Water Flashcards
What is potable water
Water that is safe to drink- it is not 100% pure water as it contains dissolved impurities
What must water have low levels of to be potable?
Why?
Must have low levels of:
- dissolved salts- can be harmful for humans
- microbes- can cause illness
How is naturally occurring fresh water made potable?
- Passing the water through filter beds to remove insoluble particles.
- Sterilizing the water to kill microbes
What methods are used for sterilization?
- Chlorine
- Ozone
- Ultraviolet light
What is desalination?
What two ways can it be done?
The removel of salt from water
Can be done by distillation and reverse osmosis
Describe how potable water can be made by distillation
Sea water is heated until it boils
Salt remains in the liquid- steam in pure water
Steam cooled and condensed to make potable water
Describe how reverse osmosis can make potable water
Water is put under high pressure and passed through a membrane
Membrane has tiny pores in it
Pores allow water molecules through- don’t allow ions and other molecules passing through
What is the disadvantages of using distillation to make potable water?
Required a lot of energy- to boil water and cool down steam to condense it
- expensive
Waste water salty- difficult to dispose of in a sustainable way- so it does not harm marine ecosystems
What are the disadvantages of using reverse osmosis to make potable water?
Requires lots of energy
- expensive
Large volumes of waste water- efficiency low
Describe the process of sewage treatment
- Screening and grit removal- remove large particles
- Sedimentation- tiny particles settle out from still water- produces sludge and effluent (the liquid which remains on top)
- The sewage sludge is digested anaerobically by bacteria
- Effluent treated with aerobic bacteria- reduce volume of solid waste
- Sterilized by either, chlorine, ozone or UV light
How is sludge treated and what are its uses?
- digested anaerobically by microorganisms
- removes organic matter
- releases methane gas- used as an energy source
- remaining digested waste dried out- form fertilizer
What is sludge?
Human waste in waste water
What are the pros and cons to sewage treatment?
Pro- small/less (than desalination of salt water) volumes of energy required
Con- lots/more (than fresh water) processes
What are the 5 stages of sewage treatment?
- Screening
- Primary sedimentation
- Biological treatment
- Secondary sedimentation
- Sterilization
What is the first stage of sewage treatment?
- Screening and grit removal to remove large particles
