Liquid purification or separation – Processes – Treatment by living organism
Reexamination Certificate
1999-03-24
2001-04-17
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Treatment by living organism
C210S612000, C210S621000, C210S630000, C435S252100
Reexamination Certificate
active
06217766
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This is the 35 USC 371 national stage of International application PCT/NL97/00418 filed on Jul. 16, 1997, which designated the United States of America.
FIELD OF THE INVENTION
The invention relates to a new sulphur-reducing bacterium and to a process for removing sulphur compounds from water.
BACKGROUND OF THE INVENTION
The presence of sulphur compounds in water is usually an unacceptable factor. In the case of sulphate, sulphite and thiosulphate, the principal drawbacks are attack on the sewer, acidification, eutrophication, and silting. One type of effluent in which sulphur compounds, in particular sulphite, are a constituent which is difficult to remove is the wash water from flue gas treatment plants. The flue gases from power stations and waste incinerators cause extensive pollution of the environment due to the presence of acidifying sulphur dioxide (SO
2
). Other types of effluents containing sulphur compounds are those originating from the printing industry, mining industry, and paper, rubber, leather and viscose industry.
The biological treatment of sulphate and sulphite and other sulphur compounds, including scrubbing liquids from flue gas desulphurisation plants, involves reduction in an anaerobic step to give sulphide, which in turn can be biologically oxidised to elementary sulphur. Such processes are known, for example from EP-A-451922, WO-A-92/17410 and WO-A-93/24416.
The advantage of such processes is that only small waste streams remain because the sulphur formed can be re-used. However, the disadvantage is that, especially when the effluent contains little organic matter, electron donors have to be added in order to provide sufficient reduction equivalents for the sulphate reducing bacteria (SRB). The most important electron donors are methanol, ethanol, glucose and other saccharides, organic acids, such as acetic, propionic, butyric and lactic acid, hydrogen and carbon monoxide. The use of these electron donors has the effect of substantially increasing the cost of this method for removal of sulphur from waste streams.
WO-A-92/17410 discloses that sulphur compounds, in particular SO
2
can be effectively removed from water by continuous or periodical use of a temperature above 45° C. during the anaerobic treatment, without large amounts of added electron donor being needed, because little or no methane is produced.
According to WO-A-93/24416, the consumption of electron donor can be reduced by selecting a minimum sulphate/sulphite concentration in the anaerobic reactor effluent and/or a minimum sulphide concentration in the reactor and/or by raising the salt concentration. Such measures are more favourable to the SRB than to the methanogenic bacteria, and therefore reduce the total demand for electron donors.
Although such measures have improved the utility of biological desulphur-isation processes, the performance is always limited by the properties of the micro-organisms used. The conventional SRB's used belong to the genera Desulfovibrio, Desulfotomaculum, Desulfomonas, Desulfobulbus, Desulfobacter, Desulfococcus, Desulfonema, Desulfosarcina, Desulfobacterium and Desulfuromonas.
SUMMARY OF THE INVENTION
A new microorganism has been found now which exhibits remarkable and useful properties in the biological reduction of sulphur compounds at high temperatures.
The new microorganism is a bacterium which was isolated from a burning coal heap in Sweden. It can produce high sulphide concentrations from higher oxidised sulphur species such as sulphate and sulphite. High sulphide concentrations, up to 2.5 g/l, can be tolerated by the bacterium without negative consequences for its vitality.
The strain as isolated is denoted as KT7 and consists of short rods, about 0.7-1 &mgr;m in diameter and 1-2 &mgr;m in length. They stain Gram positive. They are highly motile and several flagellae are visible with electron microscopy. The cells are covered by a protein surface layer. Subunits are regulary arranged with p2 or p4 symmetry.
The bacteria according to the invention fit in the group of the low-GC Gram-positives, and are related to the genus Desulfotomaculuni. They have the characteristics of strain KT7. Strain KT7 has been deposited at the DSMZ in Braunschweig, Germany, on Jun. 19th 1996 with accession number DSM 11017.
The strain K17 is capable of growing in various media. The data of growth on various electron donors and acceptors (concentration 0.1%) after incubation for 3 days are summarised in Table 1 below; the tests were performed under a 80% N
2
, 20% CO
2
atmosphere (2 bar), except for the test with molecular hydrogen which was performed under a 65% N
2
, 20% CO
2
and 15% H
2
atmosphere.
TABLE 1
e-acceptor
e-donor
sulphite
sulphate
nitrate
molecular hydrogen
+++
(+)
(+)
formate
++
(+)
n.d.
acetate
++
−
—
ethanol
+
(+)
—
lactate
+++
n.d.
(+)
isopropanol
+
n.d.
−
pyruvate
+++
n.d.
−
fumarate
(+)
n.d.
n.d.
citrate
−
n.d.
n.d.
D-glucose
(+)
n.d.
n.d.
yeast extract
(+)
n.d.
n.d.
Cell concentrations (cells/ml):
− = no growth
(+) = <10
7
n.d. = no data
+ = 1.10
7
to 3.10
7
++ = 3.10
7
to 6.10
7
+++ = >6.10
7
The bacteria according to the invention grow between 35 and 85° C., with considerable growth between 48 and 70° C. The temperature optimum is in the range 50-65° C. with a doubling time of 90 minutes. The pH range for growth is about 5 to 9, with an optimum at 6.5-7.5. The bacteria are active both as free cells and as aggregates.
Strain KT7 is strictly anaerobic. It tolerates up to 25% carbon monoxide in the gas phase. In full scale installations, it is expected that the bacteria can tolerate up to 50% carbon monoxide.
The bacterium according to the invention can be used in various anaerobic processes, especially where sulphate and other sulphur species are reduced to sulphide.
Thus, the invention relates to any process for the biological removal of sulphur compounds from an aqueous solution of dispersion wherein the bacterium as described above is used. The bacterium can be used alone, but also in combination with other, conventional sulphur-reducing microorganisms. An important advantage of the bacterium of the invention is that it can produce high levels of sulphide, about twice as much as conventional sulphur-reducing bacteria, and thus makes the sulphur-reducing process more efficient (higher capacity and/or smaller equipment and/or shorter residence times).
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patent: 4200523 (1980-04-01), Balmat
patent: 4584271 (1986-04-01), Stern
patent: 4614588 (1986-09-01), Li
patent: 4839052 (1989-06-01), Maree
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patent: 5496729 (1996-03-01), Monticello
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patent: 5587079 (1996-12-01), Rowley
patent: 5637220 (1997-06-01), Buisman
patent: 5891408 (1999-04-01), Busiman
patent: WO 93/24416 (1993-12-01), None
R. K. Nilsen et al., “Desulfotomaculum Thermocisternum sp. nov., a Sulfate Reducer Isolated From Hot North Sea Oil Reservoir”, Int. J. Stst. Bacteriol. Apr. 1996, vol. 46, pp. 397-402.
Buisman Cees Jan Nico
Dijkman Henk
Huber Harold
Krol Johannes Pieter
Stetter Karl Otto
Barry Chester T.
Biostar Development C.V.
Young & Thompson
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