Part1: The following characteristics of a chlorine contact chamber were measured

Question

Part1: The following characteristics of a chlorine contact chamber were measured and as the plant engineer you have been asked if the chamber is providing adequate contact time for the disinfection of the water. The effluent is intended for reclamation and must have a minimum retention time of 3 hours at the mean flowrate. The contact chamber is preceded by a rapid mix tank which appears to be adequate to provide mixing of the chlorine and water. Input data: Average flowrate Qavg 10,000 m3-d-1 Peaking factor 2.5 Width- W 2.5 m Length L 80.0 m Depth d 4.5 m Kinematic viscosity 1.306 x 106 m2 s1

Explanation / Answer

Average contact time is given by

tavg = Vchamber / Qavg = [ (2.5m)(80m)(4.5m) ]/[10000 m3d-1 ] = 0.09 d * (24h/d) = 2.16 h

Vchamber is the volume of the contact chamber.

As the minimum requirement is 3 h at average flow rate the chamber does not provide enough contact time for the disinfection of water.

Flow rate must be reduced or a bigger contactor need to be commisioned for 3 h contact time.

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