Energy integrated farm operation with recovery of animal feed from food waste

Abstract

A method of operating an energy integrated farm operation with recovery of animal feed from liquid food waste is described and claimed. The method involves extracting methane gas from animal manure and using the methane gas to power an electrical generator. The electricity from the generator and the methane gas itself may be used to operate a dryer. The dryer is used to dry a liquid food waste stream to yield a dry food product. The dry food product recovered has enough nutritional value to be useful as animal feed.

Description

FIELD OF THE INVENTION

[0001] This invention is in the field of farms and farm animals.

BACKGROUND OF THE INVENTION

[0002] A known byproduct of food production is liquid food waste. Typically the material in the liquid food waste stream contains a large amount of nutrients. It is industry standard practice to “treat” these liquid food waste streams as waste that needs treatment, prior to disposal.

[0003] On many farms there are “lagoons” and other concentrated holding areas for liquid food waste streams. When the liquid food waste streams are placed in lagoons or other storage areas, the nutrients present in the food waste are in a form such that it is not possible to feed the nutrients to farm animals.

[0004] It would be desirable to develop a process to transform the liquid food waste streams into usable animal feed, without putting so much energy into the process that the value of the animal feed collected is less than the value of the energy used to create the animal feed.

SUMMARY OF THE INVENTION

[0005] The instant claimed invention is a method of operating an energy integrated farm operation with recovery of animal feed from liquid food waste, comprising

[0006] providing farm animals;

[0007] providing liquid food waste;

[0008] wherein said farm animals produce manure;

[0009] wherein said manure is processed in a digester such that methane gas is produced, and

[0010] wherein at least some portion of the methane gas produced is used to generate electricity;

[0011] the improvement comprising that both, or either of, the methane gas produced by the digester and the electricity produced by the methane gas are used to power a dryer that is used to dry said liquid food waste;

[0012] wherein the dried food waste is collected for use as animal feed; and

[0013] wherein optionally at least some of the liquid food waste is contacted with bentonite clay and an anionic polymer prior to the liquid food waste being dried in the dryer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The instant claimed invention is a method of operating an energy integrated farm operation with recovery of animal feed from liquid food waste, comprising

[0015] providing farm animals;

[0016] providing food waste;

[0017] wherein said farm animals produce manure;

[0018] wherein said manure is processed in a digester such that methane gas is produced, and

[0019] wherein at least some portion of the methane gas produced is used to generate electricity;

[0020] the improvement comprising that both, or either of, the methane gas produced by the digester and the electricity produced by the methane gas are used to power a dryer that is used to dry liquid food waste;

[0021] wherein the dried food waste is collected for use as animal food; and

[0022] wherein optionally at least some of the liquid food waste is contacted with bentonite clay and an anionic polymer prior to the liquid food waste being dried in the dryer.

[0023] The recognition that methane gas is recoverable from animal manure is at least 194 years old, according to, “From Biodung to Biogas—Historical Review of European Experience” by Cord Tietjen, pp 247-259 of the book, Energy, Agriculture and Waste Management, edited by William J. Jewell, © 1975 by Ann Arbor Science Publishers, Inc.:

[0024] It was in 1808 that Humphrey Davy collected methane in his experiments with strawy cattle manure kept in a retort in a vacuum. (4). This might be considered the beginning of manure gas research, but Davy was not interested in solving energy problems with natural fuel gas; his experiments were directed toward an evaluation of rotten and unrotted manure for crop production. pp 247-248.

[0025] Farm animals that are capable of producing manure that can be processed to generate methane gas include cows, pigs, sheep and chickens. According to the reference book, “Utilization and Recycle of Agricultural Wastes and Residues,” edited by Dr. Michael L. Shuler, page 11, © 1980 by CRC Press, the relative amount of manure produced by each different species is as follows: dairy cattle produce the most manure, followed by beef cattle, followed by “swine” (swine means ‘a pig or hog’ with the term usually being used collectively), followed by sheep and then laying hens (chickens raised to lay eggs) with the least amount of manure being produced by broilers(chickens raised to be eaten). For example, one cow, in one year, produces, on average, about one and one half tons of manure. In practicing the method of the instant claimed invention, the preferred farm animals for producing manure to make methane gas are those animals that produce the most manure. Therefore, the preferred farm animals for producing manure that will be processed to make methane gas are cows and within the category of cows, the preferred cows are dairy cows.

