Water Treatment

Question 1

Name the Factors affecting disinfection.

Answer 1

1. Method of initial contact.
2. Contact time - there must be free residual of chlorine to react with organisms not yet oxidised.
3. Other factors such as the concentration of organisms, concentration of disinfectants and environmental factors such as the temperature.

Question 2

What are the properties of disinfectant?

Answer 2

1. Must be able to kill bacteria and pathogens without harming the consumers (humans and animals).
2. Must have residual stay in water for a period of time to prevent the growth of bacteria.
3. Must not alter the properties of the water such as the aesthetics (odour, colour, taste).

Question 3

What is Sedimentation?

Answer 3

Sedimentation is when the fluids moves so slowly that larger solids are able to sink to the bottom of a tank while clear water runs off the top.

Question 4

What is chlorination?

Answer 4

Chlorination is required as a disinfectant to kill bacteria and harmful pathogens and is added to the water as Cl2 in a gas form.

Question 5

What are the 3 Water treatment processes?

Answer 5

1. Physical or Mechanical process - uses a physical building and the associated forces.
2. Chemical process - the addition of chemicals such as chlorine and lime.

• precipitation - lime is added to the water to form Flocs that precipitate out.
• disinfection - the addition of chlorine to kill bacteria in the water.

3. Biological process - the use of plants in swamps to extract minerals from the water I’m order to “purify” the water.

Question 6

Name 2 water sources for domestic use.

Answer 6

1. Ground water - such as water from boreholes.

2. River water - that is pumped from a river to treatment works.

Question 7

What are the factors that affect the layout of a Water Treatment plant?

Answer 7

1. Client’s requirements.
2. Experience of the designer.
3. Availability of supplies.
4. Use of existing facilities.
5. Availability of qualified personnel.
6. Construction costs.
7. Future maintenance and operations costs.
8. Degree of treatment (How clean must the water be).

Question 8

What are the steps in a Water treatment process?

Draw a flow chart Diagram.

Answer 8

River

Coarse Screening
Travelling screening

Optional Sedimentation

Addition and mixing of chemicals 
Flocculation
Sedimentation -> to sludge dams
Filtration -> backwash to mixing and addition of chemicals. 
Disinfection

Clear Water to storage tanks or distribution systems.

Question 9

What is Breakpoint Chlorination?

Answer 9

The addition of enough chlorine to result in free residual chlorine.

Question 10

What is the Coagulation Process?

Answer 10

The aim of the coagulation process is to separate suspended particles from the water. In a section of rapid mixing, polymers are added to the water and absorb the suspended particles. The polymers have a molecular form of longish legs and stuck together to form Floc Particles. Floc particles are formed by partial bridges and become big enough or heavy enough to be filtered out (for Sedimentation to take place).