WO2009089412A1

WO2009089412A1 - Subcritical and supercritical fluid extraction of fat and drying residual solids for protein/carbohydrate content from food industry liquid or solid waste

Info

Publication number: WO2009089412A1
Application number: PCT/US2009/030542
Authority: WO
Inventors: David Brian Mitchell
Original assignee: Linde North America, Inc.
Priority date: 2008-01-11
Filing date: 2009-01-09
Publication date: 2009-07-16
Also published as: CA2749272A1

Abstract

Improved techniques for the treatment of wastewater from food processing operations, particularly from meat processing operations such as poultry, beef and pork are described. The invention focuses on not only on meeting the effluent compliance standards for wastewater, but also on the recovery of raw materials such as oils and proteins from the wastewater for revenue generating uses, such as biodiesel production and protein meat and poultry by-product materials. The use of subcritical and supercritical fluids to improve oil and protein recovery from wastewater is disclosed.

Description

SUBCRITICAL AND SUPERCRITICAL FLUID EXTRACTION OF FAT AND DRYING RESIDUAL SOLIDS FOR PROTEIN/CARBOHYDRATE CONTENT FROM FOOD INDUSTRY LIQUID OR SOLID WASTE

FIELD OF THE INVENTION

[0001] The present invention relates to methods of extracting oil from a Dissolved Air Floatation (DAF) waste solid matrix. In addition the present invention relates to drying of the remaining solids to reduce the water content and thus concentrate the protein to greater than 50% and preferably greater than 60%.

BACKGROUND OF THE INVENTION

[0002] In the food processing industry, particularly the meat processing industry, a significant amount of waste water is produced. The treatment of food processing wastewater to separate the water (and non-ionically charged soluble components) from the solids (including anionically charged soluble components) and reduce the overall waste disposal requirements is an important function within any meat processing operation. For example, the waste water is typically treated using Dissolved Air Floatation (DAF) techniques to separate the above components, resulting in a "raft" of waste solids (DAF float). Table 1 below provides data on typical poultry DAF float characteristics for both kill-cook plants and kill plants.

[0003] Data for typical DAF water quality at a poultry kill facility and chemical treatment program are shown in Figures 1 and 2. Similar data for a typical poultry kϋl-cook facility are shown in Figures 3 and 4.

[0004] Current treatment of DAF float is focused on using decanters or centrifuges to recover oils and to concentrate solids followed by composting, land application or landfill. Such traditional centrifuge operations can recover only about 60% of the oil in the DAF float, therefore missing out on potential revenue from the resale or reuse of the unrecovered oil. Further, conventional centrifuge operations are incapable of obtaining high concentrations of protein in the collected dried solids. In addition, the sludge remaining after standard centrifugal treatment bears a significant sludge disposal cost.

[0005] For all of the above reasons, there remains a need in the art for improvements to the treatment of DAF float from meat processing operations.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention provides improved techniques for the treatment of wastewater from food processing operations, particularly from meat processing operations such as poultry, beef and pork.

[0007] The present invention is focused not only on meeting the effluent compliance standards for wastewater, but also on the recovery of raw materials such as oils and proteins from the wastewater for revenue generating uses, such as biodiesel production and protein meat and poultry by-product materials and poultry meal.

[0008] The present invention provides improved wastewater treatment by using supercritical and/or subcritical fluids to improve oil and protein recovery from meat processing operations. By using supercritical or subcritical fluids, the present invention is capable of recovering higher percentages of oil from the DAF float, increasing the protein concentration of dried solids and reducing or eliminating the costs of sludge disposal. Greater detail of the present invention and benefits derived there from will be discussed below with reference to Figures 5 and 6.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is data sheet for typical DAF water quality at a poultry kill facility.

[0010] Figure 2 is a data sheet for typical DAF chemical treatment program at a poultry kill facility.

[0011] Figure 3 is data sheet for typical DAF water quality at a poultry kill-cook facility.

