Chapter 15. Elimination of waste products Nitrogenous wastes Toxins Drugs.
WASTE DISPOSAL Types of Waste Inert wastes - no chemical or biological hazards Special (hazardous)...
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Transcript of WASTE DISPOSAL Types of Waste Inert wastes - no chemical or biological hazards Special (hazardous)...
WASTE DISPOSAL
Types of Waste
Waste disposal routesLandfill Incineration Recycled Composted
UK 88 11 1 <1USA 70 30 <1Denmark 31 50 18 1
• Inert wastes - no chemical or biological hazards
• Special (hazardous) wastes e.g.– ignitable, corrosive, reactive – Carcinogenic or mutagenic (PCBs, medical waste,
radioactive waste, asbestos)– heavy metals, azides, acids/alkalis
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
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 (no dip or synform)
Hydrogeology of Area
• Rate of groundwater flow
• Gradient of groundwater flow
• Depth to water table
• Fluctuations of groundwater
Impermeable to contain leachate & landfill gas
Reduce groundwater contamination from leachate
Topography of Area
• Existing hole or steep sided quarry
• Free from disturbance (tectonic/subsidence)
A site capable of retaining waste
Groundwater
Hydraulic Gradient
Groundwater
• Pore spaces
• Joints/fractures
Water Table
Recharge
Saturated zone
Aquifers
Impermeable rock
Groundwater
Pore spaces unsaturated
Pore spaces saturated
What rocks in the UK make good aquifers?
Sandstone40% porosity
30% specific yield
High permeability
Clay
45% porosity
3% specific yield
Low permeability
Impacts of pumping water from aquifers
Impacts of pumping water from aquifers
Drawdown
Hydraulic Gradient
Cone of Depression
Impacts of pumping water from aquifers
Saline wedge
Control – reduce/stop abstraction, change pattern of abstraction ( winter not summer) or move borehole
Monitoring – chemical testing (boreholes/salinity testing)
two feet of compacted clay
strong, flexible, very thick plastic, called high density polythene (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
Agriculture
• Nitrates
• Pesticides
Industry
• Chemical leaks
• Chemical spills
• Contamination from chemical storage
Waste Disposal
• Leachates from landfill sites
• Radioactive waste
Contamination of aquifers
Contamination of aquifers
Chloride content (milligrams per litre) of leachate
Monitoring
• chemical testing of water from boreholes, springs, extraction wells• ground penetrating radar (remote sensing methods)
• electrical resistivity analysis (oil pollutants = high resistivity)
• soil gas chemical monitoring (organic pollutants give off a vapour such as methane)
borehole
Most expensive
Cheapest
Contamination of aquifers
1. Control
• clay liner
• synthetic liner
• leachate collection
total containment
Contamination of aquifers
2. Control
• build barriers to plume
• trenches filled with concrete
• hammered piles injected with cement grout
Barrier to predicted depth of pollution
Pollution localised
10 – 20m max
Contamination of aquifers
3. Control
• pump pollutant to surface for treatment/disposal
Contamination of aquifers
4. Control
• direct polluted groundwater into to bioreactive barrier
• bioreactive barrier use naturally occurring bacteria to breakdown the pollutant
• oxygen & nitrates injected into barrier to encourage decay processes
factory
pollutant
Impermeable wall to direct groundwater
Bioreactive filter
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
Hazardous Waste
What are hazardous waste materials?
What specific problems do they cause?
What factors need to be taken in to account with hazardous waste disposal?
What are the options for their disposal? (examples)
Possible Routes by Which Landfill Gas Can Migrate from a Site