HUP0101995A2 - Method for treatment of aqueous streams comprising biosolids - Google Patents

Abstract

The invention relates to the purification of aqueous media and the separation of solids of biological origin, especially proteins. The process can be used, for example, to clean water from food processing processes. HE

Description

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PROCEDURE FOR TREATING AQUEOUS STREAMS CONTAINING SOLIDS OF BIOLOGICAL ORIGIN

The invention relates to a method for treating an aqueous medium containing solids of biological origin. The invention relates generally to the purification of water from aqueous processes, and more particularly to the separation of solids of biological origin, in particular proteins, from food processing processes, such as animal processing, in particular poultry processing processes.

Aqueous media generated during food processing operations accumulate large amounts of biologically derived solids, such as proteins, carbohydrates, fats and oils. Such media include wastewaters and wash waters from the production of food products in slaughterhouses or protein extraction waters from other food processing operations, such as soybean processing and the like. The water stream must be treated, i.e. suspended solids must be separated and removed, in order to recover valuable products or before the water is discharged from the processing plant into the municipal or public water system. After separation and drying, the biologically derived solids are

93185-7340-BÉ/wood

-2- They can be used, for example, as animal feed, as plant fertilizer, in pharmaceuticals and personal care products. For example, protein extracted from soybeans can be used in infant formulas.

Biological solids consist of particles with surface charges. Typically, particles have an anionic surface charge at alkaline and neutral pH. The surface charge exerts a repulsive force between the particles, keeping them apart. For colloidally sized individual particles, such as proteins, the force of gravity is not sufficient to cause them to settle out of an aqueous suspension.

Simple separation processes such as filtration are not effective enough to separate such protein particles because they either clog the filters or the solids pass through them. The separation and thus recovery of the protein is therefore not effective enough and/or the wastewater is not environmentally suitable for disposal from the processing plant.

Various processes are known for the separation of proteins, carbohydrates, fats and oils and other biological contaminants from aqueous food processing plant effluents. Most commonly, proteins, fats and oils are separated from the aqueous medium by flocculation with metal salts, such as iron and/or aluminum salts, and anionic polymers. Since the recovered proteins, carbohydrates, fats and oils are usually used in animal feed, health considerations must be taken into account.

-3ni on metal salts used in the separation of biological solids. There is concern that recovered biological solids containing high levels of metal salts may be incorporated into the tissues of the animals fed, which are ultimately consumed by humans. Animal nutritionists also fear that metal salts may bind to phosphate in the feed, making it less nutritious. The food processing industry is therefore seeking alternatives to the use of metal salts in the separation of proteins, carbohydrates, fats and oils from aqueous media.

Although various methods are known for purifying aqueous media from food processing plants and separating solids of biological origin from them, which do not require metal salts, these methods have various disadvantages. Disadvantages include the high cost of the materials used and the excessively long reaction time required to sufficiently purify the medium. According to the invention, an economical and efficient method has been found for purifying aqueous media from food processing plants and for separating and recovering protein from them in a form suitable for subsequent commercial use.

The invention relates to a method, for example for use in the purification of aqueous media containing solids of biological origin, which comprises effectively purifying an aqueous media containing solids of biological origin.

- contacting with an amount of (1) an inorganic anionic colloid and (2) an organic polymer, wherein the organic polymer is a cationic polymer, an amphoteric polymer, or a mixture thereof, and has a number average molecular weight greater than 1,000,000;

and thus flocculated biological solids are produced.

An acid may optionally be added to the aqueous medium to reduce the pH of the aqueous stream to below 7. In one embodiment of the invention, the aqueous stream is simultaneously contacted with the anionic inorganic colloid and an acid to reduce the pH. The aqueous medium is then contacted with the organic polymer, causing the biological solids to flocculate, and the flocculated biological solids can be separated from the aqueous medium.

Biologically derived solids are typically suspended in aqueous media due to their surface charge. Surface charge is a function of pH. The invention further provides a process comprising contacting an aqueous medium containing biologically derived solids, wherein the biologically derived solids have negative surface charge sites, with an effective amount of the following to produce flocculated biologically derived solids: (a) a first organic polymer, wherein the organic polymer is a cationic polymer, the biologically derived solids

-5in order to reduce the number of surface negative charge sites on the material so that the biologically derived solid material has at least a few cationic sites;

(b) an anionic inorganic colloid; and (c) a second organic polymer, which second organic polymer is a cationic or amphoteric polymer or a mixture thereof.

If the anionic inorganic colloid is a silica-containing colloid, it is also possible to use a cationic, anionic or amphoteric polymer or a mixture thereof as the second organic polymer.

Many processing plants generate aqueous media containing biologically derived solids, such as proteins, carbohydrates, fats or oils, which aqueous media must be treated in order to recover potentially valuable biologically derived solids and/or before the aqueous media is discharged from the plant. Such aqueous media often originate from food processing plants and have a solids content of between about 0.01 and 5% by weight. The process according to the invention allows such aqueous media to be purified, whereby the solids are flocculated, optionally separated and subsequently used, for example, in animal feed.

In this specification, the term “flocculate” means to separate suspended biological solids from a medium containing biological solids.

- 6 of which, the biological solids aggregate and settle to the bottom or top of the medium in which they were previously suspended. Flocculation produces flocculated material which can optionally be physically separated from the medium. According to the invention, it is desirable that the flocculated material be as large as possible in order to facilitate separation of this material from the aqueous medium.

