Environmental Engineering Reference
In-Depth Information
Fig. 9 Effect of nitrate-reducing monocultures-decolorized medium on growth of mung bean
shoots. The bars are the averages of three replicates from each treatment, and error bars
indicate ± standard deviations from the means. Treatments used were T1 Nitrate-reducing
monoculture-decolorized medium on 7th day of incubation, T2 Nitrate-reducing monoculture-
decolorized medium on 14th day of incubation, T3 Fahreus medium (negative control) and T4 1%
Congo red solution (positive control)
of incubation were similar to that of seedlings exposed to Fahreus medium, but
higher than that of seedlings soaked in 1 % Congo red solution.
Based on the results of the toxicity of the decolorized culture medium and Congo
red towards plants, it can be deduced that the undegraded Congo red, is toxic to
both rice and mung beans as evidenced by the stunting of plant growth and low dry
weights. The effects of the denitrifying consortium decolorized medium and nitrate
reducing monoculture decolorized medium on plant growth may be attributed to the
presence of small amounts of still undegraded Congo red and also bacterial
decolorization metabolites being slightly toxic to both rice and mung beans. Many
bacteria reduce azo bonds to the corresponding amines. Several aromatic amines
can be degraded under the aerobic condition (van der Zee 2002 ). The higher plant
shoots than the negative control may be attributed to the promotion of plant growth
by the nutrients formed during bacterial decolorization which were imbibed by the
seedlings. Therefore, the decolorization of Congo red by the bacteria diminished the
severe toxic effect of the dye to the rice and mung bean plants.
7 Future Prospectives
The Congo Red Decolorizing Bacteria (CRDB), isolated from the paper factory
ef
uent, are very promising as bioremediation agents as they have shown high
decolorizing potential in the microcosm study. The CRDB can be further developed
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