[labnetwork] Fume Scrubber pH Drift

[Tom Britton]

Hello Dr. Khbeis,

We supply a fair number of fume scrubbers and here are a few tips that should solve most of the problems with scrubbers. First, the most important part of the pH system is the probe.  They last one year no more.  Always have a new probe in stock and on a regular basis replace it.    If you have to continually recalibrate the system, the probe is bad.  Next is to get the hysteresis set up correctly.  This should solve the problem.

Second.  If you over shoot on the pH, never try to buffer it back.  Send it to waste treatment and start with fresh water.  It is a logarithmic calculation and will take too much buffer to get it back and you will end up with soup.

Third.  Over flow of the scrubber is critical.  Min. .5 gpm and Max. 2 gpm.  You should always have fresh water entering the scrubber.

Hopefully this helps, but if you have any questions, please let me know.

Best Regards,

Tom Britton
Sales Manager
Critical Systems, Inc.
7000 W. Victory Road
Boise, ID 83709
Direct: 208-890-1417
Shop:   877-572-5515

[cid:image003.png at 01CD6A4D.D5309790]

www.criticalsystemsinc.com<http://www.criticalsystemsinc.com/>





From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Michael Khbeis
Sent: Tuesday, July 24, 2012 11:29 AM
To: Fab Network
Cc: Leonard Hixson
Subject: [labnetwork] Fume Scrubber pH Drift

Dear Colleagues,

I was wondering if any of you had experience in pH swings on fume scrubbers.  We inherited the facility and associated scrubber that is attached to all our gas cabinets, GRC, and fume hoods.  We have little documentation on the PM schedule and no Operating and Maintenance manuals. Basically, we are neutralizing or raising pH to 10, but then over the course of a few minutes up to several hours the system will drop to pH of <5.  Acceptable range in our AOP is 5.5 - 11. We see this swing even when tools are idle - there does not appear to be an operational indicator that tracks the system response.

System description at a high level: Age of system is 15 years.  Last media change - unknown, but plastic media looks mostly normal. Manual fill/drain, system recirculates with addition of caustic soda to balance out acidification - also manual dispense when pH is out of range.  We started a bacterial kill that was recommended in the weekly PM schedule about 3 weeks ago and starting seeing this instability in pH a week later.  We halted the PM schedule to see what impact there is, if any.

Remedies attempted:
            1) Added sodium bicarbonate to increase buffering of system.  Minimal impact.
            2) Multiple drain/flush cycles - pH was normal (7) for few minutes then dropped to 4 shortly after.
            3) pH probes were recalibrated and verified to be operational independently.

Any recommendations or anecdotal experience would be appreciated. I thank you for participating in this community.

Gratefully,

Dr. Michael Khbeis
Associate Director
Microfabrication Facility (MFF)
University of Washington
Fluke Hall, Box 352143
(O) 206.543.5101
(C) 443.254.5192
khbeis at uw.edu<mailto:khbeis at uw.edu>


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