The following materials are mentioned in the description:

Aqueous stream or aqueous medium:

In the process of the invention, the aqueous medium to be treated may originate from any processing plant that produces an aqueous medium containing solids of biological origin, such as a food processing plant. Examples of these include slaughterhouses and animal processing plants, as well as other food processing plants that produce aqueous media containing protein, fat or oil. Examples of slaughterhouses and processing plants include beef, pork, poultry and seafood processing plants. Other food processing plants include, for example, plant processing, grain processing and dairy processing plants, such as soybean, rice, barley, cheese or whey processing plants; in addition, starch and grain wet milling plants, breweries, distilleries and wineries. Among the biologically derived solids in aqueous media resulting from the aforementioned processes, we mention sugars, starches and

other carbohydrates, as well as proteins, fats and oils. For example, during the processing of soybeans, proteins are extracted with an aqueous medium and then recovered from it. The method according to the invention is particularly suitable for the treatment of aqueous media resulting from animal processing, in particular poultry processing.

Although the invention can be applied to conventional food processing processes in which an aqueous suspension of biological solids is formed, it should be noted that the invention can also be used to treat aqueous suspensions containing biological solids from the processing of animal or plant foods that are not intended for food use. For example, after separation and recovery, proteins can be used in certain cosmetic and other skin care preparations; starch also has a number of non-food applications, such as papermaking. The invention can also be applied generally to the treatment of any aqueous medium containing biological solids from non-food processing operations. In addition, although the biological solids mentioned above are generally suspended in a substantially aqueous medium, a certain amount of biological solids may also be dissolved in the medium, depending on the properties of the medium and the solids, such as pH, salinity or other parameters.

-8 The anionic inorganic colloids useful in the process of the invention may be silica-based or non-silica-based anionic inorganic colloids or mixtures thereof. Examples of silica-based anionic inorganic colloids include colloidal silica, aluminum-modified colloidal silica, polysilicate microgels, polyaluminosilicate microgels, polysilicic acid and polysilicic acid microgels, and mixtures thereof. Examples of non-silica-based anionic inorganic colloids include clays, in particular colloidal bentonite clay. Other non-silica-based anionic inorganic colloids include, for example, colloidal tin or titanyl sulfate.

The anionic inorganic colloids used in the invention may be in the form of colloidal silica sol containing about 2-60% by weight of silica, preferably 4-30% by weight of silica. The colloid may comprise particles having at least one aluminosilicate surface layer, or may be an aluminum-modified silica sol. The specific surface area of the colloidal silica particles in the sol is generally 50-1000 m ² /g, preferably about 200-1000 m ² /g, particularly preferably about 300-700 m ² /g. The silica sol may be stabilized with an alkali metal oxide such that the _SiO2 : _M2O molar ratio is between 10:1 and 300:1, preferably between 15:1 and 100:1 (M is sodium, potassium, lithium or _NH4 ). The colloidal particles are re-9-

a particle size of less than 60 nm, an average particle size of less than 20 nm, particularly preferably an average particle size of between about 1 and 10 nm.

Microgels differ from colloidal silica in that the specific surface area of microgel particles is typically 1000 m ² /g or greater, and microgels consist of small silica particles, 1-2 nm in diameter, linked together in chains and three-dimensional networks. Polysilicate microgels, also called active silicas, are materials in which the SiO ₂ : Na ₂ O ratio ranges from 4:1 to about 25:1, and are reviewed in Ralph K. Iler, “The Chemistry of Silica,” John Wiley and Sons, NY, pp. 174-176 and 225-234 (1979). Polysilicic acid generally refers to a silica that is formed in the pH range of 1 to 4 and partially polymerized, and in which the silica particles are generally less than 4 nm in diameter, which then polymerize into chains and three-dimensional networks. Polysilicic acids can be prepared, for example, by the process described in US-P-5,127,994 or 5,626,721. Polyaluminosilicates are polysilicate or polysilicic acid microgels in which the aluminum is incorporated into the particles or incorporated onto the surface of the particles, or both. Polysilicate microgels are polyaluminosilicate microgels, and polysilicic acid can be prepared and stabilized at acidic pH. Generally, better results are obtained with larger microgels.

- 10 sizes; generally, microgels larger than 10 nm in size give the best results. The microgel size can be increased by any known method, such as aging the microgel, changing the pH, changing the concentration, or other methods known to those skilled in the art.

Polysilicate microgels and polyaminosilicate microgels useful in the present invention are generally prepared by activating an alkali metal silicate under the conditions described in USP-4,954,220 or 4,927,498. However, other methods may be used. For example, polyaluminosilicate can be prepared by acidifying a silicate with mineral acids containing dissolved aluminum salts. See USP-5,482,693. Alumina/silica microgels can be prepared by acidifying a silicate containing an excess of alumina as described in US-P2,234,285.

In addition to conventional silica sols and silica microgels, other known silica sols (see for example the sols described in EP 491 879 or EP 502 089) can also be used as anionic inorganic colloids according to the invention.

Anionic inorganic colloids are used in effective amounts in conjunction with organic polymers for the purpose of producing flocculated biological solids.

-11 sunk pre. The effective amount may be from about 1 to 7500 ppm of solids, such as SiO ₂ , based on the weight of the aqueous medium solution. The preferred range is from about 1 to 5000 ppm depending on the anionic inorganic colloid. For each anionic inorganic colloid, the preferred ranges are: from 2 to 500 ppm for polysilicic acid or polysilicate microgel; from 4 to 1000 ppm for colloidal silica; and from 2 to 2000 ppm for inorganic colloidal clays, such as bentonite.

