Question

6 MGD of wastewater with a dissolved oxygen concentration of 0.9 mg/L is discharged to a river flowing at 40 ft'/sec. The river initially is saturated with oxygen. The saturation DO is 11.30 mg/L. The oxygen content of the river (mg/L) immediately after mixing is most nearly: (conversion factor: 7.48 gal= 1 ft') 1.30 9. 34 9.00 8.85 7.24 other, write your answer

Answer 1

Given 6 MGD of waster water with 0.9 mg/ l Dissolve oxygen concentration.

ie Given 7.48 G = 1 ft^3

ie 6 MGD = 1/7.48*6 Mft^3 / Day = 0.802 MFt^3/Day

So dissolved oxygen in waster water = 0.802*0.9 =

0.72 MFt^3/Day mg/L

Rivers initial flow rate = 40 *(60*60*24) = 3.456 MFT^3/Day

River's initial dissolved oxygen concentration =

40 *11.3 *(60*60*24)=39.05 MFT^3/Day mg/L

So oxygen contentent of river immediately after mixing

= (0.72+39.05)/( 0.802+3.456) =9.34 mg/L