2. onsider Example 1.5 on page 14. Design the pond size for the given boundary c

Question

2. onsider Example 1.5 on page 14. Design the pond size for the given boundary conditions. A stream with inflow rate of 5.2 m3/sec and a pollutant concentration of 10.2 mg/L will be joining the pond. A waste sewer outfall with discharge of 0.51 m3/s of waste with 130 mg/l of pollutant concentration is also confluence with the pond. The stream and sewage wastes have a decay rate coefficient of 0.20/ day. If the outgoing concentration should be maintained at 2.8 mg/L, design the pond size. (1.6 x 10 7 m3).

Explanation / Answer

Mass flow rate of stream into pond = 5.2 m3 /s x 10.2 x g /m3 = 53.04 g/s

Mass flow of stream-2 (waste ) = 0.51 m3 /s x 130 g/m3 = 66.3 g/s

total mass in = 119.34 g/s

total mass out = (5.2+0.51) x 2.8 = 15.988 g/s

decay constant * final conc * volume of pond = Totall mass in - total mass out

0.20 ( 24 * 3600 (1/s) ) * 2.8 mg / L x volume of pond = 119.34 g/s - 15.988 g/s

0.648 x10-8 g/L.s x volume of pond = 103.352 g

volume of pond = 103.352 g/s / ( 0.648 x10-8)

Thus, the volume of pond = 1.6 x1010 L = 1.6 x107 m3

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