Indian Journal of Geo-Marine Science Vol. 40(1), February 2011, pp 121-124
Biosorption of uranium and thorium by Marine micro algae N.Manikandan, C. S. Siva Prasath & S. Prakash Department of Biotechnology, Udaya School of Engineering, Udaya Nagar, Vellamodi, Ammandivillai -629204, , Tamil Nadu., India. [E.mail:
[email protected]] Received 22 December 2009; revised 24 Februry 2010 Different concentration of uranium and thorium uptake by algal biomass was studied. Chlorella salina and Isochrysis galbana was used to uptake the uranium and thorium in the present study. Different concentration of live cells of algae was also used to uptake the uranium and thorium. Increasing concentration of uranium and thorium showed decrease in absorption by Chlorella salina and Isochrysis galbana. Increase in biomass concentration has the ability to uptake more amounts of uranium and thorium. Chlorella salina absorbed more amount of metal than the Isochrysis galbana. Amount of uranium was uptake more than the thorium by Chlorella salina and Isochrysis galbana. Chlorella salina absorbed more amount of thorium. [Keywords: Chlorella salina , Isochrysis galbana, Uranium, Thorium].
Introduction The presence of heavy metals in aquatic environments is known to cause severe damage to aquatic life, beside the fact that these metals kill microorganisms during biological treatment of waste water with a consequent delay of the process of water purification1. Most of the heavy metal salts are soluble in water and form aqueous solutions and consequently cannot be separated by ordinary physical means of separation. Physico-chemical methods, such as chemical precipitation, chemical oxidation or reduction, electrochemical treatment, evaporative recovery, filtration, ion exchange, and membrane technologies have been widely used to remove heavy metal ions from industrial wastewater. These processes may be ineffective or expensive, especially when the heavy metal ions are in solutions containing in the order of 1100 mg dissolved heavy metal ions/L. Biological methods such as biosorption/bioaccumulation for the removal of heavy metal ions may provide an attractive alternative to physico-chemical methods Uranium forms more than 160 mineral species and accounts for 5% of all known minerals2&3. Thorium is estimated to be about three to four times more abundant than uranium in the earth's crust. Thorium was successfully used as an alternative nuclear fuel to uranium in the molten-salt reactor experiment.. Once released, environmental fate of these radionuclides is significantly controlled by microbial activity as natural microbial flora often executes fascinating
mechanisms of interaction with such metallic pollutants, viz., reductive/enzymatic precipitation, solubilization, bioaccumulation/biosorption, etc., which ultimately determine their environmental mobility and toxicity4&5. Some authors looked for but could find no evidence of an active uptake in diatoms6 or Chlorella. Chlorella cells grown under different culture conditions, autotrophic, heterotrophic, and mixotrophic had same ability to accumulate uranium. Henceforth, mixotrophic culture is most effective to produce a algal mass as adsorbent for uranium recovery in higher yield7&8. Present investigation was to evaluate the efficiency of Marine micro algae to absorbe uranium and thorium. It is inexpensive alternative method to the existing technologies, to remove and recover radionuclides from low-level activity wastes and to trap uranium from new promising areas. Materials and Methods Algae cultures Chlorella salina, and Isochrysis galbana were collected from CMFRI, Tutucorin. Tamilnadu, India. The stock culture was maintained by using Walne’s culture media. Walne’s media was prepared by using the composition given in Table 1. Four conical flasks were taken with 90 ml sterile sea water. About 55µl of solution A, 50µl of solution B and 25µl of solution C of Walne’s media was added to the respective four conical flask. Then to each conical flask 10% algae Chlorella salina and Isochrysis
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Table 1—Different concentration of uranium uptake by Chlorella salina Sl No 1 2 3 4 5
Uranium conc. µg ml-1 10 15 20 25 30
Uranium absorbed % 100 80 60 40 30
galbana were added respectively. Stocks were maintained at a temperature of 20°C and pH of 8.5. Cultures were illuminated with fluorescent lamps. Growth of algae cultures were daily checked and appropriate dilutions were given when required. Microscopically Identification
Algae (Chlorella salina, and Isochrysis galbana) maintained in stock solution were then viewed microscopically. The nomenclature of Chlorella salina and Isochrysis galbana were given below respectively. Nomenclature of Chlorella salina
It is spherical in shape, about 2 to 10 µm in diameter, and is without flagella. Chlorella contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast. Through photosynthesis it multiplies rapidly requiring only carbon dioxide, water, sunlight, and a small amount of minerals to reproduce. Chlorella is a single-celled alga originally rich as a source of protein, Vitamins, minerals and essential amino acids. Kingdom: Plantae Division: Chlorophyta Class: Chlorophyceae Order: Chlorococcales Family: Oocystaceae Genus: Chlorella Specific descriptor: Salina Scientificname:-Chlorella salina Nomenclature of Isochrysis galbana
Isochrysis galbana is a microalgae originally from the chrysophyte algal group. It is now classified in a new phylum of algae called haptophytes (Prymnesiophyta or Haptophyta). It was first identified by Bruce, Knight and Parke (1939) it is a small round to ovoid cell that has two flagella for locomotion. It was discovered to have high lipid content and thus a good food source for various bivalve larvae. It is now widely cultured for use in the bivalve and other aquaculture industry.
