Assignment task 1: Explain the following:
(a) the major treatment processes that water goes through to produce drinking water, including what contaminants are treated, how the process works, and what inputs (material, energy or chemical) are needed for the process to work.
(b) the major treatment processes that wastewater goes through to produce a high enough quality to release to surface water, including what contaminants are treated, how the process works, and what inputs (material, energy or chemical) are needed for the process to work.
(c) compare and contrast drinking water and wastewater treatment in terms of processes used and contaminants treated.
Assignment task 2: The wastewater treatment plant (WWTP) for Willimantic discharges the treated waste into the Willimantic River.
You are given the task to carry out a CBOD (CBOD is carbonaceous BOD, so only including the carbon portion of oxygen demand and not the ammonia portion of oxygen demand) analysis for the WWTP to know the decay rate in the stream. You conduct a series of BOD tests, each with the initial CBOD as 100 mg/L but over different time periods. The results are tabulated below:
| Trial |
Time (days) |
BOD (mg/L) |
| 1 |
0 |
100 |
| 2 |
1 |
60.1 |
| 3 |
2 |
34 |
| 4 |
3 |
14.2 |
| 5 |
4 |
8 |
| 6 |
5 |
3.88 |
The retention time in the WWTP is 36 hours. The treatment plant currently only achieves removal of BOD down to 37 mg/L. After the treated wastewater is discharged into Willimantic River, you are asked to model BOD in the stream with respect to time and distance.
The river has a velocity of 5 km d' and has an initial oxygen deficit immediately downstream of the mixing zone of 2 mg/L. Based on the decay rate of CBOD calculated from the experiment and a reaeration coefficient of 0.8 d', plot DO concentration with respect to distance. EPA has set an ultimate BOD of 25 mg/L safe for fish life in a river.
Do you think fish can survive 30 km downstream (at least 5 mg/L dissolved oxygen is minimum for fish)?
Show the critical distance where fish cannot sustain life. What is the critical point in time?