Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
2002-01-31
2003-05-27
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S743000, C210S746000, C210S220000, C210S620000
Reexamination Certificate
active
06569336
ABSTRACT:
The present invention relates to a method for optimizing and monitoring automatically, by biochemical route, the elimination parameters of metallic elements present in the ionized state in water, for example ground or surface waters, the device for implementing said method and use of said method.
More particularly, the invention concerns a method and a device for elimination by biological route of divalent elements, such as divalent iron and manganese, present in groundwater.
The invention can be extended to surface waters devoid of dissolved oxygen where these elements are present in the same state, such as the reducing hypolimnion water above a dam in a state of eutrophication.
The oxidation of minerals by biological route has already been the object of in-depth studies and practical applications. This family of methods uses the capacity of certain specific bacterial strains, indigenous and/or incorporated, to catalyse by the exothermic oxidation reactions by enzymatic conversion. In return, these exothermic oxidation reactions provide the bacteria with the energy necessary for their development. This family of methods has been applied in particular in the mining industry for many years.:
either in the domain of extractive hydrometallurgy, whose first phases consist of pulverisation of the ore, enrichment by flotation and leaching in an acid or alkaline medium; biological leaching, or “bioleaching”, often in competition now with purely chemical leaching. The most widespread applications have concerned, until recent years, the copper industry (see the work by N. N. Hughes & R. K. Poole: “Metals & Micro-organisms”, published by Chapman & Hall, 1989, and the article by D. Morin: “Biotechnologies dans la métallurgie extractive”, published in Les Techniques de l'Ingénieur, Paris 1995, No. M2238, vol. 1): the ore, more or less fractionated, is simply heaped in the open air and sprinkled with a solution of nutritive elements. This method, known under the name of “heap leaching”, does not require any precise monitoring during the operation;
or for the treatment of acid effluents containing high amounts of dissolved divalent iron. The Japanese patent No. 44717/72 describes a method in which the culture of iron bacteria was carried out in a treated effluent, and then tipped into the effluent to be treated. In the Japanese patent No. 38 981/72, the method was improved by producing the bacterial culture ‘in situ’, on supports constituted of iron oxides. A further improvement was provided by the French patent No. 2.362.793, filed in 1976, where the bacterial culture was fixed on an insoluble support, at the pH of the effluent, and where the ferrous irons (Fe
2+
) were oxidised by air blowing into an agitated reactor. The bacteria and their supports were then separated by decanting, then recycled in the reactor, as in a system for treating urban waste water by the activated sludge method. In such cases as well, control of the process does not pose any problem. In particular, the low pH level of the medium avoids any competition between the physico-chemical route and the biological route for iron oxidation, which in practice means absence of the need for monitoring the quantity of oxygen introduced and the quantity of residual oxygen in the water after treatment.
Later, it was considered that these phenomena could be applied to the elimination, by biological route, of the iron and manganese present in the dissolved state in natural water deprived of oxygen and whose pH value, contrary to the effluents mentioned above, is situated close to neutrality, roughly plus or minus one unit. In this field, even if it concerns species different from those characteristic of acid effluents, it was already known that bacteria capable of catalysing iron and/or manganese oxidation, still called ferro- and mangano-bacteria, could, thanks to exogenous enzymes and/or polymers, by detected in very diverse environments (groundwater, lake beds, emergent springs in marine bays, etc . . . ). The damage from ferro- or mangano-bacteria clogging up well drains or corroding metallic piping was already well known, these bacteria needed to be “domesticated” to make them work usefully in plants for eliminating dissolved iron and manganese.
The first observations on this subject were published by U. Hässelbarth & D. Ludemann (in the article “Die Biologische Enteisenung und Entmanganung”, Vom Wasser, 1971, vol. 38, pp. 233-253; “Removal of iron and manganese from groundwater by microorganisms”, Water Treatment & Examination, 1973, vol. 22, No. 1, pp. 62-77 and were concretised by the same authors filing the German patent No. 1.767.738. This patent describes a method for biological iron removal by oxygenation and filtration, under conditions such that the power of oxidation-reduction of the medium has a value rH higher than or equal to 14.5±0.5. The rH is an index analogous to the pH, representing quantitatively the value of the oxidising or reducing power of a medium. This rH value corresponds to the lower limit of the domain of action of ferro-bacteria. Thus a minimum condition was defined, but it only represented a threshold, moreover insufficient, for total iron removal and it did not make it possible to define the lower and upper limits on which to base the automatic regulation of the method.
Besides, the authors defined very limited and very restrictive oxygenation conditions for the method, probably because they did not have a variety of types of untreated water available. The development of this promising method was thus delayed.
At about the same time, similar studies were undertaken in France (P. Mouchet & J. Magnin: “Un cas complexe de déferrisation d'une eau souterraine”, TSM-l'eau, 1979, vol. 74, No. 3, pp. 135-143), but for very differing waters, which made it possible for the French researchers to define more precisely the limits for biological iron removal and to provide, at the 1985 “Wasser Berlin” Congress, the construction of about thirty installations based on this principle of biological treatment (see the article of P. Mouchet et al. entitled “Elimination of iron and manganese contained in groundwater: classic problems, recent progress”, published in Water Supply, 1985, vol. 3, No. 1, pp. 137-149). Besides, at the same time, the German researchers had noted that many plants could operate spontaneously on this principle (see the article by C. CZEKALLA et al. entitled “Quantitative removal of iron and manganese by microorganisms in rapid sand filters (in situ investigations)”, published in Water Supply, 1985, vol. 3, No. 1, pp. 111-123). Moreover, similar observations had stimulated French research at the beginning of the seventies.
Thus from reading the above, one can note that biological iron removal was the method studied the most and the best known at the beginning of this research, probably because the natural seeding by indigenous bacteria is relatively rapid. On the contrary, the seeding time concerning biological manganese removal, a matter of several weeks, or even two or three months, did not encourage studies on manganese removal, at least to begin with.
The results of French research, published in 1985, described among others the field of activity of ferro-bacteria, such as shown in
FIG. 4
, within which, moreover, the domain of existence of a treatment ensuring total iron elimination is submitted to more restrictive limits.
Such a diagram, drawn with ordinate the oxidation reduction potential and with abscissa the pH, is called a stability diagram. It was drawn up first by M. J. POURBAIX to study corrosion phenomena of ferrous metals, and was later extended to the speciation of the principal elements (see the works of M. J. Pourbaix entitled “Atlas d'equilibres électrochimiques à 25° C.”, published by Gauthier-Villars, Paris 1963, pp 307-321) and applied to the study of iron removal from groundwater (see article by J. D. Hem, entitled “Stability field diagrams as aids in iron chemistry studies”, published in the AWWA Journal, 1961, Vol. 53, No. 2, pp. 211-2
Bergel Joan-Yves
Mouchet Pierre C.
Barry Chester T.
Degremont
Nixon & Vanderhye
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