Organic polymers useful in the present invention include cationic and amphoteric polymers, and mixtures thereof. Organic polymers typically have a number average molecular weight greater than 1,000,000. These are commonly referred to as "high molecular weight polymers."

High molecular weight cationic organic polymers include cationic starch, cationic guar gum, chitosan, and high molecular weight synthetic cationic polymers such as cationic polyacrylamide. Cationic starches include those prepared by reacting starches with tertiary or quaternary amines to form cationic products having a degree of substitution of between 0.01 and 1.0 and a nitrogen content of between about 0.01 and 1.0 wt%. Suitable starches include potato starch, corn starch, waxy maize, wheat, rice, and oats. The high molecular weight cationic organic polymer is preferably polyacrylamide.

- 12A high molecular weight cationic organic polymers are used in an effective amount in conjunction with an anionic inorganic colloid to form a flocculated biological solid. The effective amount of the cationic polymer is from about 0.2 to 5000 ppm by weight of the aqueous medium solution. The preferred range is from about 1 to 2500 ppm.

Amphoteric polymers include amphoteric starch, guar gum, and synthetic amphoteric high molecular weight organic polymers. Amphoteric polymers are usually used in the same amount as high molecular weight cationic polymers.

The invention also relates to a method comprising contacting an aqueous medium containing a biological solid having surface negative charge sites with an effective amount of a first organic polymer to reduce the number of surface negative charge sites. The first organic polymer is a cationic polymer used to reduce the number of surface negative charge sites and to create some cationic sites. The effective amount is usually an amount sufficient to neutralize at least 1%, preferably at least 10%, of the surface negative charge sites on the biological solid. Low or high molecular weight cationic organic polymers or mixtures thereof may be used for this purpose. Low molecular weight cationic organic polymers are preferred because they have a greater cationic character and a lower

- The price is 13.

Among the high molecular weight cationic polymers that can be used are those listed above.

The low molecular weight cationic polymers that can be used have a number average molecular weight of between about 2,000 and about 1,000,000, preferably between 10,000 and 500,000. The low molecular weight polymer can be, for example, polyethyleneimine, polyamine, polycyanodiamide-formaldehyde polymer, amphoteric polymer, diallyldimethylammonium chloride polymer, diallylaminoalkyl-(meth)acrylate polymer or dialkylaminoalkyl-(meth)acrylamide polymer, acrylamide copolymer or diallyldimethylammonium chloride, acrylamide and diallylaminoalkyl-(meth)acrylate copolymer, acrylamide and dialkyldiaminoalkyl-(meth)acrylamide copolymer or dimethylamine and epichlorohydrin polymer. See U.S. Patents 4,795,531 and 5,126,014.

The first organic polymer is a high or low molecular weight cationic organic polymer or mixtures thereof, in an effective amount to reduce the number of surface negative charge sites on the biological solid. The effective amount depends on a number of factors, such as the number of surface negative charge sites present on the biological solid in the aqueous medium, the type of biological solid, and the pH of the aqueous medium. The effective amount can be determined by methods known to those skilled in the art, such as by colloidal titration. This amount is generally between about 0.01 and about 10,000 ppm of polymer compound.

- 14 parts per million by weight of the medium. The term “ppm” has been defined above.

After treatment with the first organic polymer, the aqueous medium is treated with a second organic polymer. The second organic polymer depends on the anionic inorganic colloid. The second organic polymer can be selected from cationic and amphoteric polymers and mixtures thereof for any anionic inorganic colloid. When the anionic inorganic colloid is an anionic inorganic colloid containing silica, the second organic polymer can be an anionic, cationic, amphoteric polymer or a mixture thereof. Cationic and amphoteric polymers have been described above and can be polymers of high or low molecular weight.

The anionic polymers useful in the process of the invention have a number average molecular weight of at least 500,000 and a degree of anionic substitution of at least 1 mol%. Anionic polymers having a number average molecular weight of greater than 1,000,000 are preferred. The preferred degree of anionic substitution is 10-70 mol%.

Examples of anionic polymers that can be used include soluble vinyl polymers, including acrylamide, acrylic acid, acrylamido-2-methylpropylsulfonate and/or mixtures thereof, and may be hydrolyzed acrylamide polymers or copolymers of acrylamide or a homologue thereof, such as methacrylamide, with acrylic acid or a homologue thereof, such as methacrylic acid, or even with other monomers, such as maleic acid, itaconic acid, vinylsulfonic acid, acrylamido-2-methylpropylsulfonate or other sulfonate-containing monomers. Additional anionic polymers are described, for example, in the following U.S. Patents: 4,643,801, 4,795,531 and 5,126,014.

Other anionic polymers that can be used include anionic starch, anionic guar gum, and anionic polyvinyl acetate.

Optionally, other components can be used as follows. If desired, the pH of the aqueous medium can first be reduced to below 7 with an acid. Inorganic acids such as sulfuric acid, hydrochloric acid and nitric acid are generally preferred. Other acids that can be used include carbon dioxide, sulfonic acids and organic acids such as carboxylic acids, acrylic acids and acidic anionic inorganic colloids, partially neutralized acids in which one or more protons have been replaced by a metal or ammonium ion, or mixtures thereof. Examples of acidic anionic inorganic colloids include low molecular weight polysilicic acid, high molecular weight polysilicic acid microgels, acidic polyaluminosilicates and acid-stabilized polysilicate microgels. Some of the acid-stabilized polysilicate microgels are described in the following U.S. Patents: 5,127,994 and 5,626,721.

