Potential Written Q's

Question 1

Briefly describe 3 key factors that should be considered when selecting an appropriate method of flow measurement

Answer 1

Any 3 from:
- Volume of flow
- Conditions of measurement
- Degree of accuracy required
- Cost
- Frequency of measurement

Question 2

Select 2 examples of direct discharge flow measuring methods

Answer 2

• Contracted weir
• Venturi meter

Question 3

Describe the key differences between a traditional wastewater treatment works and a wastewater treatment works that utilises the activated sludge process.

Answer 3

• Activated sludge processes are an alternative to filter beds
• Liquor is circulated around large oxidation tanks
• Tanks aim to introduce & maintain high levels of oxygen in the liquor,
  (i.e. ideal conditions for the growth of aerobic bacteria)
• This aeration process is either achieved:
• Mechanically (by the use of large rotating paddles)
• or through injection of air through diffusors
• As the liquor circulates & oxidation takes place, a certain amount of sludge is developed.

Question 4

Briefly describe which are the two main types of positive displacement pumps and the situations in which they are employed. (7 marks)

Answer 4

• Diaphragm pumps and piston pumps.
• Displacement pumps are ideal for situations involving viscous liquids or those containing suspended solids; in addition, they are largely employed for groundwater control or for de-watering on construction sites.

Question 5

Explain the significance of the discharge coefficient, Cd, in relation to the broad-crested weir equation. (6)

Answer 5

Cd can be determined by dividing the actual flow rate, Qa, by the theoretical flow rate, Qt.

As such, the Cd parameter accounts for energy losses that occur at the weir.

Question 6

Provide two examples of flow measuring methods that utilise the velocity-area approach. (2)

Answer 6

Current meters

Floats

Question 7

Describe two alternative methods that might be employed to calculate flow discharge within this type of lab flume.

(A Broad-crested weir)

Answer 7

• Use of float
• Volumetric method

Question 8

Name the three main sources of water.

Answer 8

• Lowland River Water
• Upland Reservoir Water
• Groundwater (Springs/Boreholes)

Question 9

Describe the properties of ‘lowland river water’.

Answer 9

River water, such as water from the river Thames.
- Usually has reservoir storage
- Often contaminated by sewage & agricultural run-off
- Requires extensive treatment

Question 10

Describe the properties of ‘upland reservoir water’.

Answer 10

Mainly moorland catchment, such as the Yorkshire reservoirs.
- Relatively uncontaminated (only faecal contamination)
- Highly coloured due to peaty material and metals
- Requires extensive treatment to lower turbidity and remove pathogens

Question 11

Describe the properties of ‘groundwater (boreholes/springs)’.

Answer 11

• Filtered through chalk or sandstone, can be 1000’s of years old
• Regarded as pure and needs minimal treatment
• Pesticides and solvents now being detected

Question 12

List the three main sources of water in order of least treatment to most treatment required.

Answer 12

Least -> Most

Ground water, Upland reservoir water, Lowland river water

Question 13

Name the main treatment processes in fresh water treatment from start to finish. (8)

(R, SSF, C/F, S/F, RGF, MC, O/GAC, D)

Answer 13

• Reservoirs
• Slow sand filters
• Coagulation/Flocculation
• Sedimentation/flotation
• Rapid gravity filters
• Manganese contactors
• Ozone/Granular activated carbon
• Disinfection

Question 14

Describe the ‘reservoir’ stage of water treatment.

Answer 14

• Simple but very effective.
• Most pathogens die within a 60 day storage period.

Question 15

Describe the ‘slow sand filters’ stage of water treatment.

Answer 15

• very effective at removing pathogens.
• not great at removing colour or persticides.
• ‘Schhmutzdecke’ a surface layer of bacteria acts as a filter.

Question 16

Sketch the ‘slow sand filters’ stage of water treatment.

Answer 16

Refer to cue card 3.

Question 17

Describe the ‘coagulation/flocculation’ stage of water treatment.

Answer 17

• Coagulation: Positively charged metal ions attract negatively charged collidal particles
  Followed by
• Flocculation: Chemicals are added to create ‘flocs’

Question 18

Describe the ‘sedimientation/flotation’ stage of water treatment.

Answer 18

• Flocs are allowed to settle (sedimentation)
  OR
• Flocs are made to float (by injecting air bubbles)

The sludge is then separated from the clean water.

Question 19

Describe the ‘Rapid gravity filters’ stage of water treatment.

Answer 19

• Used after coagulation/flocculation in order to remove residual flocs.

Question 20

Describe the ‘Ozone’ stage of water treatment.

Answer 20

• Ozone (O3) is injected into water to break down pesticides and organic material.

Question 21

Describe the ‘Granular activated carbon’ stage of water treatment.

Answer 21

• Used in combination with Ozone injection to remove; pesticides, organic compounds and unpleasant tastes & odours.

Question 22

Describe the ‘Chlorination/Disinfection’ stage of water treatment.

Answer 22

• Chlorine is used to kill or remove pathogens.

Question 23

Describe the ‘Manganese contactors’ stage of water treatment.

Answer 23

• Coarse sand filters used for ‘aeration’ or ‘chlorination’ of water producing a precipitation of Manganese.

Question 24

Briefly describe Rotodynamic (or continuous flow) pumps and the situations in which they are employed. (7 marks)

Answer 24

• Rotodynamic pumps rely on an impeller which rotates inside a casing and transfers energy to the fluid.
• They are typically used in permanent installations, such as water treatment works.

Question 25

What are the 3 sub-categories of ‘Rotodynamic’ pumps?

Answer 25

• Axial flow pumps
• Radial flow pumps
• Mixed flow pumps

Question 26

What are the diagram changes between a traditional WWTW and one that utilises the ‘activated sludge’ process?

Answer 26

‘Trickling filters’ are replaced with ‘Activated sludge plant’

There is also a dotted line from the secondary settlement tanks to the activated sludge plant, annotated with ‘return sludge’ and another from the secondary settlement tanks to the primary sedimentation tank labelled ‘surplus activated sludge’