Liquid purification or separation – Processes – Treatment by living organism
Patent
1980-12-24
1982-10-19
Wyse, Thomas G.
Liquid purification or separation
Processes
Treatment by living organism
210611, 210717, 210912, C02F 162
Patent
active
043549373
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a novel and very favourable process for precipitating heavy metals from wastewater.
Several industrial wastewaters contain heavy metals and sulfate--substances that are objectionable from an environmental point of view. There are mainly two types of industries discharging such wastewaters, viz. industries using acid pickling in connection with metal processing and plants for concentrating sulfide ores. A process for recovering sulfur and heavy metals from such wastewater effluents would not only protect the environment but would also be economically profitable.
Too high contents of metal and sulfate ions in wastewater will interfere with the natural biological purification process. Still more serious consequences are biological enrichment of toxic heavy metals in man's "food chain" and microbiological conversion of sulfate to toxic hydrogen sulfide, in certain cases resulting in a widespread poising of fish. Also comparatively low concentrations of metals in the wastewater may in the long run affect plant and animal life in lakes and streams since the organisms will progressively enrich the metals in the food chain.
The methods up to now mainly used or tested for the removal of heavy metals from wastewater are the following: additives. another positive ion, by means of ion exchange techniques.
The simplest of said four methods and therefore the method most commonly used at present is the first mentioned method. It involves precipitation of sparingly soluble heavy metal salts by means of e.g. a hydroxide. This precipitation has to be carried out at a certain optimal pH value. After the precipitation step the pH of the wastewater is adjusted to a value suitable for the receiving body of water. This pH adjustment may often be accomplished at the same time as the separation of heavy metal containing sludge.
Electrolytic precipitation of metals is at present hardly conceivable as a possible means for purifying wastewaters but may well be suitable for certain concentrated baths. Ion exchange techniques at present cannot either compete with chemical precipitation. This of course is mainly due to the excessively high investment costs for ion exchange plants designed for large amounts of water. Chemical extraction is possible but is cumbersome when large volumes of water are to be treated.
It is also known that a microbiological process can be utilized for the precipitation of heavy metals. In said process the water is treated with sulfate reducing bacteria which reduce the sulfate ions to hydrogen sulfide which in its turn precipitates the metal ions in the form of metal sulfides. This method, however, has not been adapted for use in actual practice, due to the fact that the whole process has been carried out in a single vessel. When performed in this manner the process gives a very finely crystalline sulfide precipitate the removal of which by sedimentation or filtration is extremely difficult.
The object of the present invention is to provide an improved microbiological precipitation process which is carried out in two steps and which can be used on an industrial scale. Said object has been attained by means of a novel process for precipitating heavy metals from wastewater containing sulfate ions, wherein the water is treated with sulfate reducing bacteria which reduce the sulfate ions to hydrogen sulfide which in its turn precipitates the metal ions in the form of metal sulfides. According to the invention said process is characterized in that the bacteria are cultured in one or more culturing vessels in the presence of a nutritive solution and a portion of the wastewater, and that the resulting aqueous solution containing hydrogen sulfide produced by the bacteria is introduced into a precipitation vessel together with the remaining major portion of the wastewater.
The precipitation carried out in said precipitation vessel produces the metal sulfides in the form of a flocky precipitate (flocs) which settles easily, especially when the wastewater contains iron(III)ions. By the us
REFERENCES:
patent: 3941691 (1976-03-01), Romanenko et al.
patent: 4200523 (1980-04-01), Balmat
Chemical Abstract 88 (1978):110.078 f, Yagisawa Mitsuo, Murakuri Yukie, Kato Yoshihiro, Tomizuka Noboru, Yamaguchi Muneo, Ooyama Jiro, Recovery of Useful Metals from Bacterial Leaching Solution and Abatement of Waste Water Acidity by Sulfate-Reducing Bacteria.
Journal of Bacteriology, vol. 97 (1979):2, pp. 594-602.
Chemical Abstracts 85(1976):106.534x, Jones, H. E., Trudinger, P. A., Chambers, L. A., Pyliotis, N. A., Metal Accumulation by Bacteria with Particular Reference to Dissimilitory Sulfate-Reducing Bacteria.
Chemical Abstracts 80 (1974):112.225v, Loginova, L. V., Ilyaletdinov, A. N., Euker, L. B., Feasibility of Biochemical Purification of Balkhash Mining and Metallurgical Plant Effluents Using Sulfate-Reducing Bacteria.
Vyrmetoder AB
Wyse Thomas G.
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