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Detection Of Chromium In Drinking Water
Chromium can be accurately measured to sub-part
per billion concentrations using widely available
analytical techniques. Total chromium concentrations
are determined by inductively coupled plasma
— mass spectrometry (ICP-MS) per EPA Method
200.8. Hexavalent chromium is measured by ion
chromatography followed by spectroscopic detection
per EPA Method 218.7. There is no accepted method
for direct measurement of Cr(III). Instead, Cr(III)
concentrations are calculated by difference, subtracting
the Cr(VI) concentration from the Cr(tot) concentration.
Technologies For The Treatment
Of Chromium In Drinking Water
Currently few utilities in the U.S. operate a full-scale
treatment system specifically designed to remove Cr(VI)
from drinking water. However, there have been a number
of bench and pilot level studies evaluating chromium
treatment technologies. Based on the results of these
studies, there are four Cr(VI) treatment technologies
capable of meeting California's 10 µg/L MCL:
• Strong base anion exchange (SBA)
• Weak base anion exchange (WBA)
• Nanofiltration/reverse osmosis membranes (NF/RO)
• Reduction/coagulation/filtration (RCF).
NF/RO membranes remove Cr(VI) by forcing
contaminated water under pressure through a semi-
permeable membrane. Hexavalent chromium, along
with other dissolved contaminants, is retained by the
membrane through a combination of size exclusion
and electrostatic repulsion effects. Depending on the
specific design of the membrane, rejection of up to
95 percent of Cr(VI) is possible. As with all NF/RO
systems, they are hydraulically inefficient. A typical
recovery (the ratio of water produced to water treated)
is 75 to 80 percent. Hence, membrane systems are
undesirable in arid sections of the country where
water resources are scarce. In addition, disposal of the
Regulatory Analysis
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