Abstract:
Hexavalent chromium (Cr(VI)) is highly soluble in water, but is widely used in industrial sectors for many
purposes. The effluent from these industrial activities is often released to the environment posing a threat to
aquatic life and to humans. Conventional methods of treating Cr(VI) often require the use of pump and treat
methods followed by the use of harmful toxic chemicals that are hard to dispose of and usually are expensive.
The study explores reduction of Cr(VI) to Cr(III) using biological means (a popular issue of bioremediation of
contaminated aquifer) in columns; control with aquifer media, system 1 inoculated with CRB (chromium reducing
bacteria) dried sludge, system 2 further amended with saw dust and system 3 amended with vegetative material
from target site as carbon source. CRB are essential and were inoculated in the columns (system 1-3) as dried
sludge, previously isolated (Enterococcus casseliflavus, Pseudomonas putida, C.istrobacter sedlakii,
Enterobacter cloacae and Enterobacter hormaechei) and tested in a batch system. The column reactors were
run for 60 days at concentrations 40, 60 and 80 mg/L. Culture isolates in the effluent of the reactors were isolated
and identified. Complete reduction was observed from all columns under different concentrations, with some
failures at certain periods before quasi steady state (determined after 40 d). At 40 mg/L more than 95 % of
Cr(VI) was reduced across the spectrum. System 3 best reduced Cr(VI) compared to other treatment column
reactors at high concentrations of 80 mg/L. System 2 carbon source didn’t enhance Cr(VI) reduction compared
to Syetem 1 with no carbon material. Algae growth was observed in the columns after operating for 40 d at
40 mg/L. Using 18s rRNA the dominant algae was identified as Chlamydomonas debaryana. As Cr(VI)
concentration was increased, both CRB and the algae were assumed to be in synergy as Cr(VI) was reduced
at influent concentration as high as 80 mg/L (double the concentration from the site). Further investigation was
done in the study to identify Cr(VI) reducing potential by algae. The use of vegetative material from the target
site in the presence of algae proved to enhance Cr(VI) reduction by CRB even though saw dust did not perform
as expected. This method has potential to be used in Cr polluted sites in South Africa with careful application.
