Classifications

• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/54—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using organic material
  • C02F1/56—Macromolecular compounds
• • C—CHEMISTRY; METALLURGY
  • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
  • C02F1/00—Treatment of water, waste water, or sewage
  • C02F1/52—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities
  • C02F1/5236—Treatment of water, waste water, or sewage by flocculation or precipitation of suspended impurities using inorganic agents

Definitions

• 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.
• biosolids such as proteins, carbohydrates, fats and oils
• aqueous streams 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.
• the biosolids When separated and dried, the biosolids have value, for example, as animal feed, crop fertilizers, in pharmaceuticals and in personal care products.
• recovered protein from soybeans may be used in infant formula.
• biosolids are comprised of particles having surface charges.
• the particles typically have anionic surface charges at alkaline and neutral pH. The surface charge generates a repulsive force between particles to keep them apart.
• 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.
• 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
• 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.
• 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 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.
• 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.
• aqueous streams comprising biosolids such as proteins, carbohydrates, fats, and oils which must be treated to remove the potentially valuable biosolids products and/or before the stream can be discharged from the plant.
• biosolids such as proteins, carbohydrates, fats, and oils
• These aqueous streams are often derived from food processing plants and have solids contents of from about 0.01% to 5% on a weight basis.
• This invention provides a process for clarification of such streams, whereby the solids are flocculated, and optional separation therefrom of the biosolids, which can be subsequently used for example, in animal feeds.
• to flocculate means to separate suspended biosolids, from a stream comprising biosolids wherein the biosolids become aggregated and separate to the top or bottom of the stream in which the biosolids had previously been suspended.
• Flocculation produces a flocculated material, which, if desired, can be physically separated from the stream.
• the aqueous stream to be treated can be from any processing plant that produces an aqueous stream comprising biosolids, such as food processing plants.
• animal slaughterhouses and animal processing plants and other food processing plants may produce aqueous streams comprising protein, 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.
• Biosolids present in aqueous streams from these processes may include sugars, starches and other carbohydrates in addition to protein, fats, and oils.
• proteins are extracted into an aqueous stream from which they are subsequently recovered.
• the present invention is especially useful for treating streams from animal processing, and more particularly, from poultry processing.
• this invention is useful in conventional food processing operations, which produce aqueous suspensions of biosolids
• this invention is also useful in treatment of aqueous suspensions of biosolids derived from processing of food (animal or vegetable) materials, which may have nonfood end uses.
• proteins are useful in certain cosmetics and other skin care formulations; starch has numerous non-food uses, including uses in paper manufacture.
• this invention is useful to treat in general, any aqueous stream comprising biosolids, which may result from non-food processing operations.
• biosolids as disclosed above, are generally suspended in a substantially aqueous stream, a substantially concentration of quantity of biosolids can also be dissolved in the stream depending on the property of the stream or the biosolids such as, for example, pH, salinity, or other parameters.
• Anionic inorganic colloids useful in the process of this invention can include silica-based and non-silica-based anionic inorganic colloids and mixtures thereof.
• Silica-based anionic inorganic colloids include, but are not limited to, colloidal silica, aluminum-modified colloidal silica, polysilicate microgels, polyaluminosilicate microgels, polysilicic acid, and polysilicic acid microgels, and mixtures thereof.
• Non-silica-based anionic inorganic colloids include clays, especially colloidal bentonite clay.
• Other non-silica-based anionic inorganic colloids include colloidal tin and titanyl sulfate.
• the anionic inorganic colloids used in this invention can be in the form of a colloidal silica sol containing about 2 to 60% by weight of Si ⁇ 2, preferably about 4 to 30% by weight of Si ⁇ 2-
• the colloid can have particles with at least a surface layer of aluminum silicate or it can be an aluminum modified silica sol.
• the colloidal silica particles in the sols commonly have a specific surface area of
• the silica sol can be stabilized with alkali in a molar ratio of SiO2:M2O of from 10:1 to 300:1, preferably 15:1 to 100:1 (M is Na, K, Li, and NH4).
• the colloidal particles have a particle size of less than 60 nm, with an average particle size less than 20 nra, and most preferably with an average particle size of from about 1 nm to 10 nm.
• Microgels are distinct from colloidal silica in that the microgel particles usually have surface areas of 1000 m ⁇ /g or higher and the microgels are comprised of small 1-2 nm diameter silica particles linked together into chains and three-dimensional networks.
