Water Treatment by Ion Exchange

I just got a call from an engineer at another office of ours. He's recruiting me to help him with a water treatment project. There is a community well that serves about 50 residences. The well water has issued with hardness and nitrate.

They are proposing to put in a dual IX system for removing both the cations (hardness) and anions (nitrate). A water treatment company is developing the IX system. We will be responsible for siting the IX package, the piping in and out of it, and a disposal field for the backwash water.

Has anyone had an experience with IX systems? I know the concepts from college but haven't done much water treatment on the job so this is pretty new to me. Anything special I should know about? Any particular challenges regarding disposal of the backwash water? Fortunately I don't have to worry about the design or O&M of the actual unit.

^^^ It has been many a year since I have had to look at Ion Exchange issues. From my end of design issues, the ion exchange unit is rented from a vendor and they service it.

Do you have access to the text Water Quality and Treatment: A Handbook of Community Water Supplies, 4th Edition, American Water Works Association (ISBN 0070015406). I used this text when I took Potable Drinking Water Design in college. Excellent text - many people in the field call it "The White Book" :true:

Chapter Nine covers Ion Exchange and provides considerable detail regarding removal of nitrates.

Feel free to PM if you have any further questions.

JR

So I take it sewer disposal is not an option? Ask the IX supplier for their best guess on the contents of the backwash effluent. They should be able to provide actual lab results from similar installations. I would think your only problem might be chlorides, if your disposal field is located in any kind of swelling clay. From what I recall, high chloride content can cause some clayey soils to seal up. Around here, our typical wastewater is around 1500 to 3000 ppm salinity (due to the nasty public water), and that doesn't seem to be enough to clog up our clayey soils. So I'm not sure how high it needs to get to cause a problem.

Just make sure you know what permits are required. Maybe the nitrogen loading could be a problem, if the local regulators watch for that in underground disposal. (I'm guessing they do, if it's alreayd a problem in the well water.)

Also ask the IX supplier what other chemicals might be added, and get the MSDS sheets. The regulators will ask for that, if they're on top of their game.

I've got a couple wastewater and water chem books from college that explain IX. I always reember the equations were a real pain in the ass to solve.

As for the permits required: I'll need a permit to construct from the water supply division, and an indirect discharge permit fo the backwah effluent from the wastewater division.

I've heard that chlorides can cause soil swelling, but based on past history at the site, the soils are pretty sandy. As for the unit itself, there is a vendor designing and manufacturing the unit based on lab tests of water samples on site. We need to design a site for the unit to go, arrange all the piping connection, and design the leach field. And get all the permits from VT DEC.

I'm thinking it should be an interesting project, and I'm excited because its actually what I went to school for, as opposed to all the site design/land development stuff I generally do.

Sandy soils should not be a problem - you can probably just design the leach field based on clear water percolation rate, with a reasonable safety factor. The only real problem would be if the regulators are worried about nitrogen loading from the discahrge and want you to model it or something like that. "Indirect discharge permit?" I haven't heard of that phrasing before. I am guessing it's the same as our land disposal of wastewater permits.

The water supply permit will probably mosly be answered by your vendor. Aside from that, they'll probably just look at your piping design real closely for cross-connections and backflow preventers, and make sure you provide all the sampling points they want.

'indirect discharge' is the term they use for leach fields and other similar systems where the wastewater is distrubuted and allowed to perc into the ground. As oopsed to a piped outfall I guess.

The state's already worried about nitrates at the site. If the well concentrations get any higher, they will exceed the MCL, hence this sytem. I'm sure we'll design the leachfield to be outside whatever setback area is erquired from the well.

It's funny for me to hear people say ... we are concerned about something like nitrates or sulfates in our groundwater because I am used to dealing with ethylhexyltetramethyldeath. I was just chastised about passively addressing iron in groundwater (concentration = 1 mg/L). I was like ... you are concerned about iron, an essential nutrient that people take in a multivitamin when you have 8 ft of vertical saturation of trichloroethylene free product???!!!!!! :huh:

As far as nitrates, my understanding is that there are screening methods (e.g. conductivity, activitity, color, etc.) that alert you as to whether the resin bed needs to be regenerated. As long as you have adequate safeguards (and a good field guy) you should be in like flynn.

