Abstract:
A method for aerobic composition of organic waste material including high flow-rate aeration, compaction of the organic material, and percolation of moister released therefrom to provide beneficial soil amendments, fertilizers, and supplemental heat sources.

Description:
This is a continuation-in-part of application(s) Ser. No. 07/969,509 filed Oct. 30, 1992, now U.S. Pat. 5,269,829, Dec. 14, 1993. 
    
    
     This invention is related generally to the aerobic decomposition of organic waste material and, more particularly, to a method and apparatus used therewith to greatly accelerate such decomposition. The past several years have been witness to a renewed interest in the environment. The special attention afforded so-called &#34;green&#34; products and methods of production attest to the fact that commercial viability is not always contrary to resource conservation. Often, environmental regulations and/or restrictions provide the impetus for innovative methods and apparatus. 
     A case in point is the recent legislative trend toward banning landfill disposal of various waste materials. Of course, many hazardous chemical and biological wastes have long been restricted, but with available landfill space becoming increasingly scarce, common yard and various related forms of vegetative organic wastes will soon require alternate means of disposal. Municipalities and other levels of government are faced with an urgent and growing problem. 
     The advantages of composting or decomposing organic material to provide various fertilizers and/or soil amendments are well-known. The challenge has always been one of adapting backyard garden techniques to processes capable of handling large volumes--such as those typically generated by municipalities--in a safe, environmentally-conscious manner. The problem has been compounded in recent years by the budgetary constraints under which most governmental units operate. Economy and fiscal responsibility are, thus, addtional on-going concerns in the art. 
     The prior art includes a variety of attempts to produce an apparatus or derive a method to decompose or compost waste organic material through the metabolic activity of aerobic bacteria. Most provide only limited success. U.S. Pat. No. 3,934,999 describes use of an aqueous bacterial inoculant and depends on absorption of solar heat to decompose a small amount of dry organic material placed in a common home garbage bag. A number of evenly spaced apertures in the bag allow passive movement of air and facilitate composting. Periodic, manual agitation of material is required and possible only because the method is restricted to exceedingly small volumes. 
     U.S. Pat. No. 3,756,784 is directed to a complex apparatus for the sequential composting of domestic refuse and includes a plurality of essentially immovable vertically-disposed chambers, each with its own agitator, waste supply and air supply. The rates of addition of air and water are a function of temperature and carbon dioxide levels in each chamber. A varying combination of air, water and agitation must be accurately administered to maintain aerobic conditions in each chamber. 
     U.S. Pat. No. 4,302,546 discloses a constantly rotating tank-like apparatus to recycle animal wastes. Carbonaceous filler materials must be added to control moisture content. Continual, low flow-rate aeration facilitates decomposition. Exhaust air is past though a scrubber to eliminate foul-smelling components which would otherwise pollute the surrounding atmosphere. 
     U.S. Pat. Nos. 3,138,447 and 3,930,799 are directed to a process and apparatus, respectively, for producing fertilizer from organic and inorganic municipal garbage. Low flow-aeration is aided by constant &#34;tumbling&#34; to prevent air channel formation. Moisture is first introduced to enhance decomposition via the addition of sewage sludge then removed during a later drying phase. Temperature and carbon dioxide levels are monitored throughout decomposition. 
     U.S. Pat. No. 4,230,676 describes an apparatus and method for decomposition using exposed windrows of organic material. Integral to both the apparatus and method is a microprocessor which monitors temperature, air/moisture content, and pH of the windowed material. A complex, adjustable injector configuration makes any additions/corrections necessary in response thereto. 
     Various prior art sources teach the use of a Beltsville or modified Beltsville system, which is necessarily limited to composting small volumes of material under tropic or warm weather conditions through use of a solar forced-air collector. Low-rate aeration and initial addition of water to loosely-arranged material characterize methods of this type. The apparatus used therewith typically includes overlapping sheets of plastic to catch rain water. 
     These are but a few examples of the prior art. Other methods and/or apparatus may be characterized as involving extensive waste analysis and monitoring, supplemental heat supplies, and agitation, among other steps or components. As is evident, a considerable number of drawbacks and problems exist in the prior art relating to the beneficial decomposition of organic waste materials. 
     There is a need for an improved aerobic decomposition method to more fully utilize the advantages associated with reusing waste materials of the sort and, at the same time, provide for a feasible, environmentally-safe alternative to landfill disposal. 
     OBJECTS OF THE INVENTION 
     It is an object of this invention to provide a method of accelerated decomposition of vegetative organic waste material, overcoming some of the problems and shortcomings of the prior art, including those mentioned above. 
