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Update
21 Jan 2019
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Boron removal
in drinking water

Introduction


Caramondani
A boron removal plant in Cyprus
Boron has been found to be potentially harmful in drinking water. A provisional guideline of 0.5 mg/L as B in drinking water was established by WHO. Water used in agriculture also has a limit in boron: citrus trees (orange, lemon etc.) are sensitive to boron in the irrigation water, and the commonly accepted limit here is also 0.5 mg/L as B.

Fresh water resources are rarely containing boron, except in very delimited areas. Sea water contains 4.5 to 5.5 mg/L of boron. When sea water is desalinated to produce drinking water, the reverse smosis membranes used in this application have a very poor boron rejection.

Fortunately, boron removal with specific ion exchange resins is very effective, and several plants have been built to polish the RO permeate.

In water, boron is present as boric acid H3BO3 or sodium borate NaB(OH)4.


Plant design example

Plant design
This example shows a combination of two-pass reverse osmosis and an ion exchange column, with several by-pass and recycling points. This scheme was used in the Cyprus plant shown above. Several alternative designs can be used.

The resin

AmberliteTM PWA10 is a styrenic resin with N-methyl glucamine functionality, uniquely specific to this application. It makes a stable complex with borate:

Complex

Regeneration is done with a strong acid (H2SO4 or HCl) followed by neutralisation with caustic soda.

Amberlite PWA10 is suitable for the treatment of drinking water. For industrial applications, Ambeerlite IRA743 is also available; it has the same functionality.


Amberlite is a trademark of Dow Chemical.



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