- 16 Metal salts may optionally be used in the process of the invention. Iron and aluminum salts are particularly useful. Acidic metal salts may also be used to reduce the pH, as they act as charge donors.

The process of the invention is described below. The process of the invention comprises treating an aqueous medium containing a biological solid, such as a protein, to reduce the amount of suspended solids (as measured by turbidity) and optionally separating the biological solids. The biological solids can be recovered for subsequent use. It is noted that the process can recover both suspended biological solids and soluble substances such as those found in blood and sugars.

The process according to the invention is carried out by contacting an aqueous medium containing solids of biological origin with an anionic inorganic colloid and an organic polymer. The aqueous medium may originate from any process in which such a medium is produced. Examples of these include animal and plant processing processes, including processes for non-food applications. The organic polymer may be a cationic or amphoteric polymer with a number average molecular weight greater than 1,000,000, or a mixture thereof. Optionally, the aqueous medium is reacted with an acid in order to reduce the pH of the medium to a value below 7. Optionally, a metal salt, in particular an iron or aluminum salt, may also be added. These reagents, the anionic inorganic colloid, the organic polymer, and the optional acid and/or metal salt, may be contacted with the medium in any sequential order, or one or more reagents may be added to the medium simultaneously. In one embodiment, the medium is contacted with the acid and the anionic inorganic colloid simultaneously.

The pH of the aqueous medium may optionally be reduced below pH 7 using any acid, examples of which have been mentioned above. When an acidic anionic inorganic colloid is used to reduce the pH of the medium below pH 7, it is possible that no additional acid or anionic inorganic colloid is required in the aqueous medium to flocculate the biological solids.

The aqueous medium is contacted with an anionic inorganic colloid and an organic polymer. This can be done before, after, or simultaneously with the pH of the aqueous medium being reduced to below 7, if a pH-lowering step is required. The inorganic colloid and the organic polymer can be contacted with the aqueous medium separately in any order or simultaneously. When the aqueous medium is contacted with a combination of anionic inorganic colloid and/or organic polymer, a flocculated biological solid is obtained.

The flocculated biological solids can optionally be separated from the treated medium, the separation is performed by

- 18: .’% r;·

- ·’**’Ti.»can be separated by conventional methods such as sedimentation, flotation, filtration, centrifugation, decantation or a combination of these methods. The separated biosolids can then be recovered and used in various fields. Surprisingly, we have also found that the biosolids recovered by the above method do not have as strong an odor when dry as those flocculated by a process using ferric chloride.

It is generally assumed that suspended biological solids, such as proteins, carry surface negative charges in the aqueous medium. The invention also includes a process comprising contacting an aqueous medium containing biological solids with an effective amount of a first organic polymer to reduce the number of surface negative charge sites on the biological solids suspended in the medium. Said first organic polymer is a cationic polymer, which is used in an amount sufficient to create some cationic sites on the biological solid. Typically, an amount of cationic polymer is added that is capable of neutralizing at least 1%, preferably at least 10%, of the surface negative charge sites on the biological solids. The first organic polymer may be a high or low molecular weight cationic organic polymer. The cationic polymer is preferably a low molecular weight cationic polymer.

The anionic inorganic colloid and a second organic polymer are added to the aqueous medium before, after, or simultaneously with the first organic polymer in the medium.

- 19 for the production of flocculated biological solids. The second organic polymer may be a cationic, amphoteric or anionic polymer or mixtures thereof depending on the anionic inorganic colloid. For any anionic inorganic colloid, the second organic polymer may be a cationic or amphoteric polymer or mixtures thereof. For an anionic organic colloid containing silica, the second organic polymer may be an anionic, cationic, amphoteric polymer or mixtures thereof.

The flocculated biological solids can be separated and recovered by known methods, as mentioned above.

The process according to the invention is illustrated by examples below.

Example 1

A sample of wash water containing biosolids and approximately 1000 ppm unflocculated protein is taken from an East Coast poultry processing plant. The initial turbidity is >200. The initial pH is approximately 7.

The following reagents were used in the experiments: high molecular weight cationic polyacrylamide, Percol 182®, manufactured by Ciba Specialty Chemicals, Basel, Switzerland, 8 ppm; silica microgel solution, Particol® MX, 120 ppm (based on SiO ₂ ), supplied by EI duPont de Nemours and Company, Inc., Wilmington, DE. Quantities are based on the weight of the wash water solution.

-20The following reagents are added.

(1) Mix 250 mL of wash water at medium speed using a Fisher Scientific Model #120 MR magnetic stirrer, available from Fisher Scientific, Pittsburgh, PA. Adjust the pH to the values given in Table 1 with dilute sodium hydroxide or sulfuric acid.

(2) At time 0, cationic polyacrylamide is added.

(3) 1 minute later, silica microgel is added.

(4) After 2 minutes, the mixer rotation speed is reduced.

(5) After 4 minutes, the mixer is stopped and the flocculated solid is allowed to settle to the bottom of the beaker.

(6) After 10 minutes, the turbidity of the wash water is measured in NTU using a Hach Ratio Turbidity Meter available from Hach Company, Loveland, CO., which provides an indication of the purity of the water and the protein recovery.

(7) After 20 minutes, a second 8 ppm polyacrylamide is added and the mixer is set to medium speed.

(8) After 21 minutes, the mixer speed is set to slow, and after 23 minutes, the mixer is stopped.

(9) Turbidity is measured after 30 minutes.

