Applications Pg 4

Determination of Biodegradation Kenetics by Respirometry

Intrinsic kinetic tests involve adding relatively high concentrations of organic substrate to small concentrations of acclimated microorganisms so that the COD/VSS ratio typically is greater than 10. Kinetic parameters are then determined by non-linear modeling using well-known relationships between biological growth and oxygen uptake. An example is shown below:


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In this example, 700 mg/L of chemical COD was added to a test culture containing 45 mg/L of active biomass. Modeling showed the following kinetic parameters: Yield coefficient, Yg = 0.42 mg VSS/mg COD removed; specific substrate conversion rate, qm = 0.35 mg COD/mg VSS/hr; specific growth rate, ╬╝max = 0.10 g VSS/g VSS-hr.


Extant kinetic tests involve adding relatively low concentrations of organic substrate to large concentrations of biomass so that the COD/VSS ratio usually is less than 0.1. Extant kinetic parameters are then determined by using non-linear modeling techniques. An example is shown below:

This example shows the results of dosing an anaerobic culture with a waste stream from a chemical production plant indicating the presence of three major groups of organic constituents. One group of readily biodegradable organic constituents was oxidized within one hour, a second group within 3 hours, and biodegradation of the third group was continuing after 6 hours. Kinetic modeling showed that 72% of the active biomass was associated with the first group, 26% with the second group and 2% with the third group. Resulting kinetic parameters are shown in the table below.

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