Hexavalent Chromium Treatment Selection Considerations
- Nicole Blute and Xueying Wu - Hazen and Sawyer
The State of California intends to regulate hexavalent chromium with a new primary maximum contaminant level (MCL) expected in draft form in July 2013. Cr(VI) and total Cr are both on the Unregulated Contaminant Monitoring Rule 3 (UCMR3), with a potential federal regulation on the horizon for Cr(VI) (or a lower standard for already regulated total Cr).
A decade of research conducted by the City of Glendale, California in partnership with many other entities identified a handful of treatment technology options for removing Cr(VI) to less than 5 ppb, including ion exchange (weak and strong base), reduction/coagulation/filtration, and membranes (NF or RO). Other possible approaches, including adsorptive media and new ion exchange resins, have emerged and are being tested. Weak and strong base anion exchange and RCF (with granular media filtration or microfiltration) have been extensively studied, and results from demonstration or full scale treatment systems will be highlighted.
The audience will gain an understanding of treatment process selection considerations, including the impact of raw water quality, integration into existing treatment trains, operations complexity, and residuals disposal options. Pitfalls in measurements for total Cr at low ppb or sub-ppb levels will also be discussed, including approaches used to overcome the challenges observed in previous testing. The next step in treatment process selection, technology testing, will also be discussed and guidance documents identified that can assist utilities in planning.
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