Problem 7. Suppose the only source of BOD in a river is untreated wastes that are being discharged from a food processing plant. The resulting oxygen sag curve has a

minimum value of DO downstream equal to 3.0 mg/L. Just below the discharge point, the DO of the stream is equal to the saturation value of 10.0 mg/L. ka = 0.2 day"; k= 0.8 day"; stream velocity is 60 miles/day. A. By what percentage should the BOD of the wastes be reduced to assure a healthy stream with a least 5.0 mg/L of DO everywhere? B. How far downstream from the discharge point would the lowest DO occur? C. What ultimate BOD (mg/L) of the mixture of river and wastes just downstream from the discharge point would cause the minimum D0 to be 5.0 mg/L. D. Sketch the oxygen sag curve before and after treatment recommended in (A), labeling the critical points (this can be a hand-drawn sketch if you wish, or on excel)

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