Why is the pH rising in my nitrifying bioreactor?

Reinald Roessler reinald.roessler at gmx.de
Mon Mar 8 13:07:02 EST 1999

I agree to what Dr Peter Harris said. It is true that
the pH can rise because of air stripping of carbonate:
CO2 leaves the system and the pH will rise. I am
working with a culture of nitrifiers in the laboratory
and observed that this effect depends on the air flow:
When the air flow is higher, the effect is stronger.
It might be interesting to you that the effect of
carbonate stripping on the pH can be measured even
when the density of active nitrifiers is high. If you
are measuring the pH in the reactor and if you are
adding just enough carbonate to have a constant pH,
then you will observe some corelations which may help
to understand what is going on. For example, if the
activity and density of the nitrifiers is high, then
the consumption of carbonate will be high. On the
other hand, if the air flow is increased, the
consumption of carbonate will decrease immediately,
because more CO2 is stripped.

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