• Polysilicate microgels also known as active silicas, have Si ⁇ 2:Na2 ⁇ ratios of 4: 1 to about 25 : 1 , and are discussed on pages 174-176 and 225-234 of "The Chemistry of Silica” by Ralph K. Iler, published by John Wiley and Sons, N. Y., 1979.
• Polysilicic acid generally refers to those silicic acids that have been formed and partially polymerized in the pH range 1-4 and comprise silica particles generally smaller than 4 nm diameter, which thereafter polymerize into chains and three-dimensional networks.
• Polysilicic acid can be prepared in accordance with the methods disclosed in U. S. Patents 5,127,994 and 5,626,721, incorporated herein by reference.
• Polyaluminosilicates are polysilicate or polysilicic acid microgels in which aluminum has been incorporated within the particles, on the surface of the particles, or both. Polysilicate microgels, polyaluminosilicate microgels and polysilicic acid can be prepared and stabilized at acidic pH.
• Microgel size can be increased by any of the known methods such as of aging of the microgel, changing pH, changing concentrations, or other methods, known to those skilled in the art.
• polysilicate microgels and polyaluminosilicate microgels useful in this invention are commonly formed by the activation of an alkali metal silicate under conditions described in U. S. Patents 4,954,220 and 4,927,498, incorporated herein by reference.
• polyaluminosilicates can be formed by the acidification of silicate with mineral acids containing dissolved aluminum salts as described in U. S. Patent 5,482,693, incorporated herein by reference.
• Alumina/silica microgels can be formed by the acidification of silicate with an excess of alum, as described in U. S. Patent 2,234,285, incorporated herein by reference.
• silica sols such as those described in European patents EP 491879 and EP 502089, incorporated herein by reference, can also be used for the anionic inorganic colloid in this invention.
• the anionic inorganic colloids are used in an effective amount, together with a organic polymer to produce flocculated biosolids.
• An effective amount can range from about 1 to 7500 parts per million (ppm) by weight as solids, e. g., as Si ⁇ 2, based on the solution weight of the aqueous stream.
• the preferred range is from about 1 to 5000 ppm, depending on the anionic inorganic colloid.
• Preferred ranges for selected anionic inorganic colloids are 2 to 500 ppm for polysilicic acid or polysilicate microgels; 4 to 1000 ppm for colloidal silica, and 2 to 2000 ppm for inorganic colloidal clays, such as bentonite.
• Organic polymers useful in the process of this invention include cationic and amphoteric polymers and mixtures thereof.
• the organic polymers will typically have a number average molecular weight greater than 1,000,000. These are generally 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 formed by reacting starch with a tertiary or quaternary amine to provide cationic products with a degree of substitution of from 0.01 to 1.0, containing from about 0.01 to 1.0 wt% nitrogen. Suitable starches include potato, corn, waxy maize, wheat, rice and oat.
• the high molecular weight cationic organic polymer is polyacrylamide.
• the high molecular weight cationic organic polymers are used in an effective amount, together with an anionic inorganic colloid to produce flocculated biosolids.
• An effective amount of a cationic polymer can range from about 0.2 to 5000 ppm based on the solution weight of the aqueous stream. 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 typically used in the same amounts as the high molecular weight cationic polymers.
• the present invention further includes a process which comprises contacting an aqueous stream which comprises biosolids possessing surface negative charge sites, with an effective amount of a first organic polymer to reduce the number of the surface negative charge sites.
• the first organic polymer is a cationic polymer, which is used to reduce the number of surface negative charge sites and to impart some cationic sites.
• An effective amount is typically an amount sufficient to neutralize at least 1%, and preferably at least 10% of the surface negative charge sites on the biosolids.
• Low or high molecular weight cationic organic polymers, or mixtures thereof can be used. Low molecular weight cationic organic polymers are preferred due to their higher cationicity and lower cost of use.
• Useful high molecular weight cationic polymers include those described above.
• Useful low molecular weight cationic polymers have a number average molecular weight in the range between about 2,000 to about 1 ,000,000, preferably between 10,000 and 500,000.
