Question

Example 7.15: According to the following information, determine whether a fish, which requires 6 \(\mathrm{mg} / \mathrm{L}\) dissolved oxygen, would survive in the river.

Given:

Waste water flow rate \(\left(\mathrm{Q}_{w}\right)=1.2 \mathrm{~m}^{3} / \mathrm{s}\)

River flow rate \(\left(\mathrm{Q}_{r}\right)=10 \mathrm{~m}^{3} / \mathrm{s}\)

River temperature \(\left(T_{r}\right)=15^{\circ} \mathrm{C}\)

River ultimate \(\mathrm{BOD}\left(\mathrm{BOD}_{r}\right)=2.3 \mathrm{mg} / 1\)

River reaeration rate \(=0.4\) per day for BOD test

BOD concentration was initially \(9 \mathrm{mg} / \mathrm{l}\), after 5 days was \(6 \mathrm{mg} / 1\) and after an indefinitely long period of time was \(2.5 \mathrm{mg} / \mathrm{l}\). Test temperature is \(20^{\circ} \mathrm{C} .10 \%\) wastewater diluted with \(90 \%\) pure water.

Assumptions:

\(\theta=1.047\)

River temperature doesn't change with wastewater discharge BOD reaction rate constant (k) is equal to rate of deoxygenation in the river (k \(_{d}\) )

Answer 1