     Another object of this invention is to provide a method for quick, efficient decomposition of large volumes of vegetative organic material as a useful alternative for landfill disposal. 
     Another object of this invention is to provide a method of decomposition which may be used with large volumes of organic material in conjunction with a light-weight, portable apparatus. 
     Another object of this invention is to provide a method of decomposition which does not require the use of a complex, expensive apparatus comprising numerous constantly-moving components prone to costly repair and maintenance. 
     Another object of this invention is to provide a method of decomposition such that the desired degree of bacterial degradation may be achieved without resort to complex and/or computerized analytic techniques. 
     Another object of this invention is to provide an odor-free method of decomposition without use of pollution-control or abatement devices. 
     Another object of this invention is to provide a method of decomposition which does not necessitate either a chemical or bacterial inoculant or an extraneous heat source such as solar radiation. 
     It is a further object of this invention to provide control of decomposition through regulation of high-flow aeration and the rates thereof. 
     Another object of this invention is to provide a method of decomposition which does not require the use of either dry, absorptive filler materials or sewage sludge to obtain suitable moisture levels. 
     It is another object of this invention to increase the rate and degree of decomposition by placement of air-intake means such that the benefits of high-flow rate aeration are enhanced and aerobic conditions are maximized throughout the various stages of the decomposition process. 
     These and other important objects will be apparent from the descriptions of this invention which follow. 
     SUMMARY OF THE INVENTION 
     This invention is a method for accelerated decomposition of large volumes of organic waste material. It overcomes certain well-known problems and deficiencies, including those outlined above. An important aspect of this invention is a novel combination of high-flow rate aeration, material compaction, and moisture percolation, all of which are used in conjunction with a unique container and air-intake combination to provide not only a viable alternative to landfill disposal, but means to produce useful soil amendments, fertilizers, and a source of supplemental heat. The inventive method allows for quick, cost-effective aerobic decomposition, such that the advantages associated with recycling waste materials may be more fully realized. 
     The present invention is directed to a method for aerobically decomposing organic material, including (1) providing a substantially moisture-retentive container having a plurality of openings, one of which is connected to means for variable high-rate air intake; (2) packing the container with an organic material having a releasable moisture content, at a pressure of about 0.1-10.0 pounds per square inch so that the material has a density of about 10-75 pounds per cubic foot such that the material is substantially heat-retentive and permits movement of moisture therethrough; (3) aerating the material at a rate of about 200-1500 cubic feet per minute to control and maintain sufficient aerobic decomposition temperatures; and (4) percolating releasable moisture throughout the organic material. Given the material/container volumes used with this method, aeration displaces the atmosphere of the container about 0.01-3.0 times per minute. In preferred embodiments of the inventive method, aeration is intermittent to control mass temperatures and optimize aerobic decomposition, the frequency of which is a function of material density and a variety of other process parameters. The method of this invention also includes a constant, but varying aeration rate, as a function of temperature and other process parameters. 
     In preferred embodiments of this invention, the container is flexible and substantially moisture-impermeable; and the air-intake means is a discharge blower connected to at least one conducting means positioned within the container and extending substantially the longest dimension of the container. In highly preferred embodiments, two substantially parallel perforated conduits are utilized. 
     In preferred embodiments of this invention, the organic material is aerated at a rate of about 400-1100 cubic feet per minute and a static pressure of at least 0.5 inches of water. In highly preferred embodiments, the organic material is aerated at a rate of about 600 cubic feet per minute and a static pressure of about 0.5-1.5 inches of water. 
     The organic material decomposed with the inventive method preferably includes a bulking agent in about 10-75% by weight of the organic material. In highly preferred embodiments, the weight of the bulking agent is about 25-50% of the total weight of the organic material. 
     In preferred embodiments of this invention, the organic material is packed into the container with a pressure of about 0.1-10.0 pounds per square inch, such that it has a density of about 10-75 pounds per cubic foot. In highly preferred embodiments, the packing pressure is about 0.5-5.70 pounds per square inch, such that the packed material has a density of about 25-35 pounds per cubic foot, whereby it retains heat generated during decomposition, yet allows movement of moisture and air therethrough. 
     The inventive method also includes moisture percolation whereby the moisture content of the organic material is released during decomposition, vaporized by heat generated, then condensed on the container surface. The sequential movement of gas and liquid phase water through the material mass not only accelerates decomposition, but promotes uniform material degradation throughout the composting process. 