• the low molecular weight polymer can be for example, polyethylene imine, polyamines, polycyandiamide formaldehyde polymers, amphoteric polymers, diallyl dimethyl ammonium chloride polymers, diallylaminoalkyl (meth)acrylate polymers and dialkylaminoalkyl
• (meth)acrylamide polymers a copolymer of acrylamide and diallyl dimethyl ammonium chloride, a copolymer of acrylamide and diallylaminoalkyl (meth)acrylates, a copolymer of acrylamide and dialkyldiaminoalkyl (meth)acrylamides, and a polymer of dimethylamine and epichlorohydrin.
• the first organic polymer a high or low molecular weight cationic organic polymer, or mixtures thereof, is added in an effective amount to reduce the number of surface negative charge sites on the biosolids.
• An effective amount is dependent on several factors, including the number of surface negative charge sites present on the biosolids in the aqueous stream, the type of biosolid, and the pH of the aqueous stream.
• An effective amount can be determined by means available and known to those skilled in the art, using techniques such as colloidal titration. Generally this amount will be in the range of from about 0.01 to about 10,000 ppm of polymer, based on total weight of the stream. The term "ppm" is defined above.
• the aqueous stream is treated with a second organic polymer.
• the second organic polymer will depend on the anionic inorganic colloid.
• the second organic polymer can be selected from the group consisting of cationic and amphoteric polymers and mixtures thereof for any anionic inorganic colloid.
• the anionic inorganic colloid is a silica-based anionic inorganic colloid
• the second organic polymer can be selected from the group consisting of anionic, cationic, amphoteric polymers and mixtures thereof.
• Cationic and amphoteric polymers are described above and can be high or low molecular weight polymers.
• Anionic polymers that can be used in the process of this 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 with number average molecular weights of greater than 1,000,000 are preferred.
• the degree of anionic substitution is 10-70 mol%.
• anionic polymers examples include water soluble vinylic polymers containing acrylamide, acrylic acid, acrylamido-2- methylpropylsulfonate and/or mixtures thereof, and can also be either hydrolyzed acrylamide polymers or copolymers of acrylamide or a homolog, such as methacrylamide, with acrylic acid or a homolog, such as methacrylic acid, or even with monomers such as maleic acid, itaconic acid, vinyl sulfonic acid, acrylamido- 2-methylpropylsulfonate, and other sulfonate containing monomers.
• Anionic polymers are further described, for example, in U. S. Patents 4,643,801; 4,795,531; and 5,126,014.
• anionic polymers that can be used include anionic starch, anionic guar gum and anionic polyvinyl acetate.
• anionic starch anionic starch
• anionic guar gum anionic polyvinyl acetate
• anionic polyvinyl acetate anionic polyvinyl acetate
• the pH of the aqueous may be first reduced to less than pH 7 using an acid.
• mineral acids such as sulfuric acid, hydrochloric acid and nitric acid are preferred.
• Other useful acids include, but are not limited to, 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 are replaced with a metal or ammonium ion, and mixtures thereof.
• Acidic anionic inorganic colloids include, but are not limited to, low molecular weight polysilicic acid, high molecular weight polysilicic acid microgels, acidic polyaluminosilicates and acid stabilized polysilicate microgels. Examples of acid stabilized polysilicate microgels are described in U. S. Patents 5,127,994 and 5,626,721.
• metal salts can be used in the process of this invention. Iron and aluminum are particularly useful. Acid metal salts can be used to reduce pH and act as a charge donor.
• the process of this invention involves treatment of an aqueous stream containing biosolids, for example, proteins, to reduce suspended solids (as measured by turbidity) and optionally to separate the biosolids.
• biosolids for example, proteins
• the biosolids can be recovered for subsequent use. It should be recognized that this process can capture both suspended biosolids as well as soluble materials, such as those present in blood and sugars.
• the process of this invention involves treating an aqueous stream comprising biosolids by contacting the stream with an anionic inorganic colloid and an organic polymer.
• the aqueous stream can be derived from any number of processes, which generate such streams, such as from animal and vegetable processing, including processing for non-food uses.
• the organic polymer is selected from the group consisting of cationic and amphoteric polymers having a number average molecular weight greater than 1,000,000, and mixtures thereof.
• the aqueous stream is contacted with an acid to reduce the pH of the stream to less than pH 7.
• a metal salt, especially an iron or aluminum salt can be optionally added.
