Treatment is done in several ways
Treatment methods such as reverse osmosis, activated alumina media filtration, manganese greensand filtration, and strong base anion exchange require oxidation of Arsenic III to Arsenic V first in order to successfully remove the arsenic.
The pH of the water also has a strong effect on adsorption efficiency. As pH changes, the charge associated with the arsenic anion also changes.
The H2AsO4- anion carries a single negative charge at or below pH 7, but it loses a proton at higher pH, resulting in a doubly charged anion, HAsO4-2. The singly charged anion is adsorbed more effectively from the solution than the doubly charged species.
In a similar manner, the charge state on the surface of the adsorbent varies with pH also. Titanium oxide has a positive surface charge below a pH of 5, and a negative surface charge at higher pH. Likewise, an iron oxide adsorbent has a positive charge below a pH of about 7, and a negative charge at higher pH.
This variation in adsorbent surface charge can explain why the adsorption capacity for arsenic is so sensitive to pH changes in the common drinking water range of 6.5 to 8.5
Iron oxide (Fe2O3)/ hydroxides (Al2O3)
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Iron-based specialty media impregnated or coated with iron oxide/hydroxides
Distillation has also been shown to remove arsenic to less than 2 parts per billion but is best used at point-of-use for smaller quantities of water.
It is easy to see how both effects — the doubly charged arsenic anion and the negative surface charge of the adsorbents — could work together to dramatically reduce efficiency at higher pH.
Using this rationale, you might expect titanium oxide to be a less effective adsorbent at normal drinking water pH conditions since it is negatively charged at an even lower pH.
However, the opposite is true. Titanium oxide has a higher adsorption efficiency for arsenic in neutral pH water than iron oxides do. At higher pH, all adsorptive media lose efficiency, but the effect is less dramatic for titanium oxide.
Anion Exchange (strong base anion exchange resins)
Ion exchange (strong base anion resin) can, in principle, be a cost-effective point-of-entry means of reducing arsenic levels, but the lack of specificity can cause the resin to require frequent regeneration if other common competing ions, such as phosphates or sulfates, are present.
If the resin is not regenerated appropriately, arsenic can concentrate on the resin and then be released into the water at a higher concentration than is present in the influent water being treated.
Finally, as with RO membranes, strong base anion resins will not effectively remove the arsenite form of arsenic.
Manganese greensand (requires regeneration)
Manganese Greensand is formulated from a glauconite greensand which is capable of reducing iron, manganese, and hydrogen sulfide from water through oxidation and filtration. Soluble iron and manganese are oxidized and precipitated by contact with higher oxides of manganese on the greensand granules. The hydrogen sulfide is reduced by oxidation to an insoluble sulfur precipitate. Precipitates are then filtered and removed by backwashing. When the oxidizing capacity power of the Manganese Greensand bed is exhausted, the bed has to be regenerated with a weak potassium permanganate (KMnO4) solution thus restoring the oxidizing capacity of the bed. 1.5 to 2 ounces of potassium permanganate, in solution, per cubic foot of Manganese Greensand is considered sufficient for normal regeneration. It is required to vigorously backwash and regenerate the bed when it is placed in service and before its oxidation capacity is totally exhausted. Operating the bed after oxidation capacity is exhausted will reduce its service life and may cause staining.
Reverse osmosis (RO) See Drinking Water
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Do not attempt to remove arsenic by boiling water. This only serves to concentrate the contaminant.
Arsenic is naturally present at high levels in the groundwater in the US.
Arsenic is highly toxic in its inorganic form.
Contaminated water used for drinking, food preparation, and irrigation of food crops poses the greatest threat to public health from arsenic.
Long-term exposure to arsenic from drinking water and food can cause cancer and skin lesions. It has also been associated with cardiovascular disease and diabetes. In utero and early childhood, exposure has been linked to negative impacts on cognitive development and increased deaths in young adults.
We must take action in affected communities to prevent further exposure to arsenic by the provision of a safe water supply.
Arsenic is found in the diet, particularly in fish and shellfish, in which it is found mainly in the less toxic organic form. There are only limited data on the proportion of inorganic arsenic in food, but these indicate that approximately 25% is present in the inorganic form, depending on the type of food. Apart from occupational exposure, the most important exposure is through food and drinking water, including beverages that are made from drinking water. Where the concentration of arsenic in drinking water is 10 µg/l or greater, this will be the dominant source of intake. In circumstances where prepared dishes are a staple part of the diet, the drinking water added through the preparation of food will be greater.