A student develops a side stream test reactor scheme to obtain µnm for nitrifyin
ID: 271609 • Letter: A
Question
A student develops a side stream test reactor scheme to obtain µnm for nitrifying bacteria. The test reactor is only 4 liters compared to a 500 m3 aeration tank. Mixed liquor is pumped from the aeration tank at a constant rate to the aerated and mixed test reactor. Influent wastewater spiked with NH4-N is also fed to the test reactor feed stream at the same rate as the mixed liquor. This is flow Qf and the total flow is QT as shown above. The hydraulic retention time of the test reactor is 6 hours. The influent NH4-N concentration of the test reactor feed stream is 60 mg/L and the test reactor effluent is 40 mg/L. By careful measurement of his SRT and nitrate production the plant engineer determines that the nitrifying bacteria concentration in the mixed liquor is 40 mg VSS/L. Thus its concentration in the test reactor feed stream is 20 mg/L. Ignore the small effect of nitrifying bacteria growth in the test reactor. The reactor DO concentration is maintained at 4.0 mg/L during the testing and the oxygen half-velocity coefficient is 0.5 mg/L. The temperature is at 20C and the nitrifying bacteria half-velocity concentration value is 0.75 mg/L. The nitrifying bacteria yield coefficient is 0.10 g VSS/g NH4-N.
What maximum specific growth rate for nitrification (i.e., µnm) is determined from the test system?
Steps:
(a) Write a mass balance on NH4-N for the test reactor, assuming the nitrifying bacteria biomass concentration in the test reactor is constant at 20 mg/L.
(b) Solve for µnm (Hint: µnm=Ynkn; Yn is given, so solve for kn based on the expression you derived from mass balance in part a).
Explanation / Answer
In attatched growth systems the waste water is in contact with a microbial film attached to the surface of a solid medium or medium.
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