Wastewater Treatment and Recycling CIVL7017
- Subject Code :
CIVL7017
CIVL7017 Wastewater Treatment and Recycling
Assignment -1: Wastewater Treatment Processes Design
Total 25 Marks
Due date 25 May 2024 Sunday @ 11:59 PM
This assignment is based on examples done during the lecture tutorial and hence would provide an opportunity to revise most calculations and clear any doubts. Students are strongly encouraged to learn the concepts and revise calculations before attempting to do this. If you put the real effort and learn, it will become easier to answer the final exam questions and will help in achieving most subject learning outcomes.
Before starting to do your assignment please determine values of x and y. The values of x, y are last two digits of your ID; y is the last digit
Table 1 shows a typical wastewater flow rate generated on a normal day from a newly developed community. Characteristics of wastewater are detailed in Table 2. Additionally, the wastewater contains rubbish such as plastic bottles, toilet paper, silt, and sand. Average wastewater temperature throughout summer and winter are 24 and 15 oC. Choose the appropriate temperature when designing the units. Identify can check your design for worst scenario (4 marks)
Q1 Design unit processes (screening, grit chamber, equalization basin, primary sedimentation tank, aeration tank & secondary sedimentation tank) using the water flow rates (Table 1), water characteristics (Table 2), design parameters and guidelines (Table 3). If more data and information are needed, please follow the reference book. (10 marks). Identify and check your design for worst scenario (4 marks)
Q2. If you are asked to add the treatment unit to remove the nitrogen, what is/are an additional unit(s) would you add or how the treatment processes will you modify? Draw the flow diagram and explain. (3 marks)
Q3. If the new unit process is designed to remove 28 mg-N/L NH3, calculate the amount of air (kg/day) to be supplied to convert ammonia to nitrate. Calculate the quantity of sludge (kg/day) produced due to NH3-N oxidation. Yield is 0.25. (2 marks)
Q4. PO4-P removal of the designed wastewater treatment process is only 30%. However, PO4-P discharge limit into the receiving water body is < 0>4-P < 0>
Q5. During the heavy raining season, the performance of the primary sedimentation tank significantly reduced due to the increased water flow rate. In such condition what would you recommend to improve the performance of the primary sedimentation tank? (1 marks)
Q6. After sometimes of operation of the wastewater treatment plant, heavy metals concentration in the inlet wastewater increased due to the discharge of the industrial wastewater. Due to the increased heavy metals concentration, the performance of secondary treatment process significantly reduced. If you are asked for the solution, what suggestion would you recommend? (1 marks)
Q7. How would you manage the sludge produced from this treatment process? Write stepwise. (2 marks)
Table 1: Details of the flow rate in a normal day.
|
Time |
Flow (m3/s) |
Time |
Flow (m3/s) |
|
0:00 |
0.0875 |
12:00 |
0.135 |
|
1:00 |
0.07 |
13:00 |
0.129 |
|
2:00 |
0.0525 |
14:00 |
0.123 |
|
3:00 |
0.0414 |
15:00 |
0.111 |
|
4:00 |
0.0334 |
16:00 |
0.113 |
|
5:00 |
0.0318 |
17:00 |
0.104 |
|
6:00 |
0.0582 |
18:00 |
0.125 |
|
7:00 |
0.0653 |
19:00 |
0.136 |
|
8:00 |
0.113 (1+y*0.04) |
20:00 |
0.127 |
|
9:00 |
0.158 (1+x*0.05) |
21:00 |
0.128 |
|
10:00 |
0.145 (1+y*0.1) |
22:00 |
0.121 |
|
11:00 |
0.137 |
23:00 |
0.11 |
Table 2: Wastewater characteristics
|
Parameters |
Concentration (mg/L) |
|
Alkalinity as CaCO3 |
75*(1+x*0.1) |
|
pH |
7.3 |
|
Suspended Solid (SS) |
220 |
|
Total dissolved solids (TDS) |
510 |
|
Chloride |
50 |
|
BOD5 |
150*(1+y*0.1) |
|
COD |
250*(1+y*0.1) |
|
Total organic carbon |
100*(1+xy*0.1) |
|
Ammonia-N |
50*(1+y*0.05) |
|
Total Kjeldahl nitrogen (TKN) as N |
45*(1+xy*0.05) |
|
PO4-P |
9.5*(1+y*0.05) |
|
Total PO4-P |
12*(1+y*0.05) |
Table 3: Details of unit processes, design parameters and design guidelines
|
Unit process |
Design parameters |
Design guidelines |
|
Screening |
Cross-sectional area, height, number of Screening |
Flow rate = peak flow (Table 1), coarse bar screen 1.0 to1.5 cm width, 4.0 to 5.0 cm clear spacing, <60>o to the horizontal, channel with 0.75 to 0.80m |
|
Grit chamber |
Volume, dimension (length, width & depth) |
Flow rate= peak flow (Table 1), horizontal flow rate = 0.25 m/s, water retention time = 1-2 min |
|
Equalization basin |
Volume |
Provide 25% excess capacity for the equipment, use Table 1. |
|
Primary sedimentation tank |
Volume, dimension (diameter, depth), number of tanks |
Flow rate= average flow rate (Table 1), overflow rate = 30+20*y m3/m2.d, hydraulic retention time = 1.5 + 0.1*x h. Circular sedimentation tank, Diameter = 3 to 50 m and water depth = 3 to 5 m. |
|
Aeration tank |
Volume, quantity of sludge produced in a day, amount of air to be supplied in a day, check F/M |
65% BOD5 is soluble BOD given in Table 2, effluent standards = 20 mg/L BOD5 & 25 mg/L SS. BOD5 of the SS is 65 % of SS. Ks = 25 to 100 mg/L BOD5, m= 1to 8 d-1, kd = 0.01to 0.30 d-1, Y =0.4 to 0.8 mg VSS/mg BOD5 removed, MLVSS = 1500 to 2200 mg/L |
|
Secondary Sedimentation Tank |
Volume, dimension (diameter, depth), number of tanks |
MLSS = 2500*(1+0.1*y) mg/L, Diameter = 3 to 50 m and water depth = 3 to 5 m. 40 to 50% of wastewater will be recirculated to the aeration tank. Follow attached the materials |
