RECOVERY OF HEAVY METALS USING Magnetospirillum sp.

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RECOVERY OF HEAVY METALS USING Magnetospirillum sp.VITRJS5

ABSTRACT:

Magnetotactic bacteria (MTB) are ubiquitous in the aquatic environment and have been identified from almost every continent. Since MTB has active metal transport system for the biominerilisation of iron oxide particles Magnetospirillum sp. has been used to study uptake and separation of various heavy metals from environment. This work investigates the ability of Magnetospirillum sp. VITRJS5 on biosorption for heavy metals. Metals were provided in previously optimized MS1 media as sole electron acceptors to determine the utilization of metals by bacteria.Heavy metals such as Cadmium(Cd), Lead(Pb), Zinc(Zn),Copper (Cu) and Nickel (Ni) were used for the recovery study.The culture study and atomic absorption spectroscopy(AAS) showed that the MTB were able to recover the metals from different samples but the proportion varied. Among the five metals used Magnetospirillum sp. VITRJS5 were able to utilize cadmium, zinc and nickel,copper are the other two metals were less utilized by the bacteria for metabolism.

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1. INTRODUCTION:

Recovery of heavy metals is important because it can promote applications which have benefits both for industry and the environment. Examples include detoxification of effluents and waste water carrying heavy metal and the removal of valuable elements such as the platinum or gold or lead or zinc,cadmium from solution.Heavy metal pollution caused by different industrial waste, is one of the major threats for ecological systems and to the inhabitants. Thus, the need for recovering heavy metals from wastewater to remove the

toxic chemical elements and recycle these metals became very important.

Conventional methods for heavy metal removal such as precipitation of metals chemically, ion-exchange, treatment by electrochemical method, and active carbon adsorption, has been done and improved. However, problems such as high expenses, low efficiency, complicated process and secondary pollution is not yet solved thoroughly. In recent years, attention has been paid towards biosorbents because of their excellent adsorption properties, low cost, and high availability. Nevertheless, separation and recovery of biosorbents from solutions are still challenges in the field.

The Magnetotactic bacteria (MTB) are promising biosorbents because it can be easily separated from wastewater using magnetic field.They are capable of forming a particular membranous intracellular structure called magnetosome. Magnetosomes have uniform, species-specific crystal habits with narrow size and shape distributions, and they are generally aligned in chains within bacteria.Magnetite (Fe3O4) or greigite (Fe3S4) are magnetic particles that are present in magnetosomes.MTB are mostly found in freshwater and oceanic sediments. Most of them are microaerophiles or anaerobe, found in or below the oxic–anoxictransition zone (OATZ). Compared with studies on the applications of MTB in the medical and environmental fields, only a few research works arefocused on MTB application in environmental remediation. The mineralization of metal ions occurs in MTB after exposure to metallic elements. Moreover, MTB showed selective reinforced competitive biosorption for Zn,Pb,Cd and other metals.The adsorption capacity of MTB for Cd2+ has been improved by cell surface display technology.Thus, more attention needs to be paid to this promising biosorbent. The application of MTB in removing and recovering heavy metals is emphasized in this paper.

Apart from magnetosome two types of granules without any membranes are found in most MTB. Phosphorus and oxygenare the most common elements in granules. P granules which is the phosphate granule may naturally contain small amounts of manganese. Other elements, such as Zn, Cd,Fe are also detected on some occasions. Granules are considered as a major site for metal accumulation.The capability of granules to assimilate metal ions may indicate a detoxification role. In addition, granules are also identified as lipid storage facilities and may act as storage compounds for energy and carbon needed in maintaining metabolism and synthesis of cellular metabolites during starvation. In this study we measured the effect of 3 heavy metals (Cd, Pb, Zn)at six different concentrations (lppm, 2 ppm,5 ppm, l0 ppm,20 ppm,50ppm) over a 72hour period on bacterial growth.

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2. MATERIALS & METHOD:

2.1MICROORGANISM : Magnetospirillum VITRJS5 (Accession number: KM289194) is a novel MTB isolated from the fresh water sediment, Ashtamudy estuary, Kerala . They are spiral in shape and move towards the earth’s magnetic field. At each end of the cell they have polar flagellum. The strain was obtained from Marine biotechnology and biomedicine lab, VIT University. The bacteria were sub-cultured in MS1 media under microaerophillic conditions.