Again, I only know about the exchanges based on contaminated groundwater recovery and treatment. Typically I am looking at the competing cations to look at the feasibility for implementing ion exchange. In many cases because of the scale-of-economy factor it is just easier to add a sequestering agent up front and an intermediate floc/coagulation process on the back-end of the treatment train. It is a bit messier because you are now generating sludges that need to be collected, removed, and disposed of but typically wins based on cost (scale of economy) and practicability for CONSISTENTLY achieving the groundwater protection standard.

Good luck - sounds like an interesting project!

JR

As far as nitrates, my understanding is that there are screening methods (e.g. conductivity, activitity, color, etc.) that alert you as to whether the resin bed needs to be regenerated. As long as you have adequate safeguards (and a good field guy) you should be in like flynn.

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Fortunately, that's not our problem. Whoever operates their water system will be in charge of that. I think about as far as we will go will be to take some samples when the system goes online so we can make a statement of initial compliance, then inspect it annually.
I don't know what it's like where you guys are, but in VT those are usually two of the permitting criteria. After something is built and operational, the engineer inspects it and file a 'certification of initial compliance', along with an as-built set of plans if changes have occured. Then there's typically an annual inspection performed by an engineer on each element of the permitted system. A report is filed with the DEC, who then issues a list of any remedial work the permitee has to do. You basically end up being the state's eyes and ears at that point.

I am used to dealing with ethylhexyltetramethyldeath

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I forget - is that asssociated with petroleum or metal plating industry?

VTEnviro said:

I don't know what it's like where you guys are, but in VT those are usually two of the permitting criteria. After something is built and operational, the engineer inspects it and file a 'certification of initial compliance', along with an as-built set of plans if changes have occured. Then there's typically an annual inspection performed by an engineer on each element of the permitted system. A report is filed with the DEC, who then issues a list of any remedial work the permitee has to do. You basically end up being the state's eyes and ears at that point.

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That is essentially what happens with the remedial systems that I review/approve. The one major departure is that my state's most liberal reporting period is semiannual - there are very few projects that report on an annual basis and even then they must be very well established to be granted such a wide berth. I depend heavily on the RP's consultants to adequately characterize and report the progress but I usually end up in a position to be disinclined to acquiesce with thier view points :17: Actually, that's not true but I do find myself often interpreting data trends somewhat differently - the real question is whether it substantially alters the 'best' approach to clean-up.

VTEnviro said:

I forget - is that asssociated with petroleum or metal plating industry?

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My program is RCRA hazardous waste so it crosses numerous industries - any industry that is likely to have a discharge of ... hazardous waste. However, my experience base is primarily with chlorinated solvents. I studied immiscible fluids in porous media extensively in school (DNAPLs primarily) and that carried over to the projects I would be assigned. I appreciate and understand the benefits, limitations, and abuses of applying natural attenuation to projects. Many of my colleagues call it natural procrastination, but I believe it really does have a place in risk-based clean-ups if applied under the right circumstances. What it boils down to is thinking outside of the box - something not many people are willing to do these days.

Funny thing, these days many of my projects are calling for restrictive covenants (land use restrictions) with engineering controls and then calling it even. Probably not a bad choice for some facilities, but the judicious application of these institutional controls has brought the inclination to submit innovative, techie approaches to a stand-still.

JR

8 feet of TCE free product???? What kind of facility could release that much TCE????

^^^ Regional bulk distributor.

Also keep in mind TCE is a DNAPL so when it is in the immiscibile phase it is driven (down) by gravity until it hits an impermeable barrier, typically clay in Florida. It isn't like your petroleum products that will float at the surface of the water table, so in terms of describing it as 'free product' it is probably more accurate to say - "There is 8-ft of saturated aquifer thickness permeated with immiscible phase TCE."

JR

8 feet?!?!? That's a swimming pool of TCE.

Glad I'm not working on that project, or the land owner who's problem it is.