Question 1. Provide brief answers to the following:
a. What is the zeta potential? What role does it play in water treatment?
b. Explain the difference between coagulation and flocculation.
c. What are the main reasons to use biological activated carbon filtration in Australia rather than traditional activated carbon techniques?
d. What is the purpose of recarbonation in water treatment?
e. What is the significance of turbidity in a water supply? Why is a low turbidity required?
f. Your organisation receives a number of complaints about an earthy odour and taste to a drinking water. What is the most likely cause and how would you alter the treatment process to account for it.
g. What are faecal coliforms and what is the test for them? Why are faecal coliforms used as an indicator of drinking water quality?
h. Why is pre-treatment of seawater necessary prior to reverse osmosis?
i. Identify four potential causes that you would investigate to explain the poor performance of a settling tank.
j. What are the key differences between a sludge from a coagulation process and a sludge from a lime softening process
Question 2. a. The table below shows the water quality for a new plant. Does the ionic analysis appear to be complete (within a 10% error)?
| Cation |
Cancentraion |
Anions |
Concentration(mg/L) |
|
Ca2+
|
180
|
HCO3
|
300
|
|
Mg2+
|
65
|
-
COQ'
|
40
|
|
Na+
|
60
|
SO, '
|
60
|
|
K+
|
20
|
|
348
|
|
Fe2+
|
0.5
|
NO3
|
35
|
|
Cd2+
|
0.2
|
|
|
b. Based on the analysis what is the likely source of the water. Why?
c. Look at the following process flow diagram for a conventional water treatment plant. Identify the mistakes in the PFD and sketch a more suitable process.
d. Would the treatment train you proposed by suitable for the treatment of the water in part a. Why or why not?
Question 3. A settling column analysis was run on a discrete suspension. Water samples were withdrawn at different time intervals from a port 2 m below the original water level. The total suspended solids analysis was performed on each sample withdrawn with the results shown below.
Calculate the theoretical removal efficiency of the suspension in a sedimentation basin that has an overflow rate of 30 m^3/m^2/d
|
t (min)
|
TSS
(mg/L)
|
|
0
|
250
|
|
60
|
153
|
|
90
|
148
|
|
120
|
138
|
|
180
|
120
|
|
260
|
70
|
|
400
|
24
|
Question 4. The table below shows a sieve analysis for filter sand. Compute the head loss across the clean stratified bed if the bed has the following properties:
Depth = 70 cm
Porosity ratio = 0.41
Temperature = 5 °C
Shape Factor = 1
Filtration Rate = 150 m^3/m^2.d
Also determine the backwash rate that would be required to just fluidise the largest particles in the filter bed.
| Sieve Number (US Sieve Series) |
Weight Fraction of Particles Retained(%) |
Geometric Mean Diameter(mm) |
| 14-20 |
0.8 |
1.09 |
| 20-25 |
4.25 |
0.77 |
| 25-30 |
15.02 |
0.65 |
| 30-35 |
16.65 |
0.54 |
| 35-40 |
18.01 |
0.46 |
| 40-50 |
15.25 |
0.35 |
| 50-60 |
15.65 |
0.27 |
| 60-70 |
9.3 |
0.23 |
| 70-100 |
2.07 |
0.18 |
Question 5. A water utility runs a conventional filtration plant. The regulator requires disinfection to achieve a log reduction of 0.5 for Giardia lamblia and 2 for viruses. Chlorine is applied to the filter effluent prior to a clearwell. A free chlorine residual of 1 mg/L is maintained in the first compartment of the clearwell, while ammonia is added ahead of the second compartment to convert free chlorine to a combined chlorine residual of 1 mg/L. The pH values in winter and summer are 8 and 7 respectively while the water temperatures are 20 °C and 5 °C. Dye tracer studies were performed and determined that during winter and summer the T10 was 8 and 13 minutes respectively in the first compartment and 38 and 56 minutes respectively in the second compartment. Use the tables on the following pages to determine whether the plant is able to meet it regulatory requirements or not.