2.2 MEDIA

The media was maintained in anoxic condition where acetate acts as the electron donor.All the anaerobic culturing was performed according to the technique proposed by Hungate (Hungate 1979). The mother culture of Magnetospirillum sp.VITRJS5 was inoculated to MS1 media with acetate as electron donor and nitrate as electron acceptor.Mother culture for this experiment was prepared by adding 1000mg/L sodium acetate and sodium nitrate each to the MS1 media. In all of the heavy metal recovery experiments acetate acts as the electron donor and the metals

were used as electron acceptors. For the metal utilizing experiment MS1 media was prepared with acetate and electron donor and metals as electron acceptor. Nitrogen was sparged to the media to make it microaerophillic, closed with butyl rubber stopper and sealed with aluminium caps. After autoclaving 2ml of culture was inoculated to the media from the inoculum and was incubated for 3-7 days (till the bacteria reaches stationary phase). This was done so that the bacteria can get adjusted to metal electron acceptor.After incubation of the culture the growth was observed,solutions present in the serum bottles were centrifuged at 10000 rpm for 10 min to remove the bacteria.The supernatant is taken for further analysis to detect the presence of metals.

The standard solutions are prepared[In case of Cd-0.1 g of CdCl2 in 100 ml of distilled water,Pb-0.159 g of lead nitratePb(NO3)2 in 100 ml of distilled water,Zn-0.12 g of ZnO and 5M HCl in 100 ml of water].

2.3 ATOMIC Absorption SPECTROSCOPY (AAS):

  • SAMPLE PREPARATION FOR AAS:
  1. STOCK SOLUTION OF THE METAL CORRESPONDING TO 1000mg/l

Approx. 1000gm from each metal (Pb,Cd,Zn,Cu,Ni) was weighed and diluted in a covered 250 ml glass beaker with 10 ml HNO3.Then 100 ml of water was added. Nitrous fumes were expelled by boiling, then cooled and transferred to 1000 ml of volumetric flask and was filled to the mark with water.

  1. STANDARD SOLUTION OF METAL CORRESPONDING TO 10 mg/l

10 ml of metal stock solution was pipette out into a 1000 ml volumetric flask. 20 ml of nitric acid was added and filled to the mark with water, and mixed well.

  1. STANDARD SOLUTION OF METAL CORRESPONDING TO 0.4 mg/l

20 ml standard solution of the metal was pipetted out into a 500 ml of

volumetric flask. 10 ml of nitric acid was added and filled to the mark with water, and mixed well. The solution was prepared on the day of use.

  • The operation was done in fume hood.

PROCEDURE FOR AAS :

  1. The sample was heated in order to get all the material dissolved.
  2. Once dissolved, the mixture was added slowly to approx. 50 ml of distilled water in a 100ml volumetric flask. The solution was diluted with distilled water to the mark.
  3. The metals were measured quantitatively with AAS and atomization was done by air-acetylene flame.
  4. The exact concentrations were calculated from calibration standards and the mean absorbance is tabulated.

3. RESULT & DISCUSSION

In this paper the results have perfectly shown that the MTB are well suited to the microaerobic condition and have the ability to uptake metal ions which get released by different heavy metals. It has been known that the MTB can degrade the heavy metals such as Zn,Pb,Cu, Ni and Cd in different percentages in different concentrations of the media which implies it can use the metal ions present in the solution and are able to grow. In culture study it showed the proper growth varied from 1-50 ppm.Depending on the concentrations in different culture bottles disparate populations of the MTB strain were seen.AAS study revealed that in case of Cadmium(Cd) ,5 samples having contents between 0.861 to 23.187.Sample 2 which had 5 ppm concentration ,had the lowest value and sample 5 i.e 50 ppm had the highest.This was plotted in a conc. v/s absorbance graph showed in Fig:1.Whereas in Lead(Pb),6 samples having contents between 0.41 to 3.29.Sample 1 i.e 1 ppm had the lowest adsorption yield and sample 6 i.e 50 ppm had the highest.It was showed in Fig:2.Zinc showed completely different result where 6 samples having contents ranging from 0.2855 to 22.9308.Sample 2 i.e 2 ppm showed the lowest concentration and sample 6 i.e 50 ppm the highest which was seen in Fig:3.

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The percentages were also calculated according the different values where it was seen the highest biosorption percentage of Cd is 59.35 % in 2 ppm which is more compare to the study done by LI Xingang and Takeyama(et al.) in 2002 and showed adsorption yield percentage as 58%.In case of Pb which showed the highest percentage of biosorption as 72 % in 2 ppm which is comparatively high than the adsorption percentage(63%) revealed by the study done by Ayla (et al.).The results for Zinc exhibited 66.6 % of metal adsorption in 5 ppm which is huge compare to the percentage (28.83%) revealed in the study done by Wang and Huiping (et al.)But among all the heavy metals used for this studies recovery of Lead was most successful.

