Solid Wastes
Jan 16, 2016
Solid Wastes
Solid Waste
SourcesProperties
Control
Treatment Methods
Salvaging and Recycling
• Mining and construction• Municipal (domestic and
commercial)• Industrial• Agricultural
• composition relating to bulk and mobility
• Degradability• Flammability• Radioactivity• Toxicity
• The link between waste and affluence!
• Built-in obsolescence
• Convenience• Disposable
products• Over packaging
• efficient use of resources and extraction efficiency• production loops eg trimmings from plastic mouldings/papercutting• Resource substitution • Re-use and recycling of resource materials to include:- composting- The scientific/technological, social and economic problems of• recycling compared with use of virgin materials with specificreference to aluminium: waste losses, eg litter, mixed alloys,- transport, labour costs, separation, identification, energy costs,- need for public co-operation
The economic and environmental advantages and disadvantages of disposal by:
• landfill and land raising on derelict land/exhausted quarries• incineration and pyrolysis of household and industrial wastes• encapsulation/vitrification of high-level radioactive waste•Salvaging and recycling•The reduction of resource exhaustion and waste production
The Essay Style Question
• Discuss the advantages and disadvantages of the methods that can be used to dispose of solid wastes (20)
taken from the Enviro Text Book p 216
Sources
• Mining, quarrying and construction
• Ash from coal-fired power stations
• Municipal waste of variable composition
• Industrial waste• Agricultural wastes e.g.
carcasses
Properties
Disposal method depends upon properties e.g. Will it degrade/compost?
• Vegetable matter, paper, cardboard and some textiles will biodegrade.
• Is it hazardous? e.g. asbestos• Is it radioactive? If so, what type of
radioactivity is being emitted?• Is it toxic to plants or animals?
But also factors such as• Land availability (e.g. for landfill• Availability of recycling facilities• Per capita waste production• Transport costs
Solid waste treatment
1. Landfill• Essentially a huge hole in the ground• Leachates are collected• Methane may also be collected and burned• May also involve land raising
2. Incineration• High temperature incineration• May involve pyrolysis
3. Encapsulation and vitrification of HL radioactive waste
HL liquid wastes are concentrated by evaporation, then stored in double-walled stainless steel tanks inside thick concrete walls awaiting vitrification – converted into a borosilicate glass within steel canisters.
Advantages and disadvantages
Method Advantages Disadvantages
Landfill / land raising Provides a use for waste land/ derelict landLand can be used after landfill sealed
Air pollution – CO2, CH4
LeachatesTrafficLitter/seagulls
Incineration Reduces volume Can provide district heatingHigh capital cost
Air pollution – particulatesAsh toxic and still requires disposal
Encapsulation & vitrification
Long-term, safe storage ExpensiveMaterial remains radioactive for thousands of years
Salvaging and recycling
• total amount of metal needed• total volume of ore needing mining
Defra (2008) reported that household recycling has increased for the third year running
Total waste sent to landfill has declined
Besides reducing waste, salvaging and recycling saves money and natural resources
e.g. collecting, remelting and remoulding metal off-cuts will reduce:
Production loop: a recycling process where an industry uses the wastes produced during the manufacturing process itself.
Resource substitution: the use of a more abundant material instead of a less abundant one e.g. using plastic instead of metal
Production loop: a recycling process where an industry uses the wastes produced during the manufacturing process itself.
Resource substitution: the use of a more abundant material instead of a less abundant one e.g. using plastic instead of metal
Compost
Consists of partly decomposed organic material that is rich in minerals e.g. nitrates
Rate of production of compost depends on factors such as:• temperature• moisture content• aeration
Produced from waste plant material e.g. grass cuttings, fallen leaves and vegetable waste by the action of aerobic microorganisms
Slatted container to allow air to enter
Waste plant material
Compost
The respiration of the microorganisms generates heat which kills weed seeds and some plant pathogens
14
Compost heap
External air
0 1 2 3 4 5 6 7 8 9 10 11 12 13
Time/weeks
-10
0
10
20
30
40
50
Temp. oC
Why does the compost temperature drop in weeks 9-14?
