Liquid purification or separation – Processes – Treatment by living organism
Patent
1995-08-04
1997-02-18
Lithgow, Thomas M.
Liquid purification or separation
Processes
Treatment by living organism
210614, 210617, 210631, 210916, 208236, C02F 172
Patent
active
056038321
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for removing hydrogen sulphide from oil-containing water and equipment therefor.
Oil-containing water like ballast water and contaminated water co-produced with petroleum, may when stored in absence of oxygen cause odour problems in the form of hydrogen sulphide (H.sub.2 S) and mercaptans.
H.sub.2 S is produced by sulphate reducing bacteria: S+organic acids.
Organic matter like oil, is broken down to simple organic compounds that are used by the sulphate reducing bacteria according to the equation. Sulphate is present in sea water. Also other sulphur compounds might cause production of hydrogen sulphide.
A method to eliminate the product ion of sulphur-containing components and/or remove such components from the water phase is to add air or oxygen. In this way already formed sulphide will oxidize, and further growth of the sulphate reducing bacteria will be prevented when aerobic conditions appear. However, this method has several drawbacks. That is the solubility of oxygen which is relatively low in water and the comminutation of oxygen which might be a problem. Air pockets do easily occur, and gases that may release from the water phase may form explosive mixtures together with air. Additionally, it might be easier for the H.sub.2 S to leave the waiter phase, and this will make the situation even worse.
Further, addition of hydrogen peroxide will oxidize H.sub.2 S and other sulphur compounds. This method is unfavourable in the way that the reaction time is long (3-5 hours), at pH <8.5 solid sulphur will precipitate, there will be an explosion hazard, and as hydrogen peroxide is a very reactive compound, side reactions might easily occur if there is any impurities present. Because of this, stringent demands regarding cleaning and security must prevail. Fulfilling such demands will increase the working costs.
Still another method to reduce the H.sub.2 S content, is to add iron (Fe.sup.2+) to the oil-containing water. During this addition, H.sub.2 S will precipitate as solid iron sulphide (FeS). However, sludge in the form of FeS, will cause problems, and additionally the pH will be lowered. Mercaptans will not precipitate.
In U.S. Pat. No. 4,911,843 a process to prevent formation of hydrogen sulphide in waste water and also to remove dissolved hydrogen sulphide from waste systems by adding nitrate ions described. In this process however, the nitrate is added directly into the pipeline. In this way there will not be any controlled formation of a biofilm, and the biofilm which may occur by chance on the walls of the pipeline will not be very effective because of its relatively small surface. When treating waste water like sewer water, the main objection is to prevent formation of sulphide, and this problem is solved by adding nitrate at the start of the pipeline. However, this method will not solve the sulphide problems in oil-containing water in a satisfactory way, as such a medium already contains sulphide.
Also other patents prior to U.S. Pat. No. 4,911,843 describe addition of nitrates or nitrites to sewage in order to reduce hydrogen sulphide and/or control objectionable odours. (See for example U.S. Pat. Nos. 3,300,404, 3,966,450, 4,108,771, 4,446,031 and 4,681,687.)
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for eliminating emission of hydrogen sulphide and other sulphur compounds from oil-containing water, which is not burdened with the above mentioned drawbacks.
Another object of the invention is to provide a suitable equipment for performing the method.
The method according to the invention is based on an active biofilm in a reactor tank. Sulphide-containing water and nitrate are continuously supplied to the reactor tank, and after remaining in the reactor tank for some time, purified water where >90% of the H.sub.2 S-amount is removed, are taken out of the tank.
The equipment according to the invention comprises a bioreactor, where the reactor tank is provided with an inlet an
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Henshaw, "Biological Removal Of Hydrogen Sulfide From Refinery Wastewater And Conversion To Elemental Sulfur", File 35:Dissertation Abstracts Online 1861-1994/Apr., University of Windsor, Canada, vol. 30/03 of Masters Abstracts, p. 821.
Eskilt Jan P.
H.o slashed.yvik Henrik
Hovland Jon
Green Theodore M.
Lithgow Thomas M.
Norsk Hydro a.s.
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