-21 Table 1

Try number Wash water pH Confusion 10 minutes 30 minutes 1. 8.0 88 63 2. 6.9 79 55 3. 6.5 77 42 4. 5.5 25 2 5. 4.5 30 1 6. 3.5 10 2

As can be seen from Table 1, the turbidity decreases after the addition of cationic polymer and silica microgel. Better results can be observed at lower pH. Turbidity improves after the second addition of polyacrylamide, with the best results again being obtained below pH = 7.

Example 2

The wash water from the poultry processing process mentioned in Example 1 is used with several different anionic inorganic colloids. The anionic inorganic colloids listed below are used:

Ludox® SM colloidal silica, 30% by weight silica sol, specific surface area 300 m ² /g.

Ludox® HS-30 colloidal silica, 30% by weight silica sol, specific surface area 230 m ² /g.

-22Ludox® 130 colloidal silica, 30 wt% silica sol, specific surface area 130 m ² /g.

Ludox® colloidal silicas are available from E. I. duPont de Nemours and Company, Wilmington, DE.

BMA-670, a low “S” value colloidal silica sol, specific surface area = 850 m ² /g, is available from Eka Chemicals AB, Bohus, Sweden.

Colloidal silica sol, 4 nm, specific surface area = 750 m ² /g, is available from Nalco Chemical Company, Naperville, IL.

Particol® MX, polysilicate microgel, specific surface area = 1200 m ² /g, manufactured by EI du Pont de Nemours and Company.

The high molecular weight cationic organic polymer was Percol 182®.

For all experiments, we follow the following procedure:

(1) In a beaker, while stirring at medium speed, adjust the pH of 250 ml of the poultry processing wash water mentioned in Example 1 to 4.5 with dilute sulfuric acid.

(2) An anionic inorganic colloid is added to the acidified wash water at minute 0, expressed as 40 ppm SiO ₂ based on the weight of the wash water solution.

(3) After 1 minute, 4 ppm of high molecular weight cationic organic polymer is added.

(4) After 2 minutes, set the mixer speed to the slowest setting.

(5) After 4 minutes, turn off the magnetic stirrer.

(6) After 10 minutes, measure the turbidity of the wash water above the flocculated solids.

The results are given in Table 2.

Table 2

Colloid Turbidity after 10 minutes Ludox® SM 15 Ludox® HS-30 24 Ludox® 130 28 BMA-670® 11 Nalco S1O2 sol 11 Particol® MX 2.5

As can be seen from Table 2, various anionic inorganic colloids can be used, all of which are effective in reducing the turbidity of protein-containing wash water. The flocculated biological solids settled from the water to the bottom of the beaker.

Example 3-8

In these examples, a second poultry processing wash water is used, which contains approximately 1390 ppm.

-24agents are added: low molecular weight cationic organic polymer, diallyldimethylammonium chloride polymer (polydadmac); anionic inorganic colloids: Nalco colloidal silica gel sol, Particol® polysilicate microgel and bentonite clay; and high molecular weight cationic organic polymer, Percol 182®, polyacrylamide (PAM). The amounts of the added reagents are given in Table 3-8 in ppm relative to the weight of the wash water solution.

Example 3 (comparative)

250 ml of wash water is stirred at medium speed. At time 0, Polydadmac is added. After 10 seconds, an anionic inorganic colloid is added. After 15 seconds, stirring is stopped and the wash water is poured into an air flotation apparatus consisting of a 300 ml tall beaker equipped with a sintered glass sprayer (medium porosity, 30 mm diameter) placed in the center of the beaker.

Air is sprayed into the wash water at a flow rate of approximately 50 ml/min at 1 psi until the 4th minute is reached, then the air spray is stopped. Turbidity is determined at the 5th and 10th minutes.

Table -253

Haunted number Polydadmac Colloid Confusion ppm Naico sol SiO ₂ , ppm Particol®MX SiO ₂ , ppm 5 minutes 10 minutes 1 10 20 >200 >200 2 10 40 >200 >200 3 10 20 >200 >200 4 10 40 >200 129 5 16 20 >200 >200 6 16 40 >200 >200 7 16 20 >200 >200 8 16 40 >200 112

As can be seen from Table 3, combining a low molecular weight cationic organic polymer and an anionic inorganic colloid is not sufficient to reduce turbidity to produce a purified wash water. No flocs were formed in runs 1, 2, 5 and 6. A small amount of dispersed flocs were formed in runs 3, 4, 7 and 8, which contained protein solids, but the flocs could not be separated from the wash water.

Example 4

The procedure described in Example 3 is repeated, except that an additional step is added, during which a high molecular weight cationic organic polymer, oleoacrylamide, is added 10 seconds after the

-26In Table 4, we give the amounts of reagents added and the results obtained.

Table 4

Try number Polydadmac Colloid PAM Confusion ppm Nalco sol ppm, S1O2 Particol® MX ppm, SiO ppm 5 minutes 10 minutes 9 10 20 6 >200 66 10 10 40 6 >200 57 11 10 20 6 65 32 12 10 40 6 38 19 13 16 20 6 >200 >200 14 16 40 6 185 82 15 16 20 6 120 44 16 16 40 6 15 12

As can be seen from Table 4, adding a high molecular weight cationic polymer to the combination of a low molecular weight cationic polymer and anionic inorganic colloid improves wash water purification by reducing turbidity. In runs 9, 10, 11, 12, 15 and 16, large-volume flocs are formed that separate at the top and/or bottom of the wash water. These flocs can be recovered. In run 13, when a large amount of cationic polyadmac is added, the amount of anionic inorganic colloid added is not effective enough to sufficiently neutralize the negatively charged sites present on the solid, so that the turbidity is reduced.