CADMIUM

STANDARDS

Conc. (mg/l)

Mean Absorbance

100

0.0257

200

0.0453

300

0.0671

CADMIUM

M.ABS

SAMPLES (mg/L)

CONTROLS (mg/L)

0.0001

1.187

2

0

0.861

5

0.0006

2.286

10

0.0003

5.983

20

0.0017

23.187

50

Fig1:Effect of concentrations on recovery of Cd on MTB

LEAD

STANDARDS

Conc. (mg/L)

Mean Absorbance

100

0.1144

200

0.1888

300

0.2128

LEAD

ABS

SAMPLE(mg/L)

CONTROL(mg/L)

0.0005

0.41

1

0.0016

1.44

2

0.0025

2.2

5

0.0021

1.82

10

0.0016

1.4

20

0.0038

3.29

50

Fig2:Effect of concentration on recovery of Pb on MTB

ZINC

STANDARDS

Conc. (mg/L)

Mean Absorbance

100

0.0021

200

0.004

300

0.0054

ZINC (Zn)

ABS

SAMPLE

CONTROL

0.0019

0.4376

1

0.0018

0.2855

2

0.0028

3.33

5

0.0032

5.219

10

0.0031

6.503

20

0.0017

22.9308

50

Fig3: Effect of concentration on recovery

of Zn on MTB

4.CONCLUSION

In this work, MTB had been successfully used as the adsorbent for adsorption of heavy metal ions from artificial freshwater sample. The results show that pH and biomass concentration highly affected the uptake capacity of the biosorbent for the biosorption of the metal ions. Temperature can not affect significantly on adsorption of metal ions. Time dependence studies showed that the adsorption equilibriums of both metals were achieved within 5 min.The percentage for the uptake of the metal ions by MTB varied depending on the type of metal used.

LEAD (Pb)

CONCENTRATIONS (mg/l)

Percentage (%)

1ppm

41

2ppm

72

5ppm

44

10ppm

18.2

20ppm

7

50ppm

6.58

CADMIUM (Cd)

CONCENTRATIONS (mg/l)

Percentage (%)

2ppm

59.35

5ppm

17.22

10ppm

22.86

20ppm

29.91

50ppm

46.37

ZINC (Zn)

CONCENTRATION (mg/l)

Percentage (%)

1ppm

43.76

2ppm

14.27

5ppm

66.60

10ppm

52.19

20ppm

32.15

50ppm

45.86

So the MTB might be proposed as an alternative to more costly traditional methods for the removal and recycling of heavy metals from wastewateror freshwater orleaching .The equilibrium biosorption and

kinetics results are essential for further works, especially for the adsorption process evaluation and design.All of the given data fitted well into experimental study of this paper. This unique finding indicates the high possibility to recover heavy metals like Cd ,Pb ,Zn, Cu, Ni from wastewater or freshwater using the method of “MTB biosorption and magnetic separation”, which was simple, effective and environmentally friendly.

Finally,increased effort should be given to the isolation and study of other Magnetospirillum sp. strain with potentially unique feature of biomineralization process.Understanding how those can be used in recovery of huge number of heavy metals which are useful in various way.

REFERENCES:

  • A.S. Bahaj, D.C. Ellwood, J.H.P. Watson, "Extraction of Heavy Metals using Microorganisms in High Gradient Magnetic Separation,"IEEE Trans. Magn., vol. MAG-27, no. 6, pp. 5371-5374, 1991.
  • R.P. Blakemore, "Magnetotactic Bacteria," Science, vol. 190, pp. 377-379, 1975.
  • R.P. Blakemore, D. Maratea, R.S. Wolfe, "Isolation and Pure Culture of a Freshwater Magnetic Spirillum in Chemically Defined Medium,"

Jnl. Bacreriology, vol. 140, no. 2, pp 720-729, 1979

  • “Spectrochemical Analysis by Atomic Absorption and Emission” by L.H.J.Lajunen, Royal Society of Chemistry,1992.
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  • Chen C, Ma Q, Jiang W, Song T (2011) Phototaxis in the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1 is independent of magnetic fields. Appl Microbiol Biotechnol 90:269–275.
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  • Dr. Thomas G. Chasteen; Dept of Chemistry, Sam Houston State University Huntsville,Texas
  • National Oceanic and Atmospheric Administration. Retrieved December 24, 2012