Abstract |
The purpose of the present study was to establish means of removing the chromate (Cr(VI)) from spent regenerant solution, thus rendering it a non-toxic brine. In the bench-scale study, the Cr(VI) was reduced to Cr(III) and then precipitated as Cr(OH)3(s). Sulfite, hydrazine, and ferrous sulfate were tried as reductants. Sulfite and hydrazine operated best at pH less than 2 while ferrous sulfate performed well in the neutral pH range. Ferrous sulfate reduction proved to be the lowest cost treatment method for the regenerant brine. For a 4 MGD treatment system utilizing 70% bypass flow and reducing the chromium from the 0.050 mg/L to 0.035 mg/L in the blended product water, the spent regenerant brine treatment cost was quite low--$1.50/million gal of product water. For a 0.1 MGD treatment system, the corresponding cost was $460/million gal of product water. |