Question

A wastewater discharge has a flow equal to upstream flow of the river it is being discharged into. The river upstream has a DO of 7 mg/L, and negligible BOD. The wastewater discharge has an ultimate BOD of 50 mg/L, and negligible DO. It is determined that it would cost an equal amount of money to reduce the BOD to 25 mg/L or to increase the DO to 8 mg/L. Which alternative, considering DO sag, would you judge to be better for the river? Justify your argument with appropriate calculations. Data temperature=20°C deoxygenation rate coefficient, ka = 0.3/d reaeration rate coefficient = 0.9/d.

Answer 1

Ans:- (ose-1:- if BoD is recued from 25 mgle ro 50 my le Xiver. warte of water Bon After mixing E- 25x a toxa 12.5 mg/4 zQ DO 7 x Q toxQ = 3.5 mgle 20 Satusabion Do at 20°c = 9.2 mallit Initical oxygen defecit cy mix at mixing mixing point De 9.2 -3.5 5.7 ingle of mix at a point of waste discargo ullimate BOD L. = 12.5 mgle - 0.91d ; Kd =0-31d KR f- Hd 0.9 8-1 dificit -18-12 De = critical maximum laty dle L

12.5 39 3 Dc.3 2- 1-(3-1) (3-1) 57 12.5 9. 12.5 3 3447-017 1215 Dc 8.122 ( cục - Tt if Do is Increased to smo la BOD of river L soxa of oxQ 25 mgle. 2Q Do of river 70 + 8xQ 705 myle 22 oxygen deficit I Do 9.2 7.5 = 117 myll 25 for calculating De 3) (31) 1.7 LS Deos Det 13(-34

Dc S-1 + 9 | воо Case of decrease in oxygen reficiency is more in и 50, Increase in be good for giver. please give one herubs up for this Answers Comments if you Сke. any dout's ри+ го hun хоці,