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