Biosorption of Heavy Metals from Aqueous Solution using Bacillus Licheniformis

Int. J. Pure Appl. Sci. Technol., 10(2) (2012), 12-19. 15
Effect of pH:
The pH of the solution is the most critical parameter for metal sorption as it influences both the
bacterial surface chemistry as well as solution chemistry of soluble metal ion. Different metals show
different pH optima for their biosorption (Donmez et al. 1999; Saeed and Iqbal 2003).
Fig.1 shows % removal of heavy metal ions at pH- 2.5, 3, 3.5, 4, 4.5. It was found to be in the range
of 14 – 95 %. Maximum biosorption was observed at pH 3.5 for iron and chromium ion with removal
efficiency of 95% and 52% respectively. pH 2.5 was found to be optimum for Cu ion giving the
maximum removal efficiency of 32%. The results suggested that acidic pH (2.5 to 3.5) was optimum
for biosorption of these heavy metals using B.licheniformis. Among the three metal ions removal
efficency for iron (63-95 %) was found to be maximum.
Zhou et al, (2007) have also reported acidic pH optimum (pH 2.5) for Cr (VI) ion using dead biomass
of B. licheniformis isolated from polluted soil sample with 85 % metal removal efficency. B.
licheniformis CCO1 reported by Clausen (2000) exhibited removal efficiency of 93% and 8% for
copper and chromium respectively. However our results indicated 60% removal efficiency when a
mixture of Cr (VI), Cu (II) and Fe (III) ions was used. This showed higher metal removal efficiency
of living biomass of B. licheniformis (NCIM 2471), thereby suggesting its possible application in
multiple metal removal in effluent treatment.
Effect of Incubation Temperature:
Fig.2 shows effect of incubation temperature on metal biosorption. Maximum % removal of metal ion
was observed at 28°C. Removal efficiencies were 95%, 52% and 38% for Fe (III), Cr (VI) and Cu (II)
respectively at 28°C. Such high binding efficiency of iron ion by B.licheniformis was also reported by
Beveridge et al. (1982). Teichoic acid, teichouronic acid and peptidoglycan were shown to be
important biomolecules involved in metal binding as mentioned earlier. Iron binding was found to be
reduced by 38% when teichoic acid was removed and by 60 % when both teichoic acid and
teichouronic acid were removed. McLean et al. (1990) observed similar results in uptake of iron and
suggested participation of gamma-glutamyl capsular polymer of the organism, other than these
biomolecules. To our knowledge this is the first report showing 95% biosorption of iron using living
cells of B.licheniformis.
Determination of MTC:
Using colorimetric method, MTC of B.licheniformis for three metal ions viz. hexavalent chromium
ion, cupric ion, ferric ion and for mixture of these three metal ions in a same sample were determined
(Fig 3). As indicated in fig.3, MTC for hexavalent chromium ion was 1200 mg L -1. In case of cupric
ion and ferric ion, the MTC was above 1500 mg L -1 , whereas the MTC for set having mixture of all
the metal in a sample was 1000 mg L -1 . These results suggested that the organism has high metal
tolerance for copper and iron as compared to chromium. In light of our observations, living biomass
of B.licheniformis could be used efficiently and effectively in removal of heavy metals from effluents.
Conclusions
Our results demonstrated that the use of live cells of B.licheniformis in waste water treatment would
prove an eco-friendly, multipurpose and cost efficient alternative to conventional methods. This work
will be helpful in i) developing technologies useable for in situ bioremediation using B.licheniformis
ii) construction of large scale bioreactor iii) promoting its detail study of binding mechanism and
other technological parameters to improve the feasibility in the process application.