Transcript Water Supply Infrastructure

CIV911 Water Supply
Engineering
Dr P J Sallis
Dr C A Weatherell
Dr D Werner
Prof T Donnelly
Dr G Parkin
Introduction to Module
and Coursework
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Main components of water supply
Why water needs treating
Main water treatment unit processes
Summary and scope of design coursework
Further reading
Main Components of Water Supply
River
Impounding Reservoir
Trunk Main
Water
Treatment
Plant
Feeder Main
Service Reservoir
Distribution Main
Distribution Network
What needs to be removed from the water?
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Colour
Suspended solids
Turbidity
Pathogens
Hardness
Taste and odour
Harmful chemicals
Drinking water should be:
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Palatable
Safe
Clear
Colourless
Odourless
Reasonably soft
Non-corrosive
Low organic content
Main Water Treatment Unit Processes
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Screening and storage
Aeration
pH adjustment
Coagulation
Flocculation
Clarification
Filtration
Disinfection
Tertiary processes
Monitoring
Sludge removal
Screening and storage
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Preliminary screening
Storage
Fine screening
Microstraining
Aeration
• Why?
– Reduces taste and odours
– Reduces corrosiveness
– Oxidises iron and manganese
• Types
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Bubbled air
Cascade
Fountain
Packed towers
Diffusers
pH Adjustment
• Why?
– To ensure maximum efficiency of processes
– To avoid metal corrosion
– To avoid salt deposition
• Acids used to decrease pH
• Alkalis used to increase pH
– Lime
– sodium carbonate
– Caustic soda
Coagulation
• Small particles left after screening
– Negatively charged
– Repel each other
– Settle very slowly
• Adding a coagulant
– Destabilises the particles
– Induces aggregation into larger flocs
– Larger flocs settle quickly
• Common coagulants
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Aluminium sulphate (alum)
Aluminium hydroxide
Iron chloride
Lime
• Rapid mixing required
– Flash-mixer
– Mixing channel
Flocculation
• Gentle mixing after coagulation
– Paddle mixer
– Turbine mixer
• Increases chance of particles colliding
• Larger flocs formed
Clarification
• Settlement of flocs
– Water flows upward
– Flocs settle downwards
– Thick sludge blanket develops
– Further flocculation occurs
– Clarified water flows over weir
– Sludge bleeding regularly
• Many designs
– Inclined plate, parallel plate, tube settlers
Filtration
• Removal of residual fine solids by
– Downward flow of water through layers of sand and gravel
• Filter must be cleaned when
– Particles clog the surface
– Flow rate becomes too low
• Rapid sand/gravity filters
– Coarse sand
– High flow, small
– Regular back-washing
• Slow sand filters
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Fine sand over course sand or gravel
Low flow, large
Biological as well as physical treatment
Remove pathogenic bacteria, taste, odour, nitrogen and phosphorus
Top layer of sand replaced every few months
Expensive
Disinfection
• Residual pathogen bacteria and viruses
• Complete sterilization not feasible
• Ozone disinfection
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Efficient
Expensive
Required on-site manufacture
Lack of residual disinfection
• Ultraviolet radiation disinfection
– Effective if exposure time is adequate
– Used in small scale
– Lack of residual disinfectiom
• Chlorination disinfection
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Readily available
Cheap
Provides residual disinfection
Not as aggressive as ozone
Very reactive (e.g. with organic compounds and ammonia)
Tertiary Processes
• Soluble inorganic residuals
– Precipitation softening
• Lime, soda ash
– Ion exchange softening
• Natural zeolite resins
• Non-biodegradable organic residuals
– Activated carbon
• Granular (GAC)
• Powdered (PAC)
Monitoring
• Routine monitoring
– of pH, residual chlorine, fluoride, aluminium,
iron, dissolved oxygen, colour, turbidity,
ammonia, total organic carbon, nitrate, flow
– before, after and between processes
• Fish monitors
– Before and after treatment
– For trace contaminants
– Fish response triggers alarms
Sludge Removal
• Large amounts of thin slurry produced in water treatment
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Gelatinous hydroxide sludge from coagulation and clarification
Precipitation sludge from water softening
Back-wash water from sand filters
Wash-water from microstrainers
Spent fine sand and PAC
• Sludge treatment
– Dry in shallow lagoons
– Dewater in filter press
• Sludge disposal
– Landfill site
– Spread on land
– Incinerated
Summary and Scope of Design Coursework
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Screening and storage
Aeration
pH adjustment
Coagulation
Flocculation
Clarification
Filtration
Disinfection
Tertiary processes
Monitoring
Sludge removal
Water supply infrastructure
Further Reading
• Twort, A.C., Ratnayaka, D.D. & Brandt, M.J.
(2000) Water Supply, 5th Edition. Arnold / IWA
Publishing, London.
• Hammer, M.J. & Hammer, M.J.Jr. (2001) Water
and Wastewater Technology, 4th Edition.
Prentice Hall, New Jersey.
• Kiely, G. (1998) Environmental Engineering,
International Edition. Irwin/McGraw-Hill
• Viessman, W. Jr. & Hammer, M. J. (1998) Water
Supply and Pollution Control, 6th Edition.
Addison Wesley Longman, California.