Example 5 (comparative)

The procedure described in Example 3 was repeated using bentonite clay as the anionic inorganic colloid. Table 5 shows the amounts of reagents added and the results obtained.

Table 5

Try number Polydadmac Bentonite Confusion ppm ppm, S1O2 5 minutes 10 minutes 17 10 100 >200 >200 18 10 200 >200 >200 19 16 100 >200 >200 20 16 200 >200 >200

As can be seen from Table 5, combining a low molecular weight cationic organic polymer with bentonite as an anionic inorganic colloid is not sufficient to reduce turbidity and produce purified wash water. Very finely dispersed flakes are formed which cannot be separated from the wash water.

Example 6

The procedure described in Example 5 was repeated using bentonite clay as the anionic inorganic colloid. The amounts of reagents added and the results are given in Table 6.

Table -286

Try number Polydadmac Bentonite PAM Confusion ppm ppm, SiO ₂ ppm 5 minutes 10 minutes 21 10 100 6 >200 147 22 10 200 6 84 46 23 16 100 6 >200 >200 24 16 200 6 158 77

As can be seen from Table 6, adding a high molecular weight cationic polymer to a combination of a low molecular weight cationic polymer and anionic inorganic colloid, bentonite, improves wash water purification by reducing turbidity. In runs 21 and 23, finely dispersed flakes are formed that do not contain enough effective bentonite to neutralize the cationic sites present in sufficient numbers. In these runs, the solids do not separate well. In runs 22 and 24, large volume flakes are formed that separate at the top and bottom of the wash water.

Example 7

250 ml of wash water is mixed at medium speed. Its pH is reduced to 3.5 by adding dilute sulfuric acid. At time 0, an anionic inorganic colloid is added. After 10 seconds, a high molecular weight cationic poly

-29 is loaded into a submerged air flotation apparatus. Air is bubbled into the wash water at a flow rate of 50 ml/min at 1 psi pressure until the end of the 4th minute, when the air spray is stopped. Turbidity is determined at the 5th and 10th minutes. The data are given in Table 7.

Table 7

Haunted number Colloid, ppm, SiOj PAM Confusion Nalco Salts Particol® MX Bentonite PPm 5 minutes 10 minutes 25 20 6 163 151 26 40 6 136 125 27 20 6 29 17 28 40 6 12 10 29 100 6 >200 131 30 200 6 90 38

As shown in Table 7, when the pH of the wash water is lowered and then both an anionic inorganic colloid and a high molecular weight cationic organic polymer are added, the turbidity is reduced. In all experiments, compact flakes ranging from fine to large in size are formed, containing solid proteins, which separate at the top and/or bottom of the wash water. The proteinaceous flakes can be recovered.

Example 8

250 ml of poultry processing wash water is mixed at medium speed. The pH is adjusted to 3.5.

- High molecular weight cationic polyacrylamide (PAM) was added at 30 seconds. At 30 seconds, the agitation was stopped and the wash water was charged to the air flotation apparatus described in Comparative Example 3. The wash water was sparged with air at a rate of 100 ml/min at 1 psi for 4 minutes, at which time the air sparging was stopped. Turbidity was determined at 5 and 10 minutes. The liquid was then drawn from the air flotation apparatus through a sieve at 12 minutes, and the turbidity of the drawn liquid was also measured. The protein-containing solids were collected on the sieve. The data and results are given in Table 8.

Table 8

Try number Particol® MX ppm, SiO PAM ppm Confusion 5 minutes 10 minutes Aspirated fluid 31 20 6 51 30 28 32 40 6 14 10 13

As can be seen from Table 8, the turbidity of the wash water decreases with time. In addition, the example illustrates the separation of solids from the wash water, as the solids are collected on the sieve. The turbidity of the aspirated liquid differs only slightly from the value measured at 10 minutes, indicating that the solids are

-31 - ·ί. ^£

Example 9

An additional wash water sample is obtained from an East Coast poultry processing plant containing approximately 1000 ppm of non-flocculated biological solids and a turbidity greater than 200.

The polysilicate microgel solution, Particol® MX, is stabilized with sulfuric acid. The microgel solution is aged for various periods of time before use, the aging periods are given in Table 9.

250 ml of wash water is stirred at medium speed. At time 0, high molecular weight polyacrylamide, Percol® 182, is added at a concentration of 8 ppm by weight of the wash water solution. At the end of minute 1, the acid-stabilized aged polysilicate microgel solution is added at a concentration of 120 ppm by weight of the wash water solution. Experiments are performed for each aging time. At minute 2, the stirring speed is set to slow. At minute 5, the stirring is stopped. At minute 15, the turbidity of the wash water is measured.

Table 9

Aging time Confusion 15 seconds 122 5 minutes 39 15 minutes 21 45 minutes 5

-32As can be seen from Table 9, the use of acid-stabilized polysilicate microgel in combination with cationic polyacrylamide is sufficient to reduce the turbidity of the wash water without first lowering the pH to below 7. Furthermore, the results show that aging the polysilicate microgel for a longer period of time results in a further reduction in turbidity. In another experiment, performed with a similarly aged microgel solution, it was found that the average microgel size was 5 nm at an aging time of 15 seconds, while at an aging time of 45 minutes this increased to 230 nm.

