How to remove Tannin from my well water

[sujith1984]

Hi All,
I am new to this forum, in-fact I am new to water treatment (I am software engineer),
I recently bought a house (I put all my earnings plus a home loan), the only water source of that house is a tube well and the water has yellow color if it is in a clear glass and orange color (petrol like color) if it is in a bucket. I tested the water and found that it has iron contents 2.3 ppm and color is due to Tannin. PH is on the lower side , about 6. I contacted a local water treatment company they were able to remove the iron but not the color of water.
So I started experimenting on my own, I bought a handheld tds meter and found that the tds varies from season, 150 PPM to 220 PPM , the highest on rainy seasons.
I learned from the internet that tannin can be removed using anion resin, which can be regenerated using caustic soda solution.
I contacted the local water treatment company and as per him

1. Resin treated water will cause skin irritation.
2. Resin needs to be replaced every month.​

I am not ready to trust him because he failed to deliver results once plus he never heard the word tannin in his career.
I would like to hear from the experts, I have 6 month old kid and clear water is really a problem for me now , any help is highly appreciated.
An additional info - My kitchen RO + UV water purifier is giving me perfect clear water.

Best Regards
Sujith

 

[ashtree]

Sujith,

Its good that your RO is delivering clear water but you might find in time that the iron is fouling both the RO membranes and UV tubes.
There are a number of ways that Tannin could be removed but Tannin can be a generic term for lots of things that leave residual colour in the water.

One way that might be successful which will remove the iron as well is to dose with calcium or sodium hypochlorite. This will oxidise the iron and most likely the "taninn" and will form a precipitate which will settle. You could use unstabilised pool chlorine at a dose rate of about 5 mg/l of active ingredient but the actual dose would need to be established by trial and error. You will probably have to pass the water through a filter (5 micron)to get a really clean water. At pH 6 the reaction will be relatively slow.

Dont use the chlorinated water in the RO as this will probably chew out you membrane quickly.

You could also try aerating the water to remove the iron which will settle out however most of the tannin will probably remain.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[sujith1984]

Thanks for your reply Ashtree .
In-fact I have a whole house filter installed, which successfully removes the chlorine and additionally I have installed an iron removal stage in my RO + UV filter.
I tried using stable bleaching powder but, as you said the reaction is slow, actually its not settling but my whole house filter is able to filter it. Tried liquid chlorine + alum (Suggested by a chemist) the settlement is slow , even taking 2 days to settle.
I tried by adding liquid chlorine + alum in a glass I can see white fumes (cloud like) in the top and clear water in the bottom in seconds.

The chemist also said that tannin is mainly due to wood decay.

 

[ashtree]

Sujith

Did you "flocculate" the alum. That is when you first add the alum you should give the water i vigorous stir for a few seconds then very slowly stir it for at least a few minutes. This allows the alum floc to form. You may have overdosed the alum may have been one reason why it did not settle. You would probably only need 10mg/l if that.
Does your house filter contain activated carbon? If it does you are probably burning your carbon absorption capacity quickly treating the water into which you have dosed bleach. If possible you would still be better to let the water settle for some time before filtering it.


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[sujith1984]

Yes Ashtree, I may have overdosed alum considering your 10mg/L suggestion.Yes my whole house filter contain activated carbon as 3rd stage (its a 3 stage filter).
I will try dosing as per your suggestion and let you know the result.

 

[bimr]

Sujith,

The traditional method to remove tannin is with alum flocculation. This will require a separate flocculation tank plus a water filter.

Most homeowners have neither the time, expertise, or equipment to handle this process. Flocculation will be difficult because of the wildly varying flow that will be experienced in a residence. Alum is also slightly acidic and difficult to handle.

You will probably be better served to just use the RO process to remove the tannins.

 

[cvg]

you might want to investigate to find out why the water quality is so poor. Is it the well or the water pipes? It might be worthwhile to fix the problem at the source.

http://www.idph.state.il.us/envhealth/factsheets/ironFS.htm

 

[sujith1984]

@Ashtree, Thanks for the help, I tried dosing alum (about 30 gms to a 500 L storage tank) and stirred it for few minutes and that worked, morning the water was clear .

@Bimr I use the RO filter for bathing my kid, drinking and kitchen purposes, but for whole house use RO will be costly , considering the electricity consumption and waste water.

@cvg, its the well, I collected water from well directly and tested.