     The method of this invention also contemplates monitoring the internal temperature of the organic material to determine the timing of aeration and rate thereof required for optimal decomposition. Likewise, the method may also include an initial injection of water into the organic material to promote optimal decomposition. 
     As previously noted, the method of decomposition as revealed through this invention, has certain advantages, most of which relate directly to the ease and rate at which a useful degree of decomposition may be achieved. Natural composting requires up to two years under typical conditions. The apparatus and method of this invention enables large volumes of organic waste material to be decomposed much more quickly and at a fraction of the cost of conventional equipment and methods. Volumes approximating 1,000 cubic yards of waste may be sufficiently decomposed within four months or less with concomitant volume reduction of nearly 80 percent. 
     Conservative estimates indicate a typical city with a population of 750,000 may produce, on an average annual basis, 45,000 tons of yard and related waste, which would otherwise be landfilled. When considered with the fact that useful by-products and a supplemental heat source may be derived from what would otherwise be a costly refuse problem, the benefits available through use of this method to municipal governments, as well as others similarly situated, are immediately evident. 
     As detailed more fully below, aerobic bacterial composition is a very exothermic process. Temperatures exceeding 130° F. are typically generated. As such, the high flow-rate aeration component of this inventive method may be used to provide a supplemental heat source for a variety of functions, including the winter-heating of a greenhouse or similar such structure, in which case the organic material decomposed is that produced during the growing season. 
     Regardless, the material remaining upon completion of decomposition is a useful soil amendment and fertilizer for residential or agricultural use in that it provides excellent aeration and water-retention qualities, along with nutrients to any soil to which it is introduced. It may also be used in conjunction with various road and highway projects to prevent surface erosion. 
     As discussed above in preferred embodiments, the container used herewith is, preferably, a collapsible bag commercially available from several sources in diameters from 6 feet and lengths up to 250 feet. Costly repair and down-time associated with apparatus of the prior an are avoided by an absence of components moving against the weight of a large volume of waste material. Furthermore, the preferred containers are light-weight and portable such that it may be relocated once decomposition is complete. 
     As significant as these attributes are, perhaps the most important benefits derived from use of the container apparatus of this invention are those more directly related to the environment. The preferred container eliminates wind-borne debris and prevents potentially-hazardous decomposition leachates from running into and contaminating surface water. Together with odorless decomposition, these advantages make use of this method ideal for municipalities composting near residential areas. 
     The preferred discharge blower component effects high flow-rate aeration and is a useful compliment to the preferred bag container. Light weight and simplicity of design promote easy assembly and allow both the blower and one or more perforated conduits to be moved with the container when or as needed. 
     Low cost and maintenance are important advantages associated with use of the preferred apparatus of this invention. Likewise, the water injector and temperature monitoring means which may be used with the method of this invention are also effective without significantly increasing the cost of decomposition, an important consideration to municipalities and others restrained by budget limitations. 
     Aerobic decomposition is predominantly a function of the internal temperature of the waste material and aerobic bacteria indigenous to it, and proceeds at temperatures from about 90-160° F. As a rule, at temperatures above or below this range bacterial activity declines. An inventive aspect of this method includes control of decomposition through the onset and rate of aeration. It has been established that changes in aeration rates may be used to effect almost-immediate response in mass temperature. Likewise, intermittent aeration at the aforementioned rates may also effect the same temperatures control at the various stages of the decomposition process. As a result, the internal temperature of the decomposing material be adjusted to within 5° F. of the desired temperature condition without resorting to expensive, complex microprocessors other analytic methods of the prior art. 
     The need for complete aerobic decomposition is immediately obvious once the internal temperature of the organic mass exceeds the desired range for any length of time. The gaseous by-products of anaerobic decomposition tend to be foul-smelling and are widely-considered a form of pollution completely unacceptable to those unfortunate to reside in close proximity. The method of this invention prevents anaerobic bacterial activity such that decomposition proceeds effectively without offensive odors or the need for auxiliary scrubbing or control devices. 
     As inferred above, bacteria indigenous to the waste material may be utilized without adding extraneous decomposition-enhancing chemicals or bacterial cultures. Inasmuch as inoculants of this sort are relatively expensive and require additional monitoring, a considerable cost-savings compared to methods of the prior art may be realized. Nonetheless, a reasonable equivalent of the inventive method described herein contemplates circumstances underwhich the addition of chemical and/or bacterial inoculants may benefit the decomposition process. 
