Why is the pH rising in my nitrifying bioreactor?

bfinger1 at my-dejanews.com bfinger1 at my-dejanews.com
Tue Mar 2 12:05:22 EST 1999

We have an 80 L, suspended growth nitrifying bioreactor.  The
feed stream has approximately 800 ppm ammonium and flows in at
15.3 mL/min.  The reactor is sparged with air at a rate of 50
L/min.  From experience and the literature we know the pH should
be dropping in this reactor.  The pH in other fixed-film reactors
we have operated with this feed stream has always gone to 6.5 or
lower.  We are getting approximately 40% nitrification, but the
darn pH keeps rising towards 8.  We have to periodically add acid
(HCl) to keep the free ammonia concentration below a toxic level.
 Were thinking some sort of CO2 related buffering is going on.
Any ideas on why this is occurring would be greatly appreciated

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