Question

2. A river with a pollutant concentration of 7 mg/L discharges 57 m/s into a 10,000,000 mo lake. The discharge leaving the lake has a concentration of 6 mg/L. What is the decay coefficient for the lake which has only one inlet and one outlet. a. 0.05 day-1 b. 0.06 day? c. 0.07 day d. 0.08 day? e. 0.09 day-1 f. 0.10 day-1 g. 0.11 day 1 h. 0.12 day 1 1. 0.13 day1 1. 0.14 day-1 k. 0.15 day 1 Answer:

Answer 1

Answer of part A Given data: 10000000 m3 Volume of lake Inlet concentration of pollutarnt Cin 7mg/l 11 Outlet concentration of pollutant Cout 6mg/l Decay rate K Write the mass balance equation for chemical dC dC V.- Qin. CinQout. Cout + V.- dt dT7reaction Where, = -K. C (- sign represent that K is dt/reaction decay rate)

So, dC V. Qin Cin - Qout. Cout V. K. C = dt 10000000 m3 V and Qin Qout 57m3/s 11 Put the values, dC At steady state, V. dt 0, So, Qin Cin Qout Cout - V.K. V. K. C 0 57 x 7 -57 X 6 1000000 x K x 6 0

57 K = 10000000 x 6 K 9.5 x 107 x 86400day 0.082 d 1 Hence correct option is d. 0.08 d

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