[0012] Figure 4 is a data sheet for typical DAF chemical treatment program at a poultry kill -cook facility.

[0013] Figure 5 is data sheet for subcritical fluid oil extraction at a poultry kill facility in accordance with an embodiment of the present invention.

[0014] Figure 6 is data sheet for subcritical fluid oil extraction at a poultry kill- cook facility in accordance with an embodiment of the present invention.

[0015] Figure 7 is a process flow diagram for the operation of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] A gas becomes a liquid when the pressure is increased. There is a temperature and pressure phase at which the liquid is subcritical and increasing the temperature (critical temperature), pressure (critical pressure) or both above the critical point creates a supercritical fluid. The supercritical fluid has liquid like densities and a viscosity similar to that of normal gases. As a result the supercritical fluid has a diffusivity that is about two orders of magnitude higher than that for typical liquids. Diffusivity of subcritical fluids can also be greater than ambient typical liquids. This allows the supercritical and/or subcritical fluids to diffuse more readily through solid matrices, thus facilitating more rapid and complete extractions in comparison to heating the wastewater substrate in a centrifuge operation.

[0017] The present invention provides methods of extracting greater than 90% of the available oil from a DAF waste solid matrix. The remaining solids are then dried to reduce water content from greater than 60% water content down to less than 10% moisture content. The solids drying process can be completed simultaneously with the oil extraction or can be performed prior to or after the oil extraction.

[0018] DAF waste is generally referred to as a solid waste despite having solids concentrations ranging from only 6% to 25%. Because of the relatively high percentage of liquid in the DAF waste, it can be sheared to have a viscosity similar to water. Conventional oil extraction technology heats the DAF solids to 180°F by direct or indirect steam injection and then uses a decanter or centrifuge to extract the oil. As noted above, typical extraction efficiency for such known technology is about 60%.

[0019] In accordance with one embodiment of the present invention, subcritical butane at a temperature of approximately 78⁰F or 25°C and a pressure of approximately 15 psig is used to extract the oil. Butane is supercritical at 152⁰C and 550 psig. The properties of subcritical and supercritical fluids can be altered by combination with other fluids. Therefore, in accordance with the present invention, a combination of two or more stibcritical fluids or a combination of an organic solvent with subcritical butane could be used. Further, the use of supercritical fluids, and particularly supercritical carbon dioxide is used for various purposes in many industries, including the food industry. Supercritical carbon dioxide is supercritical at a temperature of 31.1⁰C and 1070 psig and above. The present invention contemplates the use of combinations of supercritical carbon dioxide with other fluids to provide advantageous use in wastewater treatment.

[0020] Following extraction of the oil using subcritical or supercritical fluids in accordance with the present invention, the remaining solids can be dried using a variety of methods, such as sublimation. By freezing the water-solids sample and then reducing the temperature and pressure below the triple point, the water sublimates and the solids are dried below the protein denaturing temperature. When it is desirable to maintain separation of solids from drying operations of a variety of process streams, multiple sublimation chambers can be used. Alternatively, multiple aqueous streams can be processed within specific time limits to generate segregated solids streams. Alternative drying methods include evaporation at atmospheric, reduced pressures or vacuum.

[0021] Current methods for the separation of oils from wastewater comprise adding coagulant and flocculant chemicals to the DAF to separate blood protein, fat (emulsified, particulate and non-emulsified) and organic/inorganic particulate solids from the wastewater. The solids are then disposed of to land or may be dewatered to about 20%-40% solids and disposed to landfill. Alternatively, oils can be extracted using a centrifuge and the solids are then disposed to land. However, the oil extraction efficiency for centrifuge operations is only about 60%.

