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 In-House and Field Research

 

EPA investigates various arsenic removal technologies in order to evaluate their effectiveness. In‑house research consists of a variety of activities that include studies on adsorptive media coagulation, filtration, iron removal, and other processes using bench-scale and pilot-scale methodology. These studies have resulted in a number of technical reports on:

  • Methods to preserve water samples for arsenic (III) and arsenic (V) speciation tests
  • Oxidation methods for converting arsenic (III) to arsenic (V)
  • Methods for the treatment of residuals from arsenic removal processes
  • Design manuals for adsorptive media, ion exchange, and iron removal processes
  • Cost programs for estimating adsorption media, ion exchange, and iron removal processes

EPA’s ongoing arsenic research is improving analytical methods, treatment process optimization, distribution system integrity, and management of residuals from arsenic treatment. The research projects include:

Arsenic Removal Methods

Adsorptive Media Method

In this method, arsenic ions are removed from water by available adsorptive sites on an adsorptive media. When all available adsorptive sites are filled, some of the spent media can be regenerated or simply thrown away and replaced with new media. Granular activated alumina was the first adsorptive media successfully used. Other media that have been used with success are various types of iron oxide composite.

Anion Exchange Method

Anion exchange is a process that involves exchanging ions from a solution onto a resin. It works the same way a household water softener does, except that it removes arsenic, specifically arsenic (V), instead of calcium. For arsenic removal, an anion resin in chloride form is used. Anion exchange resins also remove other anions such as sulfate, nitrate, and uranium. When the resin becomes saturated with arsenate and other anions, it must be regenerated. In the regeneration step, sodium chloride brine is flushed through the resin where the adsorbed arsenate and other anions are replaced with chloride ions.

Coagulation/Filtration and Iron Removal Method

Iron removal processes can be used to remove arsenic. That means that areas with high iron concentrations requiring an iron removal process can use one process to remove both iron and arsenic. The capacity to remove arsenic during iron removal processes depends on a number of factors, including the amount and form or arsenic present, pH, amount and form of iron present, and the existence of competing ions such as phosphate and silicate. The advantage of this process is that it uses naturally occurring iron in the water for the process. However, the arsenic removal efficiency of the filtration system can be enhanced by adding iron to the source water.

Reverse Osmosis/Membrane Separation Method

Membrane separation, or reverse osmosis, technolgies are effective arsenic treatment processes for small water systems. Reverse osmosis is a pressure-driven membrane separation process capable of removing arsenic from water by means of:

  • Particle size
  • Dielectric (insulation) characteristics
  • Hydrophilicity (the tendency of a molecule to be dissolved in water)
  • Hydrophobicity (the association of nonpolar groups or molecules in an aqueous environment that arises from the tendency of water to exclude nonpolar molecules)

This process also effectively removes other contituents from water, including organic carbon, salts, dissolved minerals, and color. This treatment process is relatively insensitive to pH, although pH adjustment may be required to protect the membrane from fouling. Liquid residual consists of membrane reject water, generally high in total dissolved solids. The liquid wastewater likely contains high levels of arsenic and other constituents rejected from the source’s water. This renders the liquid wastewater a hazardous waste that must be treated before disposal or sent to a sanitary sewer.

Contact

Tom Sorg
513-569-7370


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