Arsenic: How to Remove It from Water

Posted December 24th, 2013

How to Remove Arsenic from Water

There are many treatment strategies that can be used to reduce arsenic in water.  A Water Conditioning and Purification article (paper issue, Dec. 2013)  listed the following as effective arsenic treatments.  They are listed in alphbetical order, not order of effectiveness.

1. Activated Alumina

2. Coagulation-assisted filtration

3. Electrodeionization

4. Granular ferric hydroxide

5. Ion exchange

6. Lime softening

7. Nanofiltration

8. Reverse osmosis.

Of these, three are by far most commonly used for residential treatment: Activated Alumina, Granular Ferric Hydroxide, and Reverse Osmosis.

This is not to suggest that a home owner can simply get a reverse osmosis unit or an activated alumina filter and assume he has solved the arsenic problem.  Arsenic is potentially life-threatening and it should not be taken lightly.  Treating arsenic is actually fairly complicated, although the basics that you need to consider are these:

In water, arsenic exists as arsenite (As III)  or arsenate  (As V).  The most common is As(V).  Usually if water contains dissolved oxygen and the pH is 7 or above, As(III) will naturally be oxidized to As(V).

Common treatment methods like reverse osmosis, activated alumina, and ferric hydroxide filtration remove As V well but not As III.  Therefore, the usual practice is to use an oxidizer in front of the treatment process to assure that the Arsenic in the water exists as arsenate.   Of the commonly used oxidizers, chlorine, potassium permanganate and ozone work very well.  Also useful is filtration through Filox, which has proven to be an effective oxidizer for Arsenic.

More detailed information on  this topic can be found on the Pure Water Occasional website.