[0022] An important advantage of the present invention is the achievement of both increased oil extraction and increased protein concentration. The present invention provides much greater oil extraction efficiency than from standard centrifugal operations and also provides for the recovery of valuable by products. For example, fat recovered according to the present invention can be used to manufacture biodiesel or can be burnt in on site boilers. Further, the solids obtained by the present invention have much higher protein concentrations and therefore meet the criteria defined by the Association of American Feed Control Officials (AAFCO) to be utilized as "Meat By-Product" if from cows and pigs or "Poultry By-Product" if originating from poultry. Moreover, the present invention makes it possible to obtain further commercial benefit from the separation process by recovering additional valuable by-products such as specific amino acids or proteins. Amino acids can be recovered by an additional treatment of the proteins separated from the wastewater. For example, lysine can be extracted using a second subcritical or supercritical fluid. Further, proteins and/or protein particulates can be recovered by treatment of the protein solids to remove contaminants, such as prion proteins, using a supercritical CO2 process.

[0023] Figures 5 and 6 show some results of using the present invention for subcritical oil extraction in combination with conventional DAF chemistries at a poultry kill facility and a poultry kill-cook facility respectively. As shown in both Figures 5 and 6, the percentage of oil recovered is increased to 90%, a significant improvement over the 60% obtained by traditional centrifugal operations. Consequently, annual revenue that can be obtained from oil recovery is increased by 50% when using the present invention. In addition the protein content of the dried solids is raised to about 60%, as much as 50% higher than that obtained from centrifuge methods. This allows for revenue generation from use of such solids as cattle, poultry or companion animal feed. Further, a significant reduction or elimination of sludge disposal costs that are necessaiy for conventional centrifuge operations is achieved.

[0024] A simple process flow diagram for the present invention is shown in Figure 7. The purpose of the design is to extract oil more efficiently than current centrifugal extraction technologies, As shown in Figure 7, the DAF float is initially sheared to reduce the viscosity and then contacted with a subcritical or supercritical hydrocarbon in a column. The hydrocarbon has a specific gravity less than 1.0 and thus rises in the column where the continuous phase has a specific gravity of 1.0. As the hydrocarbon contacts the solids, non polar compounds such as the tri, di and mono glycerides of the poultry, pork or beef fat, are extracted. The hydrocarbon and oil mixture then exit the top of the column where a reduction in pressure and addition of heat via a heat pump vaporizes the hydrocarbon component, leaving the fat (oil) to be separated in a cyclone and collected. Greater than 99.9 % of the hydrocarbon is recovered, then cooled and repressurized and returned to the extraction/recovery cycle for reuse.

[0025] The solids and water (minus the oil) exit the bottom of the column. This mixture can then be dried using any appropriate process. For example, the mixture is conveyed to a vacuum chamber where the temperature is reduced until it freezes. Vacuum is then applied and the ice (water) sublimates leaving the protein and inorganic solids as a finely dispersed powder. Alternatively, the mixture could be contacted with a gas to cool the mixture below the triple point of water (approximately 0.01⁰C and 0.0887 psig) to again sublimate the ice (water) and leave a solids content greater than 90% solids, less than 10% moisture. In either case, the resulting solids have a greatly increased protein percentage. In particular, prior art centrifugal techniques generally achieved protein percentages, of only about 35%. Furthermore the 60% water content in a centrifugal operation would prevent this material being used directly as an animal feed since it would putrefy and have an offensive odor and free fatty acid and peroxide content. The solids obtained by the present invention have protein concentrations greater than 50% and preferably greater than 60% on a dry weight basis.

[0026] The hydrocarbons used in the column may be any hydrocarbon that has a specific gravity less than 1.0. For example, butane has a specific gravity of about 0.6 and therefore easily rises in the column. Butane has subcritical temperatures and pressures of about 25⁰C and 15 psig respectively. Other subcritical and supercritical liquids that can be used in the present invention include carbon dioxide, methane, ethane, propane, ethylene, propylene, methanol, ethanol, acetone etc.

[0027] Experiments were carried out to determine the efficacy of the present invention. The procedures and results are set forth below.