• reduced food available for the microorganisms• more competition so growth rate reduced• less oxygen becomes available• change in water / pH slows growth
LandfillThe government has set targets under the Landfill Directive for LAs to recycle an increasing proportion of domestic waste
Material
Glass
Plastics
Paper and card
Scrap metal
Compost
Total
Thousand Tonnes
470
90
1100
420
1320
3400
ControlVolume of waste tends to increase with affluenceIncreased purchase of :• All goods packaging etc• Disposable goods • Goods with built-in obsolescence
ControlVolume of waste tends to increase with affluenceIncreased purchase of :• All goods packaging etc• Disposable goods • Goods with built-in obsolescence
Domestic waste production 2007
Aluminium recycling
Aluminium is widely used in cans and aircraft etc as it is light and strong
Social, economic and environmental consequences of the production of aluminium from bauxite ore in Jamaica
• Villagers relocated • Forests/ crops cleared• Topsoil removed• Bauxite recovered using opencast mines• Bauxite dissolved in sodium hydroxide
using high temperature and pressure• Alumina precipitated out• Alumina electrolysed to produce aluminium• Contaminated mud is dumped off site
Aluminium recyclingRecycling coke cans helps avoid all this!..and:• saves fossil fuels• reduces air & water
pollution• reduces water use
Problems• Public motivation• Aluminium often used in alloys-separating the metals is expensive• Collection and transport costs and transport pollution• Labour costs –collection is often labour-intensive• Unsorted wastes may be difficult/expensive to recycle
% reduction inRecycled Materials
Aluminium Glass Paper Steel
Energy usage 90-97 4-32 23-74 47-74
Air pollution 95 20 74 85
Water pollution 97 - 35 76
Mining wastes - 80 - 97
Water usage - 50 58 40
Aluminium recycling
Recycling provides significant proportions of the United Kingdom's metals consumption and saves money
The Recycling Scorecard
There are other benefits. For example, using recycled steel instead of virgin ore to make new steel leads to typical reductions of:
86% in air pollution - 40% in water use - 76% in water pollution
The world metal recycling industry employs 1.5 m people & supplies > 550 mt of secondary materials annually to steelworks and foundries
More on landfill
Landfill Sites
Many old landfills are poorly designed and major environmental hazard. They are not designed for 50, 100 or 1000 years into the
future
There are 4000 operational and 4000 closed landfill sites in the UK
Two types of landfill in the UK are • leach and disperse (old sites)
• containment and treatment (new sites)
What Happens in a Landfill Site?
Rain water dissolves & reacts chemically &
biologically with waste
Leachate
Landfill Gas
Leachate
• toxins kill aquatic life• eutrophication in rivers
• precipitates iron
• kills vegetation
• pathogens/bacteria
• non-hazardous materials can decompose into hazardous products
• serious groundwater pollution
Landfill Gas
methane
Landfill Gas
Loscoe, Derbyshire - 1986
Landfill Gas
Loscoe, Derbyshire - 1986
Methane escape from the Loscoe Landfill caused an
explosion in 51 Clark Avenue near the site as gas escaped via highly permeable sandstones
Possible Routes by Which Landfill Gas Can Migrate from a Site
Caves & natural cavities
Highly permeable strata
Fissured & fractured strata
Mine shafts
Gas vents Tree roots
Highly permeable strata
Underground services e.g. sewer pipes
Desiccation cracks in soil
Landfill Site Selection
Geology of Area• Porosity & permeability of rock
• Resistance to weathering
• Joints & fracture systems in rock
• Dip of rock strata
Hydrology of Area
• Rate of groundwater flow
• Gradient of groundwater flow
• Depth to water table
• Fluctuations of groundwater
Impermeable to contain leachate
Reduce groundwater contamination
Topography of Area
• Existing hole or steep sided quarry
• Free from disturbance (tectonic/subsidence)
A site capable of retaining waste
two feet of compacted clay
strong, flexible, very thick plastic, called high density polyethylene
(HDPE) known as a geomembrane.
one-foot layer of gravel with pipes running through it. The leachate
collects in these pipes and is pumped out of the landfill and
filtered.
very tough fabric, called a geotextile fabric, to protect the
pipes.
top layer is about one foot of compacted soil to protect the
entire liner system from the waste.
Each evening, large trucks roll over the landfill to crush the day's
rubbish and then cover it with 15cm of soil so the waste doesn't
smell or attract flies and rats.
When an area of the landfill is completely full, it is capped with clay and soil. This final
landfill cover helps keep rainwater out of the waste and
reduces the amount of leachate that forms.
Site Preparation
Modern Landfill Site
Site Management & Monitoring
• monitoring groundwater for chloride & ammonia in plumes
• monitoring unsaturated zone for gases
• venting of methane gas by boreholes
• porous pipes to transfer leachate into sumps for collection & removal
Site Restoration
Uses
• Parkland
• Recreation
• Open spaces
• Greenbelt
• Low level industrial development
• Housing
Site Restoration
Trumps Farm is a former sand pit which was used by Surrey County Council for the disposal of household waste from the early
1980s until its closure in 1998.
The overall objective of the works is to reinstate the landfill to pasture and
meadow, to a landscape typical of the area and create a variety of wildlife habitats.
Site Restoration
Problems
• Methane gas hazard – leakage through permeable rocks
• Ground instability on completion - subsidence
• Groundwater pollution
• Landfill site needs to remain accessible for over 25 years to manage & monitor
Non-hazardous
Waste Disposal
Landfill Sites
Factors Affecting Site
Selection
Site Management &
Monitoring
Site Preparation
What happens in a landfill site
PollutantsProblems of
LeachateProblems of Landfill Gas
Problems after site is restored
Radioactive Waste
• Nuclear presents a special problem
because of its long half life, it remains
radioactive for thousands of years.
• In UK stored for 50 years to cool prior to solidification and storage
• Then it needs to be isolated for 250, 000 years
Radioactive Waste
1. What is the difference between high level and low level radioactive waste (how are they
caused)?
2. What specific problems do they cause?
3. What factors need to be taken in to account with high level radioactive waste disposal?
4. What are the options for high level radioactive waste disposal? (give examples)
5. How is low level radioactive waste disposed?
6. What are the geological factors that need to be taken into account when building an
underground repository?
Hand outs to print for your file on next 2 slides
Possible Routes by Which Landfill Gas Can Migrate from a Site