• reagents anionic inorganic colloid, organic polymer and optional acid and/or metal salt, can be contacted with the stream in any sequential order, or one or more can be contacted simultaneously with the aqueous stream.
• the stream is simultaneously contacted with an acid and the anionic inorganic colloid.
• the optional reduction of the pH of the aqueous stream to less than pH 7 can be accomplished with any acid, examples of acids being described above.
• an acidic anionic inorganic colloid is used to reduce pH of the stream to less than pH 7, no additional source of acid or anionic inorganic colloid may be needed to flocculate the biosolids in the aqueous stream.
• the aqueous stream is contacted with an anionic inorganic colloid and an organic polymer. This may occur prior to, subsequent to, or simultaneously with, reducing pH of the aqueous stream to less than pH 7, should a pH reduction step be desired.
• the inorganic colloid and the organic polymer can be contacted with the aqueous stream separately, in either order, or simultaneously.
• the combination of contacting an anionic inorganic colloid and an organic polymer with the aqueous stream produces flocculated biosolids.
• the flocculated biosolids can optionally be separated from the treated stream by conventional separation processes such as sedimentation, flotation, filtering, centrifiigation, decantation, or combinations of such processes.
• the separated biosolids can subsequently be recovered and used in numerous applications. It has also been surprisingly found that the recovered biosolids from this process have reduced odor when dry relative to those recovered from a process using ferric chloride as part of a flocculating system.
• the present invention further provides a process which comprises contacting an aqueous stream comprising biosolids with an effective amount of a first organic polymer to reduce the number of surface negative charge sites on the suspended biosolids in the stream.
• the first organic polymer is a cationic polymer and is used in an amount sufficient to impart some cationic sites to the biosolids. Typically sufficient cationic polymer is added to neutralize at least 1%, and preferably at least 10% of the surface negative charge sites on the biosolids.
• the first organic polymer can be a high or low molecular weight cationic organic polymer.
• the cationic polymer is a low molecular weight cationic polymer.
• An anionic inorganic colloid and a second organic polymer are contacted with the aqueous stream prior to, subsequent to, or simultaneously with the first organic polymer, to produce flocculated biosolids in the stream.
• the second organic polymer is selected from the group consisting of cationic, amphoteric, and anionic polymers, and mixtures thereof, depending on the anionic inorganic colloid.
• the second organic polymer can be selected from the group consisting of cationic and amphoteric polymers and mixtures thereof.
• silica-based anionic inorganic colloids the second organic polymer can be selected from the group consisting of anionic, cationic, amphoteric polymers and mixtures thereof.
• the flocculated biosolids can be separated and recovered by known techniques, such as those mentioned above.
• a sample of a wash water containing about 1000 ppm of un-flocculated protein containing biosolids was obtained from an Eastern Shore poultry processing plant.
• the initial turbidity was > 200.
• the initial pH was about 7.
• the following reagents were added in all of the runs to a beaker: high molecular weight cationic polyacrylamide, Percol 182®, available from Ciba Specialty Chemicals, Basel, Switzerland, 8 ppm; silica microgel solution, Particol® MX, 120 ppm (Si ⁇ 2 basis), available from E. I. duPont de Nemours and Company, Inc., Wilmington, DE.
• the amounts given were based on the solution weight of the wash water.
• the reagents were added as follows.
• the poultry processing wash water of Example 1 was used with several different anionic inorganic colloids.
• the following anionic inorganic colloids were used:
• Ludox® SM colloidal silica, 30 wt% silica sol, surface area 300 m ⁇ /g.
• Ludox® HS-30 colloidal silica, 30 wt% silica sol, surface area 230 m ⁇ /g.
• Ludox® colloidal silicas are available from E. I. du Pont de Nemours and Company, Wilmington, DE.
• Colloidal silica sol, 4 nm, surface area 750 m ⁇ /g, available from Nalco Chemical Company, Naperville, 111.
• the high molecular weight cationic organic polymer was Percol 182®. The following procedure was followed for all of the runs:
• a second poultry processing wash water containing about 1390 ppm of biosolids was used in these examples.
• the initial turbidity was > 200.
• the following reagents were added to the wash water per the quantities provided below in Tables 3-8: a low molecular weight cationic organic polymer, diallyldimethylammomum chloride polymer (polydadmac); anionic inorganic colloids: Nalco colloidal silica sol, Particol® polysilicate microgel, and bentonite clay; and; a high molecular weight cationic organic polymer, Percol 182®, polyacrylamide (P AM).
