Consider a lake with 100 × 106 m2 of surface area for which the only source of phosphorus is the effluent from a wastewater treatment plant. The effluent flow rate is 0.4 m3 /s, and its phosphorous concentration is 10 mg/L. The lake is also fed by a stream having 20 m3 /s of flow with no phosphorous. If the phosphorous settling rate is estimated to be 10 m/yr, estimate the average phosphorous concentration in the lake. What level of phosphorous removal at the treatment plant would be required to keep the average concentration below 0.010 mg/L

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Am acquifer is recharged by precipitation that infiltrates through fertilised fields. The concentration of nitrate in the groundwater is 1.25mg/l. Th4 nitrate is carried by flowing groundwater into a large fish pond the farmer has on her property. The average linear velocity of the groundwater is 0.087m/day and the aquifer porosity is 0.25. The aquifer has an approximate saturated thickness of 2.55m (depth of saturated soil above bedrock). The flow path into the pond is 87wide. What is the mass loading of nitrate into the pond in units of g/day?

3. A completely mixed pond of volume, V, has an influent steady-state flow, Q, entering with a BOD, concentration of L, and a dissolved oxygen (D.O.) concentration of C, (see the illustration below). Assume a first-order BOD decay constant, k,, and a first-order reaeration coefficient of k, as indicated: Q = 107 L/day k2 Co = 0.23 day 4 mg/L D.O. %3D V = 2 x 108 liters 0.20 day %3D C* =10 mg/L D.O. (saturation level of D.O.) Lo.6 V.C.L a) What would be the allowable maximum influent BOD, concentration (L) in order to maintain the steady-state dissolved oxygen concentration in the pond (C) above 2 mg/L D.O.? b) If the initial BOD, concentration in the pond (at time 0) is 5 mg/L what will the BOD, concentration be three days after the waste input is begun (with L equal to the amount you arrive at in part (a))?