Kingdom: Chromista Phylum: Haptophyta Class: Prymnesiophyceae Order: Isochrysidales Family: Scarabaeoidea Genus: Isochrysis Specific descriptor: Galbana Scientific name: Isochrysis galbana Preparation of the uranium and thorium solutions
All uranium (Merck Ltd) and thorium (Merck Ltd) solutions were prepared form uranyl nitrate and thorium nitrate. Uranium and thorium solutions of different concentrations were prepared. Uranium and thorium uptake experiment
Experiment of metals uptake, the algal cells in the linearly growing phase was collected by centrifugation at 6000 rpm for 5 min. Cells were then washed three times sterile distilled water and resuspended in 10 ml water. A known volume of each cell suspension, equivalent to one mg dry mass per ml of uranium or thorium solution, was added, mixed well and incubated at 20°C after 12 h of shaking at 150rpm and 20°C. Biomass was separated by centrifugation at 6000rpm for 5 min and supernatant used for metal estimation9. Different concentration of Uranium and thorium uptake by live cells of algae
The ability of the algae biomass under investigation to absorb uranium and thorium was evaluated. Algal cell in the linearly growing phase was collected by centrifugation at 6000 rpm for 5 min. Cells were then washed three times sterile distilled water and re-suspended in 10 ml water. Two mg dry mass per ml of uranium or thorium solution was added. Uranium concentration range from 10 µg U mL–1 , 15 µg U mL–1, 20 µg U mL–1, 25 µg U mL–1 and 30 µg U mL–1. Thorium concentration range from 4 µg Th mL–1, 8 µg Th mL–1, 12 µg Th mL–1, 16 µg Th mL–1 and 20 µg Th mL–1 . After 12 h of shaking at 150rpm and 20°C biomass was separated by centrifugation at 6000rpm for 5 min and supernatant used for metal estimation. Different concentration of live cells of algal biomass to uptake uranium and thorium
To study the effect of biomass concentration, the experiment of metals uptake, the algal cells in the linearly growing phase was collected by centrifugation at 6000 rpm for 5 min. Cells were
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then washed three times sterile distilled water and re-suspended in 10 ml water. A different volume of each cell suspension was added per ml of uranium or thorium solution, different algae cell concentrations ranging from 0.2–3 mg dry mass per ml were added to the solutions containing 30 µg U mL–1 and 16 µg Th mL–1.
