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, somewhere downstream, equal to 3.0 mg/L (see Figure P5.27). Just below the discharge point, the DO of the stream is equal to the saturation value of 10.0 mg/L.

FIGURE P5.27

(a) By what percent should the BOD of the wastes be reduced to assure a healthy stream with at least 5.0 mg/L of DO everywhere? Would a primary treatment plant be sufficient to achieve this reduction?

(b) If the stream flows 60 miles per day, has a reaeration coefficient kr equal to 0.80/day, and has a deoxygenation coefficient kd of 0.20/day, how far downstream (miles) would the lowest DO occur?

(c) What ultimate BOD (L0 mg/L) of the mixture of river and wastes/just downstream from the discharge point would cause the minimum DO to be 5.0 mg/L?

(d) Sketch the oxygen sag curve before and after treatment recommended in (a), labeling critical points (DOmin location and value).

Transcribed Image Text:

(1/8m) (4 10.0 3.0 60 mi/day k=0.80/d ka=0.20/d DO (1/8m) (4 10.0 3.0 60 mi/day k=0.80/d ka=0.20/d DO

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Given data Saturation dissolved oxygen of st... View the full answer