<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 12 (filtered medium)"><style><!--
/* Font Definitions */
@font-face
{font-family:Helvetica;
panose-1:2 11 6 4 2 2 2 2 2 4;}
@font-face
{font-family:Helvetica;
panose-1:2 11 6 4 2 2 2 2 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman","serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.apple-tab-span
{mso-style-name:apple-tab-span;}
span.apple-style-span
{mso-style-name:apple-style-span;}
span.EmailStyle19
{mso-style-type:personal-reply;
font-family:"Calibri","sans-serif";
color:#1F497D;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dr. Khbeis,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>We have a Harrington fume scrubber at Birck. Your experience is the opposite of ours. In our case, the sump pH typically climbs to around 9.2 and stays there. We are fine with that since our POTW requirements call for a discharge pH of 5.0 – 10.0. The scrubber system was built with a caustic feed pump assuming that the pH would typically drop during normal operations, but in my five years at Birck the caustic pump has never been required. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Without knowing your facility’s chemicals, gases, or processes, I assume that your scrubber’s incoming airstream is similar to ours since we are connected to the same types of equipment. If that is true, then my first thought is that perhaps there is a gas leak somewhere in one of your cabinets or process tools since your scrubber pH drops even when tools are idle. Do you have a toxic gas monitoring system? If so, it should have identified the leak and be in alarm if it is functioning correctly. I do not think that the beaker quantities of acids typically used in fume hoods would produce enough fumes to cause the pH to drop so quickly. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>This is a bit of a long shot, but do you use ultrapure water for the scrubber sump make-up? If so, the moving airstream would quickly dissolve CO<sub>2</sub> into the water and form a dilute carbonic acid. In that event, I could see the pH dropping to as low as 3.5. The cost of producing UPW typically precludes its use in such applications but the formation of carbonic acid would indeed cause the pH to drop.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Please feel free to contact me directly should you have any additional questions and I will do my best to assist you.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-family:"Calibri","sans-serif";color:#1F497D'>Jeff Kuhn<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Facility Engineer<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Birck Nanotechnology Center<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Purdue University<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>1205 W. State St.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>West Lafayette, IN 47907<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Ph: (765) 496-8329<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Fax: (765) 496-2018<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in'><p class=MsoNormal style='margin-left:.5in'><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'> labnetwork-bounces@mtl.mit.edu [mailto:labnetwork-bounces@mtl.mit.edu] <b>On Behalf Of </b>Michael Khbeis<br><b>Sent:</b> Tuesday, July 24, 2012 1:29 PM<br><b>To:</b> Fab Network<br><b>Cc:</b> Leonard Hixson<br><b>Subject:</b> [labnetwork] Fume Scrubber pH Drift<o:p></o:p></span></p></div></div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p><p class=MsoNormal style='margin-left:.5in'>Dear Colleagues, <o:p></o:p></p><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>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. <o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>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.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Remedies attempted: <o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><span class=apple-tab-span> </span>1) Added sodium bicarbonate to increase buffering of system. Minimal impact.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><span class=apple-tab-span> </span>2) Multiple drain/flush cycles - pH was normal (7) for few minutes then dropped to 4 shortly after. <o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><span class=apple-tab-span> </span>3) pH probes were recalibrated and verified to be operational independently.<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Any recommendations or anecdotal experience would be appreciated. I thank you for participating in this community. <o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'>Gratefully,<o:p></o:p></p></div><div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p><div><div><div><div><p class=MsoNormal style='margin-left:.5in'><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Dr. Michael Khbeis<br>Associate Director<br>Microfabrication Facility (MFF)<br>University of Washington<o:p></o:p></span></p></div><div><p class=MsoNormal style='mso-margin-top-alt:0in;margin-right:0in;margin-bottom:13.5pt;margin-left:.5in'><span style='font-size:13.5pt;font-family:"Helvetica","sans-serif";color:black'>Fluke Hall, Box 352143<br>(O) 206.543.5101<br>(C) 443.254.5192<br><a href="mailto:khbeis@uw.edu">khbeis@uw.edu</a><br><br><o:p></o:p></span></p></div></div></div></div><p class=MsoNormal style='margin-left:.5in'><o:p> </o:p></p></div></div></body></html>