Example 10

A 250 ml soybean whey solution from Protein Technologies, Inc. containing 0.51% protein was mixed at medium speed. Dilute hydrochloric acid was added to adjust the pH to 2.5. At minute 0, 160 ppm BMA-9 colloidal silica, available from Eka Chemicals AB, Bohus, Sweden, was added to the solution, based on the weight of the soybean solution. The solution was mixed at medium speed for 10 minutes, then 8 ppm (based on the weight of the soybean solution) of high molecular weight polyacrylamide, Percol 182®, was added and the solution was mixed for 10 minutes. The mixture was filtered through glass filter paper 934AH, available from Whatman, Clifton, NJ, to yield 0.11 g of solid protein. The filtered solution contained 0.416% protein.

-33- ί.’-'Ον’:

contains, which means that the protein content of the solution has decreased by 20%.

Example 11

Wastewater from an East Coast poultry processing plant is treated in a continuous process according to the invention. Sulfuric acid is added to the flowing wastewater in sufficient quantity to reduce the pH of the solution to 3.7, and Particol® MC polysilicate microgel, 95 ppm SiO ₂ by weight of the flowing liquid solution, is added simultaneously. A cationic polyacrylamide, Percol 182®, is added downstream (approximately 30 seconds later) from the point of addition of the acid and microgel, at 4 ppm by weight of the flowing solution. The stream is passed to a dissolved air flotation (DAF) unit where the solids float to the surface and are collected for recovery. The remaining aqueous stream is analyzed and the chemical (COD) and biological (BOD) oxygen demands and the total suspended solids (TSS) are determined.

COD is determined using the Hach COD Test Kit available from Hach Company, Loveland, CO, and TSS is determined using the Standard Methods for Examination of Water and Wastewater, Procedure 2450 D (published by the American Public Health Association, American Water Works Association, and Water Environment Federation). BOD is determined using the Standard Methods for Examination of Water and Wastewater, Procedure 5210 (published by the American Public Health Association, American Water Works Association, and Water Environment Federation).

It is determined by the procedure marked -34. The data are given in Table 10.

Table 10

Treatment COD, mg/l BŐD, mg/l TSS, mg/l none 2970 1393 N/A* Example 11 180 180 67

*N/T = not tested, but this number is usually around 1000 mg/l before treatment.

As can be seen from Table 10, the process according to the invention reduces the chemical and biological oxygen demand of wastewater generated in a continuous flow process of an actual poultry processing plant.

Example 12 A suspension of 980 g of Staley Pearl Starch, an unmodified corn starch, in water was stirred at medium speed. At time 0, 10 ppm _SiO2 , based on the weight of the starch suspension, was added in the form of Particol® MX, an acid-stabilized polysilicate microgel solution. The mixture was stirred for 15 seconds, and at the 15th second, 2 ppm high molecular weight polyacrylamide, based on the weight of the starch suspension solution, was added.

-35- : . -. X:

··· · · · · · · · is measured, the turbidity is then 46. The test is repeated, with the only difference being that 20 ppm SiO ₂ is used in the form of Particol® MX. At the 45th second, the turbidity is then 29. In a third comparative test, the addition of Particol® MX is omitted. The turbidity is then 186.

Example 13

A wastewater sample is taken from an East Coast poultry processing plant. The wastewater has a COD value of >2100 ppm, an initial turbidity of >200, and a pH of 6.1. 250 mL of wastewater is placed in a 400 mL beaker. The wastewater is stirred at 275 rpm using a mechanical propeller stirrer. The pH of the wastewater is adjusted to 5.5 by adding dilute sulfuric acid. At time 0, Particol® MX, a silica microgel, is added to the wastewater. At 15 seconds, Percol® 182, a cationic polymer, polyacrylamide (PAM), is added. At 25 seconds, 10 seconds after the polymer is added, the stirrer speed is reduced to 150 rpm. The mixing is stopped 40 seconds after the polymer addition. The wastewater is sampled for turbidity measurement at 35 and 95 seconds after the mixing is stopped. After the turbidity measurement at 95 seconds, the pH of the mixture is also measured. The flocculated wastewater is then resuspended by stirring the mixture for 30 seconds at 150 rpm. After 1 minute, the mixing is stopped and the wastewater is taken for COD measurement.

-We take 36 samples.

COD was measured using a Milton Roy Spectronic 20 spectrophotometer at 620 nm using 0-1500 ppm COD colorimetric assay vials (manufactured by CHEMetrics, Calverton, VA). Table 11 lists the amounts of reagents added and the results obtained in these experiments (runs 33 and 34).

Example 14

The procedure described in Example 13 is repeated with the same wastewater sample. However, instead of adding acid, 32 ppm FeCl is added 15 seconds before the addition of Particol® MX. The times in Example 13 are therefore shifted by 15 seconds. The amounts of reagents added and the results obtained for Experiment 35 are given in Table 11.

Table 11

Try number Particol® MX, ppm, S1O2 Cationic PAM, ppm Confusion Final pH COD, ppm 35 seconds 95 seconds 33 120 12 33 32 5.68 475 34 80 12 10 9 5.63 386 35 120 12 16 14 5.61 415

As can be seen from Table 11, some acids

-37 can be used to measure turbidity and chemical oxygen demand in wastewater containing biological solids.

