Water Treatment

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munna1501 Active Contributor Join Date: Aug 2010 Posts: 12	Water Treatment 09/09/2010 1:05 AM
	Hi I need to know the relation between Total dissolved solids and hardeness if there any? RO can reduce the TDS , does it have any affect on hardness also or if we want treatment for TDS<500ppm and hardness 5 ppm, Does we require to install softener alonwith RO
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#2 "Re: Water Treatment" by kevinm on 09/09/2010 11:12 PM (score 5)
#4 "Re: Water Treatment" by kel giesbrecht on 09/10/2010 8:11 AM (score 2)

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#5 "Re: Water Treatment" by LAA_Lucke on 09/10/2010 12:13 PM (score 1)

Mikerho

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Re: Water Treatment

09/09/2010 9:30 AM

Here is an excerpt from this website:

Selecting a Reverse Osmosis System

When selecting a reverse osmosis system, the following factors must be considered:

Is the water supply potable?

An RO system should be used with water that is already deemed bacteriologically safe for human consumption or is adequately disinfected or sterilized on a continuous basis. RO systems can include ultraviolet lights.

Is the feed water supply chlorinated or unchlorinated?

If the water is unchlorinated, a TFC membrane should be chosen due to its greater resistance to bacterial attack. If the water is chlorinated, a CTA membrane that is not chlorine sensitive may be chosen or a TFC membrane that is sensitive to chlorine may be used with the addition of a carbon pre filter. The membrane will need to replace approximately every 2 years, depending on the water quality and quantity. Most systems use TFC membranes.

What is the daily quantity of pure water required?

A suitable residential system should be capable of producing in excess of a minimum of 1/2 gallon of drinking water per person per day. Residential systems typically produce 15 to 25 US gallons per day of pure drinking water. Commercial/Industrial units can produce up to 40000 US gallons per day of pure drinking water and should be sized according to their application.

Is the water supply adequately pretreated?

If present, any contaminant such as iron, manganese or hydrogen sulfide must be adequately reduced or removed by pretreatment in accordance with membrane tolerances. If necessary, the feed water should be treated to reduce hardness to a maximum of 10 gpg to prevent premature fouling of the membrane.

What is the level of TDS (total dissolved solids)?

Drinking water should have a TDS of below 500. City water on the West Coast of Canada has a low TDS of 25, while many other areas have a TDS of 200+. Well water can have a TDS of 1000 to 5000. Sea water has a TDS of 40 000 and the Black Sea can be up to 60 000 TDS. Residential RO units can tolerate up to 2000 TDS. Brackish water RO units can take up to 6000 TDS. Desal RO units are used for higher levels and the membrane pressure vessel will run at approximately 900 psi.

What is the pH of the feed water?

The pH in most city water supplies is 6.9 to 7.5. In many West Coast cities the water can have a low natural pH level, as low as 5.5, making the water very corrosive to copper piping. pH is a logarithmic scale. For example, a pH of 6.9 is ten times more acidic than a pH of 7.0

Is a booster pump required?

A booster pump may be required if your incoming water pressure is less than 50 psi, or you have a TDS count of over 1000, or the inlet water temperature is very low.

If you need definitions to some of the words, there are sites such as dictionary.com.

Sounds like you really need to do some investigation and study the things that you find.

When you have a clearer picture of what water hardness is, and how water softeners and RO systems work, then come back with specific and detailed questions and we'll do what we can to help.