• Amounts of reagents added are provided in Tables 3 -8, all amounts are in ppm, based on the solution weight of the wash water.
• Example 3 The same process as in Example 3 was followed except with the added step of adding a high molecular weight cationic organic polymer, polyacrylamide, 10 seconds after the addition of the anionic inorganic colloid. Mixing was stopped 15 seconds after the addition of the polyacrylamide. Table 4 provides the quantities of reagents added and results.
• Example 3 The process of Example 3 was repeated with use of bentonite clay as the anionic inorganic colloid.
• Table 5 provides the quantities of reagents added and results.
• Example 5 The process of Example 5 was repeated using bentonite clay as the anionic inorganic colloid.
• Table 6 provides the quantities of reagents added and results.
• An aqueous waste stream from an Eastern Shore poultry processing plant was treated on-stream in accordance with this invention in a continuous process.
• To the waste stream was added simultaneously, sufficient sulfuric acid to reduce the pH of the stream to 3.7 and Particol® MX, polysilicate microgel, 95 ppm Si ⁇ 2, based on the solution weight of the stream.
• Downstream (about 30 seconds) from the point of addition of the acid and the microgel was added cationic polyacrylamide, Percol 182® , 4 ppm, based on the solution weight of the stream.
• the stream was directed to a dissolved air flotation (DAF) unit, where the solids were floated to the surface and skimmed off for recovery.
• DAF dissolved air flotation
• the remaining aqueous stream was tested for chemical (COD) and biological oxygen demand (BOD) and total suspended solids (TSS).
• COD chemical
• BOD biological oxygen demand
• TSS total suspended solids
• COD was determined using a Hach COD Test Kit, available from the Hach Company, Loveland, CO.
• TSS was determined by Method 2450 D from "Standard Methods for Examination of Water and Wastewater", published jointly by the American Public Health Association, American Water Works Association and Water Environment Federation.
• BOD was determined by Method 5210 from “Standard Methods for Examination of Water and Wastewater”.
• the process of this invention reduces chemical and biological oxygen demand of the waste stream in a continuous flow process of an actual poultry processing plant.
• a sample of wastewater was obtained from an Eastern Shore poultry processing plant.
• the wastewater had a COD of > 2100 ppm, an initial turbidity of > 200, and a pH of 6.1.
• Into a 400 ml beaker was placed 250 ml of the wastewater.
• the wastewater was stirred using a mechanical propeller type stirrer at 275 rpm.
• the pH of the wastewater was adjusted using dilute H2SO4 to pH
• COD was determined using 0-1500 ppm COD colorimetric analysis ampules from CHEMetrics, Calverton, VA and a Milton Roy Spectronic model 20 spectrophotometer set at 620 nm wavelength. Table 11 provides the quantities of reagents added and results for these runs, which are 33 and 34.
• Example 13 The process of Example 13 was repeated using the same wastewater sample. However, instead of adding acid, 32 ppm of FeC_3 was added 15 seconds prior to addition of the Particol® MX. All times from Example 13 are shifted by adding 15 seconds. Quantities of reagents added and results are provided as Run 35 in Table 11.
• the wastewater was sampled for turbidity measurements at 35 and 95 seconds after mixing was stopped. The pH was measured after the 95 second turbidity measurement. The flocculated wastewater was then re-suspended by mixing for 30 seconds at 150 ⁇ m. After 1 minute, the agitation was discontinued the wastewater was sampled for COD measurements. Table 12 provides the quantities of reagents added and results.
• Example 13 The process of Example 13 was repeated with the difference of adding base, sodium hydroxide to increase pH to 6.5 prior to the addition of the Particol® MX. The remaining steps were performed without change. Table 13 provides the quantities of reagents added and results.

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• Chemical & Material Sciences (AREA)
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• Hydrology & Water Resources (AREA)
• Engineering & Computer Science (AREA)
• Environmental & Geological Engineering (AREA)
• Water Supply & Treatment (AREA)
• Organic Chemistry (AREA)
• Inorganic Chemistry (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)
• Peptides Or Proteins (AREA)
• Treatment Of Liquids With Adsorbents In General (AREA)
• Biological Treatment Of Waste Water (AREA)

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