water

Question 1

hard water

Answer 1

water that will not easily form a lather with soap

Question 2

temporary hardness

Answer 2

hardness that can be removed by boiling the water

Question 3

permanent harness

Answer 3

hardness that cannot be removed by boiling the water

Question 4

flocculation

Answer 4

the coming together of small suspended particles in water

Question 5

flocculating agent

Answer 5

added to water to coagulate suspended particles and help sedimentation to take place

Question 6

B.O.D. (biochemical oxygen demand)

Answer 6

• the amount of dissolved oxygen consumed by biological action
• when a sample of water is kept at 20°C in the dark for five days

Question 7

eutrophication

Answer 7

the enrichment of water with nutrients, leading to the excessive growth of algae and other plants

Question 8

primary treatment of sewage

Answer 8

a mechanical process in which large solids are removed by screening and some suspended solids are removed by settlement

Question 9

secondary treatment of sewage

Answer 9

a biological oxidation process in which the levels of suspended and dissolved organic materials are reduced

Question 10

tertiary treatment of sewage

Answer 10

the removal of phosphorus compounds by precipitation and the removal of nitrogen compounds by biological and ion-exchange methods

Question 11

the principle of colorimetry

Answer 11

the amount of absorbance of light by a coloured solution is proportional to the concentration of the solution