Thanks all for your reply.

 

[bimr]

cvg is letting you know that there may be problems with the well itself. There should not be tannins in well water. Tannins are more frequently found in very shallow wells, or wells under the influence of surface water

 

[dfmorvan]

Hi Sujith

there are specialized resins for tannin removal. They are usually weak base resins and can be cleaned quite efficiently.
Look up for "organic scavenger resin", some manufacturers have specialized ion exchange resins to do that which can be regenerated with salt insted of caustic soda. I suppose you are in India ? However organic matter and tannin can be present under different forms (ie type and size of molecules) and all will not be removed by the resin. Usually you have to combine coagulation with resins and/or RO to be able to remove the largest part of the tannins/ Organics.
For Iron at low pH you can try to use a water softener if the iron is dissoved and not precipitated (meaning Fe II instead of Fe III)

 

[sujith1984]

Hi,Dfmorvan
Thanks for your suggestions. Yes I am from India, I talked with a so called water treatment expert about a resin media filter and he was saying like
1. Resin treated water will cause skin irritation.
2. Resin needs to be replaced every month.
Is that true?

 

[bimr]

Whether the resin treated water affects the skin will depend on several factors. A change in water quality as a result of the use of resin of a water treatment technique will have an different effect on different skin types. Depending on ethnicity, some people have dryer skin or skin with more moisture.

The resin lifetime is difficult to predict and will depend on which resin that you are using.

One would think that the cost of the resin treatment will not generally be economical.

Think that the best approach would be to obtain a better water supply. Water from wells should be crystal clear because of the filter action of the path that the water through the aquifer. Even the iron is dissolved prior to addition of air, which causes it to come out of solution. The fact that your water has tannins indicates that there is a problem with the well. It is more practical to fix the well than to try to remedy the bad water.

 

[dfmorvan]

Hi Sujith

It is difficult to give an precise opinion with so little data. Do you have some more water analysis ? By which method did the WT company remove the iron?

As for resin causing irritation, it depends on what you are regenerating the resin with. If you use salt to regenerate a softener you'll exchange calcium and magnesium against sodium. No irritation issue there. Of course should you use some caustic soda to regenerate anionic resin, the produced water would be basic as you would exchange in this case all anions (ion with a minus charge, like chloride or sulfate) against OH- ions which would make pH go up.

There are some domestic or industrial systems where one puts some layer of anionic/tannin resin on top of the cationic resin used to soften water. Anionic resin will exchange some tannins against chloride (although the mecanism here is not really ion exchange...) and dissolved iron plus hardness salts against Sodium.
Could be worth a try, but I do not know the price of a domestic softener plus special resin in India or if you can find specific tannin resin easily. There is also the issue that tannin can form complexes with iron, making it more difficult to be removed.

To summarize :
I would say that, with pH around 6, iron should be under the Ferrous (Fe2+) form. It should not be precipitated and could be removed by some cationic resin (softener type) regenerated with Salt brine (using the Na). The iron may also be complexed by tannins and so be more difficult to remove. Of course the resin will foul over time but not too quickly. It should take some years.

Tannin can be adressed with a layer of specific anionic resin on top of the softening resin, regenerated also with brine in the same vessel and at the smae time as the softening resin. It will use the chloride ion from the brine. There should be no skin issues as the exchanged salts will be sodium and chloride which is table salt at low concentration. Tannin resin will last several years normally.

 

[sujith1984]

Thanks dfmorvan,
I am attaching the test report I have (I dont think it is a detailed chemical analysis), as of now alum dosing is doing the trick ok clearing the water but it takes the whole night to settle the sediments.

 

[dfmorvan]

Hi

Yes, it sort of confirms my first impression. Your water is not very hard (50 ppm as CaCO3) and so a combination of anionic resin and softening resin could give some good results. I know only of 2 Resin suppliers in India Ion exchange and Thermax, but for a small application like this you'll have to go thru a reseller. Try to find a softener, remove 20 % of the resin and replace if with anionic resin. Brine well, twice a week to avoid irreversible adsorption of the tannins on the resin.
Best thing to do would be a test with a small quantity of resin in a bottle to see if the anionic resin works well with your local type of tannins.

 

[sujith1984]

Thanks dfmorvan, I will try that , but the problem is availability of raw materials , I could find some softeners with cation resin online , but anion resin is hard to find.