Liquid purification or separation – Processes – Treatment by living organism
Patent
1995-06-28
1996-05-28
Wyse, Thomas G.
Liquid purification or separation
Processes
Treatment by living organism
210611, 210630, 210631, 210632, 210906, 210912, C02F 334, C02F 162, C02F 164, C12N 912
Patent
active
055208118
DESCRIPTION:
BRIEF SUMMARY
This invention relates to metal accumulation and is more particularly concerned with the removal of metals from water containing such metals, for example, for one or more of the following purposes: process, for example water which has been used in the treatment of precious metal ores, and soils for the purpose of removing heavy metals from such soils.
It has been previously proposed in "An immobilised cell bioprocess for the removal of heavy metals from aqueous flows", L. E. Macaskie, J. Chem. Technol. Biotechnol. 49 357-379 (1990), to effect heavy metal removal using Citrobacter sp. wherein the biomass is cultivated using glycerol-2-phosphate to prepare the biomass cells in the correct physiological state for metal removal. Metal removal relies upon the co-presentation of the metal with glycerol-2-phosphate (G2P) in an amount of up to 5 mM as a phosphate donor for metal accumulation by the immobilised cells. The G2P is enzymically cleaved to glycerol (a potential energy source for the cells) and inorganic phosphate, an efflux of which intercepts the incoming metal and results in the precipitation of crystalline heavy metal phosphate. Whilst such process is efficient in removal of heavy metals from solution, it has the disadvantage that it uses expensive glycerol-2-phosphate.
It is an object of the present invention to provide a technique which does not rely on the use of an expensive medium such as glycerol-2-phosphate.
In one of its aspects, the present invention resides in the use of one or more polyphosphate-accumulating microorganisms to accumulate polyphosphate which is then enzymatically cleaved in the presence of water containing one or more metals to produce phosphate ions which react with the metal(s) in the water in order to precipitate metal phosphate. Such metal phosphate may be crystalline or it may be mixed with other precipitated species such as the hydroxide.
In another of its aspects, the present invention resides in the use of phosphate ions produced upon cleavage of polyphosphate to remove metal(s) from solution by precipitation as metal phosphate(s).
Metals which are susceptible to the techniques of the present invention are those having a phosphate of low water solubility, for example, cadmium, lead, copper, manganese, cobalt, nickel, calcium, yttrium, strontium, uranium, lanthanum, lanthanides, plutonium, americium and neptunium.
In a preferred process, a polyphosphate-accumulating microorganism is cultivated in a culture medium under conditions where the microorganism can synthesise and utilise adenosine triphosphate (ATP), and then ATP synthesis/utilisation is modified whereby to cause the microorganism to utilize polyphosphate as an alternative energy source resulting in the production of said phosphate ions which can then react with the metal ions to produce precipitation of metal phosphate.
The microorganism is preferably a polyphosphate-accumulating bacterium, and may, for example, be polyphosphate-accumulating Acinetobacter bacterium. It is known per se (see Y. Comeau et al, Wat. Res. vol.20, No. 12, pp 1511-1521) (a) that certain microorganisms are capable of accumulating polyphosphate reserves under aerobic conditions and of utilising such polyphosphate under anaerobic conditions to produce phosphate; and (b) that this can be used to induce biological phosphorus removal in an activated sludge treatment by providing an anaerobic treatment zone upstream of the standard aerobic process. However, as far as we are aware, it has never been previously proposed to utilise the polyphosphate accumulated by such micro-organisms as a source of phosphate for removing heavy metals from solution. Thus, the present invention relies on the use of polyphosphate as the main source of phosphate for metal accumulation via enzymically mediated metal bioaccumulation or biomineralisation.
A particular example of a known polyphosphate-accumulating Acinetobacter bacterium is Acinetobacter calcoaceticus ATCC 23055 (NCIMB 10694). Another example of a known polyphosphate-accumulating microorganism is Kl
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Dick Rosemary E.
Macaskie Lynne E.
British Nuclear Fuels PLC
Wyse Thomas G.
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