Chapter 6.1
Choosing appropriate technologies
TRP Chapter 6.1 1
Hierarchy of preferred waste
management options
Source: David C Wilson 1993, 1997, 2001
TRP Chapter 6.1 2
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
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
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
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
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
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
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
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
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
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
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
Physical treatment - example of
application
Filtration - Belt filter
TRP Chapter 6.1 14
Source: Guyer, Howard H Industrial processes and waste stream management, Wiley
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
Chemical
treatment example of
application
Neutralisation
TRP Chapter 6.1 16
Source: Guyer, Howard H Industrial processes and waste stream management, Wiley
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
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
Biological treatment
Biodegradation 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
Biological treatment - example of
application
Activated Sludge treatment
TRP Chapter 6.1 20
Source: Guyer, Howard H Industrial processes and waste stream management, Wiley
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
TRP Chapter 6.1 21
Stabilisation and solidification example of application
Drums of solidified waste
Source: David C Wilson
TRP Chapter 6.1 22
Thermal treatment
Thermal treatment of waste:
 Incineration
 allows energy recovery, materials recycling
 Pyrolysis
 Gasification
 allow recovery of useful materials
TRP Chapter 6.1 23
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
Thermal treatment - example of
application
Rotary kiln incinerator
TRP Chapter 6.1 25
Source: Guyer, Howard H Industrial processes and waste stream management, Wiley
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
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
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
Treatment & disposal methods
for certain waste types
Recovery
Incin
Effluents, washwaters
Treatment
Immob/ation
x
Acids, alkalis
x
Heavy metals
Residues
x
Toxic inorganics
x
Reactive wastes
x
Non-toxic inorganics
Landfill
x
Solvents, oils
x
x
Residues
x
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
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
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
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
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