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CO2 and BOD



Dear P2Techies:

A client makes high quality woolen goods.  They are permitted for, and use,
CO2 for neutralization (to lower the pH) in their onsite treatment plant.
The CO2 forms carbolic/carbonic acid which lowers the pH.  The pH has to be
kept low in the process tanks in order to keep the colors in the fabric.  As
a buffer, and for final pH adjustment, they add granular citric acid to the
final contact tank.  The problem is, the citric acid dramatically increased
the BOD level and Packard is charged for sewer use based on the pounds of
BOD they're discharging.  It's expensive.

Apparently, it's extremely difficult, even with monitoring probes, to match
the citric acid volume to the exact pH in order to reduce the citric acid
(and BOD) loading of the discharge.  There's a pH alarm on the final tank
and when it goes off, the workmen quickly shovel the citric acid into the
tank.  They're using 6,000 to 10,000 lbs of the stuff per year.

Good P2 calls for better process monitoring/control, either mechanical or
human as that's the real cause of the problem.  She said she'd consider a
visit from our office, but in the meantime,  could we research another
chemistry to help them adjust their pH.  The citric acid was already a P2
strategy since it was purchased to replace a RCRA hazardous acid.  Is there
another non-hazardous acid treatment which wouldn't result in the high BOD
problem?

Thanks.
Lin K Hill
NHPPP
603-271-2902