www.ca-nv-awwa.org 25
Davis Cr-6 Study, continued from page 11
The biological treatment process utilized is
the NSF 61-approved fluidized bed bioreactor
(FBR) technology. The FBR is an active,
fixed-film bioreactor that fosters the growth
of microorganisms on a hydraulically fluidized
bed of fine media. The small, fluidized
media provides an extremely large active
surface area upon which microorganisms
can grow. An electron donor (i.e., NSF 60
approved acetic acid) is provided to the FBR
where it is used by the microbes in the denitrification/
chrome reduction process. End
products are nitrogen gas, reduced chrome,
carbon dioxide, water, and biomass.
The bench scale pilot demonstrated that
effective Cr-6 reduction to concentrations
less than 1 μg/l is achievable. Total organic
carbon (TOC) residual was higher than
expected and could present water quality
challenges if Cr-6 effluent concentrations
below 1 μg/l need to be maintained. The
proof of concept pilot was successful in demonstrating
the efficacy of an FBR system for
co-removal of constituents including Cr-6,
total chromium, nitrate, perchlorate, and
selenium. However, this bench scale pilot
was limited in its ability to offer accurate data
that can be used to scale up to a full sized
system and the researchers recommended
a demonstration scale project to evaluate
among other issues, the impacts of chlorine
added for disinfection, including the potential
of reformation of Cr-6 and formation of
disinfection byproducts.
Davis has also participated in the CA-NV
AWWA Chromium 6 Technical Advisory
Group, which has been meeting on a regular
basis to develop factual information
about Cr-6 compliance efforts and issues
throughout California. The state’s current
Cr-6 standard is 50 mg/l for total chromium,
and it’s anticipated the California
Department of Public Health (CDPH) will
set a MCL in the 1.0 to 25 mg/l range. S
Editor’s Note: At press time the Draft MCL was
expected to be released by CDPH within the
month (July). The new regulation will be the subject
of a special panel of experts at the CA-NV
AWWA Annual Fall Conference in Sacramento.
Source will continue to cover questions about
Cr-6 regulation, as well as techniques and cost
of treatment, as new developments warrant.
/www.ca-nv-awwa.org
