Environmental Engineering Reference
In-Depth Information
perchlorate from contaminated drinking water, groundwater, and soil have included the
following approaches:
• Ion exchange
• Bioreactor/bioremediation
• Composting
• Permeable reactive barrier
• Phytotechnology
• Membrane technologies (electrodialysis and reverse osmosis)
• Sorption by media such as activated carbon or other absorbents
These technology approaches are briely summarized below.
32.2.1 Ion Exchange
Ion exchange has been used for full-scale removal of perchlorate from drinking water,
groundwater, surface water, and other water discharges. During the ion-exchange process,
ions held electrostatically on the surface of a solid are replaced or exchanged by ions in a
solution of a similar charge. The most commonly used ion-exchange media are synthetic,
strongly basic, anion-exchange resins. Ion exchange has been used at test sites to reduce
perchlorate concentrations to <4 μg/L; however, it is expensive and generally too expen-
sive for treating larger volumes of water. Water chemistry does impact the effectiveness
of ion-exchange media. The media can be used both as the main ilter and/or as a polish-
ing ilter for other water treatment processes such as biological treatment of perchlorate
(Federal Remediation Technologies Roundtable [FRTR], 2005; Gu et al., 1999).
Monofunctional and bifunctional anion-exchange resins are commonly used for per-
chlorate treatment. Bifunctional resins consisting of two functional groups are used for
a broader range of ionic strengths than monofunctional resins (FRTR, 2005). Some resins
used for perchlorate removal include a polyvinylbenzylchloride backbone cross-linked
with divinylbenzene, to form quaternary ammonium strong-base anion exchange sites
(Gu et al., 1999, 2002, 2003).
Ion-exchange resin beads are usually packed into a column and contaminated water
passed through the bed of resin beads. Contaminant ions are exchanged for other ions such
as chlorides or hydroxides in the resin (FRTR, 2005). Ion exchange is often preceded by treat-
ments such as iltration and oil-water separation to remove organics, suspended solids, and
other contaminants that can foul the resins and reduce their effectiveness. Ion-exchange
resins must be periodically regenerated to remove the adsorbed contaminants and replenish
the exchanged ions (FRTR, 2005). Regeneration of a resin typically involves three steps:
1. Backwashing
2. Regeneration with a solution of ions
3. Final rinsing to remove the regenerating solution
Regeneration results in a backwash solution, a waste-regenerating solution, and a waste
rinse water (EPA Ofice of Solid Waste and Emergency Response [OSWER], 2002). It has
been reported (Gu et al., 1999) that nearly 110,000 bed volumes of water contaminated with
