted to burn hazardous wastes • Suitable for interim and long term use • Avoids need for new facility • Saves on fuel costs in cement making TRP Chapter 6.1 24

  25. Thermal treatment - example of application Rotary kiln incinerator TRP Chapter 6.1 25 Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

  26. Simple options 1 • Solar evaporation ponds can be used for sludge dewatering or drying • Very small quantities of difficult wastes can be encapsulated in cement, prior to landfill • Existing industrial boilers can be adapted to burn wastes TRP Chapter 6.1 26

  27. Simple options 2 • Not suitable for long term or widespread use: • Evaporation pits can be used for very small quantities of solvents, where recovery or incineration is not practicable • Engineered open-pit incinerators can be used to burn small quantities of hazardous wastes in isolated areas • Oily sludges can be stabilised by mixing with sand or similar material, and weathering TRP Chapter 6.1 27

  28. Outdated technologies? Several technologies were used in Western countries in the past but have now been discontinued or severely limited. These include: • Long term storage • Ocean dumping • Ocean incineration by special vessels • Deep well injection • Disposal in salt mines • Land deposit of toxic organic wastes • Solvent evaporation • Co-disposal of non-stabilised hazardous wastes TRP Chapter 6.1 28

  29. Treatment & disposal methodsfor certain waste types Recovery Incin Treatment Immob/ation Landfill Effluents, washwaters x Acids, alkalis x Heavy metals x x Residues Toxic inorganics x x Residues Reactive wastes x Non-toxic inorganics x x Solvents, oils x x Resins, paints, organic sludge x x Organic chemicals x x x Petsicides x x PCBs, chlorinated hydrocarbons x Putrescible, biodegradable wastes x x TRP Chapter 6.1 29

  30. Technology assessment • How to evaluate overall aspects of technology choice? • Environmental Technology Assessment (EnTA) can examine the broader implications of a technology option. Process is similar to LCA but applied to technologies rather than products • Environmental Impact Assessment evaluates the location and societal implication of a technology or development project • Risk Assessment examines the hazards and risk reduction measures from a technology or process TRP Chapter 6.1 30

  31. Key considerations • Waste reduction and avoidance by generators should always be a priority • Role of on-site vs off-site technologies • Need to consider residues from treatment processes and their disposal • Transitional technologies may be used until final high-quality installations are available TRP Chapter 6.1 31

  32. Key questions when choosing technologies • Who can undertake technology assessment? • Which wastes are not acceptable? • Transport - how are the wastes received? • How to monitor the wastes received? • Who will design the plant? Train the operators? • What features address specific national aspects? • How simple/sophisticated is plant operation? • How is plant performance monitored? • What other environmental impacts are possible? • What workplace hazards are likely? • What is the permitting procedure? Is an EIA needed? TRP Chapter 6.1 32

  33. Chapter 6.1 Summary • In order to choose appropriate technologies, need to: • address options at top of hierarchy • consider principles of treatment • evaluate treatment and disposal options • select technology - on-site or off-site - to suit waste type and circumstances • consider simple options • try to avoid outdated technologies • undertake technology assessment TRP Chapter 6.1 33

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