Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-07-15
2001-07-03
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C435S262500, C435S830000, C435S832000, C435S863000
Reexamination Certificate
active
06254777
ABSTRACT:
The invention relates to a process for bacterial treatment by microorganisms that are able to degrade at least one ether, particularly the methyl-tert-butyl ether and/or the tert-amyl methyl ether and/or the ethyl tert-butyl ether that are contained in aqueous effluents.
It pertains particularly to the water treatment industry.
It is known that the methyl-tert-butyl ether, which is referred to below by the term MTBE, as well as the tert-amyl methyl ether, which is referred to below by the term TAME, are ethers that can be used particularly as oxygenated additives in unleaded gasolines to enhance their octane ratings. The rising use of additives such as MTBE, TAME or ethyl tert-butyl ether, which is referred to below by the term ETBE, involves large stored and transported volumes that are mixed with gasolines in particular. It is therefore necessary to know what happens to these compounds in case of accidental dumping, leading to pollution of the soil and groundwater or surface waters. MTBE is an ether that is produced by condensation of ethanol on isobutene; TAME is an ether that is produced by condensation of the methanol on isopentene and ETBE is an ether that is produced by condensation of the ethanol on isobutene. The structure of these compounds, which comprise an ether bond as well as a tertiary carbon, is such as to make them very resistant to biodegradation by the microorganisms that are present in the environment.
Recent literature that relates to the biodegradation of alkyl ethers that are used particularly in the gasolines indicates that the metabolism of these compounds in the environment is not a common phenomenon and that it is relatively slow, both under aerobic conditions and under anaerobic conditions (Salanitro, J. P., 1995, “Understanding the Limitations of Microbial Metabolism of Ethers Used as Fuel Octane Enhancers”: Curr. Op. Biotechnol., 6:337-340).
The applicant isolated aerobic bacteria
Gordona terrae
CIP I-1889 and
Rhodococcus equi
CIP I-2053 that have the capacity of degrading ETBE, and their use was the subject of a patent application (FR97/09455).
Among the previously discovered bacteria that make it possible to degrade ETBE in solution in water, ETBE is used at least partly as a carbon source by these bacteria, and its degradation ends in the accumulation of tert-butanol (TBA).
Another new aerobic bacterium was discovered by the applicant (
Pseudomonas cepacia
CIP I-2052), and this bacteria is able to use TBA as produced as a carbon source by degrading it until carbon dioxide is formed (mineralization).
The use of these two types of bacteria that degrade ETBE into TBA, on the one hand, and that mineralize TBA, on the other hand, in a mixed culture in ETBE makes possible the essentially total degradation of the ETBE that is contained in effluents.
One of the objects of the invention is to describe an aerobic process that uses these new bacteria for the treatment of polluted waters for the purpose of degrading the MTBE, ETBE or TAME that are contained in solution.
It has been noted that these microorganisms that are capable of degrading ETBE were capable of degrading MTBE and TAME and that their use in water treatment processes made it possible to lower significantly the residual concentrations of MTBE and/or TAME and more generally of compounds that contain at least one alkoxy group and in particular a tert-alkoxy group in urban or industrial waste waters or contaminated aquiferous layers, referred to under the general name of effluents, that are contaminated by these products or by fuels that can contain these oxygenated products.
In a more detailed manner, the invention relates to a process for treating aqueous effluents that contain at least one ether, advantageously methyl tert-butylether (MTBE) and/or tert-amylmethylether (TAME) and/or ethyl-tert-butyl-ether (ETBE) to reduce the concentration of said ether, characterized in that at least one bacteria that is selected from the group that is formed by
Gordona terrae
CIP I-1889 and
Rhodococcus equi
CIP I-2053 is grown in the presence of a suitable growth substrate, and the ether that is contained in the effluents is degraded in the presence of said substrate by the biomass of said bacteria that are thus produced.
According to a characteristic of the process, when the aqueous effluents contain primarily MTBE, it is possible to degrade advantageously the MTBE that is contained in the effluents by also introducing there, jointly or separately, at least one bacteria that is selected from the group that is formed by
Pseudomonas cepacia
CIP I-2052
, Arthrobacter globiformis
ATCC 53596
, Bacillus coaaulans
ATCC 53595
, Pseudomonas stutzeri
ATCC 53602 and
Mycobacterium vaccae
JOB5 ATCC 29678.
In this type of use, the tert-butylether group is degraded into tert-butyl alcohol (TBA) and the essentially total degradation of TBA into carbon dioxide and into water is carried out by the addition of bacteria that are mentioned that have the capability of advancing on the TBA that is thus produced. These stocks,
Gordona terrae
CIP I-1889
, Rhodococcus equi
CIP I-2053 and
Pseudomonas cepacia
CIP I-2052 have been filed by the applicant at the Institut Pasteur (CNCM, 25 rue du Docteur Roux, F-75724 PARIS CEDEX 15). Any other bacterium that is able to grow on the TBA can enter the framework of this invention.
According to another characteristic of the process, when the effluents contain primarily TAME, it is possible to degrade the TAME that is contained in the effluents by also introducing there, jointly or separately, a bacterium
Pseudomonas cepacia
CIP I-2052, which has the capability of also advancing on the tert-amyl alcohol (TAA) that is produced from degradation of TAME and of degrading it approximately totally into carbon dioxide and water. Any other bacterium that is able to grow on TAA can enter the framework of this invention.
According to another characteristic of the invention, the bacteria
Gordona terrae
CIP I-1889 and
Rhodococcus equi
CIP I-2053 are generally inoculated on a growth substrate, which can be, for example, at least one compound that is selected from the group that is formed by ethanol, isopropanol, n-butanol, n-pentanol, a monosaccharide, a disaccharide, dibutyl ether, ethyl butyl ether, ethyl tert-butyl ether, acetone, ethylene glycol, diethylene glycol, glycerol and tryptone.
Other growth substrates that are based on carbon and hydrogen can be provided. Each bacterium can grow differently in the presence of a given type of substrate.
Excellent results have been obtained by using ethanol and/or acetone as a growth substrate.
This particular growth substrate can be introduced at a concentration that does not exceed the toxicity threshold of this substrate for the bacterium that is being considered and advantageously between 0.1 mg/L and 5,500 mg/L of effluents.
The bacteria can tolerate a wide-range of concentrations of ether. Preferably, it is possible to degrade aqueous effluents that contain a concentration of ether, and in particular MTBE or TAME or ETBE, that is at most equal to 5,000 mg/L and more particularly between 0.01 mg/L and 400 mg/L. It is always possible, nevertheless, to dilute the effluent to operate under optimum conditions that are compatible with the degradation capacities of the bacterial stocks.
In the case where the aqueous effluents contain ethyl tert-butyl ether (ETBE) as a contaminant, this ETBE can be used at least partly as a growth substrate and therefore as an energy source.
The process that is derived from the use of these bacteria is applicable for treating in particular effluents that are polluted by MTBE, TAME and/or ETBE, so that the concentrations of MTBE or TAME or ETBE in the releases are compatible with the standards in force.
These bacteria were isolated from activated sludges that are collected at a sewage purification plant of urban waste waters that were treated according to specific microorganism enrichment techniques. The resulting bacterial stocks
Gordona terrae
CIP I-1889 and
Rhodococcus equi
CIP I-2053, which w
Fayolle François
Hernandez Guillermina
Le Roux François
Vandecasteele Jean-Paul
Barry Chester T.
Institut Francais du Pe'trole
Millen White Zelano & Branigan P.C.
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