Example 15

The procedure described in Example 13 is used, testing the same wastewater sample as described therein, except that the pH-lowering step is omitted and the organic polymer is changed. At time 0, Particol® MX is added, and at 15 seconds, a low molecular weight cationic polymer, polyamine (Agelfloc® A50HV, available from Ciba Specialty Chemicals), is added. At 30 seconds, a second organic polymer is added, which is either cationic polyacrylamide (PAM), Percol® 182, or anionic polyacrylamide (PAM), Percol® 155 PG, also available from Ciba Specialty Chemicals. At 40 seconds, i.e. 10 seconds after the polymer addition, the mixing speed is reduced to 150 rpm. Mixing is stopped 40 seconds after the polymer addition. The wastewater is sampled at 35 and 95 seconds after the mixer is stopped and the turbidity of the samples is measured. The pH is determined after the second turbidity measurement at 95 seconds. The flocculated wastewater is then resuspended by stirring at 150 rpm for 30 seconds. Stirring is stopped 1 minute later and the wastewater is sampled for COD measurement. The amounts of reagents added and the results obtained are given in Table 12.

-3812. Table

Haunted Particol® MX, ppm, S1O2 Polyam in ppm Cationic PAM, ppm Anionic PAM, ppm Confusion Final PH COD, PPm and .to close 35 seconds 95 seconds 36 50 40 12 185 84 6.03 444 37 50 40 12 33 28 5.98 429 38 100 40 12 5 4 5.99 415 39 100 40 12 6 3 5.99 540

As can be seen from Table 12, various organic polymers can be used in various combinations with anionic colloid. In order to purify wastewater and reduce chemical oxygen demand, low molecular weight cationic polyamine is used in experiments 36 and 38 together with high molecular weight polyacrylamide. In experiments 37 and 39, the polyamine is used in combination with anionic polyacrylamide.

Example 16

The procedure of Example 13 was repeated except that a base, sodium hydroxide, was added to raise the pH to 6.5, and then Particol® MX was added to the mixture. The remaining steps were carried out without change. The amounts of reagents added and the results obtained are given in Table 13,

Table -3913

Try number Particol® MX, ppm, S1O2 Cationic PAM, ppm Confusion Final pH COD, ppm 35 seconds 95 seconds 40 80 12 55 55 6.42 766 41 40 12 34 34 6.51 628

As can be seen from Table 13, wastewater can be purified and its chemical oxygen demand can be reduced at pH close to 7 by using an anionic colloid and cationic polymer.

Claims (18)

-40Patent claims 1. A method comprising contacting an aqueous medium containing solids of biological origin with an effective amount of (a) an inorganic anionic colloid and (b) an organic polymer, wherein the organic polymer is a cationic polymer, an amphoteric polymer, or a mixture thereof; and thus flocculated biological solids are produced. 2. The method of claim 1, characterized in that it comprises, before step (a), an additional step consisting of contacting the aqueous medium with an effective amount of a first organic, namely cationic polymer, thereby reducing the number of negative charge sites on the biological solids. 3. The method according to claim 1 or 2, characterized in that the anionic inorganic colloid is present in the aqueous solution at a concentration of 1 to 7500 ppm based on the weight of the aqueous medium solution, and the organic polymer is present in the aqueous medium at a concentration of 0.2 to 5000 ppm based on the weight of the aqueous medium solution. 4. The method according to claim 1, 2 or 3, characterized in that the anionic inorganic colloid -41 a polysilicate, polyaluminosilicate, polysilicic acid microgel or a mixture thereof. 5. The method according to claim 4, characterized in that the size of the anionic inorganic colloid is greater than 10 nm. 6. The method according to any one of claims 1-5, characterized in that the organic polymer is a cationic polymer. 7. The method of claim 6, wherein the cationic polymer is polyacrylamide, cationic starch, cationic guar gum, chitosan, or a mixture thereof. 8. The method according to any one of claims 1-5, characterized in that the organic polymer is an amphoteric polymer. 9. The method of any one of claims 1-8, further comprising separating and recovering the flocculated biological solids. 10. The method according to any one of claims 1-9, characterized in that an acid is added to the aqueous medium, thereby reducing the pH of the aqueous medium to a value below pH 7. 11. The method of claim 10, wherein the acid is sulfuric acid, hydrochloric acid, nitric acid, carbon dioxide, sulfonic acid, carboxylic acid, acrylic acid, acidic anionic inorganic colloid, partially neutralized acid, or a mixture thereof. 12. The method according to claim 10, characterized in that the acid is sulfuric acid, hydrochloric acid, nitric acid or a mixture thereof. 13. The method of claim 10, wherein the acid is an acidic anionic inorganic acid selected from the following: low molecular weight polysilicic acid, high molecular weight polysilicic acid microgel, acidic polyaluminosilicate, acid stabilized polysilicate microgel, or a mixture thereof. 14. The method of claim 10, 11, 12 or 13, characterized in that the medium is simultaneously contacted with the acid and the anionic inorganic colloid. 15. The method of any one of claims 2-14, wherein the first organic polymer is a low molecular weight cationic polymer having a number average molecular weight of between 2,000 and 1,000,000. 16. The method according to any one of claims 2-14, -43characterized in that the first organic polymer is a high molecular weight cationic polymer having a number average molecular weight greater than 1,000,000. 17. The method according to any one of claims 2-16, characterized in that the anionic inorganic colloid is a silica-containing anionic inorganic colloid; and the organic polymer is a cationic, anionic or amphoteric polymer. 18. The method according to claim 17, characterized in that the anionic inorganic colloid containing silica is colloidal silica, aluminum-modified colloidal silica, polysilicate microgel, polyaluminosilicate microgel, polysilicic acid, polysilicic acid microgel or a mixture thereof. Instead of the notifier, the authorized person DANUBIA Patent and Trademark Office Ltd. Eva Baranyi's patent attorneys