A wastewater is flowing into a biological processing unit at a flow rate of 100

Question

A wastewater is flowing into a biological processing unit at a flow rate of 100 MGD The concentration of BOD in the wastewater is 100 mg/L. The wastewater will be treated through a set of two reactors in series. The first reactor has a retention time of 10 hours and the second reactor has a retention time of 4 hours. Apply a substrate utilization rate (rut) of-50 mg BOD L-1d-1 and atof-20 mg BOD L-41 in the second reactor. Flow is recycled from the effluent of the second reactor back to the inflow of the first reactor (a) Determine the effluent concentration if the recycle rate is 0.25 Qinflow (b) Determine the effluent concentration if the recycle rate is 2 Qinflow (c) How does recycle effect effluent concentration? 2.

Explanation / Answer

Flow rate = 100 MGD = 378541180 l/d

BOD concentration in waste water = 100 mg/l

a) considering 0.25Qinflow = 378541180 *0.25 = 94635295 l/d

first reactor utilization rate = 50 mg/ld and second reactor = 20 mg/ld

Total = 70 mg/ld

Therefore 30 mg/ld is remaining after first and second reactors

Effluent concentration = 30 mg/l and amount = 30 * 94635295 = 2839058850 mg.

b) considering 2Qinflow = 2*378541180 = 757082360 l/d

Effluent concentration = 30 mg/l

and amount = 30 * 757082360 = 22712470800 mg.

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