[water] potable water & sewage

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Potable Water

Water that is safe to drink; it must have sufficiently low levels of dissolved salts and microbes.

Main Sources of UK Potable Water:

• ground water → aquifers

• surface water → lakes, rivers and reservoirs

Purification of Water:

1. passing the water through filter beds to remove insoluble particles

2. sterilising the water to kill microbes using sterilising agents eg. chlorine, ozone or UV light

Desalination

The removal of salt from water eg. distillation and reverse osmosis

Distillation

A separation technique which involves a solution being heated so that the solvent evaporates before being cooled to form a pure liquid.

Reverse Osmosis

A method of purifying water by forcing it under pressure through a semi-permeable membrane, removing the salt from the water.

Process of Distillation:

1. salt water is heated

2. water boils and water vapour enters the condenser

3. the water vapour condenses due to the cold water in the condenser

4. pure water is then collected in a beaker

5. salt is left behind in the (distillation) flask

Process of Reverse Osmosis:

1. high pressure is applied to salt water

2. this forces the salt water to pass the semi-permeable membrane

3. salt molecules are not small enough to pass the membrane, meaning only water molecules passes → results in pure water

Grit

Small pieces of rock.

Effluent

Liquid waste or sewage discharged into a river/sea.

Slurry

A semi-liquid mixture, typically of fine particles of manure, cement, or coal suspended in water.

Sources of Waste Water:

• domestic waste water eg. toilets, baths, washing

• agricultural run off from fields and slurry from animals

• industry waste from factories → this involves the removal of harmful chemicals, not just harmful microbes

1st Stage of Waste Water Treatment

Screening / Grit Removal → removes large, insoluble materials eg. twigs, plastic bags etc.

2nd Stage of Waste Water Treatment

Sedimentation → this is where the water is left to stand still and let the heavier solids sink to the bottom (sludge) and the lighter matter (effluent) to float to the top.

3rd Stage of Waste Water Treatment

Aerobic Digestion of Effluent → involves separating the effluent from the sludge and pumping air into the effluent to encourage the breakdown of organic matter and other microbes by aerobic digestion.

4th Stage of Waste Water Treatment

Anaerobic Digestion of Sludge → involves separating the sludge from the effluent and allowing bacteria to break it down.

5th Stage of Waste Water Treatment

• treated effluent is released back into the environment eg. rivers

• treated sludge is used as natural gas and fertiliser → methane gas is released and the remaining ‘sludge’ is used as a fertiliser

Mnemonic for Waster Water Treatments

Sewage Gets Sorted At Anfield