If the population and water use of Quamta (Problems 9–29 and 9–30) are growing at 5% per year with a corresponding increase in wastewater flow, how many years’ growth may be sustained before secondary treatment becomes inadequate? Assume that the treatment plant continues to maintain an effluent BOD5 of 30.00 mg · L−1.
The town of Edinkira has filed a complaint with the state department of natural resources (DNR) that the city of Quamta is restricting its use of the Umvelinqangi River because of the discharge of raw sewage. The DNR water quality criterion for the Umvelinqangi River is 5.00 mg · L−1 of DO. Edinkira is 15.55 km downstream from Quamta. What is the DO at Edinkira? What is the critical DO and where (at what distance) downstream does it occur? Is the assimilative capacity of the river restricted? The following data pertain to the 7-year, 10-day low flow at Quamta.
Parameter | Wastewater | Umvelinqangi River |
Flow (in m3 · s−1) | 0.1507 | 1.08 |
BOD5 at 16°C (in mg · L−1) | 128.00 | N/A |
BODu at 16°C (in mg · L−1) | N/A | 11.40 |
DO (in mg · L−1) | 1.00 | 7.95 |
k at 20°C (in day−1) | 0.4375 | N/A |
Speed (in m · s−1) | N/A | 0.390 |
Depth (in m) | N/A | 2.80 |
Temperature (in °C) | 28 | 28 |
Bed-activity coeff. | N/A | 0.200 |
Under the provisions of the Clean Water Act, the U.S. Environmental Protection Agency established a requirement that municipalities had to provide secondary treatment of their waste. This was defined to be treatment that resulted in an effluent BOD5 that did not exceed 30 mg · L−1. The discharge from Quamta (Problem 9–29) is clearly in violation of this standard. Given the data in Problem 9–29, rework the problem, assuming that Quamta provides treatment to lower the BOD5 to 30.00 mg · L−1.
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