Liquid purification or separation – Processes – Treatment by living organism
Patent
1993-12-06
1995-12-12
Wyse, Thomas
Liquid purification or separation
Processes
Treatment by living organism
210612, 210630, 210631, 95181, 95235, C02F 328, B01D 5300, C01B 1724
Patent
active
054746825
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method 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, eutrophication and silting. In addition, heavy metals, which are particularly undesired because of their toxic properties, are frequently also present in water containing a large amount of sulphur compounds.
Industries which produce effluents containing sulphur compounds include the viscose and edible oils industry, tanning, paper, rubber, printing and photo-graphic industries, metallurgic industry and mining industry.
Wash water from flue gas treatment plants is a type of effluent which contains sulphur compounds, in particular sulphite, that can be removed only with difficulty. Flue gases from power stations and waste incinerators cause extensive pollution of the environment due to the presence of acidifying sulphur dioxide (SO.sub.2). The harmful effects of acidification are generally known.
Two types of method are available in general for the removal of sulphur-containing compounds, that is to say physicochemical methods and biological methods.
Physicochemical treatment methods include ion exchange and membrane filtration (electrodialysis and reverse osmosis). Disadvantages of such methods are the high costs and the large stream of waste which results. In the case of flue gas treatment, absorption on lime or ammonia is usually employed. In this case large amounts of gypsum or ammonium sulphate are formed; a part of these wastes could be re-used. However, particularly in the case of gypsum the possible uses are becoming ever fewer because the quality demands for gypsum are becoming ever more stringent.
In the case of a biological treatment, sulphate, sulphite and other sulphur compounds are reduced by sulphate-reducing bacteria in an anaerobic step to give sulphide, which in turn can be oxidized to elementary sulphur. The advantage of such a method 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, hydrogen and carbon monoxide. The use of these or other electron donors has the effect of substantially increasing the cost of this method of removal of sulphur from waste streams.
Organic compounds having two or more carbon atoms are found to decompose under anaerobic conditions to give hydrogen and acetate. The hydrogen can be used as an electron donor for the reduction of sulphate and sulphite and the like, but, under normal conditions, about 50% of the acetate is converted to methane by methane producing bacteria (MPB). Methanol (C-1) is converted to methane for about 90% under normal conditions. Methane formation has the disadvantages that additional electron donor has to be added (increasing the costs) and that a gas stream contaminated with H.sub.2 S is formed which has to be washed and burnt off in the flare.
It has been found that sulphur compounds can be effectively removed from water by continuous or intermittent use of an elevated temperature during the anaerobic treatment, without large amounts of added electron donor being needed, because little or no methane is produced.
According to the method of the invention, the sulphur compounds are therefore removed by subjecting the water to an anaerobic treatment with bacteria which reduce sulphur and/or sulphate, if necessary with the addition of electron donors, and carrying out the treatment, at least for a portion of the time, at an elevated temperature, in particular a temperature of more than 45.degree. C.
The elevated temperature can be used continuously or virtually continuously, for example when an inexpensive energy sourc
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patent: 4183810 (1980-01-01), Baenens et al.
patent: 4384956 (1983-05-01), Mulder
patent: 4519912 (1985-05-01), Kauffman et al.
patent: 5227069 (1993-07-01), Van Dort et al.
patent: 5269929 (1993-12-01), Sublette et al.
By J. Maree et al., "Biological Sulphate Removal in an Upflow Packed Bed Reactor", 1985, vol. 19, No. 9, pp. 1101-1106, Great Britain.
By F. Plahl-Wabnegg et al., "Biologische Schwermetallentfernung bei Industrieabwassern", 1984, vol. 125, pp. 424-426.
Paques B.V.
Wyse Thomas
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