The work investigated the efficiency of
microbial fuel cells (MFCs) for the treatment of alkaline
hexavalent chromium containing wastewater. When lactate
was used as the metal chelator in alkaline (pH 8) abiotic
cathodes, hexavalent chromium concentration dropped
from 10 mg l
-1 to undetectable levels within the first 45 h
of operation. Power density produced in the pH 8 abiotic
cathodes was up to 21.4 mW m
-2
, and in the pH 9 cathodes
up to 2.4 mW m
-2
; these values were well comparable
with other values found in the literature for
biologically catalysed cathodes, even at lower pH values.
When
Shewanella oneidensis
MR-1 was present in a
hexavalent chromium reducing cathode at pH 8, current
production contributed by 26 % to the total hexavalent
chromium reduced during the 36 days of operation. On the
other hand, when hexavalent chromium (10 mg l
-1
) was
controllably added in the anode where
S. oneidensis MR-1
was present, up to 73 % of current decreased immediately
after every hexavalent chromium addition; this toxic effect
remained even after hexavalent chromium was depleted in
the anode and strongly indicates that the presence of
hexavalent chromium in the anodes of MFCs must be
avoided. Overall, our results indicate that alkaline hexavalent
chromium wastewater can be effectively remediated
in the cathodes of MFCs, provided that a metal chelator is
present in the cathodes and that hexavalent chromium is
not present in the anodes.