[0026] According to “Cutting Energy Costs”, from the 1980 Yearbook of Agriculture, published by the U.S. Department of Agriculture, on page 54, “It is estimated that for each 1,000 pounds of body weight of dairy cattle, 44 cubic feet of methane containing 26,000 Btu's can be produced each day.” (Note: Btu stands for “British thermal unit” and a British Thermal Unit is defined as the quantity of heat required to raise one pound of water one degree Fahrenheit.)

[0027] The processing of animal manure to generate methane gas is a known technology. See: “Methane Production From Waste Organic Matter”, David A. Stafford, Dennis L. Hawkes and Rex Horton, © 1980 by CRC Press, Inc., “Biomass Gasification”, Edited by T. B. Reed, © 1981 by Noyes Data Corporation and “Lessons Learned from Existing Biomass Power Plants”, G. Wiltsee, February 2000, National Renewable Energy Laboratory, Contract No. DE-AC36-99-GO10337.

[0028] U.S. Pat. No. 4,100,023 describes and claims a digester and process for converting organic matter to methane and fertilizer; U.S. Pat. No. 4,274,838 describes and claims an anaerobic digester for organic waste; U.S. Pat. No. 4,759,454 describes and claims a manure digester and power generating system; U.S. Pat. No. 5,096,579 describes and claims an anaerobic digester; and U.S. Pat. No. 6,299,774 describes and claims an anaerobic digester system. European Patent Application No. 486140, describes and claims an anaerobic digester and European Patent Application No. 26619, describes and claims an anaerobic digester for organic waste.

[0029] The preferred digester is an anaerobic digester. Anaerobic digestion, also known as anaerobic fermentation, is a biological process by which organic matter is decomposed in the absence of air to yield methane (CH4) and carbon dioxide (CO2).

[0030] Anaerobic digesters are commercially available from R(esource).C(conservation).M(anagement). Digesters™ Inc., P.O. Box 4715, Berkeley, Calif. 94704, (510) 658-4466, www.rcmdigesters.com.

[0031] An anaerobic digester is operated by first having liquid manure streams enter an in-ground tank. The liquid waste decomposes as it moves through the tank. The tank is lined with heat pipes to maintain a temperature of from about 25° C. to about 40° C. (from about 77° F. to about 104° F.). This temperature range is excellent for the development of methane producing bacteria. In operating the anaerobic digester in the process of the instant claimed invention the preferred operating temperature is at the high end of the operating temperature range and the most preferred operating temperature is about 40° C.

[0032] The methane producing bacteria digest the liquid waste. As part of the digestion process, the bacteria release methane gas. An impermeable cover placed on the digester traps the methane gas. The fact that the methane gas remains trapped within the digester reduces odors associated with alternate forms of manure processing such as open lagoon drying and other concentrated holding areas. This reduction of odors is of huge benefit to the farm owner. In fact, this benefit is realized regardless of what use is eventually made of the methane gas.

[0033] Operation of the anaerobic digester is a skill known to persons of ordinary skill in the art of processing manure in an anaerobic digester. There is an extensive discussion in the reference, “Resource Potential and Barriers Facing the Development of Anaerobic Digestion of Animal Waste in California”, December 1977, published by the California Energy Commission, P 500-99-002, of both the technological and commercial factors involved in the setting up and operation of anaerobic digesters at sites within California. This reference contains information about equipment, plant layout and operating parameters for anaerobic digester operations at a number of different farm sites. This entire document is to be considered incorporated by reference, into this patent application.

[0034] In the method of the instant claimed invention, collected methane can be used as fuel to run the engines that drive generators to produce electricity and also, or also, as fuel to be burned to power the dryer used to dry the liquid food wastes.

[0035] In addition to supplying electricity, a by-product of electrical power generation is the heat created by the generator engines. It is an aspect of the “energy-integrated” features of this invention that the heat from these generator engines could be used to provide heat for the water pipes used in the continued operation of the anaerobic digester. This is an important consideration when operating an anaerobic digester during periods of very cold weather. When cold weather is present and an anaerobic digester is being operated, there is a real potential for an unwanted interruption of operation of the digester when the liquid manure streams become so viscous, because of the cold temperatures, that it is difficult to transport them through the digester.

[0036] Therefore, it is very useful that this “by-product” generator heat can be used to further the operation of the anaerobic digester.

