Transcript Chromium-6 and Bioremediation

Chromium-6 and
Bioremediation
O
HO-Cr-OH
O
Paula Warren
What is Cr-6?
Cr-6 is one of the most commonly occurring toxic pollutants present in
wastewaters discharged from electroplating, dye and pigment manufacturing,
wood preserving and leather tanning industries. Cr-6 is not only highly
toxic, but also is mobile and has a long residence time in surface and
groundwater. It poses a health risk to humans and animals, and impairs the
development and growth of most plants.
The main chemical dealt with in the Erin Brockovich toxic water case was Cr-6.
O
O
O = Cr – O + oxidizing agent = O = Cr = O
O
O
The Study
Choo T P; Lee C K; Low K S; Hishamuddin O Accumulation of chromium (VI) from aqueous
solutions using water lilies (Nymphaea spontanea). Chemosphere (2006), 62(6), 961-7.
Journal code: 0320657. ISSN:0045-6535. PubMed ID 16081131 AN 2006069706 In-process
for MEDLINE
Water lilies were found to be able to survive in
waters containing heavy metals. They are
aesthetically pleasing, and do not interfere with
crops on irrigated land or with fish production.
Using Water Lilies for
Bioremediation
The night bloomer tropical water lily (Nymphaea spontanea) have extensive roots
and provide large surface area for the biofilm formation (the slimy layer) and
thus enhance the microbial activities.
Water lilies are able to extract the Cr-6 from the wastewater. The study shows
how effective this method is.
How is the metal absorbed?
-Plasma membrane and Passive Diffusion
Metal ions are adsorbed on the cell
walls via passive diffusion or moved
from the roots to the apex of the
plant.
Passive diffusion is the simplest transport process as
molecules moves across membrane without the help of
any specific transport system. Molecules move across
membrane and set up an equilibrium of
concentration (driven by entropy considerations)
Results
Cr-6 solutions at [ ] of 1, 2.5, 5, and 10 mg/l were used in the study
to assess the metal accumulation of water lilies. pH=6.0-6.5.
Also used a metal solution with Cu and Cr-6, since Cu
commonly occurs with Cr-6 in electroplating wastewater.
With an increasing metal [ ], the water lily increased the amount of
Cr-6 it took up. ~16% uptake of its dry weight!
% uptake= (Co – Ce/Co) x 100%
Co = [initial] , Ce = [remaining Cr-6]
Removal of Cr-6 by water lilies after
7 days exposure (Table 1)
Table 1.
Removal of Cr(VI) by water lilies after seven days’ exposure
Initial Cr(VI) concentration
(mg/l)
1.0
2.5
5.0
10.0
Cr(VI) concentration in plants
(mg/g dry weight) a
Concentration factor
0.775 ± 0.022
1.374 ± 0.099
1.467 ± 0.063
2.119 ± 0.093
946
655
319
225
a= Mean of three replicates ± standard error.
Removed by Plant
(mg/g)
Amount Cr Uptake in Plants from Inital
Solution Concentrations
So, there was an increased amount of
Cr-6 a cumulated by the water lily
with the increase of metal
concentration. As the plant was
introduced to more metal and Cr-6, it
was able to continue to absorb at a
higher amount.
2.5
2
1.5
1
0.5
0
1
2.5
5
Initial Concentration (mg/l)
10
Uptake of Cr-6 by water lilies
exposed to different initial [Cr-6].
Fig. 1
Uptake of Cr(VI) by
water lilies exposed to
different initial Cr(VI)
[ ]s.
--initial [ ] 1.0 mg/l;
--initial [ ] 2.5 mg/l;
--initial [ ]5 mg/l;
--initial [ ] 10 mg/l.
Cr-6 uptake increased in all the treatments (Cr-6
alone, both Cr-6 and Cu-2(bianary metal), and
electroplating waste) for the first 5 days and then
remained constant for the binary metal and the
waste solutions, but continued to increase
uptake in the singe metal solution.
Cr(VI) accumulation by water lilies subjected
to different treatments.
** single metal solution containing 2.5 mg/l
Cr(VI);
** binary metal solution,
** waste solution, both containing 2.5 and 0.5
mg/l Cr(VI) and Cu(II), respectively;
** metal free control.
Conclusion
Using water lilies could be an effective, aesthetic way to reduce the
harmful substance of Cr-6 from wastewater and electroplating
refuge. Water lilies were observed to assist in bioremediation of
this toxic chemical while still remaining healthy.
May not be the Most effective resource for bioremediation, but it
does not creep up on crops like duckweed does.
Would be worth investing a small amount of $$ in to help reduce
the amount of heavy metals in the wastewater, and to help
reduce other, more costly methods of removed these metals.
The Study:
Choo T P; Lee C K; Low K S; Hishamuddin O Accumulation of chromium (VI) from aqueous
solutions using water lilies (Nymphaea spontanea). Chemosphere (2006), 62(6), 961-7.
Journal code: 0320657. ISSN:0045-6535. PubMed ID 16081131 AN 2006069706 In-process
for MEDLINE