chloride toxicity: anion exchanger for chloride removal

[darknectar]

Hi folks, this is my first post! I'm not a reefer, rather I'm a professional aquaponic/vermiponic farmer... I hope you don't kick me out! A lot of my education about water chemistry has come from reef forums...you folks seem to be a bit more chemistry oriented than the farming community.

We chronically have chloride toxicity in our nutrient solution. We're in San Diego and city water has about 140ppm chloride, 120ppm sodium, 8.2pH, EC 1000 uS/cm, 150ppm carbonate, 120ppm Ca...etc. Veggies don't take up much sodium or chloride, so it accumulates in our reservoir until it becomes toxic.

We don't want to remove everything from the water, just the sodium and chloride. (the thread is named "chloride removal" because there's more info about sodium removal out there, and I can solve that issue separately) The calcium and carbonates are beneficial. We also don't like wasting 50% of our water with RO. We use 400 gallons/day and water is expensive here. We also can't afford to constantly be throwing away cuft of DI resin. Farmers don't make anything, everything has to be the highest economy.

Here's what I'm thinking...let me know if you think this will work, as it would be an expensive experiment.

1)
We would use a water softener system, where the brine canister contains potassium bicarbonate (KHCO3, highly soluble, pH 8.2) and the exchange canister would contain cation and anion resin beads. The idea is that the potassium gets exchanged with the sodium, and the carbonate gets exchanged with chloride.

2)
We would use two water softeners in sequence. First one with brine of Potassium Chloride(already proven) or Calcium Chloride(?) and exchange canister with cation resin. Second one with brine of potassium carbonate(KCO3, ph 11.5 ) or potassium bicarbonate(KHCO3) or potassium hydroxide or calcium hydroxide or calcium oxide or wood ash (wood ash contains everything that was just listed, and is caustic once dissolved...we like free materials)


If this can work, which cation and anion resins should we purchase? If it can't work, how would you create an economical solution for removing sodium and chloride?

Thank you!

 

[Dan_P]

Hi folks, this is my first post! I'm not a reefer, rather I'm a professional aquaponic/vermiponic farmer... I hope you don't kick me out! A lot of my education about water chemistry has come from reef forums...you folks seem to be a bit more chemistry oriented than the farming community.

We chronically have chloride toxicity in our nutrient solution. We're in San Diego and city water has about 140ppm chloride, 120ppm sodium, 8.2pH, EC 1000 uS/cm, 150ppm carbonate, 120ppm Ca...etc. Veggies don't take up much sodium or chloride, so it accumulates in our reservoir until it becomes toxic.

We don't want to remove everything from the water, just the sodium and chloride. (the thread is named "chloride removal" because there's more info about sodium removal out there, and I can solve that issue separately) The calcium and carbonates are beneficial. We also don't like wasting 50% of our water with RO. We use 400 gallons/day and water is expensive here. We also can't afford to constantly be throwing away cuft of DI resin. Farmers don't make anything, everything has to be the highest economy.

Here's what I'm thinking...let me know if you think this will work, as it would be an expensive experiment.

1)
We would use a water softener system, where the brine canister contains potassium bicarbonate (KHCO3, highly soluble, pH 8.2) and the exchange canister would contain cation and anion resin beads. The idea is that the potassium gets exchanged with the sodium, and the carbonate gets exchanged with chloride.

2)
We would use two water softeners in sequence. First one with brine of Potassium Chloride(already proven) or Calcium Chloride(?) and exchange canister with cation resin. Second one with brine of potassium carbonate(KCO3, ph 11.5 ) or potassium bicarbonate(KHCO3) or potassium hydroxide or calcium hydroxide or calcium oxide or wood ash (wood ash contains everything that was just listed, and is caustic once dissolved...we like free materials)


If this can work, which cation and anion resins should we purchase? If it can't work, how would you create an economical solution for removing sodium and chloride?

Thank you!

Have you consider doing this on small scale to test various resins?

 

[Randy Holmes-Farley]

Do you know that very high potassium and bicarbonate is ok? You may just trade one problem for another (such as calcium insolubility).

I personally think a better idea is a full normal di or ro/di and then add back the ions you think you want instead of what’s randomly left over from tap water.

process 1 will remove most things and replace them with potassium and bicarbonate, but will be hard to monitor for depletion.