[0028] Experimental Result 1

Subcritical butane has a higher viscosity than supercritical butane and therefore may not be expected to extract fat as efficiently, particularly fat that has been insolubilized by the coagulant and flocculant chemistries used in the DAF. To determine if the subcritical butane could penetrate a solid matrix and also extract oil more efficiently than a standard centrifuge operation, the solids were collected from a typical centrifuge operation (solids heated to 19O⁰C prior to being centrifuged) and then further treated in accordance with the present invention. The centrifuge had extracted all the oil it was capable of extracting, i.e. 55.25% of the oil that was present in the DAF float. Treatment of the solids from the centrifuge in accordance with the present invention resulted in more oil being extracted as well as more complete drying of the solid (protein) content to 90% - 100% solids (0-10% moisture). Specific results are shown in Tables 2 through 5 below.

Table 2

Sample charged to % Moisture Solids charged to "Moisture' ' charged to subcritical butane subcritical reactor subcritical butane reactor reactor (g) (calc) (g) (calc) (g)

50.58 54 .24 23.14 27.43

[0029] It is noted that the protein analyses (29% protein) was on a wet base basis from the decanted solids and after subcritical butane extraction. This would equate to 78.48% protein on a dry weight basis. As noted above, the centrifugal system recovered only 55.25% oil. The subcritical butane system of the present invention recovered 78,091 mg of an available 96,000 mg/kg in the decanted solids that was not recovered in the centrifuge process. Therefore, the present invention recovered 81.34% of the oil that the centrifuge process could not recover (78K/96K mg/kg). Assuming that the subcritical butane would also recover the original 55.25% of oil that the centrifuge process can recover then the overall oil recovery would be 91.65%. The subcritical butane recovery of the present invention is almost 166% more efficient than standard centrifuge processes.

[0030] In addition the centrifuge generates a 40% solids cake that must then be disposed of, typically to landfill at a cost of $32-$50/ton. This can add up to an annual cost of $150,000 to $300,000. The present invention greatly increases the solid content of the cake, i.e. to more than 90% solid (less than <10% moisture). As a result the protein content of the solids is concentrated to more than 60% and can be used for rendered products. The shelf life is excellent since the moisture content is negligible. Therefore, the protein by product from the present invention, technically called Poultry By-Product or Meat By-Product as noted above, has a revenue generating value and can be sold as animal feed (dog, cat, chicken etc.). From a typical plant, this could result in a revenue stream of $700,000/year for the protein versus a disposal cost of $300,000 per year for centrifuge solids.

[0031] Experimental Result 2

Further experimental results are shown in Tables 6 through 8 below.

Table 7

Sample charged to subcritical Solids recovered from "Oil" recovered from butane reactor (g) reactor (g) subcritical reactor (g)

412.67 15.27 18.61

[0032] An analysis of the O&G by hexane indicated that there was approximately 4.5% fat, showing that the extraction efficiency is excellent. In addition, the remaining solids after the oil extraction have a protein content of approximately 2.75% of 3.8% or 72.36% on a dry weight basis that would be recovered after drying the solids in accordance with the present invention.

[0033J Experimental Result 3

Tests were carried out to show the ability of the present invention to recover oil from the waste water of poultry treatment facilities. Table 9 includes the results of these tests. In particular, these results show that in the majority of applications, greater than 90% of the oils may be recovered.

