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Arsenic Removal

Arsenic is found in just about all ground water and exists as either a tri (+3) or penta (+5) valent anion specie. It is largely a naturally occurring contaminant. When the EPA recently decreased the MCL from 50 ppb (parts per billion) to 10 ppb, many wells once considered safe now had to be treated. One of the most common treatment methods for municipally supplied water is to first oxidize the tri-valent arsenic to penta-valent with ozone or chlorine and then use a co-coagulent such as ferric chloride or an aluminum salt to co-precipitate the arsenic and filter it out. Activated alumina is also an effective media for arsenic removal for use in pressure filters.

Of the more recent media developments used for arsenic removal are the granular ferric hydroxide and ferric oxides commonly known as GFH and GFO and the hybrid ion exchange resins that are treated with an active ferric functionality to bind with arsenic, allowing easy removal. One such resin is the ArsenXnp from Purolite Company.

Systems using ArsenXnp are usually designed as a lead/lag configuration with a monitoring port in between the two units. Although ion exchange at heart, the ArsenXnp resin is actually an adsorbant and there are several factors to be considered making up a proper design. Check out my article on this web site for more detail.

Arsenic removal systems should be lead/lag with complete redundancy. Municipal systems are often designed at 2 to 3 gpm/cu ft of media for economic residence times while residential units are often run up to 5 gpm/cu ft (with a recution of capacity). Throughput capacities can range from 50,000 to 500,000 gallons per cu ft depending on the variable and feed water composition. Municipal and larger systems can be regenerated using a proprietary technique generally done off site by a licensee. Disposal of the spent media is generally as ordinary landfill but because of the high adsorptive capacity per cu ft, spent media can be considered as a haz waste by some states.

Strong base anion resin using salt regeneration can also be used for arsenic removal in residential systems. If there is a need to use strong base anion for the removal of other contaminant (ie uranium or nitrate), the process can often be accomplished with a single resin in a single tank. Check with us.

Systematix also produces a series of specialty cartridges (See our site listings for Aqualine™ Cartridges) that can be used alone as under-counter filters, R/O polishers or in-lines.