10. (14 Points] A pond with a volume of 270 m2 is receving a ayw steady flow of

Question

10. (14 Points] A pond with a volume of 270 m2 is receving a ayw steady flow of 6,000 Umin of a according to non-conservative waste which contains 46 mg/L of a chemical knont G gL leaving the first-order reaction kinetics. The concentration has beeaply. over a period of time and it appears that steady-state conditions apply. at type of model should be used to solve this problem (CSTR, plug flow,or batch)? ( p b) What is the rate constant? (10 pts c) What is the residence time in the lagoon? [3 pts)

Explanation / Answer

since the pond is expected to be well mixed, the CSTR model would be more appropriate. In case of CSTR, there will be thorough mixing.

for a CSTR, based on mass balance for steady state conditions

T= space time = V/VO= (CAO-CA)/KCA

where V= volume of pond = 270 m3 and volumetric flow rate,V0= 6000L/min, 1000L= 1m3, flow rate= 6000/1000 m3/min= 6 m3/min, space time = 270/6=45 min

CAO= concentration at the inlet of pond= 46 mg/L and CA= concentration at the exit of pond=5 mg/L

Hence residence time =space time = 45 min

K= (CAO-CA)/CA*T= (46-5)/45* 5 = 0.1822/min

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