[labnetwork] Reclaimed Water Issue

[Kuhn, Jeffrey G]

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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