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Related Articles


total hardness

total hardness

total hardness

Dear Sirs

Please your recommendation We need our final product water total hardness between 70 and 120 mg/ltr. To be use for Dairy applications( water type RO permeate)

Thank you

RE: total hardness

Stabilization by addition of caustic hydroxide alkalinity is the most widely used approach for desalinated permeate. Stabilization can also be achieved by carbonate alkalinity adjustment, remineralization by blending with source water(s) and the use of caustic soda-carbon dioxide.

RE: total hardness


in the past we remineralization by blending with raw water but we stop that because our raw water high with chlorides and this cause corrosion to network pipe of the factory

RE: total hardness

How about using an anion ion exchange resin on the raw water to remove the chlorides.

RE: total hardness

May be if we use an anion ion exchange resin on the raw water to use it as blending it will effect on Langelier Saturation Index LSI of product water. please advise

RE: total hardness

our water goals:
PH: 7 - 7.5
TH: 8 - 12 degree F
TAC : 8 - 10 degree F
LSI : -0.5 to 0.5

I Hope someone advise me to achieve our goals. please note we use now NaOH and calcium hypochlorite for post treatment

Thank you

RE: total hardness

Anion exchange will not be feasible. It is just too expensive. Anion exchange will have little affect on the Langelier.

What are the other cations and anions in the water? Is this a wastewater recycle or a potable water application.

RE: total hardness

Thank you bimr for your reply

It's potable water application.
please find below our well water analysis:
ASPECT Limpide
Turbidité NTU 10.00
Température °C 43.60
Conductivité µs/cm 6,270.00
TDS mg/l 4,702.50
pH 7.01
TH °F 120.00
Ca++ °F 95.00
Mg++ °F 25.00
TA °F 0.00
TAC °F 38.00
Fer dissous mg/l 0.06
Chlorures °F 235.00
Sulfates mg/l 400.00
Silice mg/l 27.80
Nitrates mg/l 12.50
Indice de RYZNAR 5.30
Indice de LARSON 7.28

RE: total hardness

The RO system will remove 90+ percent of the ions.

Based on that, you should be able to blend 10-15% of raw water with 85-90% RO permeate and meet your target of final product water total hardness between 70 and 120 mg/L.

The chloride will be approximately 50 mg/L. At this concentration chloride is not typically corrosive. Perhaps you have MIC, in which case you should be feeding a disinfectant (chlorine).

The RO permeate will have a pH in the 6 range. The low pH is caused by the rejection of the alkalinity while carbon dioxide passes through the RO membrane. Post treatment is necessary with an alkali to raise the pH (remove the carbon dioxide) and make the water less corrosive.

RE: total hardness

in fact our raw water also contains H2S.
we had blending raw water with permeate before but we stopped that because we face alot of corrosion on network pipe

RE: total hardness

Agree, blending will not work with hydrogen sulfide.

RE: total hardness


H2S should be removed prior to RO.

RE: total hardness

The hydrogen sulfide may be being removed with the RO system.

RE: total hardness

please according to raw water analysis above what do you think the best pretreatment and please what is your recommendation to achieve our final water target with respect Langelier Saturation Index LSI

Thank you

RE: total hardness

To provide a specific answer, all of the details of the water quality and capacity need to be provided.

Without knowing more, stabilization by addition of caustic hydroxide alkalinity is the most widely used approach for desalinated permeate.

Then, you mentioned reblending. Later you mentioned hydrogen sulfide.

Without the details, it is a game of 20 questions.

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