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Environmental Sciences Seminar Abstract Removal of heavy metal by
using microalgae Removal of Hg, Pb and Cd in wastewater was investigated using microalgae that were isolated in Thailand. Amoung 35 strains obtained, 20 strains exhibited high tolerance and 14 strains exhibited high removal ability of these heavy metallic ions. Of these a cyanobacterium Tolypothirx tenuis, exhibited high level of tolerance to Hg, Pb and Cd and high Cd removal ability over a wide range of temperature and pH's. The Cd removal reached a plateau within 30 min, and was the type that could be described by the Langmuir isotherm equation. Thus, it was suggested to be due to adsorption of Cd onto the microalgal surface. The adsorption of Cd was not strongly affected by the presence of Na, K, Ca and Mg ions. Cadmium adsorption was greatly increased by pretreating the cells with 0.1 M NaOH. Experiments were also done to include removal of Cd from hard water that had high concentrations of Ca2+. Langmuir parameters were calculated and the amounts of Cd adsorbed were compared for different concentrations of Ca2+. Results showed that NaOH pretreated cells showed increased Cd adsorbing ability in the presence of Ca2+. Pretreatment with NaOH was also found to have application to other cyanobacteria tested. These results suggest that biomass of NaOH treated filamentous cyanobacteria could be utilized as a novel biosorbent for Cd removal, even from hard water containing high concentrations of Ca2+and/or Mg2+. Our results suggested that NaOH-pretreatment T. tenuis might be applicable for removal of Cd from surface and ground water in certain outdoor situations. |
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