| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 10.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 17.10.00 |
| PATENT TITLE |
Method for treatment of aqueous streams comprising biosolids |
| PATENT ABSTRACT |
A process is provided which can be used to clarify substantially aqueous streams and optionally separate biosolids, especially proteins, from food processing operations which comprises contacting an aqueous stream comprising biosolids with an anionic inorganic colloid and an organic polymer, to flocculate the biosolids. -------------------------------------------------------------------------------- |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 19.05.99 |
| PATENT REFERENCES CITED |
Tiande Cai et al., Stabilization of Poultry Processing By-Products and Poultry Carcasses Through Direct Chemical Acidification, Bioresource Technology 52, 52, pp. 69-77, 1995. G. D. Najafpour et al., Biological Conversion of Poultry Processing Waste to Single Cell Protein, Bioresource Technology, 48, pp. 65-70, 1994. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A process comprising contacting a substantially aqueous stream comprising biosolids with an effective amount of: (a) an anionic inorganic colloid selected from the group consisting of polysilicate microgels, polyaluminosilicate microgels, and polysilicic acid microgels, and mixtures thereof; and (b) a cationic polyacrylamide having a number average molecular weight greater than 1,000,000; to produce flocculated biosolids. 2. A process comprising contacting an aqueous stream, which comprises biosolids possessing surface negative charge sites, with: (a) an effective amount of a first organic polymer, which is a cationic polymer, to reduce the number of surface negative charge sites on the biosolids so that the biosolids have at least some cationic sites; (b) an effective amount of an anionic inorganic colloid selected from the group consisting of polysilicate microgels, polyaluminosilicate microgels, and polysilicic acid microgels, and mixtures thereof; and (c) an effective amount of a cationic polyacrylamide having a number average molecular weight greater than 1,000,000; to produce flocculated biosolids. 3. The process of claim 1 or 2 wherein the anionic inorganic colloid is in an amount of 1 to 7500 ppm based on the solution weight of the aqueous stream and the polyacrylamide is used in an amount of 0.2 to 5000 ppm, based on the solution weight of the aqueous stream. 4. The process of claim 1 or 2 wherein the anionic inorganic colloid has a microgel size of greater than 10 nm in diameter. 5. The process of claim 2 wherein the first organic polymer is a low molecular weight cationic polymer having a number average molecular weight in the range of 2,000 to 1,000,000. 6. The process of claim 2 wherein the first organic polymer is a high molecular weight cationic polymer having a number average molecular weight greater than 1,000,000. 7. The process of claim 1, 2, 5, or 6 further comprising separating and recovering the flocculated biosolids. |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for clarification of substantially aqueous process streams, and more particularly to separation of biosolids, especially proteins, from food processing operations, such as animal processing, especially poultry processing. 2. Description of the Related Art Large amounts of biosolids, such as proteins, carbohydrates, fats and oils, are collected in aqueous streams during food processing operations, such as waste and wash waters from the slaughter of animals for food products and other food processing operations such as extraction of proteins during soybean processing, and the like. The aqueous stream must be clarified, i.e., have suspended solids separated and removed to recover valuable product or before being discharged from the processing plant to a municipal or public water system. When separated and dried, the biosolids have value, for example, as animal feed, crop fertilizers, in pharmaceuticals and in personal care products. In one particular example, recovered protein from soybeans may be used in infant formula. These biosolids are comprised of particles having surface charges. Typically the particles have anionic surface charges at alkaline and neutral pH. The surface charge generates a repulsive force between particles to keep them apart. For individual particles of colloidal size, such as proteins, gravitational forces are insufficient to cause them to settle out of the aqueous suspension. Simple separation methods, such as filtration, are ineffective to separate these protein solids due to blinding of filters or ability of the solids to pass through them. Thus separation and hence, recovery of the protein may be low and/or a waste stream may not be environmentally acceptable for discharge from the processing plant. Techniques for removal of proteins, carbohydrates, fats and oils, and other biological contaminants from aqueous food processing streams are known. A common practice is to separate the protein, fats and oils from the aqueous stream by flocculation with metal salts, especially iron and/or aluminum salts, and anionic polymers. As it is common to use the recovered proteins, carbohydrates, fats and oils in animal feed, there are health issues when metal salts are used to separate biosolids. There is concern that the recovered biosolids have high levels of metal salts, which may build up in the tissues of the animals to whom the feed is given, these tissues being subsequently consumed by humans. Animal nutritionists are also concerned that metal salts may bind to phosphates in the feed so that they are less available as a nutrient. The food processing industry has sought alternatives to the use of metal salts for separation of proteins, carbohydrates, fats, and oils from aqueous streams. While methods have been disclosed for clarification of aqueous streams from food processing plants and separation of biosolids therefrom which do not require metal salts, each of these suffer from disadvantages such as high costs of materials and long reaction times to sufficiently clarify the stream. The present invention provides an economic and efficient process to clarify aqueous streams from food processing and to separate and recover protein in a form capable of subsequent commercial use. SUMMARY OF THE INVENTION The present invention provides a process, for example for use in clarification of aqueous streams comprising biosolids, the process comprising contacting an aqueous stream comprising biosolids with an effective amount of: (1) an anionic inorganic colloid; and (2) an organic polymer, wherein the organic polymer is selected from the group consisting of cationic polymers and amphoteric polymers and mixtures thereof, and has a number average molecular weight of greater than 1,000,000; whereby flocculated biosolids are produced. The aqueous stream can be contacted with an acid, if desired, to reduce pH of the stream to less than pH 7. In one particular embodiment of this invention, the aqueous stream is contacted simultaneously with the anionic inorganic colloid and an acid to reduce the pH. Subsequent contact of the organic polymer with the stream causes flocculation of the biosolids, such that the flocculated biosolids can be separated from the stream. Biosolids are typically suspended in aqueous streams due to surface charge effects. Surface charge will depend on pH. The present invention further provides a process which comprises contacting an aqueous stream comprising biosolids, wherein the biosolids possess surface negative charge sites, with an effective amount of: (a) a first organic polymer, wherein the first organic polymer is a cationic polymer, to reduce the number of surface negative charge sites on the biosolids, so that the biosolids have at least some cationic sites; (b) an anionic inorganic colloid; and (c) a second organic polymer, wherein the second organic polymer is selected from the group consisting of cationic and amphoteric polymers, and mixtures thereof; to produce flocculated biosolids. Alternatively when the anionic inorganic colloid is a silica-based colloid, the second organic polymer can be selected from the group consisting of cationic, anionic, and amphoteric polymers, and mixtures thereof. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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