[labnetwork] Reclaimed Water Issue

[John Shott]

Jeff:

Although we don't have an identical system, we do use a reclaim water 
system.  While I'm not sure that I can offer a great solution, I can 
tell you that your description of the problem as a "brown, slimy, 
stringy, substance" really sounds very similar to what we have seen.

Let me describe for you and others what our reclaim water system is like:

Our two, big 25,000 CFM building scrubbers consume something like 4 GPM 
... which, as you know, is a lot of water over the course of a month.  
To reduce "one-time-use" of industrial water in that system, we have a 
system that pumps the output of our acid waste neutralization tank (as 
long as the pH is between 5.5 and 10) to the scrubber and uses that 
water as the makeup water for our two scrubbers.  The feed into our AWN 
system includes waste chemicals from our wet bench cleaning stations 
(note: things containing HF are collected in a separate tank/drain 
system), DI water once it have been used, and industrial water from a 
handful of small, local tool-specific burn boxes and scrubbers.  
Although we tried it at one point, we no longer try to reclaim RO reject 
water.

In the early months of this year, in particular, we were seeing a 
significant buildup of a "brown, slimy, stringy substance" in the sump 
of our main scrubbers that was clinging to the walls, clogging the inlet 
to the spray pumps, etc.  While I think that you may have done more 
scientific analysis than we to identify this stuff, we were wondering 
whether some of our wet vacuum pumps (we still us a significant number 
of wet pumps) were "belching" pump oil vapors that were collecting in 
our scrubber system and causing this problem.  While we never convinced 
ourselves that there was any validity to our pump oil vapor hypothesis, 
we certainly did see a build up of a material that sounds a lot like 
what you were seeing.  It was sufficiently severe that we had to 
schedule a mid-year shutdown of the scrubbers to have them cleaned.  
Although I'd need to check some records to be sure, that is the time of 
the year when we often get a higher fraction of ground water mixed into 
our supply.  Most of the year, the water that we get from the Hetch 
Hetchy water system is pretty good, produces minimal scale, is easy on 
DI systems, etc ... but during the winter months we often get a higher 
mix of ground water that necessitated more frequent resin bed changes, etc.

So, while I can't offer you a solution, I think that we have seem 
something that sounds very similar to what you are experiencing and 
would be eager to coordinate our efforts to help further study this and 
come up with a good solution.  I've cced our building facility engineer 
as well as some of our lab senior technical staff in hopes of making 
them aware of this discussion.  You are welcome to send me email 
directly if there is any need for further off-line discussion, 
comparison, and brainstorming.

Thanks,

John


On 10/3/2012 10:16 AM, Kuhn, Jeffrey G wrote:
>
> Good Day All,
>
> The campus water supply at Purdue is quite hard. As a result, we have 
> seen a significant buildup of scale in our exhaust scrubber, liquid 
> ring vacuum pumps, and burn boxes. This required periodic shutdowns to 
> remove the scale, which was expensive and time consuming. We have 
> since installed a water reclaim system to capture RO, ultrafilter, and 
> EDI reject streams for use as makeup water for the systems mentioned 
> above. The water from those waste streams has been softened, thus we 
> eliminated the scaling issue.
>
> Unfortunately, in solving the scaling issue we have created a new 
> problem. A brown, slimy, stringy, substance builds up in the storage 
> tank. It clings to the tank walls, peels off in sheets, and gets 
> pumped to the points of use where it causes fouling. It settles to the 
> bottom of the storage tank and coats the tank walls and process 
> piping. We have to semi-annually drain and clean the tank to prevent 
> severe fouling at the points of use.
>
> We have verified that the material is not viable (I was surprised by 
> this). Analysis shows that it is primarily comprised of iron. Purdue 
> uses ground water that is high in iron for its potable water supply. 
> In order to protect the water distribution infrastructure, a 
> monophosphate-based agent is added to the water in order to sequester 
> dissolved iron. This helps prevent the iron from oxidizing and 
> precipitating inside the piping system. It would seem that their 
> sequestering agent is strong enough to prevent the dissolved iron from 
> being completely removed by IX in the UPW system softeners.
>
> My belief is that dissolved iron becomes concentrated at the RO in the 
> reject brine stream and then oxidizes in the storage tank, combining 
> with phosphate to form the slime we are seeing. I do not believe the 
> ultrafilter or EDI loop reject streams are major contributors to the 
> problem due to the high purity of these waters. We do not have enough 
> information yet to prove or disprove my theory.
>
> I realize that this is a rather unusual problem, but I was hoping that 
> some of you may also have installed reclaim water systems and can 
> provide some insight as to how to deal with this issue. We are 
> considering installing a filtration system, but it is expensive and I 
> am not yet convinced that it will solve the problem.
>
> Thank you in advance for your feedback.
>
> 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
>

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