Suppose you are to design a chlorination tank for killing microorganisms in the

Question

Suppose you are to design a chlorination tank for killing microorganisms in the efuent from a wastewater treatment plant. It is necessary to achieve 99.99% kill in a wastewater ow of 100 m3/hr. Assume the disinfection is a rst-order reaction with a rate constant of 0.2 min1. A) First, calculate the tank volume if the contact tank is a CMF reactor. B) Then, calculate the tank volume if the contact tank is a plug-ow reactor. C) Last, what is the retention time of both reactors? *Please answer all parts of the question*

Explanation / Answer

1) The charactestic CMF equation for a first order reaction is

KT= XA/(1-XA), T= Rention time

XA= conversion =0.9999, K= 0.2.min ( Rate constant)

KT= 0.9999/(1-0.9999)=9999

T= 9999/0.2 =49995 min

when the tank is PFR, the characteristic equation is

-ln(1-XA)= KT

-ln(1-0.9999)= 0.2*T

T= 46.05 min

but T= V/VO =46.05

V = volume of reactor and Vo= 100m3/hr= 100/60 m3/min=1.67 m3/min

T= 46.05 =V/1.67

V=46.05*1.67=76.9 M3

c) retention times : CSTR: 49995 min and PFR = 46.05 min

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