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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