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kevinm Guru Join Date: May 2009 Location: Wolfe Island, ON Posts: 1357 Good Answers: 109	#2 Re: Water Treatment 09/09/2010 11:12 PM
	munna1501 TDS is the measure of all the ions in the water. If the TDS is based on conductivity all the ions will have a positive or negative charge ( cations and anions). If it is true TDS you will also measure neutral ions like silica and dissolved organic carbon. The hardness is a part of the TDS. It is difficult to tell you without an analysis of the water as to what portion of the TDS is hardness. Hardness is essentially a measure of the calcium and magnesium ions in the water and is reported as mg/L or ppm as CaCO₃. Hardness can be observed as spots on glasses after they have been washed in hard water. A typical analysis of water from a limestone aquifer would have a hardness level of about 45% of the TDS. It will vary in the presence of excess sodium ion. Softened water will have hardness levels of close to zero. A softener will replace hardness with 1 mg/L of sodium for each 2.176 mg/L of total hardness removed. For example if you have a raw water hardness of 400 mg/L, your softened water will have 400/2.176=184 mg/L of sodium. Sodium does have some health implications in persons with circulatory or renal conditions. Softening should not change the TDS but rather it will replace the hardness ions with an equivalent of sodium. Softened water on glasses will wipe off but hardness spots will not easily rub off. Reverse osmosis usually gets upwards of 90% TDS removal. If you are going to use reverse osmosis it is a condition that the water be softened prior to the reverse osmosis application. Hardness ions will not readily flush off the R/O membrane and in fact its crystals can cause tears in the membrane to render your R/O treatment useless. So yes soften the water before R/O as pretreatment. Mikerho has posted some other information from another site, It is generally good advice. __________________ If they want holy water, tell them to boil the hell out of it.
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kel giesbrecht Active Contributor Join Date: Feb 2009 Posts: 24 Good Answers: 1	#4 In reply to #2 Re: Water Treatment 09/10/2010 8:11 AM
	Kevinm is pretty much as close as you can get i just wanted to add to his answer. Pre-treatment for the RO membrane filters is usually a micro or ultra membrane filter. This is done to reduce the TDS in the water, as this will cause frequent backwashes and fouling of RO filters. The RO filter is also known as the softening filter in that it will remove the calcium and the magnesium. Another pretreatment that is also being used now if the water is being treated on a municiple scale is using a flash mix of alum to form a floc that the ultra filters can remove much easier. Doing this also means you can use a water source that fluctuates in turbidity more greatly. like surface water does.
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kevinm Guru Join Date: May 2009 Location: Wolfe Island, ON Posts: 1357 Good Answers: 109	#6 In reply to #4 Re: Water Treatment 09/10/2010 4:26 PM
	GA Kel. Surface water has different consideration when R/O is applied and pretreatment is essential. Kev __________________ If they want holy water, tell them to boil the hell out of it.
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AGuest Power-User Join Date: Aug 2010 Posts: 108	#3 Re: Water Treatment 09/10/2010 2:19 AM
	mumma1501, TDS will precipitate and form scaling on your RO membrane. There are various ways to resolve this issue: Pretreat the water (Ion exchange, Lime softening, pH adjustment (some membranes are more sensitive to pH than others so be careful with this) and Scale inhibitors to mention just a few) Design the RO system to limit the permeate recovery, since scaling is a function of concentration of scaling ions. Calcium carbonate (CaCO₃)is the most common scaling issue followed by what is known as the sulfate scales (Calcium sulfate (CaS0₄), Barium Sulfate (BaS0₄)), followed by the fluoride scales and then by the Silica scales. The hardness ions are formed from the sulfate scales. So there may or may not be a link between TDS and hardness in your particular case, it is impossible to tell without actually seeing an analysis of your water (as was stated in the previous post). There are rules of thumb on what pretreatment is needed for RO systems but your best bet would be to speak with the RO system designer as they will have/ should have carried out an analysis of your water. It is also worth reviewing the RO data sheets aswell. Personally I have never seen an RO system without some form of pretreatment but that is just my personal experience. __________________ "New and stirring things are belittled because if they are not belittled, the humiliating question arises, 'Why then are you not taking part in them?' " - H. G. Wells
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LAA_Lucke Guru Join Date: Feb 2010 Posts: 1013 Good Answers: 36	#5 Re: Water Treatment 09/10/2010 12:13 PM
	Very simply put: TDS is reduced by the RO to almost zero. In doing so, it also reduces the Hardness. Using a softener before the RO will reduce the hardness by replacing the calcium ions with sodium ions (these do not precipitate to scale the pipes...) but the TDS is not going to be appreciably reduced since you are replacing the dissolved Calcium Carbonate etc with the Sodium carbonate etc. Then the RO will remove the TDS and will not have to worry too much about the Calcium compounds sticking on the membrane.... better efficiency and longer life for the RO membrane.
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