Question

The initial ultimate BOD after mixing of the River is 12.0 mg · L−1. The DO in the River after the wastewater and river have mixed is at saturation. The river temperature is 10◦C. At 10◦C, the deoxygenation rate constant (kd) is 0.30 day−1, and the reaeration rate constant (kr) is 0.40 day−1. Determine the critical point (tc) and the critical DO.

Answer 1

Answer:

$t_c = 2.87\ DAYS$

Explanation:

Given data:

Initial BOD level is $12 mg l^{-1}$

temperature of river is 10 degree C

Rate constant is $kd = 0.30 day^{-1}$

Reaeration rate constant is kr $0.40 day^{-1}$

As DO in river is at saturation hence initial Da is zero

critical temperature is calculated as

$t_c = \frac{1}{K_r - k_d} ln[ \frac{k_r}{k_d}(1 -Da\frac{k_r -k_d}{k_d L_a})]$

$t_c = \frac{1}{K_r - k_d} ln[ \frac{k_r}{k_d}(1 -0)]$

$t_c = \frac{1}{0.40 - 0.30} ln[ \frac{0.40}{0.30}(1 -0)]$

$t_c = 2.87\ DAYS$