     This inventive method anticipates the possibility that the addition of moisture may be required to enhance the rate of decomposition with certain extremely dry waste materials. However, with most organic wastes, the natural moisture content has been found sufficient, foregoing the need to add sewage sludges or other high-water-content materials which may have a corrosive, deleterious effect on any apparatus used. Conversely, too much water does not impede this method. Because excessive moisture only enhances percolation and decomposition, filler materials of the prior art are not needed to absorb water. 
     The method of this invention would not seem appropriate for the aerobic decomposition of organic material. Aeration systems of the prior art stress the use of low flow-rates in combination with loosely-arranged waste material either constantly or periodically agitated to encourage aerobic conditions. The use of high flow-rate aeration, intermittent or otherwise, with compacted material and percolation of moisture is contrary to the art, and the excellent results obtained were quite unexpected. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of apparatus suitable for employing the method of this invention are shown in the accompanying drawings, of which: 
     FIG. 1 is a sectional view of an apparatus which can be used with this invention; 
     FIG. 2 is a top view of the apparatus; 
     FIG. 3 is a side view of the apparatus; 
     FIG. 4 schematically shows in partial cross-sectional view a preferred apparatus configuration for use with the invention; and 
     FIG. 5 is a schematic top view of a multiple container and air-intake apparatus. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The drawings illustrate embodiments of an apparatus which may be used to employ the method of this invention. The apparatus includes bag 10 and air conduit 16 attached to blower 20. 
     As best shown in FIG. 1, bag 10 is provided with a plurality of substantially evenly-spaced openings 14 though which air conduits 16 are inserted. Joints 18 allow conduits 16 to be used in a series configuration. Once bag 10 is sufficiently packed with organic waste material, fastener means 12 secures the open end, creating a substantially moisture-retentive container. 
     Air conduits 16 are connected to discharge blower 20 which, when in operation, provides high flow-rate aeration throughout bag 10. Conduits 16 extend substantially the depth of bag 10. Perforations 22 spaced along conduits 16 allow air forced therethrough to permeate the vegetative matter. Homeostatic air flow is achieved though incorporation of exhaust vents 24, preferably located in the upper portion of bag 10 between conduits 16. Temperature monitoring means may also be used in conjunction with the method of this invention. In such case, apertures 26, as are shown and described in FIG. 1, are made through bag 10 for insertion of such means into the material mass. 
     As best shown in FIGS. 2 and 3, water injection means 28 may be employed with the method of this invention. If so, such means may be inserted through holes 30 into an upper portion of bag 10 and the organic matter contained therein. Preferably, injection means 28 is in a series configuration such that it is aligned between and at right angles to conduits 16. 
     In highly preferred embodiments and as shown on FIG. 4, conduit 16 is aligned and configured relative to container 10 such that conduit 16 extends substantially the length of container 10. In highly preferred embodiments, conduit 16 is positioned in a lower portion of container 10 to enhance the extent and rate of decomposition. During aeration, homeostatic airflow is maintained by one or more vent means 24 positioned relative to conduit 16 to ensure aerobic conditions throughout the material packed in container 10. 
     As shown in FIG. 5, multiple containers 10 may be arranged with a single air intake means to increase the volume of organic material decomposed. While other configurations are possible, as shown in FIG. 5 a parallel array of containers 10 may be used in conjunction with blower 20 and conduits 16. Depending upon the volume of material decomposed, more than one conduit 16 can be utilized to achieve the aerobic conditions discussed herein. As shown in FIG. 5, dual substantially parallel conduits 16 are used to enhance aeration, but other numbers and configurations can be utilized. While not shown specifically in either FIGS. 4 or 5, it will be understood by one skilled in the art made aware of this invention that conduits 16 are preferably perforated to an extent sufficient to distribute the high-flow air rate generated by blower 20 throughout the organic mass. Likewise, sufficient vent means 24 are also used, though not shown specifically in FIG. 5. 
     High flow-rate aeration and an apparatus to provide the same are used in conjunction with the aerobic decomposition described herein. In accordance with this invention, a container packed with vegetative organic material is aerated--preferably, intermittently--at a rate of about 200-1500 cubic feet per minute to obtain optimal aerobic decomposition conditions. At aeration rates below this range, anaerobic bacteria and odiferous metabolic by-products predominate; aeration in excess of this rate appears to create conditions disruptive to aerobic bacterial activity, and can be used to lower internal mass temperature if it rises above the optimal aerobic range during any one stage of the decomposition. Under certain process conditions and depending upon the waste used excessive high-flow rate aeration dries the mass and inhibits decomposition. 
