AWWA ACE63128

Communities that soften groundwater with ion exchange systems typically useconcentrated salt solutions (brine) to regenerate exchange capacity. This results in wastebrine containing high total dissolved solids, mainly chlorides and sulfates. Theseresiduals can affect operations at publicly-owned treatment works (POTW's) and mayresult in National Pollutant Discharge Elimination System (NPDES) discharge permitviolations. This paper presents novel and cost-effective solutions developed formanaging ion exchange residuals at the City of Crystal Lake, Illinois. These solutionsmay be especially useful for groundwater systems that may be having problemsmanaging waste residual streams from ion exchange systems.Crystal Lake has five water treatment plants (WTPs) and two wastewater treatmentplants. The water treatment plants use zeolite-based ion exchange with sodium chlorideregenerant. The waste brine from the ion exchange systems contains an averagechlorides concentration of 1700 mg/L, which is more than three times the anticipatedIllinois 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-formweak acid cation (WAC) exchange with sulfuric acid regenerant;Alternative 3 - Converting the sodium-form ion exchange system to a hydrogen-formstrong acid cation (SAC) exchange with sulfuric acid regenerant;Alternative 4 - Treating waste brine from the existing sodium-form ion exchangesystem with a hydrogen-form strong acid cation exchange system (i.e, closing thewaste stream loop); and,Alternative 5 - Replacing the existing ion exchange treatment processes withmembrane and/or electrodialysis reversal (EDR) treatment systems.Because the source water quality differed among the water treatment plants (e.g., deepwells versus shallow wells), different alternatives had to be considered for each facility.A chlorides mass balance model was developed to investigate the chloride residualsresulting from each alternative at each WTP. A cost-benefit analysis was developedbased upon the results of the model. Alternatives 1 and 4 were selected for potentialimplementation at two WTPs. These alternatives were selected for pilot testing andfurther investigation for their overall cost-effectiveness (capital and operations andmaintenance), least impact on water and wastewater operations, reuse of existingfacilities, and the ability to maintain consistent high quality drinking water. The City iscurrently conducting bench- and pilot-scale testing of the selected alternatives to verifyand optimize the design criteria and conditions of service. Includes tables, figures.

Product Details

Edition:

Vol. - No.

Published:

06/01/2006

Number of Pages:

12

File Size:

1 file , 360 KB