Water Treatment Processes

Question 1

List 4 water treatment processes.

Answer 1

Limited treatment (filtration).
Coagulation.
Softening.
Disinfection and fluoridation.

Question 2

What does SOFTENING do and how?

Answer 2

Remove hardness:
Chemical addition
Sedimentation of precipitates
Final filtration.

Question 3

What does COAGULATION do and how?

Answer 3

Removes suspended solids: Chemical addition

Flocculation and settling

Question 4

What are 3 sources of water?

Answer 4

Groundwater.
Upland surface water.
Lowland surface water.

Question 5

List the following cleanest to dirtiest:
Groundwater
Upland surface water
Lowland surface water

Answer 5

Groundwater
Upland surface water
Lowland surface water

Question 6

Which is cleaner and why?
Upland surface water
Lowland surface water

Answer 6

Upland surface water:
Cleaner but often further from cities.

Lowland surface water includes agricultural waste and pollutants from human settlements - requires most treatment but is often the closest to cities.

Question 7

List the treatment sequence for excellent quality groundwater from a borehole.

Answer 7

Borehole > Aeration > Disinfection > Fluoridation > Service reservoir > Distribuution.

AirDisinfFluSeRD

Question 8

Compared to excellent quality groundwater sources, what additional treatment step is required for moderate quality groundwater sources?

Answer 8

Rapid sand filtration

after Aeration

Question 9

What are standard sizes for:
Coarse screens.
Fine screens.
Micro screens.

Answer 9

Coarse (100mm)
Fine (6mm)
Micro (20-40 microns)

Question 10

What is the advantage of a storage lake?

Answer 10

Buffers flow and quality variations.

Question 11

When is pre-treatment required and what does aeration pretreatment do?

Answer 11

For poor quality water.
Removed VOCs
Releases excess H_2S and CO_2 > increases pH
Increases DO (good for organic and inorganic pollution).

Question 12

Chlorination is a form of chemical pre-treatment. When do you use it and what does it achieve?

Answer 12

For low turbidity water with high microbe count.
Oxidises Mn and Fe.
Reduces ammonia.
Kills pathogens.

Question 13

Activated carbon is a form of pre-treatment. What does it remove?

Answer 13

Photosynthetic algae.
Colour.
Odour.
Some organics.

Question 14

What does a coagulant treatment do?

Answer 14

Removes colloidal particles / suspended solids which cause colour / turbidity. e.g. algae, bacteria organics, inorganics.

Question 15

List some common coagulants

Answer 15

Alum (Al_2(SO_4)_3) @pH5-7
Ferric Sulphate (Fe_2SO_4)
Ferrous Sulphate (FeSO_4) @pH>9.5
Ferric Chloride (FeCl_3)

Question 16

What are coagulant aids and what do they do?

Answer 16

Silica, clays, polymers.
Improve rates and efficiency.
Increase density of slow settling flocs.
They are expensive and often unnecessary.