Why is the pH rising in my nitrifying bioreactor?

bfinger1 at my-dejanews.com bfinger1 at my-dejanews.com
Thu Mar 4 18:15:48 EST 1999

Hi Lesley, The influent TOC is ~ 50 ppm.  Influent alkalinity is ~ 2000 mg
CaCO3/L.  Yes, we can balance the nitrogen pretty well.  As long as we keep
teh pH<8, nitrogen leaves the system as NH4, NO3, and NO2.  Our air flow rate
is 250 X stochiametric.  I've got to believe that some really simple water
chemistry is going on, that we do not understand....

In article <7bh6ql$hj1$1 at news.tudelft.nl>,
  "Lesley Robertson" <l.a.robertson at stm.tudelft.nl> wrote:
> bfinger1 at my-dejanews.com wrote in message
> <7bh5ob$35k$1 at nnrp1.dejanews.com>...
> >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
> What else is in your influent? Organics? Bicarb?
> Does your N-balance close? That is, are you recovering all the NH4+ as
> itself of NO2-/NO3-?
> Lesley Robertson
> Delft

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