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

[Robert Pollina]

Jeff,
  Thank you so much for the comments/ suggestions.  I'm considering every
suggestion made.  I agree our make-up water is the first place to begin.
 Although I test and calibrate ph sensors monthly it has been over a year
since they were installed, I'll order new sensors today.  I'm searching for
fumehood contaminents and other potential problems up-stream of our
Scrubber that may be "seeding" the sump tank.  I will monitor the initial
and operating conductivity of our sump water.  I am looking into
retrofitting  our system to use softened water instead of city-water.  The
"whiffle-ball" media is clean and functioning properly, mist screens are
clean and unobstructed.  I will purchase a biocide as suggested.
Thanks again, I'll post an update to Labnetwork and let you know how it
goes.
-Robert

On Tue, Nov 27, 2012 at 4:31 PM, Kuhn, Jeffrey G <kuhn1 at purdue.edu> wrote:

>  Robert,****
>
> ** **
>
> Based on your description of the airstream entering your scrubber, you
> should not have this problem - but obviously you do. I have a few questions
> and comments:****
>
> ** **
>
> **·         **Your conductivity setpoint of 5000 uS concerns me for two
> reasons:****
>
> **o   **Assuming your make-up water conductivity is around 750 uS
> (typical for the Midwest), then you are running between six and seven
> cycles of concentration. That creates a lot of nutrients in the scrubber
> sump that bacteria can use to grow and multiply. The 7.5 to 9.5 pH you
> mention is a good operating range, but is also ideal for bacteria growth
> under those conditions.****
>
> **o   **If you are using high-hardness potable water for sump make-up
> (again, typical for the Midwest), then you will almost certainly create
> scaling on the scrubber packing as the calcium and magnesium precipitate
> out. This scale will eventually decrease the airflow through the packing by
> clogging the air paths and will result in a gradual increase in your
> exhaust fan speed as it tries to maintain your static pressure
> requirements. ****
>
> **·         **My biggest curiosity lies in where the bacteria are coming
> from. Are there any BSL hoods tied into the scrubber, or are there any
> other biological agents that could be “seeding” the sump?****
>
> **·         **Is there any way that free acids, bases, etc. could be
> getting into the sump? Typically, the small amount of fumes from lab hoods
> should not cause a rapid change in pH or conductivity.****
>
> **·         **Is your pH and conductivity instrumentation calibrated
> routinely? Conductivity instruments tend to be relatively stable but pH
> instrumentation should be calibrated monthly – even more often if history
> indicates that it is necessary. pH electrodes should be replaced at least
> annually.****
>
> **·         **When you drain and refill your sump, what conductivity and
> pH numbers do you see initially and how rapidly do they change?****
>
> **·         **Are you certain that the scrubber is of sufficient size to
> handle the load (CFM, static pressure, face velocity, etc)? ****
>
> ** **
>
> I’d like to make the following recommendations as a starting point:****
>
> ** **
>
> **·         **Measure the conductivity of your make-up water, then set
> your blow down to maintain the sump at 3X that value initially. Run that
> way for a while and see how it impacts the problem.****
>
> **·         **Verify that your pH and conductivity instrumentation has
> been calibrated and replace the pH sensor if it has aged beyond a year or
> so.****
>
> **·         **Audit your system for the possible introduction of liquids
> or other materials from sources other than the fume hoods. ****
>
> **·         **If you do data collection through Siemens, Johnson
> Controls, etc., trend the fan operation to see if it is speeding up over
> time with no additional demands being placed on the exhaust (an indication
> that fouling is occurring).****
>
> ** **
>
> If you try these things, please let us know if there are any improvements.
> ****
>
> ** **
>
> Good luck!****
>
> ** **
>
> 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 *Robert Pollina
> *Sent:* Tuesday, November 27, 2012 7:37 AM
> *To:* labnetwork at mtl.mit.edu
> *Subject:* [labnetwork] Fwd: Requesting expertise/ experience with
> Scrubber by-products in Fab.****
>
> ** **
>
> Struggling with Scrubber equipment and sending e-mails!  Hope you saw this
> e-mail Michael and Jeff.****
>
> ---------- Forwarded message ----------
> From: *Robert Pollina* <rpollina at umich.edu>
> Date: Mon, Nov 26, 2012 at 7:50 AM
> Subject: Re: [labnetwork] Requesting expertise/ experience with Scrubber
> by-products in Fab.
> To: Rizik <rizik at intengr.com>
>
>
> Michael,****
>
> Thanks for the reply.****
>
> I will provide some details of our operation.****
>
>   The five gallons of by-product I mentioned refers to a yellow-brown skin
> of Fusarium fungus and Negative Rod bacteria that forms on the surface of
> the recirculating tank.  This material forms, grows and clogs the spray
> heads and pumps in the system.  This material is removed by hand each day.
> ****
>
>   The ph of the water in the recirculating tank is maintained between 7.5
> and 9.5.  The ph is controlled with a ph sensor in the tank and an
> automated Sodium Hydroxide (50% solution) feed pump system.  A constant
> flow of fresh "city provided" water is maintained at 1/2 gallon per minute
> to make up for evaporation.****
>
>   We use this Scrubber system to scrub the acidic fume hood exhaust air
> from our labs.  ****
>
>   A conductivity sensor helps to maintain a solution that can efficiently
> deliver the desired result.****
>
>   A manual "blow-down" valve adds fresh water to the system while ejecting
> old tank water to the drain to assist in maintaining a conductivity reading
> below 5000u.****
>
> The Scrubber tank is completely drained and refilled each week as total
> dissolved solids always exceeds the ability for a quick blow-down to lower
> conductivity to a good level after 5-7 days of lab operation. ****
>
> An in-line strainer  collects the same material and is cleaned daily.****
>
>   I hope this furthers your understanding of our equipment (Harrington
> Scrubber)  and procedures.   Looking forward to hearing from you, let me
> know if more info is needed****
>
> -Robert.****
>
> ** **
>
> On Sun, Nov 25, 2012 at 9:44 AM, Rizik <rizik at intengr.com> wrote:****
>
> 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] *On Behalf Of *Robert Pollina
> *Sent:* Wednesday, November 21, 2012 5:32 AM
> *To:* 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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