[0034] The present invention provides many advantages over known wastewater treatment techniques. In particular, the extraction efficiency of the DAF fat/oil from the waste stream is significantly greater than that for a centrifuge or decanter. The present invention provides a 65% increase in the amount of oil extracted with a total oil extraction efficiency of about 90%. In addition, the heat required for oil extraction in accordance with the present invention is about 100⁰F lower than for a centrifuge operation. Therefore, the proteins in the DAF float are not denatured and can be recovered for revenue generating use. Operating costs are also significantly lower because of the lower processing temperature. Another advantage of the present invention is that the solids concentration after oil extraction is increased 100% to 3000% i.e. from 3-50% solids DAF float to more than 90% solids. This provides an increased shelf life and decreased objectionable odor of the solids. As noted the solids are a valuable by product because the protein content is increased from 3% (DAF Float) to more that 60%. A further advantage of the present invention is that solids and oil can be sold and the water that was extracted from the proteins can be either reused in the food processing plant or disposed of. It is also believed that the lower processing temperature of the present invention reduces free fatty acid formation, thus providing a more desirable quality for use of the oil in biodiesel manufacture. [0035] The present invention is specifically beneficial as compared to centrifugal operations in a number of ways. As noted above, the present invention provides for higher oil recovery as compared to the traditional centrifuge techniques. In addition, maintenance costs are considerably reduced at least in part because of low rpm equipment and fewer moving parts associated with the present invention. Utility costs, such as heat, electric, etc, are also decreased by using the present invention, in some cases greater than fifty percent. The costs of disposal, associated with hauling volumes are much less. Because the operation of the present invention is less complex, operator supervision is lower. The present invention can be installed for approximately the same initial investment as a centrifugal operation and turndown capabilities are less than fifty percent.

[0036] Additional benefits arising from the present invention are gained from the use of supercritical carbon dioxide for a further separation following the oil separation. In particular, contaminates can be removed from the proteins and specific amino acids may be recovered.

[0037] It is anticipated that other embodiments and variations of the present invention will become readily apparent to the skilled artisan in the light of the foregoing description, and it is intended that such embodiments and variations likewise be included within the scope of the invention as set out in the appended claims.

Claims

1. A method for treating wastewater from a food processing operation, comprising: shearing a DAF float to reduce viscosity; extracting non polar compounds from solids and water in the DAF float by contacting the sheared DAF float with a subcritical or supercritical hydrocarbon.

2. The method of claim 1 further comprising: vaporizing hydrocarbons from the extracted non polar compounds; separating the non polar compounds in a cyclone separator; and recovering the vaporized hydrocarbons.

3. The method of claim 1 further comprising: removing water from the separated solids to obtain a dry solid material.

4. The method of claim 3 wherein extracting non polar compounds and removing water are performed simultaneously.

5. The method of claim 3 wherein removing water comprises a sublimation process, or an evaporation process at atmospheric, reduced pressure or vacuum.

6. The method of claim 3 wherein the dry solid material has less than 10% moisture content.

7. The method of claim 3 wherein the dry solid material has a protein concentration greater than 50% on a dry weight basis.

8. The method of claim 7 wherein the dry solid material has a protein concentration greater than 60% on a dry weight basis.

9. The method of claim 3 wherein the dry solid material qualifies as a meat by product.

10. The method of claim 3 further comprising recovering amino acids from the dry solid material.

1 1. The method of claim 10 wherein the amino acid is lysine and is recovered by extraction using a subcritical or supercritical fluid.

12. The method of claim 3 further comprising recovering proteins or protein particulates from the dry solid material.

13. The method of claim 12 wherein the protein is prion proteins amino and is recovered by treatment with supercritical carbon dioxide.

14. The method of claim 1 wherein the hydrocarbon has a specific gravity of less than 1.0.

15. The method of claim 14 wherein the hydrocarbon is butane, carbon dioxide, methane, ethane, propane, ethylene, propylene, methanol, ethanol or acetone.

16. The method of claim 1 wherein the DAF float is obtained from a meat processing operation.

17. The method of claim 16 wherein the meat processing operation is a poultry processing operation, a pork processing operation or a beef processing operation.

18. The method of claim 1 wherein the non polar compounds are monoglycerides, diglycerides, triglycerides or combinations thereof.

19. The method of claim 1 wherein the hydrocarbon in subcritical butane at a temperature of 25⁰C and a pressure of 15 psig.

20. The method of claim 1 wherein the hydrocarbon is supercritical carbon dioxide.

21. The method of claim 1 wherein the hydrocarbon is a mixture of two or more subcritical fluids, a mixture of a subcritical hydrocarbon and an organic solvent or a mixture of two or more supercritical fluids.