Communities that soften groundwater with ion exchange systems typically use
concentrated salt solutions (brine) to regenerate exchange capacity. This results in waste
brine containing high total dissolved solids, mainly chlorides and sulfates. These
residuals can affect operations at publicly-owned treatment works (POTW's) and may
result in National Pollutant Discharge Elimination System (NPDES) discharge permit
violations. This paper presents novel and cost-effective solutions developed for
managing ion exchange residuals at the City of Crystal Lake, Illinois. These solutions
may be especially useful for groundwater systems that may be having problems
managing waste residual streams from ion exchange systems.
Crystal Lake has five water treatment plants (WTPs) and two wastewater treatment
plants. The water treatment plants use zeolite-based ion exchange with sodium chloride
regenerant. The waste brine from the ion exchange systems contains an average
chlorides concentration of 1700 mg/L, which is more than three times the anticipated
Illinois Pollution Control Board (IPCB) limit of 500 mg/L.
Crystal Lake and CDM investigated several alternatives for lowering the chlorides limit,
including: Alternative 1 - Converting the sodium-form ion exchange system to a selective
(calcium-form) ion exchange system for barium removal only;
Alternative 2 - Converting the sodium-form ion exchange system to a hydrogen-form
weak acid cation (WAC) exchange with sulfuric acid regenerant;
Alternative 3 - Converting the sodium-form ion exchange system to a hydrogen-form
strong acid cation (SAC) exchange with sulfuric acid regenerant;
Alternative 4 - Treating waste brine from the existing sodium-form ion exchange
system with a hydrogen-form strong acid cation exchange system (i.e, closing the
waste stream loop); and,
Alternative 5 - Replacing the existing ion exchange treatment processes with
membrane and/or electrodialysis reversal (EDR) treatment systems.
Because the source water quality differed among the water treatment plants (e.g., deep
wells versus shallow wells), different alternatives had to be considered for each facility.
A chlorides mass balance model was developed to investigate the chloride residuals
resulting from each alternative at each WTP. A cost-benefit analysis was developed
based upon the results of the model. Alternatives 1 and 4 were selected for potential
implementation at two WTPs. These alternatives were selected for pilot testing and
further investigation for their overall cost-effectiveness (capital and operations and
maintenance), least impact on water and wastewater operations, reuse of existing
facilities, and the ability to maintain consistent high quality drinking water. The City is
currently conducting bench- and pilot-scale testing of the selected alternatives to verify
and optimize the design criteria and conditions of service. Includes tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 360 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 12 |
| Published : | 06/01/2006 |
