Decreasing waste brine volume from anion exchange with nanofiltration: Implications for multiple treatment cycles

Korak, Julie Ann

Citeable URL: https://scholar.colorado.edu/concern/articles/zc77sr62x

Abstract

Ion exchange (IX) is a technology for removing hexavalent chromium from water, butwaste brine disposal makes implementation cost prohibitive in many communities. Nanofiltration(NF) can be integrated to decrease the waste brine volume by 70% and reuse the permeate (NF-reuse) as brine in the next IX regeneration. However, the accumulation of impurities and resultingimpact on IX regeneration and loading efficiency have not been evaluated through comparativemass balances or post-regeneration batch tests. Combining pilot-scale experiments withresponse surface modeling, impurities in waste brine are predicted to reach a pseudo steady stateover 10 loading-regeneration-NF-reuse cycles, simulating long-term operation at full-scalefacilities. Side-by-side regenerations show that NF-reuse brine does not impact the IXregeneration efficiency of chromium, sulfate or inorganic carbon. Regeneration efficiencyincreases for vanadium and uranium by 30-60% using the NF-reuse brine, which may decreaselong-term fouling and reduce the frequency for strong acid regenerations. With NF-reuse,additional nitrate loads onto the IX resin during regeneration, which may impact the timing and magnitude of chromatographic peaking. During loading, arsenic exhibited chromatographicpeaking at concentrations 220% higher than the influent concentration, exceeding regulatorythresholds under all regeneration scenarios. Arsenic leakage also occurred during the first 500bed volumes with NF-reuse. Vanadium and chromium both exhibited faster breakthrough in thesecond loading cycle, demonstrating the importance of evaluating pilot-scale processes overmultiple loading and regeneration cycles. Bench-scale studies need to be guided by full-scale IXoperating constraints and evaluate factors beyond the contaminant of concern to fully identifypotential impacts of implementing NF brine management. A supplemental spreadsheet is includedfor utilities to screen NF for system-specific testing.

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