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Chapter 6.1

Choosing appropriate technologies

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Hierarchy of preferred waste management options

Source: David C Wilson 1993, 1997, 2001

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Waste avoidance and minimisation

• Top of the waste hierarchy

• Reduces pressure on treatment and disposal facilities

• Reduces costs

• Saves resources

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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 cleaningRecycling - materials may first require cleaning or separation

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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

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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

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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

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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

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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

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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?

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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

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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?

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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

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Physical treatment - example of application

Filtration - Belt filter

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

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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

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Chemical treatment - example of application

Neutralisation

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

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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

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Physico-chemical treatment - example of application

Precipitation Flocculation Sedimentation

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

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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

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Biological treatment - example of application

Activated Sludge treatment

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

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Stabilisation and Solidification

Converts waste into insoluble rock-like materials Stabilisation - treats waste to minimise 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

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Stabilisation and solidification - example of application

Drums of solidified waste

Source: David C Wilson

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Thermal treatment

Thermal treatment of waste: Incineration allows energy recovery, materials recycling Pyrolysis Gasification allow recovery of useful materials

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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

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Thermal treatment - example of application

Source: Guyer, Howard H Industrial processes and waste stream management, Wiley

Rotary kiln incinerator

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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

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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

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Outdated technologies?

• 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

Several technologies were used in Western countries in the past but have now been discontinued or severely limited. These include:

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Treatment & disposal methodsfor certain waste types

Effluents, washwaters x

Acids, alkalis x

Heavy metals x xResidues

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

LandfillRecovery Incin Treatment Immob/ation

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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

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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

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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?

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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