Daily Question 2015.7.27 (EIA Discussion): 3 Wealth points for replies, plus 5 Wealth points for correct answers (single-choice question)
Thread Content
This post was last edited by Zhang Xiaopeng on 2015-7-30 at 10:37. Under the condition of constant and uniform flow in a single river, it is assumed that a certain degradable pollutant follows a first-order degradation law, with the degradation rate K1 remaining constant along the flow path. The concentration of this pollutant 20 km downstream of the emission point is 50% lower than at the emission site; if there are no other pollution sources within 40 km downstream of the emission point, then the pollutant concentration there is also () lower than that at the emission site. A. 70% B. 75% C. 80% D. 85% Correct answer: B. 1. Assuming some simple values based on the given information: Co = 1. It can also be assumed that C20 = 0.5. The formula becomes: 0.5 = 1 × exp(-k20/86400u), which implies that exp(-k20/86400u) = 1/2. 2. To find the concentration at 40 km: C40 = 1 × exp(-k40/86400u) = 1 × exp(-k20/86400u) × exp(-k20/86400u) = 0.25. This shows that C40 is 75% lower than the concentration at the discharge point.
The pollutant concentration decreases compared to that at the emission point B
B.75%! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
In a single river under steady and uniform flow conditions, assuming that a certain degradable pollutant follows a first-order degradation law with a constant degradation rate K1 throughout the flow. The concentration of this pollutant 20 km downstream of the emission point is 50% lower than at the emission site; if there are no other pollution sources within 40 km downstream of the emission point, then the pollutant concentration there is also () lower than that at the emission site. A. 70% B. 75% C. 80% D. 85% B
Correct answer: B. 75%.
In a single river under steady and uniform flow conditions, assuming that a certain degradable pollutant follows a first-order degradation law with a constant degradation rate K1 throughout the flow. The concentration of this pollutant 20 km downstream of the emission point is 50% lower than at the emission site; if there are no other pollution sources within 40 km downstream of the emission point, then the pollutant concentration there is also lower than at the emission site (B). A. 70% B. 75% C. 80% D. 85%
In a single river under steady and uniform flow conditions, assuming that a certain degradable pollutant follows a first-order degradation law with a constant degradation rate K1 throughout the flow. The concentration of this pollutant 20 km downstream of the emission point is 50% lower than at the emission site; if there are no other pollution sources within 40 km downstream of the emission point, then the pollutant concentration there is also lower than at the emission site (B). A. 70% B. 75% C. 80% D. 85%
In a single river under steady and uniform flow conditions, assuming that a certain degradable pollutant follows a first-order degradation law with a constant degradation rate K1 throughout the flow. The concentration of this pollutant 20 km downstream of the emission point is 50% lower than at the emission site; if there are no other pollution sources within 40 km downstream of the emission point, then the pollutant concentration there is (A.70%) lower than that at the emission site.