[0037] The electricity generated is used to operate the dryers that are drying the liquid food waste streams so that a dried food product is created.

[0038] The collected methane can also be used as a direct fuel for those types of dryers that directly burn methane in order to generate the heat required for drying.

[0039] Therefore, the dryer(s) suitable for use in the instant claimed invention could be operated solely on electricity, operated solely by burning methane for fuel or the dryer could use a combination of electricity and methane to generate the necessary heat to dry the food waste. The preferred dryer is dependent upon the energy required in order to dry the liquid food waste. Some of the dryers that could be used could also be configured such that it is possible for them to use so-called “waste” heat produced from the electrical generator to dry selected liquid food wastes.

[0040] The food wastes being processed using this invention typically have enough liquid present in them that they are referred to as “liquid food wastes”. It is the intent of conducting the method of the instant claimed invention that these liquid food wastes so dried would be selected such that they contain sufficient nutritional value such that once these liquid food wastes are dried, they would become marketable dry food products for use in the animal feed industry.

[0041] It is very common in the food industry to generate liquid food waste that still contains usable nutrients. Typical liquid food wastes streams can come from many different sources. These sources include, but are not limited to, processing facilities for the dairy industry, the canning industry, the dried cereal industry and other food industries. For purposes of this invention the preferred liquid food waste streams come from dairy manufacturing plants.

[0042] Typically liquid food waste from dairy manufacturing plants, includes two basic types of streams. The first is milk and/or milk related products that simply were not included within the final product. This type of material is considered “virgin” food material. This type of liquid food waste is considered to be edible at the time of its creation. The second type of typical liquid food waste stream is “everything else”. That refers to “everything else” that is currently being sent to the wastewater treatment plant is processed. The valuable “food” components of these streams are the protein, fat, and other traditional nutrients associated with milk and dairy products.

[0043] The ability of the operator of the method of the instant claimed invention to capture value from these food wastes makes this invention highly commercially significant. In fact, the operator can not only make money selling dried food waste as animal feed but the operator can also make money by collecting fees from the “owners” of the food waste on the theory that the owners of the food waste would previously have had to pay a “waste disposal” fee (known as a “tipping fee” in the industry) for disposal of the food waste; now that the food waste can be converted into usable animal feed a similar type of ‘processing fee’ can be charged to the owner.

[0044] There are many types of dryers that can be used to process the liquid food waste according to the method of the instant claimed invention. The preferred dryer is the dryer described and claimed in U.S. Pat. No. 5,570,517, Slurry Dryer, which patent issued on Nov. 5, 1996. U.S. Pat. No. 5,570,517, is incorporated by reference, in its entirety, herein. The preferred drying system using the preferred dryer would typically include the following equipment: an “agitated air” (known as an “AGA”) dryer, a variable speed feeding system, a burner system, a burner can, a system exhaust fan, an air flow control valve, a cyclone separator and a rotary airlock. All of these pieces of equipment are commercially available from companies that make and supply these types of dryers.

[0045] Additional optional equipment would include a back mixing system for hard to handle materials and an air recycle system to recover from about 25% to about 60% of the Btu(s) consumed in the drying process. Use of the air recycle system could reduce discharged process air to the atmosphere by from about 85% to about 90%.

[0046] As mentioned previously, the preferred type of liquid food waste streams are those food waste streams generated by dairy manufacturing plants. These liquid food waste streams are preferred because of their high protein and fat levels, which make dried animal feed made with them to be of a relatively “high” nutritional value. Furthermore, liquid food waste streams from dairy manufacturing plants are preferred because, according to the “2000 Statistical Abstract of the United States”, as of 1999, there were about 111,000 farms in the United States that had milk cows and there were about 1,258,000 “dairy manufacturing plants” that were capable of processing milk and producing milk products, with a concomitant “production” of liquid food waste; which means this number of farms with milk cows and dairy manufacturing plants, ensures that there would be a “steady supply” of liquid food waste available to be processed by the method of the instant claimed invention.

[0047] Certain liquid food waste streams may be such that they are difficult to dry. These liquid food waste streams may be contacted with a combination of a slurry of bentonite and an anionic polymer as described in U.S. Pat. No. 5,204,007, entitled, “Method of Clarification of Waste Water for Production of Animal Feeds”, and U.S. Pat. No. 5,759,568, entitled, “Method for Producing Animal Foodstuff from Waste”. U.S. Pat. No. 5,204,007 and U.S. Pat. No. 5,759,568 are incorporated by reference, in their entirety, herein.

