Chemistry: molecular biology and microbiology – Process of utilizing an enzyme or micro-organism to destroy... – Destruction of hazardous or toxic waste
Patent
1995-08-02
1998-01-13
Pratt, Helen
Chemistry: molecular biology and microbiology
Process of utilizing an enzyme or micro-organism to destroy...
Destruction of hazardous or toxic waste
B09B 300, C12S 100
Patent
active
057078572
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
This invention concerns the rehabilitation of polluted soils. It concerns particularly a method of treatment of industrial soils polluted by hydrocarbons and other biodegradable organic compounds.
The elimination of hydrocarbons contained in soils is essentially accomplished by the natural presence in the ground of aerobic bacteria which finds its only source of hydrocarbonic nourishment in those hydrocarbons. The biodegradation of the hydrocarbons is, therefore, a natural phenomenon, the speed of which depends on several factors, mainly on the concentration of the hydrocarbons and the characteristics of their hydrocarbonic chain, but also on other nutrients, which the microorganisms need for their vital functions.
In land areas in which carbon is found in excess due to pollution, bacteria consume, during aerobic fermentation phases, 15 to 30 times more carbon than nitrogen, depending on the biodegradability of the hydrocarbon (whether it is more or less biodegradable). The factors which limit biodegradation are then the nutrients in deficit, essentially nitrogen, then phosphorus among the middle elements and, to a lesser degree, sulphur and potassium. It is possible to limit this effect with respect to the elements in deficit so as to re-establish the optimal conditions for bacterial functioning if one fixes the weight ratios to be:
The nutritional complements necessary for the invention are those which are applied agriculturally with traditional chemical fertilizers. Also it has been advocated that complete fertilizers as commercially available or in similar formulations be used for biodecontamination and applied in a manner similar to conventional fertilization. Since the processes of degradation of hydrocarbons are noticeably longer than those which preside over vegetative assimilation in the realm of higher vegetation, preference has been given to formulations similar to slow fertilizers. The description of such an application can be found in the international application W091/19039 (Grace-Sierra Hort. Prod. Co.). Nevertheless, the efficacity of this process is limited because the pollution in question consists of hydrocarbon which generally is not uniformly distributed in the contaminated soil and because the distribution of the secondary nutrient which is added in hydrophilic form in a slow fertilizer does not completely establish conditions that are desirable for total biodegradation.
This invention remedies this disadvantage by introducing, in a rehabilitation process for a soil contaminated by hydrocarbons and other biodegradable products, a mixed treatment comprising the supply of a source of nutrients for micro-organisms under a double form, oleophilic and hydrophilic, along with an agent for aerating the soil.
The source of secondary nutrients for the micro-organisms in oleophilic form is derived from microemulsions of nourishing substances of N/P type in an aqueous solution in an external phase constituted by an organic fat-soluble solvent. These microemulsions are described in French Patent No. 80 20178, published under the number 2,490,672 (S.N.E.A. P) and its Certificate of Addition No. 81 16626, published under the number 2,512,057.
The source of secondary nutrients in hydrophilic form is a fertilizer programmatically distributed of the N/P/K type, or more simply of the N/P/O type, since the introduction of potassium is not generally necessary to the biodegradation conditions sought. In order to apply the invention more easily, according to principles which will be explained later, it is preferable to have at least two formulations, for example one 18/1/0 and one 15/7/0. The present fertilizers are formulated in slow-release form so as to avoid their being too rapidly washed away by precipitation. There is only the natural diffusion of the nutrients in order to assure the establishment of the ideal conditions of the local distribution of the secondary nutrients to the point in which the hydrocarbonic pollution has settled. It is advisable, therefore, to have a distribution as
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CECA S.A.
Pratt Helen
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