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Comparison of water softener and Reverse Osmosis

Common methods in saline water treatment for industrial water or soft water is the use of water softener or reverse osmosis (RO). Each of these methods has advantages and disadvantages that must be evaluated and compared before selecting by engineers in various industries. This paper attempts to compare the water softener and RO reverse osmosis method Guides for choosing these products

The comparison between water softener and reverse osmosis has been done in two general technical and economical areas. In the technical section, a comparison has been made between the output parameters of the RO reverse osmosis and the water softener and it has been evaluated in the economic sector in terms of initial and current costs.
Since the water softener package is designed to cool down the water and produce soft water from the boiler, the cooling tower is generally designed to reduce the overall hardness of the water; therefore in comparison with the RO reverse osmosis system, it reduces all solution and has many limitations.

 
water softener package for water treatment

Comparison of the reverse osmosis RO and water softener in boiler water production

As we have said, the most common type of water used in our country is boiler water consumption. Boiler in the industries has the responsibility of the production of super-high pressure (super heat) or hot water at different temperatures. It is natural if it increases water deposits on the wall of the boiler's heat exchangers, the efficiency of the boiler will lower and increase energy costs.

To solve this problem, the water treatment system at the boiler input is used for the primary water (make up). Common methods of boiler water treatment is reverse osmosis (RO) or water softener. In some cases, the ion exchange system Mixe bed or the method of electron exchange of ions is EDI which unlike other methods is not so popular.

The purpose of the purification is to ensure that the boiler will maintain its efficiency and in fact, each methods of water treatment should be compared with the common standards in this area. Therefore, the standard input water to the boiler or (boiler) should be compared with water purified by water softener or RO reverse osmosis.

Here, the American Association of Boiler Builders (ABMA) which examines the quality of water entering to the boiler. Each of the water treatment methods including cationic hardening or reverse osmosis should be compared with this table.
In the following table, the acceptance criterion for (ABMA) is given for working pressure 60~40 bar.

 

Description

Unit

Guide value

Item

feed water

mg/lit

0.02

O2- dissolved oxygene

feed water

mg/lit

0.05

Fe- total Iron

feed water

mg/lit

0.03

Cu- total copper

feed water

mg/lit CaCO3

0.5

T-total hardness

feed water

 

8.5-14

pH

feed water

mg/lit

0.05

Oil matter

boiler water

 

10-11

pH

boiler water

mg/lit

30

SiO2

boiler water

mg/lit CaCO3

400

Alkinity M

boiler water

mg/Lit CaCO3

50

Alkalinity P

boiler water

μ S/cm

4000

EC

boiler water

mg/lit

500

TDS

boiler water

mg/lit

10

PO4

boiler water

mg/lit

100

TSS


 
In the above table, data is entered for boiler pressure at 40 to 60 atmospheres. Contact for the TARHOKAR company for the standard of other work pressures of the boiler.

Comparison of the RO Reverse osmosis and water softener to reduce hardness

The water softener system in comparison to the reverse osmosis is simply able to remove the temporary water hardness and is not designed to eliminate permanent water hardness. While the total difficulty is constant stiffness plus temporary hardship. In the standard boiler at a pressure of 40 atmospheres, the total hardness should be less than 0.5 mg / lit CaCO3.

Comparison of the reverse osmosis (RO) and water softener in reducing salinity (TDS and electrical conductivity)

In a water softener package with ion exchange of sodium in the resin core with calcium and magnesium, so the temporary hardness decreases. Therefore, in each period (cycle), the function of the machine requires a high amount of sodium which is supplied by water and salt. Water and salt increase the TDS of water which gradually increases the TDS of water to blow down the boiler. Whereas, this is not permitted according to boiler instruction. In reverse osmosis, compared with water softener, because the whole water soluble are removed based on the molecular size of the particles, so the TDS and the electrical conductivity of the water are reduced.

Comparison of the reverse osmosis RO and water softener in the removal of silica (SiO2)

Another key factor which causes the formation of very severe sedimentation on boiler equipment is silica ion in particular type of colloid. Silica sediment such as high calcium carbonate precipitation (such as high boiler temperature) is saturated and prevents from the transfer of heat is in the boiler. The water softener system is by no means capable of separating silica ions. In the standard pot steam, SiO2 should be less than 200 ppm in water Blow down. While RO reverse osmosis can remove silicon ions Soluble. Regarding the possibility of saturation of silicon ions on reverse osmosis membranes and prevention methods should be studied in the article.
 
Reverse osmosis for water treatment

Comparison of the reverse osmosis RO and water softener in the removal of phosphate

Reduction of phosphate ion (PO4) is another recommended parameter of the standard. It is impossible to remove this ion by the hardening system. While compared to the RO reverse osmosis system, this ion can easily be removed in membranes.

Comparison of the reverse osmosis (RO) and water softener in drinking water production

In standard No. 1053 of the Institute of Standards and Industrial Research of Iran, the optimum amount of drinking water is given in terms of solution solubility, hardness, pH and other physical and chemical quantities. In this standard, the optimum total water hardness is 200 mg / lit CaCO3 and total solution soluble, or TDS is equal to 1000 mg / lit.

Regarding the use of a water softener package compared to RO reverse osmosis in order to produce drinking water, it should be noted that in reverse osmosis package (RO) all cations, anions, viruses and bacteria are due to their larger molecular size than water in the membrane. (Membranes) are removed and by eliminating all solutes and dissolved ions in water, efficiency is about 99.5%. This method is used to produce drinking water.

But there are limitations in the production of drinking water by water softener. In water softener, water hardness reduce and by increasing sodium levels, there is no change in salinity or TDS and in some cases even increases. In addition to, other harmful ions for drinking sulfate and nitrate in the cationic hardening package will not be removed as compared to reverse osmosis RO from water.
In general, the water softener method is not suitable for drinking water except in specific cases.

Economic comparison of RO reverse osmosis and water softener

The water softener package due to the performance of the resuscitation needs to be accurately applied and should be on an average of one to two times a day rinsed and restored by the operator. In comparison, the reverse osmosis unit in the pre-treatment section requires back washing as well as substitution Microfilter. But since the operation in the reverse osmosis unit RO is much less than water softener, operator operations are much lower compared to water softener.

On the other hand, the initial cost of purchasing a RO reverse osmosis unit is much higher than water softener and also the cost of replacing reverse osmosis membranes is higher than the cost of water softener resins.
In summary, the reverse osmosis RO method has a higher initial cost than water softener. But its water quality is better.