     In preferred embodiments of this invention, aeration proceeds at a rate of about 400-1100 cubic feet per minute. In highly preferred embodiments, accelerated decomposition may be achieved with a flow rate of about 600 cubic feet per minute. Air flow must be conducted at a sufficient static pressure to achieve the desired aerobic decomposition. Pressures of at least 0.5 inches of water are needed to force the preferred volumes of air through the air conduits. Studies show that pressures of 0.5-1.5 inches of water provide excellent results with most waste materials. 
     Bulking agents such as straw, wood chips, and the like may be used with the method of this invention. Inclusion of these materials promote aeration and enhance aerobic decomposition by creating air spaces and passages within the vegetative mass. As a result, optimal aerobic temperatures may be obtained more readily and adjusted by air-flow rates more efficiently. 
     As stated above, a bulking agent may comprise about 10-75 percent by weight of the organic material to be decomposed. The exact amount utilized depends, in large part, on the compaction susceptibility of the waste material which, in turn, depends upon its moisture content and particulate size. It has been found with most waste materials the bulking agent should be about 25-50 percent of the total weight of the organic material. The exact amount used may vary with the air flow-rate utilized. 
     It is essential that the organic material be compacted into the container apparatus to retain heat generated during decomposition and further enhance aerobic bacterial activity. Unlike methods of the prior art, most of which include means to prevent compaction, a preferred method of this invention entails filling a container with moderate pressure. The pressure utilized varies and depends, in part, on the moisture content of the material to be decomposed. 
     Typically, pressures of about 0.5-5.0 pounds per square inch are employed during packing process. With materials such as grasses which have a relatively high moisture content, the pressure used will tend toward the lower end of this range; higher pressures will result in a mass density which may preclude sufficient aeration and lead to unwanted anaerobic decomposition. Conversely, materials such as dry leaves are packed with pressures near the upper end of the aforementioned range. In these situations, too little pressure results in a material mass with insufficient heat retention qualities. To some degree, packing pressures may be modified for a given material and moisture content through adjustment of the amount of bulking agent used. Packing may be accomplished through use of apparatus well-known to those made familiar with this invention. Blowers and auger-type devices which supply sufficient, constant pressures of the sort described herein may be successfully. 
     High flow-rate aeration is accompanied by percolation of moisture throughout the material mass. The preferred bag container used in conjunction with this inventive method permits accumulation of moisture as it is released from the decomposing material. As decomposition proceeds, the internal temperature rises and the released moisture vaporizes, passing though the material and condensing on the surface of the bag container. The combination of repeated percolation of moisture and high flow-rate aeration enhances aerobic bacterial activity and accelerates decomposition. 
     To decompose especially dry vegetative material, the method of this invention contemplates initial injection of water to approximate a suitable moisture content equivalent to about 20-65% of the weight of the material. Typically, only one such injection is required as the moisture is thereafter continually recycled through the percolation step described above. 
     Preferred bag 10 may be made using a variety of materials, including polyethylene and other similar durable, flexible plastics. Any material utilized must resist tears when openings are introduced as exhaust vents or for the insertion of one or more aeration conduits, yet must be flexible and extendible enough to accommodate the collection of a significant amount of moisture once decomposition begins. It has been found that a polyethylene bag with a thickness in excess of 6 mil provides excellent results under the decomposition conditions employed with this method. Thinner materials do not provide the strength and flexibility needed to process large volumes of waste material. 
     Preferred polyethylene bags range from 10-250 feet in length and have 6-12 feet diameters. For volumes effectively decomposed through use of this method, a 100-foot bag provides excellent results. Such containers are available from sources well known to those skilled in the art and include AG-BAG Corporation of Warrenton, Oreg., among others. 
     Blower 20 and conduits 16 may also be obtained from a variety of sources well-known to those made aware of this invention. In particular, excellent results will be obtained through use of a blower with means to provide intermittent aeration and/or vary flow-rates such that internal mass temperatures may be adjusted as needed to provide optimal decomposition conditions. One such blower, suitable for employing the method of this invention, is available from Dayton Electric Manufacturing Company of Chicago, Ill. 
     While the principles of this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention. For example, the container apparatus used in conjunction with this method may include various mesh-type materials which permit retention of heat and allow condensation of internal moisture. Likewise, organic materials are not necessarily limited to the yard and related waste described. Waste paper, animal refuse, lake algae, and a variety of other organic materials are suitable for decomposition through the method of this invention. Other advantages and features of the invention will become apparent from the claims hereinafter, with the scope of the claims determined by the reasonable equivalents as understood by those skilled in the art.