Biotechnological purification of soil and water containing heavy

Details Biotechnological purification of soil and water containing heavy Biotechnological purification of soil and water containing heavy

1997-10-27

1999-10-19

Chiesa, Richard L.

Liquid purification or separation

Processes

Treatment by living organism

210610, 210611, 210616, 210912, 210747, 435174, 4352625, 405128, C02F 300, C02F 334

Patent

active

059683597

DESCRIPTION:

BRIEF SUMMARY
The invention concerns a method of cleaning up heavy metal-laden soils and waters using microorganisms.
It is known that soil containing heavy metals is bagged and dumped or deposited only after being mixed with concrete or after a thermal treatment (vitrification). Heavy metal dumps are protected from leaching due to water penetrating at the sides by installing sheet pilings. However, no safe long-term storage is guaranteed due to the dumping of soluble heavy metal compounds, so they constitute a permanent risk.
For cleaning up water polluted with heavy metals, it is possible to precipitate iron hydroxide by adding iron sulfate and milk of lime, and bind it to the heavy metal by adsorption to iron hydroxide and separate it. However, a disadvantage here is that wastewater purification is performed only when the heavy metal content is medium to high, because it is a cost-intensive process with a high consumption of chemicals. To achieve extensive adsorption of heavy metals, it would be necessary to use large quantities of precipitating agents, which would subsequently have to be dumped with heavy metals at a great expense. This leads to a considerable increase in volumes and quantities for disposal.
In U.S. Pat. No. 4,789,478 a method for treating waters containing heavy metals is disclosed, in which Citrobacter freundii is used. This microorganism is classified in Risk Group 2 in the Genetic Technology Safety Ordinance (GenTSV), and so it can cause illness in humans. The temperature range and the narrow pH range in which this microorganism produces its effect is disadvantageous. It is furthermore intolerant of large concentrations of heavy metals, so that it cannot be used for cleaning up soils contaminated with heavy metals.
WO-A-94/02211 describes a decontamination process for soils contaminated with organic metal compounds wherein, starting with anaerobic conditions in the soil growth of sulfate reducing bacteria is stimulated by the repeated administration of nutrients, especially a carbon source. In particular, this state of the art proposes the addition of yeast extract as part of the nutrient solution. The sulfate reducing bacteria indirectly cleave the organometals by producing hydrogen sulfide. This reacts with the organometals to form metal sulfides. This process, however, is very slow and is inhibited by pH levels below pH 5 and high heavy metal concentrations.
The invention is therefore addressed to the problem of preventing the leaching out of toxic heavy metals into the ground water or their ascent into the upper layers of the soil without the need for coffering out old pollution and of purifying water contaminated with heavy metals in a wide range of concentration, temperatures and pH, without the need to fear the occurrence of illness due to microorganisms.
This problem is solved by a method for decontaminating water and soils contaminated with heavy metals, by establishing conditions in soils and waters by the addition of yeast under which the microorganisms present therein form a hydrogen sulfide and causing the hydrogen sulfide to react with the heavy metals to produce metal sulfides.
By the controlled biological formation of hydrogen sulfide the site of the heavy metals.
The object of this invention is therefore to prevent leaching of toxic heavy metals into groundwater or capillary ascent into the upper strata of soil without requiring excavation of old pollution burdens, and to purify heavy metal-laden water in a wide range of concentrations, temperatures and pH values to remove the heavy metals without any fear of an outbreak of diseases due to microorganisms.
This object is achieved by a method of cleaning up water and soil polluted with heavy metals by adjusting conditions in the water and soil to be treated so that the microorganisms present there will form hydrogen sulfide, and optionally adding apathogenic facultative anaerobes that are particularly tolerant of heavy metals to produce hydrogen sulfide, and allowing the hydrogen sulfide to react with the heavy metals to form meta

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