Table 2—Different concentration uranium uptake by Isochrysis galbana
Results and Discussion Algae cultures Chlorella salina, and Isochrysis galbana were procured from CMFRI, Tutucorin. Tamilnadu, India. Algae was maintained in Walne’s media at 20° In Table: 1 showed the different concentration of uranium uptake by Chlorella salina. Two mg of cell mass was added per ml of solution. The 100% of uranium was removed at 10 µg U ml-1. The 80% of uranium was absorbed at 15µg U ml-1. The 60 and 40% removal was achieved at 20 and 25 µg U ml-1. Lowest concentration of uranium of 30% was observed at 30 µg U ml-1. Uptake of different concentration of uranium by Isochrysis galbana was showed in the Table: 2 .It uptake 80% uranium at 10 µg U ml-1. The 70 and 40% uranium was uptake at 15 and 20µg U ml-1. Lowest absorption of 30% was achieved at 25 and 30 µg U ml-1. Uptake of different concentration of thorium by the Chlorella salina was shows in the Table: 3. Highest concentration of 90% of thorium was uptake at 4µg Th ml-1. Lowest absorption of 50% achieved at 20µg Th ml-1.In Table: 4 showed different concentration of thorium uptake by the Isochrysis galbana. The highest absorption of 70% of Thorium was achieved at 4µg Th ml-1. Uptake of 20µg Th ml-1 was achieved at 30%. In the above results, observed that the increasing the metal concentration is to decrease the uptake ability of algae. Chlorella salina has the ability to remove the uranium and thorium than the Isochrysis galbana. Low uranium and thorium concentration there was a small number of metal ions compared to the large surface area with active site. Thereby ,It was easy for each metal ions to find it place on the cell surface on the other hand, not all metal ions could be absorbed by increasing the metal concentration, living a the residual amount of free metal ions. The different concentration of cell mass was used to uptake the 30µg U ml-1 and 20µg Th ml-1. Live cell of algal bio mass of Chlorella salina to uptake the uranium was shown in the Table 5. Lowest uptake of uranium was achieved at 0.2gm of cell mass. Highest concentration of uranium was achieved at 3gm of
Table 3—Different concentration of thorium uptake by Chlorella salina
Sl No
Uranium conc. µg ml-1
Uranium absorbed %
1 2 3 4 5
10 15 20 25 30
80 70 40 30 30
Sl No
Thorium conc. µg ml-1
Thorium absorbed %
1 2 3 4 5
4 8 12 16 20
90 80 70 60 50
Table 4—Different concentration of thorium uptake by Isochrysis galbana Sl No
Thorium conc. µg ml-1
Thorium absorbed %
1 2 3 4 5
4 8 12 16 20
70 60 50 40 30
Table 5—Different concentrations of live cells of Chlorella salina to uptake the uranium Sl No
Cell mass conc. mg
Uranium absorbed %
1 2 3 4 5 6
0.2 0.8 1.6 2.0 2.4 3.0
10 10 20 35 50 60
cells per ml of solution, it uptake 60%. Uptake of uranium by the different cell mass of Isochrysis galbana was shown in the Table:6 . The 0.2g of cell mass absorbs lowest uranium from the solution. The 60% of uranium uptake was achieved at 3gm of cells. To study the effect of cell biomass of Chlorella salina to uptake the thorium was shown in the Table: 7. The 0.2gm of cell mass uptake the 10% of thorium. The 90% of thorium was uptake by the 3gm of algae cell mass. Thorium uptake by the different concentration of cell mass of Isochrysis galbana was shown in the Table: 8. the 0.2g of cell uptake the 10% of thorium and the 3gm of cell absorbed the 70% thorium. Above results showed the, increasing the cell mass concentration has the ability to uptake uranium and thorium from the solution. Cell mass of Chlorella salina to absorbed more metals from the solution than the Isochrysis galbana. There was a large surface area with active site.
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Table 6—Different concentration of live cells of Isochrysis galbana to uptake the uranium Sl No
Cell mass conc. mg
Uranium absorbed %
1 2 3 4 5 6
0.2 0.8 1.6 2.0 2.4 3.0
10 20 30 40 50 60
Table 7—Different concentration of live cells of Chlorella salina to uptake the Thorium Sl No
Cell mass conc. mg
thorium absorbed %
1 2 3 4 5 6
0.2 0.8 1.6 2.0 2.4 3.0
10 20 30 50 60 70
References 1
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3
4
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6
7 Table 8—Different concentration of live cells of Isochrysis galbana to uptake the Thorium Sl No
Cell mass conc. mg
Thorium absorbed %
1 2 3 4 5 6
0.2 0.8 1.6 2.0 2.4 3.0
10 20 60 70 80 90
8
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