Water heavy metal bioremediation

The non-biodegradable water soluble heavy metals are either oxidized or reduced by the microorganisms and produce less soluble species. The less soluble form of these metals which are formed due to microbial reactions are adsorbed or precipitated/co-precipitated on the surface of the adsorbent and the extra cellular protein of the microorganisms in the biolayer (Srivastava and Majumder, 2008 Vails and Lorenzo, 2002). The methylation of metals is also another important route for bioremediation of heavy metals in water (White et al, 1997). Though the microbial action on metal ion transformation is still a matter of research, it is assumed that there are two paths. In one path oxidation or reduction of heavy metal ions takes place by extra cellular enzymes where the metal ions do not enter into the bacterial cell. In the other path the metal ions are transported into the microbial cells by trans-membrane proteins and are converted to other less soluble forms by metabolic actions of enzymes in the cells followed by subsequent excretion from the cells, yet both the paths are plasmid mediated (Vails and Lorenzo, 2002). Whether the microbial action on a metal ion is performed by only one path or by both the paths is a matter of research. 

Bioremediation of waste water containing heavy metals such as Pb", Ci by non-soluble complex formation with a PE of opposite electrical charge [12]. 

A more constrained opportunity for nitrate bioremediation arose at the US-DoE Weldon Spring Site near St. Louis, Missouri. This site had been a uranium and thorium processing faciUty, and treatment of the metal had involved nitric acid. The wastestream, known as raffinate, was discharged to surface inpoundments and neutralized with lime to precipitate the metals. Two pits had nitrate levels that requited treatment before discharge, but heavy rains in 1993 threatened to cause the pits to overflow. Bioremediation by the addition of calcium acetate as a carbon source successfully treated more than 19 million liters of water at a reasonable cost (75). 

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