[0048] The slurry of bentonite and anionic polymer may be added to the liquid food waste stream at any point between the “creation” of the liquid waste stream in the dairy manufacturing plant and the dryer itself.

[0049] The addition of a slurry of bentonite and an anionic polymer would only be necessary if the liquid food waste stream was relatively hard to dry. That is why this is an optional, {not required step} in the process of the instant claimed invention.

[0050] Bentonite is available commercially from many sources. One such source is American Colloid Company, 1500 West Shure Drive, Arlington Heights, Ill., (800) 426-5564, (847) 392-4600, www.colloid.com.

[0051] Anionic polymers suitable for use in the instant claimed invention include emulsion polymers and dry polymers. Suitable anionic polymers are available from Ondeo Nalco Company, Ondeo Nalco Center, Naperville, Ill. 60563, (630) 305-1000. Because the dried material recovered from the dryer is targeted for use as animal feed, anionic polymers suitable for use in the instant claimed invention should have GRAS (generally recognized as safe) status. The current list of suitable anionic emulsion polymers with GRAS status, available from Ondeo Nalco Company, includes Nalco® GR105 (30 mol percent anionic), Nalco® DT 9812 (45 mol % anionic) and Nalco® DT 9813 (a 30 mol % anionic high molecular weight polymer). The current suitable anionic dry polymer, with GRAS status, available from Ondeo Nalco Company, is Nalco® D9818 (35 mol % anionic),

[0052] The following example is presented to be illustrative of the present invention and to teach one of ordinary skill how to make and use the invention. This example is not intended to limit the invention or its protection in any way.

EXAMPLE

[0053] Seaview Farms is a dairy farm with adjacent dairy manufacturing plant, located in western Illinois.

[0054] The farm has a current herd of about 50 dairy cows, with each cow, producing, on average, about 40 kilograms of manure a day. The dairy manufacturing plant annually produces about 12 million pounds of a medium desirable type of liquid food waste stream.

[0055] After an on-site visit and survey, the following equipment is installed:

[0056] 1. An anaerobic digester, with supporting pumps, tanks and piping.

[0057] 2. A methane powered electrical generator with support wiring, piping and pumps.

[0058] 3. A partially methane powered dryer suitable for drying a liquid food waste stream, wherein the electrical power to operate the dryer comes from the methane powered electrical generator and any methane required to power the dryer also comes from the anaerobic digester.

[0059] 4. Suitable pumps and piping and tanks such that it is possible to add a slurry of bentonite and a GRAS anionic polymer to the liquid food waste stream upon demand. These materials may be added to the liquid food waste stream at any point between their “creation” in the dairy manufacturing plant and the dryer itself.

[0060] The equipment is set up, test run and operated continuously for one solid month. Extrapolating the results, here is what it is possible to generate if the liquid food waste stream has a total solids content of about 18% and is dried without addition of bentonite and a GRAS anionic polymers. The calculation is that in one year it is possible to produce about 2.4 million pounds of an about 90% dry animal feed product.

[0061] It is anticipated that the dry animal feed product collected for sale will have the following nutritional value: 1 Protein 11-12% Fat  9-10% In vitro DDM (DDM stands for Digested Dry Matter 96% and it is a measure of how much of the food is able to be used by the consuming animal.)

[0062] The present method has been described in an illustrative manner. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims

1. A method of operating an energy integrated farm operation with recovery of animal feed from liquid food waste, comprising

providing farm animals;

providing liquid food waste;

wherein said farm animals produce manure;

wherein said manure is processed in a digester such that methane gas is produced, and

wherein at least some portion of the methane gas produced is used to generate electricity;

the improvement comprising that both, or either of, the methane gas produced by the digester and the electricity produced by the methane gas are used to power a dryer that is used to dry said liquid food waste;

wherein the dried food waste is collected for use as animal feed; and

wherein optionally at least some of the liquid food waste is contacted with bentonite clay and an anionic polymer prior to the liquid food waste being dried in the dryer.

2. The method of claim 1 in which said farm operation is a dairy farm.

3. The method of claim 1 in which said liquid food waste is liquid food waste from a dairy manufacturing plant.

4. The method of claim 1 in which said liquid food waste is contacted with bentonite clay and an anionic polymer prior to the liquid food waste being dried in the dryer.