1. In this tutorial old exam questions are elaborated by a fellow campus student. We encourage you to elaborate the questions yourself with or without the elaboration.

2. Description

A surface water treatment plant consists of:coagulation / flocculation – tilted plate sedimentation – upflow rapid sand filtration – activated carbon filtration 

The average raw and clear water quality is given in the table below.

 

The design flow of the treatment plant can be determined with the following data:

Average yearly capacity: 100,000,000 m³ / year

Maximum peak factor: 1.1

Questions

1. Give comments on the type of raw water at the treatment plant.

2. What is the main purpose of the coagulation / flocculation process and what are the water quality parameters to be improved?

3. The coagulant dose is relatively high. Explain what iron salt is used in this treatment plant, what is the dosage and what is the observed coagulation mechanism.

4. The sedimentation tank consists of 6 parallel lanes of 11.6 m x 11.6 m x 6.3 m (length x width x depth).Determine the surface loading of the tilted plate sedimentation tank.

5. The settling properties of the flocs is given in the graph below.

Determine the removal efficiency of the flocs.

6. What can be done to increase the removal efficiency of the flocs (mention at least 2 measures)?

7. The up flow filters have a filtration velocity of 5 m/h; a grain size of 1 mm (d10); a bed height of 1.5 m; a supernatant water level of 1 m. The proposed maximum head loss (after clogging) is 1.5 m. Backwashing is done with an expansion of 20%.What are the main advantage and the main disadvantage of an upflow filter?

8. Calculate the clean bed resistance of the filter bed.

9. Sketch the Lindquist diagram for the static situation, after and just before backwashing and comment on that.

10. Draw a hydraulic line scheme of the three processes (coagulation / flocculation-sedimentation-filtration) of the treatment plant.

1. Description of present situation

The treatment chain of a surface water treatment plant consists of:Flocculation – sedimentation – rapid sand filtration

The Rhine water has a turbidity of 10 - 200 NTU and a suspended solid content of 5 - 50 mg/l.

The sedimentation tank has a length of 200 meter, a width of 10 meter and a depth of 2.2 meter.

The flow rate of the sedimentation tank is 1000 m3/h. The temperature of the water is 10°C.

The sedimentation tank should remove sand grains (ρ= 2600kg/m3) with a diameter of 0.05 mm.

Formula sheet

Use this formula sheet for answering the questions below.

2. QUESTION 1

 (2 points possible)Calculate the sedimentation velocity of the sand grains.

Enter the numerical value for the sedimentation velocity below measured in mm/s:

unanswered

What is the sedimentation velocity measured in m/h?

unanswered

  You have used 0 of 1 submissions

3. QUESTION 2

 (3 points possible)What is the surface loading?

Enter the numerical value measured in m/h

unansweredEnter the numerical value for the surface loading measured in mm/s

unansweredDoes the sedimentation tank meet the requirements for surface loading?

Yes No1. Description of present situation

The treatment chain of a surface water treatment plant consists of:Flocculation – sedimentation – rapid sand filtration

The Rhine water has a turbidity of 10 - 200 NTU and a suspended solid content of 5 - 50 mg/l.

The sedimentation tank has a length of 200 meter, a width of 10 meter and a depth of 2.2 meter.

The flow rate of the sedimentation tank is 1000 m3/h. The temperature of the water is 10°C.

The sedimentation tank should remove sand grains (ρ= 2600kg/m3) with a diameter of 0.05 mm.

Formula sheet

Use this formula sheet for answering the questions below.

2. QUESTION 3

 (11 points possible)To improve the flow conditions the sedimentation tank should be modified. For this modification 2 alternatives have been proposed. In both alternatives an extra floor has been constructed (see figure below).

Indicate which modification gives the highest efficiency. Use the criteria of surface loading as well as the influence of factors which decrease efficiency: turbulence, instability and bottom scouring which are detailed in the table below.

Evaluation of Option A:

1. What is the surface loading for option A?

Enter the numerical value below in m/h to 2 decimal places

unanswered2. What is the Reynolds number and indicate if the flow is laminar or turbulent.

Enter the numerical value for the Reynolds number below:

unanswered

Status: unsubmitted3. What is the Camp number and indicate if the flow is stable or not.

Enter the value as ______x 10-5.

unanswered

Status: unsubmitted

Evaluation of Option B:

1. What is the surface loading for option B?

Enter the numerical value below in m/h to 2 decimal places.

unanswered2. What is the Reynolds number and indicate if the flow is laminar or turbulent.

Enter the numerical value for the Reynolds number below:

unanswered

Status: unsubmitted3. What is the Camp number and indicate if the flow is stable or not.

Enter the value as ______x 10-5.

unanswered

Status: unsubmitted

Compare option A and B

Which option gives the highest efficiency?

1. Description of present situation

The treatment chain of a surface water treatment plant consists of:Flocculation – sedimentation – rapid sand filtration

The Rhine water has a turbidity of 10 - 200 NTU and a suspended solid content of 5 - 50 mg/l.

The sedimentation tank has a length of 200 meter, a width of 10 meter and a depth of 2.2 meter.

The flow rate of the sedimentation tank is 1000 m3/h. The temperature of the water is 10°C.

The sedimentation tank should remove sand grains (ρ= 2600kg/m3) with a diameter of 0.05 mm.

Formula sheet

Use this formula sheet for answering the questions below.

2. QUESTION 4

 (1 point possible)A new rapid sand filtration installation is required. Experiments have been done with filter columns (L = 0.75 m) to determine the grain diameter of the rapid sand filtration installation. The results of the experiments are given in Figures 1 and 2.

Figure 1 – Effluent quality as a function of time and grain size

Figure 2 – Resistance as a function of time and grain size

What diameter do you choose when the following requirements have to be met:

ce smaller than 0.5 mg/l

resistance smaller than 1 m

Status: unsubmitted

  You have used 0 of 1 submissions

3. QUESTION 5

 (1 point possible)When the running time of a filter should be 36 hours, how large should the supernatant water level be for a filter with grain size of 0.8 mm to avoid negative pressures in the filter bed?

Status: unsubmitted

  You have used 0 of 1 submissions

4. QUESTION 6 (1 point possible)The clean bed resistance of the filter with grain size of 0.9 mm is 0.5 m. Calculate the clean bed resistance when the filter is filled with filter material with a grain size of 0.7 mm.

0.32 m 0.64 m 0.83 m 1.62 m

  You have used 0 of 1 submissions