Evaluation of ion exchange resin-water treatment

[tractable09]

Dears,

I am new to water treatment side and I am given a task to evaluate existing ion exchange resin performance. In a simple flow scheme, Water at 230 T/hr is passed through a cation exchanger ----->Anion Exchanger.......>Mix bed polisher.......>polish water tank.
I have started with Cation exchanger and I have lab results with me.
Lab Result of Cation Exchanger:
Inlet:
Ca = 34 ppb
Na = 16 ppb
Ammonia = 2221 ppb
Sulphate = 2121 ppb
Total Cations = 125 meq/L
Total Anions = 144 meq/L
Ph = 7.26
I get confused here as If I sum Cations (Na, Ca, NH4) they do not bcomes equal to 125 meq/L, neither Anion Sulphate of 2121 ppb is equal to total Anions 144 meq/L
Outlet results:
Ca = 340 ppb
Na = ND
Ammonia = ND
Sulphate = 62.42 ppb
pH=3.53
Now comes the 2nd confusion, how Ca can increase after passing water through Cation exchanger?
and Why SO4 came down at out let?
How the pH came down at outlet?
Really appreciated if anyone experience can throw light, thanks in advance.
Regards,

 

[ione]

You can start with this:

34 ppb of Ca++ = 34*10^(-3) ppm of Ca2+ = 34*10^(-3)/20 mEq/l = 0.0017

16 ppb of Na+ = 16*10^(-3) ppm of Na+ = 16*10^(-3)/23 mEq/l = 0.0007

2221 ppb of NH4+ = 2221*10^(-3) ppm of NH4+ = 2221*10^(-3)/18 mEq/l = 0.123 mEq/l


Total cations = 0.125 mEq/l = 125 microEq/l

 

[tractable09]

Thanks ione for the reply,
Means lab has wrongly mention microeq/L as meq/L.
If I do same for SO4(-2),
2121ppb of SO4(-2) = 2121/1000 mg/L = 2121/1000 * 96/2 meq/L= 101meq/L
but lab has shown Total Anion = 144 meq/L, again lab is wrong here or my understanding is not correct.

ok for evaluation if we take individual values of cations and anions, Pl. look at the other questions i have asked, thanks.

 

[ione]

If the total amount of anions is made of sulphates then you should have:
2121 ppb of SO4-- = 2121*10^(-3) ppm of SO4-- = 2121*10^(-3)/48 mEq/l = 0.044 mEq/l = 44 microEq/l.

After the cationic column the amount of Ca++ must decrease. Check units maybe it was ppm upstream and ppb downstream.

If you have a demi station (and it seems so), after the cationic column which removes positive ions, water enterS an anionic column where negative ions are removed (H2SO4 + 2 OH- ------> 2 H2O + SO4--).

If your system does not foresee the presence of a degaser between the cationic and the anionic column in order to remove carbon dioxide, then it is possible to have a reduction of the pH.

And now the best advice I can give you: have you tried to discuss the results with the lab which has carried out the analysis? If not it would be strongly recommended.

 

[shahyar]

Why do you have: "cation exchanger ----->Anion Exchanger.......>Mix bed polisher" for such a pure water?
A mixed bed is enough for this application and I doubt that those separate vessels of Cat and An. can do anything on a water with ppb level of ions.
The other thing is that the second water analysis shows it is for water right after "Cation Exchanger". It is because of Acidic ph. Ph will drop after Cation exchanger but after anion one, the ph will be the same as inlet water ph. However, the first column doesn't do anything on Anions(e.g. Sulfate) but your sulfate dropped in the second water analysis!