A lake with a constant volume of 10 x 10^6m^3 is fed by a pollution-free stream with a flow rate of 50 m^3/s. A factory discharges 5 m^3/s of a non conservative waste with a concentration of 100 mg/L into the lake. The pollution has a reaction rate coefficient K of 0.35/day. Assuming the pollution is well mixed in the lake, find the steady-state concentration of the pollution in the lake.

Poorly treated municipal wastewater is continuously discharged directly into a lake. The discharge from the wastewater plant into the lake occurs at a flow of Qd = 1 m3/hr. The concentration of phosphate (PO43, M = 95 g/mol) in the discharge flow (Cxd) that is decaying with first-order kinetics is 100 mg/L. The lake is a well-mixed water body of 100 m3. (Phosphate is naturally uptaken by algae with a first- order decay rate constant equal to 0.20/day.) The concentration of phosphate in the incoming river (Cx,r) is 10 mg P/L. The incoming river flow rate is Q, = 10 m3/hr. %3D a) Which of the following equations represent the correct mass balance equation? O va = CxQr - CxdQd -QoutCxvout" kCx,outV %3D O 0 = Cx,Qr + CxdQd -QoutCxvout" kCx,outV X,r O 0 = CxQr + CxdQd -QoutCxvout- kV O 0 = Cx,dQr + Cx,,Qd -QoutCxout- kCxoutV

Fifteen kilograms of contaminant is spilled into a stream 5 m wide and 1 m deep. The flow in the river is 2 m3/s, the longitudinal diffusion coefficient is 3 m2/s, and the decay constant is 50 d−1.  A) Determine the maximum concentration in the stream at a drinking-water intake 1 km downstream from the spill. B) How would this concentration be affected if the decay constant is actually one- half of the estimated value?

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Flow rate:  1.5 m3/s Pollution: pesticide permethrin Lake size: 100m x100m x 2.5m Steady state concentration of permethrin leaving the lake is 1.4 ppm Average cross-sectional area of the river is 2.7 m2. Half-life of permethrin in this environment is 19 hrs. What is the concentration of permethrin entering the lake and what distance downstream of the outlet would the concentration be less than 1 ppm?

15.10. Name the six most important oxidants in the aquatic environment, and how the redox p po- tential regulates their reactivity.

An identified source of irrigation water has ion concentrations of Nat, Catt and Mgt as 20, 10 and 8 mill-equivalent per liter, respectively. The SAR of this water is approximately:

A desalination plant produces 10,000 m3/day of brine with concentration of 80 g (gram)/L. This brine will be thrown into the ocean. But the concentration has to be  lowered to 60 dS/m. How much seawater should be mixed with the brine if the seawater  has a salinity of 3%.? Calculate how much salt is in the brine in Tons/day.

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