In process 2, KOH in the second one will leave the final pH quite high.

 

[Spare time]

You don't have to throw away waste water. Its just water that went through a sediment and carbon filter. I use my waste water to water plants and flowers so maybe you could run the waste water through something extra if you are concerned about the contents there?

 

[darknectar]

Have you consider doing this on small scale to test various resins?

not yet, but probably will...

 

[darknectar]

Do you know that very high potassium and bicarbonate is ok? You may just trade one problem for another (such as calcium insolubility).

I personally think a better idea is a full normal di or ro/di and then add back the ions you think you want instead of what’s randomly left over from tap water.

process 1 will remove most things and replace them with potassium and bicarbonate, but will be hard to monitor for depletion.

In process 2, KOH in the second one will leave the final pH quite high.

Yes, our biggest supplement to our nutrient program is potassium bicarbonate. At a point it would become excessive, but if for example we were to calibrate the exchange so that about 50% of sodium is replaced with potassium and 50% of chloride is replaced with bicarbonate, I think that would put pretty much everything in balance...like sodium and chloride would enter our reservoir at the same rate the plants take it up (so it won't accumulate) and we would no longer need to supplement potassium bicarbonate.

Yes, we can handle a higher pH and higher OH or CO3. Nitrification is extremely efficient in our system and we always are adding calcium carbonate magnesium carbonate and potassium bicarbonate, to keep the pH at 6.0. Without supplemented carbonates, the pH would crash and all biological processes would stop.

What were you referring to "calcium insolubility"? I'm aware that calcium carbonate is not very soluble, but we have plenty of naturally occurring acids in our system that dissolve the calcium carbonate, basically at the rate we need it to dissolve so that the pH stays around 6.0.

What do you mean by "hard to monitor"? From my understanding, water softener systems somehow know when to flush with brine.

 

[darknectar]

You don't have to throw away waste water. Its just water that went through a sediment and carbon filter. I use my waste water to water plants and flowers so maybe you could run the waste water through something extra if you are concerned about the contents there?

unfortunately, all our plants are for sale, and we need them to be top quality. Sure, we can give waste water to plants, which would be good enough for a home garden, but for top quality produce, it won't work. With the exception that if it were to rain regularly (which it doesn't in San Diego), the rain would flush out toxicities. Unfortunately, around here that's not very possible especially now entering three consecutive years of La Nina, which means 1/2 as much annual rain as "normal" for California

 

[Randy Holmes-Farley]

Yes, our biggest supplement to our nutrient program is potassium bicarbonate. At a point it would become excessive, but if for example we were to calibrate the exchange so that about 50% of sodium is replaced with potassium and 50% of chloride is replaced with bicarbonate, I think that would put pretty much everything in balance...like sodium and chloride would enter our reservoir at the same rate the plants take it up (so it won't accumulate) and we would no longer need to supplement potassium bicarbonate.

Yes, we can handle a higher pH and higher OH or CO3. Nitrification is extremely efficient in our system and we always are adding calcium carbonate magnesium carbonate and potassium bicarbonate, to keep the pH at 6.0. Without supplemented carbonates, the pH would crash and all biological processes would stop.

What were you referring to "calcium insolubility"? I'm aware that calcium carbonate is not very soluble, but we have plenty of naturally occurring acids in our system that dissolve the calcium carbonate, basically at the rate we need it to dissolve so that the pH stays around 6.0.

What do you mean by "hard to monitor"? From my understanding, water softener systems somehow know when to flush with brine.

I don't think partial replacement is going to work well. It's going to replace most of it until it depletes, then replace little of it.

The calcium insolubility I'm referring to is the calcium in the water or the soil with the high bicarbonate in the exchanged water.

What is the TDS in the tap water to be treated? If it is low, this may not be a big deal, but if it is high, I'm concerned you are underestimating both the potassium and the bicarbonate that would be present.

 

[darknectar]

I don't think partial replacement is going to work well. It's going to replace most of it until it depletes, then replace little of it.

The calcium insolubility I'm referring to is the calcium in the water or the soil with the high bicarbonate in the exchanged water.

What is the TDS in the tap water to be treated? If it is low, this may not be a big deal, but if it is high, I'm concerned you are underestimating both the potassium and the bicarbonate that would be present.

thanks for your continued help.

