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Removing excess conductivity

10/25/2009 1:15 PM

We are planning to install a water treatment plant in area where ground water is very hard. Softening brings down hardness from about 450ppm to below 10ppm. However the conductivity remains in high, over 500 uS/cm which is not desirable for drinking water.

I am aware RO is a feasible solution, but we are concerned about the high capital and operating costs.

Is there a cheaper and simpler option to bring the conductivity to reasonable levels?

This purification system is part of our CSR program and is to be located in a rural part of Sri Lanka, in the Eastern province.

Electricity is available, but finding skilled people to operate complex systems such as RO is also another reason I wish to avoid RO.

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Guru
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#1

Re: Removing excess conductivity

10/25/2009 1:28 PM

However the conductivity remains in high, over 500 uS/cm which is not desirable for drinking water.
I don't agree with that statement.
Surely it depends what is causing the high conductivity?
Sodium chloried for example would be bad, but some calcium compounds are beneficial to the bones.
The water where I live (Essex UK) is about 0.7mS (relatively hard).

Del

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Guru
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#2

Re: Removing excess conductivity

10/25/2009 8:38 PM

What are you using the water for? Drinking or electronics production? If it's for drinking, there's no need to soften it; in fact, softening is counterproductive because it increases the sodium content of the water. That wouldn't be good for people with hypertension and kidney problems. You should only soften part of the water and use it to dilute the rest to reduce the hardness; to get rid of the sodium, you can use ion exchange resins.

Anyway, you might want to consider this method. It's certainly cheap and effective.

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Guru
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#3

Re: Removing excess conductivity

10/25/2009 11:20 PM

You are absolutely correct in your desire to avoid RO in your environment. Although very effective when operated and maintained properly, such systems can multiply your cost of water production by a factor of 4 or more, just on the basis of the cost of electricity. The real kicker though, is the limited availability of skilled people to maintain the system. My experience tells me you could expect something like six months service out of an RO system under these conditions, in spite of manufacturer's warranty...

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Guru
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#4

Re: Removing excess conductivity

10/25/2009 11:29 PM

Regarding the "excessive conductivity", I agree with the others that you must first determine what is causing the conductivity before you can determine if this is really harmful or undesirable for drinking water. As others have noted, high mineral content is not necessarily detrimental, and may, in fact, be healthier to drink. It all depends on the minerals dissolved in the water. One thing that must be watched however, is that the chemical composition of the water does not change radically as the aquifer is drawn down during normal usage. If there is electricity available nearby, there is a good chance that there are potential pollution sources nearby that could leach in to the aquifer and destroy it for consumption purposes.

In short, hardness and conductivity testing are nice for monitoring water condition testing, but really do not provide enough information to establish if the water is truly safe to drink. You need a complete chemical analysis for that.

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#5

Re: Removing excess conductivity

10/26/2009 12:38 AM

Your water softener replaces water hardness cations (Ca, Mg, Fe, etc.) with Sodium (Na). Not the best choice for drinking water, but good for washing or process water. Passive solar distillation is your cheapest bet in rural areas, you will need both chemical and bacterial testing to determine final safety in undeveloped areas. The old polyethylene covered pit with the feed water drizzled in around the upper edge like they used to teach Boy Scouts is a good system for single-family use.

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Guru
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#6

Re: Removing excess conductivity

10/26/2009 8:08 AM

A conductivity of over 500μS/cm at 20degC would fall within World Health Organisation parameters for "potable water".

The conductivity level is equivalent to a well-water source available here, which is drunk after filtering to below 5μm and zapped with an ultraviolet source for rendering any bacteria innocuous.

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#11
In reply to #6

Re: Removing excess conductivity

11/03/2009 6:44 AM

Guys & gals (if any),

I am sorry for not keeping you informed of the progress. I have been extremely busy!

We went ahead and implemented this CSR project and I am happy that system is working well.

This is for a school. There are only 2 wells in the village and one in in the school.

Raw water hardness is over 450ppm and with our treatment comes down to below 20ppm.

Conductivity of raw water is around 550 μS/cm and goes up slightly to around 600┬ÁS/cm.

Water after treatment is crystal clear,free of bacteria & virus very much suitable for drinking, million times better than what we start with. It passes all guidelines by WHO and also maximum permissible national limits.

However under national standards there are two parameters Maximum Concentration Desirable and Max. Conc. permissible. For conductivity it is 3500 & 750 respectively while for hardness it is 250 and 600.

Still I feel if we can improve on the parameter conductivity I would love to do it. In fact what I expected was input from someone who has used low pressure membranes ultra filtration or nano filtration. I wish to know whether ultra or Nano membranes make a difference in conductivity. I know for sure RO membranes do, but they need high pressure pumps and process is more complicated.

By the way for these poor people who had been living a hellish life of 3 decades under ruthless LTTE terrorists and hypertension and/or Sodium is and will not be a problem for at least one generation!

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Guru
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#12
In reply to #11

Re: Removing excess conductivity

12/08/2009 8:12 AM

"I wish to know whether ultra or Nano membranes make a difference in conductivity."

No: they can only remove molecular size suspended solids. Only RO membranes can remove dissolved ions.

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Power-User

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#13
In reply to #12

Re: Removing excess conductivity

12/10/2009 2:00 AM

Thanks Dvader, Your contributions in this field have been always very helpful.

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Power-User

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#7

Re: Removing excess conductivity

10/26/2009 11:49 AM

Dear Sisira,

Suggest go through information available at

http://barc.gov.in/technologies/home.html.

Bhaba Atomic Research Center, Government of India have developed number of technologies aimed at providing potable drinking water to poor and back ward regions of third world countries.

Regards

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Guru

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#8

Re: Removing excess conductivity

10/26/2009 6:16 PM

Sisira:

You state that the conductivity of your water is greater than 500 uS/cm (at 25 degrees C ?) but not by how much. You state a hardness of 450 mg/L (as CaCO3?) but we do not know what other ions exist. If the hardness is correct as stated and reported as CaCO3 then the conductivity of your reported water is at least 900 uS/cm or higher. Conductivity is really a quick and dirty way to measure dissolved solids in a water supply. Not entirely accurate but suitable for most water analysis. Is background sodium high? Conductivity of ground water is frequently higher than this reported level. If the water is only for potable use, most healthy people will tolerate drinking water with a conductivity approaching 2000 without complaints of taste. If the major cation is sodium then the taste threshold conductivity may lower to about 1400 uS/cm. If the major cations of the supply of water are calcium then the taste threshold for conductivity can increase to about 2300 uS/cm. Most other domestic issues with high conductivity are often not problematic until the conductivity is over 1000 uS/cm. I do suggest you provide a good set of lab certified analysis showing all major ions, pH, alkalinity and with a corrected conductivity to within at least 5% of the measured ions. Is softening a good idea? How much water are you trying to supply? People with heart or renal issues may want a different quality than the general healthy population. I also realize that WHO guidelines for TDS is 500 mg/L and that relates to a conductivity of about 840 uS/cm or so. A word of warning, if the SO4 concentration is high, the measured conductivity will be reported much lower than the calculated level. Better info please.

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Guru
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#9

Re: Removing excess conductivity

11/03/2009 3:07 AM

You need to spend money to make money like hiring people with skill.

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Power-User

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#10
In reply to #9

Re: Removing excess conductivity

11/03/2009 5:58 AM

well can you please explain what you mean?

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Anonymous Poster (1); cwarner7_11 (2); Del the cat (1); DVader1000 (2); kevinm (1); krishnan.ng (1); maveric_manic (1); PWSlack (1); Sisira (3)

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