[labnetwork] Requesting expertise/ experience with Scrubber by-products in Fab.

[Kuhn, Jeffrey G]

Robert,

We have a large Harrington scrubber here at Birck, but it operates in a somewhat different way than what you describe. The "scrubbing agent" in our case is circulated water - not NaOH. Caustic is used only as needed to maintain the pH within the desired range. Ideally, you would want your circulating water to have an approximately neutral pH and not add caustic until it drops below at least 7.0. What I believe you are referring to when you mention the "lower tank" is actually the sump itself. Perhaps your design is different??? Just for reference, our scrubber is rated for 42,000 cfm and our circulation rate is about 400 GPM.

We perform monthly bacteria testing using dip slides and, when needed, add a measured amount of isothazilinone-based biocide to kill the bacteria. This is only needed once or twice per year, usually in the summer months. We have never had to shut down for removal of the types of biological material you mention. Our fouling issues were always related to lime scale due to hard water make-up, but that issue has been mitigated by the introduction of softened make-up water.

In my opinion, you should never need to deal with removal of biological material if your scrubber is operating correctly. I totally agree with Rizik in his response below as to the need for answers to his questions. I would also add that you need to control both your conductivity via periodic blow-down, and should minimize your cycles of concentration (depending on the make-up water parameters) to around 2-3 cycles. You should not let the pH get too high. Around pH = 9.5 is the upper limit I'd like to see. It is not so much the pH of the water that does the scrubbing, but rather the water itself. The addition of caustic is simply to keep the pH within certain limits so it can be discharged to your POTW (or WWT system if you have it), and to protect internal components from corrosion.

Regards,

Jeff Kuhn
Facility Engineer
Birck Nanotechnology Center
Purdue University
1205 W. State St.
West Lafayette, IN 47907
Ph:  (765) 496-8329
Fax: (765) 496-2018



From: labnetwork-bounces at mtl.mit.edu [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Rizik
Sent: Sunday, November 25, 2012 9:44 AM
To: 'Robert Pollina'; labnetwork at mtl.mit.edu
Subject: Re: [labnetwork] Requesting expertise/ experience with Scrubber by-products in Fab.

Please try to answer the following questions before we provide our recommendation:


1.       Daily removal of 5-gallons of concentrated solution - Do you mean caustic solution? If yes, what is the concentration?

2.       Is NaOH injection to the recirculating water stream being controlled by a pH Controller to maintained a predetermined pH level?

3.       What are you trying to scrub?

4.       What is the makeup water flow rate?

5.       Doe you control Total Dissolved Solids in the recirculating water? If yes, is it controlled by a TDS sensor & controller?

6.       Does the recirc water go through a periodic purge cycle or does it continue to circulate and water is replenished only when water level in the basin drops?



Rizik Michael, PE
Principal
Integrated Engineering Services
Office: +408 261 3500, Ext. 201
Cell:      +408 718 0927


From: labnetwork-bounces at mtl.mit.edu<mailto:labnetwork-bounces at mtl.mit.edu> [mailto:labnetwork-bounces at mtl.mit.edu] On Behalf Of Robert Pollina
Sent: Wednesday, November 21, 2012 5:32 AM
To: labnetwork at mtl.mit.edu<mailto:labnetwork at mtl.mit.edu>
Subject: [labnetwork] Requesting expertise/ experience with Scrubber by-products in Fab.

Good morning,

  I maintain the exhaust Scrubbers serving our wet-benches and fumehoods here at the Nanofabrication Lab at the University of Michigan.
Exhaust air passes through our Harrington Scrubber where Sodium Hydroxide solution is sprayed over a "whiffle-ball-like" material, and a favorable PH is reached before the air is vented to atmosphere.  The NaOH solution is collected in a lower tank and recirculated to the spray heads. PH sensors and Conductivity sensors call for more NaOH and city supplied fresh water as needed.

  Problem: Large amounts of Fusarium , Negative rod and Rototurula bacterias and fungi are created in the tank and must be removed to keep the Scrubber operating properly. This by-product is removed almost daily, often exceeding five gallons of concentrated solution.

  I'm hoping someone has experience with this same equipment and unwanted Fusarium growth.
How do we better control production of this by-product?   What are the proper safety procedures for maintenance staff?
Are there other issues I am not aware of concerning this equipment,  its operation, maintenance and safety?

  Any assistance in this matter would be greatly appreciated.

Robert Pollina
University of Michigan
Electrical Engineering and Computer Science
Nanofabrication lab
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