Arsenic

What is Arsenic?

Arsenic is naturally occurring in North America and often occurs alongside iron and manganese. Arsenic commonly occurs in two forms in water: Arsenite (III) neutral charge and Arsenate (V) negative charge.

Generally, Arsenite (III) must be oxidized to Arsenate (V) prior to treatment. Effective pre-oxidants include chlorine, potassium permanganate, ozone, hydrogen peroxide and ultraviolet light. There are several identified methods for removing arsenic from water. Tonka Water has experience in various arsenic removal technologies including developing IMAR™ media for use in arsenic removal.

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Tonka Water Arsenic Removal Technologies

Tonka Water offers pilot testing to optimize an existing plant or to assist in the design of a new plant.  

IMAR Media Filtration

IMAR™ is a proprietary dual media formula of anthracite and sand, designed for optimal filter efficiency and performance when removing arsenic. IMAR™ is engineered to provide uniform interstitial openings in the filter bed, promoting the capture of solids throughout the entire filtration depth. IMAR™ media is shipped, handled and installed identical to conventional filter medias. IMAR™ has the ability to capture primary and secondary contaminants and remove them to lower levels than conventional media while filtering at higher rates. IMAR™ is not a coated media requiring special conditioning and does not cause the accumulation of contaminants.

IMAR™ is NSF/AWWA compliant and backwashes at lower rates compared to other media types. IMAR™ is less prone to media blinding and has high solids storage capacity while optimizing headloss in filtration mode.

IMAR™ is formulated to increase arsenic capacity, maximize flow rates and maintain an optimized head loss. This media is a mixture of two naturally occurring mineral components, each of which is a non-proprietary conventional water treatment media.

The medias are naturally-mined generic silica sand and naturally-mined generic anthracite. The exact gradations and quantities of each are customized by Tonka Water for each application.

Ion Exchange Systems

Anion exchange can remove As (V) at greater than 95 percent efficiency. Strong base anion exchange resins, commonly used for nitrate removal, are the only effective resins for arsenic removal. In considering the behavior of arsenic in solution, it is important to recognize that the As (V) molecule is chemically similar to that of sulfate.

Anion exchange is not effective if high levels of competing anions such as sulfates (>120 mg/1), nitrates, fluorides, or TDS are present in the water. In such cases, pre-treatment is necessary. The EPA recognizes anion exchange as a Best Available Treatment technology (BAT) for removing arsenic from water. One significant drawback to anion exchange processes is the waste regenerate solution, which, due to its high arsenic concentration and corrosive nature, is subject to stringent disposal requirements.

Membrane Filtration Systems

Reverse Osmosis (RO) and Nanofiltration (NF) can provide arsenic removal efficiencies of 95 and 90 percent, respectively. Membranes are not affected by changes in pH or the presence of other inorganic constituents. The principal disadvantages of RO and NF are high-cost and water recoveries as low as 60 percent. The large percentage of wasted water associated with membrane technology makes the use of these systems impractical in the Western United States, where water supply can be limited, unless additional equipment is installed to recover the reject water.

Contact us with your water treatment needs

Each plant has different design parameters involving various chemical feed systems with variations in detention times and filtration media. Because each arsenic situation is unique, we offer pilot testing to optimize an existing plant or to assist in the design of a new plant. Call your Tonka Water Representative for more information on arsenic removal or any other water treatment needs.

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