What I mean by partial replacement is that half of our water does not go through the ion exchanger and half does.

The TDS is about 450ppm.

We can handle an increase of carbonate/bicarbonate. Our carbonate level is 150ppm. We can probably go up to 250ppm CO3 without negative effects. We have 140ppm chlorides and want to get it below 70ppm

How about this for an economical solution? If we were to only use an anion exchanger and use sodium bicarbonate to flush, we should not see an increase in sodium, and most of the chloride ions should be swapped for bicarbonate. correct me if I'm wrong, but that would +140ppm of bicarbonate, which has half as much potential for hydrogen as carbonate...so the 140ppm of bicarbonate has the same ability to neutralize an acid as 70ppm of carbonate? so that's the equivalent of 150ppm + 70ppm = 220ppm carbonate total after ion exchange?


If we were to flush the anion exchanger with calcium hydroxide (a lot more expensive) would that raise the pH more than flushing with a carbonate or bicarbonate? I'm assuming flushing with carbonate or bicarbonate would have the same pH increase? because a single carbonate (-2 charge) would swap for two chlorides vs a bicarbonate would swap for one chloride?

 

[Randy Holmes-Farley]

Oh, I see, yes, sending just part of the water through it can give a partial effect.

Carbonate will raise the pH more than bicarbonate, even with just half as much swapped in, and hydroxide will raise it higher still.

At 500 ppm tds (500 mg/L) in the tap water, theirs is something like 0.009 M of anion present, which would give a pH just under 12 if it were all swapped for hydroxide.

 

[darknectar]

Thanks!

Oh, I see, yes, sending just part of the water through it can give a partial effect.

Carbonate will raise the pH more than bicarbonate, even with just half as much swapped in, and hydroxide will raise it higher still.

At 500 ppm tds (500 mg/L) in the tap water, theirs is something like 0.009 M of anion present, which would give a pH just under 12 if it were all swapped for hydroxide.

Thanks! so do you think this is worth doing a little experiment? It looks like about $100

I was going to buy these and put them in this sequence:
3x10" canisters

Reverse Osmosis and Reactor Canisters

We carry a wide variety of reverse osmosis canisters, and depending on your system or reactor we most likely have the canister to fit your needs. The most common RODI systems along with the BRS systems use the 10" Canister with 1/4" ports. The standard and dual BRS Reactors use the same 10"...

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sediment filter

2.5" x 10" Purtrex Depth Sediment Filters

Most sediment filters in aquarium RO systems are inexpensive surface filters that quickly lose their effectiveness when the surface becomes clogged. Purtrex Depth Sediment filters are true graded density filters that capture larger particles at the surface and smaller particles towards the...

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1 micron carbon filter (for chloramine)

BRS Universal Carbon Block Filter - 1 Micron

Why does BRS recommend this? We spent a ton of time researching and testing to find the best carbon block available while still being reasonable when it comes to price. There are other filters that work well however do not last as long. By simply just looking down the center of the carbon block...

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10" cartridge

2.5" x 10” Clear Refillable Cartridge for DI Resin (Standard)

Compatible with most refillable DI systems Filling a DI Cartridge is easy. The most important thing to remember is to tightly pack the DI resin into the cartridge. Loose DI will cause the water to channel through the DI greatly reducing the effectiveness. How to refill an empty DI Cartridge...

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anion resin

PRO Series Anion DI Resin (Color Changing) - Part 2

Changes from Blue to Amber when exhausted Anion Single Bed Color Changing DI Resin is great for people that want to be more efficient with their deionization resin usage. Single bed resins do require the use of a cation and anion resin followed by a mixed bed resin, but produce much better...

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I already have equipment to test calcium, potassium, magnesium, carbonate, chloride and pH. So I could run it with a few different flow restrictors (300ml/min, 200, 100)...then test every hour to see how it's changing the ions...then figure out when the anion resin needs flushing...flush with sodium bicarbonate...then retest.

Or would you recommend setting up the experiment differently?

 

[darknectar]

@Randy Holmes-Farley Not sure if you saw my last question... I appreciate all the feedback you've given so far. Thank you.

 

[Randy Holmes-Farley]

I'm not sure I understand the setup. There is no RO anywhere?

In order
sediment
carbon
anion

No cation resin anywhere?