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In: Civil Engineering

# Consider a lake with 65 × 106 m2 of surface area for which the only source...

Consider a lake with 65 × 106 m2 of surface area for which the only source of phosphorous is the effluent from a wastewater treatment plant. The lake is receiving a flow rate of 1 m3/s from the wastewater treatment plant, which has a phosphorous concentration of 20 mg/L. The lake is also fed by a stream having 20 m3/s of flow with no phosphorous in it. If the phosphorous settling rate is estimated to be 10 m/yr. (a) Write down the phosphorous mass balance equation for the lake and draw a control volume diagram for the lake showing influent streams, effluent streams, point-discharge source. (b) Estimate the average phosphorous concentration in the lake at steady-state. (c) Bonus Q: What level of phosphorous removal at the treatment plant would be required to keep the average lake concentration below 0.02 mg/L?

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