Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2001-03-09
2004-08-24
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C210S666000, C210S727000, C210S905000, C210S734000
Reexamination Certificate
active
06780330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a process for treatment of substantially aqueous process streams, and more particularly to the removal of biomaterials from food processing operations, such as animal processing, especially poultry processing.
2. Description of the Related Art
Large amounts of biomaterials, both soluble and insoluble, such as proteins, carbohydrates, fats and oils, are collected in aqueous streams during food processing operations. These streams can be 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 treated to remove the biomaterials for recovery of valuable product or for discharge of the stream from the processing plant to a municipal or public water system. When separated and dried, the biomaterials 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.
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 biomaterials. There is concern that the recovered biomaterials have high levels of metal salts, which may build up in the tissues of the animals to which 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.
An improved process to treat aqueous streams comprising biosolids is disclosed in U.S. Pat. No. 6,132,625. Therein, a combination of an inorganic anionic colloid combined with a cationic polymer removes biosolids from aqueous streams. While this process is highly effective for removing biosolids, there can remain an undesirably high amount of soluble biomaterials in the stream. For value as a feed, fertilizer, in pharmaceuticals or personal care products, in addition to limitations placed by public water systems on content of discharged water, it is desirable to remove greater amounts of soluble biomaterials. The present invention meets these needs.
SUMMARY OF THE INVENTION
The present invention provides a process that can be used in treatment of aqueous streams comprising soluble biomaterials, the process comprising in sequence,
(1) adjusting the pH of a substantially aqueous stream comprising soluble biomaterials to less than or equal to pH 3 to produce a first pH-adjusted stream;
(2) adjusting the pH of the first pH-adjusted stream to greater than pH 3 to produce a second pH-adjusted stream; and
adding an effective amount of a flocculant to the second pH-adjusted stream.
DETAILED DESCRIPTION
This invention process can be used for reducing the amount of soluble, insoluble, and/or dispersed biomaterials of a substantially aqueous stream, whereby the biomaterials are flocculated, and optionally separated for subsequent use, for example, in animal feeds. The term “stream” is interchangeable herein with “fluid”, which can be in a moving or still form in a container, vessel, or processing equipment. The process comprises adjusting the pH of a substantially aqueous to less than or equal to pH 3 to produce a first pH-adjusted stream. The pH of the first pH-adjusted stream is adjusted to greater than pH 3 to produce a second pH-adjusted stream. An effective amount of a flocculent is added to the second pH-adjusted stream to produce a flocculated material.
As defined herein, to flocculate means to separate both soluble materials and insoluble suspended biomaterials, from a stream comprising biomaterials wherein the biomaterials become aggregated. Flocculation produces a flocculated material, which, if desired, can be physically separated from the stream. In the present invention, it is desirable to maximize the size of the flocculated material in order to facilitate removal of this material from the stream.
Materials
Aqueous Stream
In the process of this invention, the aqueous stream to be treated can be from any processing plant that produces an aqueous stream comprising soluble biomaterials, such as food processing plants. The aqueous stream can also contain biosolids, which can be recovered along with the soluble biomaterials in the process of this invention. The aqueous stream can also contain dispersed biomaterials such as fats or oils. For example, animal slaughterhouses and animal processing plants and other food processing plants may produce aqueous streams comprising soluble proteins, fats and oil. Animal slaughterhouses and processing plants include those for cattle, hogs, poultry and seafood. Other food processing plants include plants for vegetable, grain and dairy food processing, for example, plants for processing soybeans, rice, barley, cheese, and whey; plants for wet-milling of starches and grains; as well as breweries, distilleries and wineries. For example in processing soybeans, proteins are extracted into an aqueous stream from which they are subsequently recovered. The present invention is especially useful for treating streams containing soluble proteins from animal processing.
This invention is also useful in treatment of aqueous suspensions containing soluble biomaterials derived from processing of food (animal or vegetable) materials, which may have non-food end uses. For example, when separated and recovered, proteins are useful in certain cosmetics and other skin care formulations; starch has numerous non-food uses, including use in paper manufacture. Further still, this invention is useful to treat in general, any aqueous stream comprising soluble biomaterials, which may result from non-food processing operations.
pH Adjustment
The pH of an aqueous stream comprising soluble biomaterials is typically above pH 3, more typically above pH 6. Therefore an acid or other reagent that can effectively reduce pH to less than or equal to pH 3 is first added. Though any acids or reagents that can effective reduce the pH can be used, mineral acids such as sulfuric acid, hydrochloric acid, nitric acid, and mixtures thereof are preferred. Other useful acids or reagents to reduce pH to less than or equal to 3 include, but are not limited to, sulfonic acids, and organic acids such as carboxylic acids, acrylic acids, partially neutralized acids in which one or more protons are replaced with a metal or ammonium ion such as ammonium sulfate, and mixtures thereof. Acid metal salts can also be used to reduce pH to less than or equal to pH 3.
For adjustment to pH greater than pH 3, any suitable additive capable of increasing pH to greater than pH 3 can be used. Typically a base is used, preferably sodium hydroxide or lime because of cost and availability.
Flocculant
Flocculants useful in the process of this invention include organic polymers, optionally in the presence of an anionic inorganic colloid and/or a metal salt, such that the concentration of biomaterials, in particular soluble biomaterials in the aqueous stream is effectively reduced. The polymer can be a cationic organic polymer, amphoteric organic polymer, anionic organic polymer, or mixtures thereof. Low or high molecular weight organic polymers, or mixtures thereof can be used.
High molecular weight cationic organic polymers will typically have a number average molecular weight greater than 1,000,000. These polymers include cationic starch, cationic guar gum, chitosan and high molecular weight synthetic cationic polym
E. I. du Pont de Nemours and Company
Hruskoci Peter A.
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