Organics Removal with Anion Exchange

by TJ Stroebl
Tonka Equipment Company


The Village of Ohio, Illinois recently commissioned their new water treatment plant to remove iron, manganese, arsenic, and color from the groundwater supply, by installing an integrated Tonka treatment system.  A Dualator® VI, which incorporates aeration, detention and filtration, is used to remove the iron, manganese and arsenic. The unit is 11 feet in diameter and is designed to operate at 275 gpm. A Tonka ORGANIX™ anion exchange system was installed downstream of the Dualator® to remove dissolved organic compounds associated with color.



Proving the process
During 2006-2007, Tonka conducted a pilot study on site under the supervision of the Village engineer, Willet, Hoffman & Associates.  The study showed that removal of iron, manganese and arsenic was feasible with Tonka’s Dualator® VI system; however, color was not consistently removed to acceptable levels with this process alone.  In anticipation of this, Tonka had also piloted anion exchange downstream of the filters, and the result was that anion exchange consistently yielded exceptionally colorless water.

Assuring Consistent Organics Removal results
Tonka has been utilizing anion exchange for over ten years to remove dissolved organic matter (NOM) associated with color and disinfection by-product formation.  Organic matter is removed when ionized carboxylic groups on these large organic molecules exchange with chloride ions on a specially selected resin.  Additional removal is achieved by means of adsorption within the resin pores due to electrostatic, hydrophobic, and Van der Waals interactions.  The Tonka ORGANIX™ System operates similar to a water softener, using a bed of ion exchange resin inside an ASME pressurized vessel. It is periodically regenerated with a sodium chloride brine solution, controlled by a custom designed control panel.


Pilot study is a critical step
The extent of NOM removal depends on the specific molecular weight distribution of the dissolved organics and varies among water sources:  Tonka has seen between 50 and 90 percent removal of NOM at various locations throughout the US.  This means that piloting is critical for any site considering what to do for organic removal.  Piloting at Ohio, IL predicted organic-induced color removal from 45 CU to less than 5 CU, and we’re happy to say that the full scale system is achieving these results