Abstract:
A compost tea system uses a water-holding tank for containing process water. Compost is immersed into the water in the tank in baskets defining a filter media. Air is pumped into membrane disk diffuser modules in the tank and the liquid is sparged with fine bubbles to thoroughly agitate the liquid, extract nutrients and microorganisms from the compost, and to ensure a high concentration of dissolved oxygen in the liquid. The high level of oxygen selects for desired aerobic organisms to produce a rich compost tea. The finished tea is drained out of the tank and the tank and its components are easily cleaned and sanitized.

Description:
FIELD OF THE INVENTION 
     This invention relates to compost tea, also known as compost extract, and more particularly, to apparatus and methods for producing compost tea. 
     BACKGROUND OF THE INVENTION 
     Compost teas are being used with increased frequency by both commercial agricultural enterprises and home gardeners for the many benefits they offer, such as control of root and foliar diseases via the action of beneficial microorganisms, and as a source that adds nutrients to plants and soil. Simply described, a compost tea is an aqueous extract of compost that is produced by extracting nutrients and microorganisms from compost. The extraction is often coupled with production aeration, agitation and microbial foods to increase the microbial density of the resulting extract—the tea. Some of the many benefits of compost teas have been recognized for many years. However, teas are becoming more and more recognized as important agricultural tools since they provide an alternative method of addressing such common agricultural concerns as disease control and nutrient supplementation. Among other benefits, compost tea generally provides an organic product that is economically manufactured and applied to crops and soil, and which allows the reduction or elimination of non-organic crop pesticides and fertilizers. 
     There are several known general methods of making compost teas—all of the methods rely upon high quality compost as a starting material to ensure a high quality extract. Various manufacturing techniques are used to leach a complex nutrient and microbiologically rich aqueous extract from the compost. The quality of the tea in terms of nutrient makeup and concentration and in terms of microbiological load and diversity depends to a large degree on the quality of the compost starting material, the food or nutrient package added to feed the microorganisms and on the method used to make the tea. Regardless of how it is made, liquid compost tea may be applied to plants in the form of a foliar spray, for instance to combat disease. Used in this way the tea provides an active method of controlling plant pathogens through mechanisms such as inhibition of spore germination, antagonism, and microbial competition with various plant pathogens. When applied as a spray, the tea also provides quickly usable nutritional supplements for the plant. Teas may also be applied directly to the soil to add nutrients to the soil and to increase the microbial density and diversity. 
     Given the complex microbial diversity found in high quality composts, and the rich nutrient makeup of composts, it is natural that compost teas have a similarly complex microbiological and macro, micro and trace element composition. The number and type of bacteria found in compost teas varies of course with many factors, including the bacterial species found in the starting compost, and the manner in which the tea is extracted. Thus, compost from a source such as animal manure will have a substantially different microbial load than compost derived from a plant origin, and a tea made from such composts will likewise have different microbial diversity. Nonetheless, and generally speaking, a high quality compost tea will be rich in aerobic bacteria, yeasts and fungi, as well as many varied nutrients. The methods of manufacturing the teas are designed to enhance the presence of such desirable components. 
     There are numerous methods of manufacturing compost teas, and the known methods involve both production of the liquid extract and aeration to ensure aerobic flora are selected and reproduce at a high rate. One of the simplest methods of making tea, and also one of the earliest reported methods involves covering compost with water, stirring the combination and allowing it to soak (and ferment) for a period of between 2 to 21 days. The liquid is then separated from particulate material by straining through cheesecloth and may be applied to crops and soil with ordinary spray equipment. 
     While this simple method produces an acceptable, low cost compost tea, it has been recognized that aerating the liquid to increase the concentration of dissolved oxygen in the liquid can enhance the growth of aerobic microorganisms and decrease tea production time production. One simple method of aeration is to create a trough by cutting a pipe in half lengthwise and drilling plural holes in the pipe to allow drainage. The pipe is laid on its side and is suspended over a tank. Compost is filled into bags such as burlap and laid in the trough. Water is then sprayed over the burlap. As the water filters through the compost it extracts nutrients and microbiological organisms. The water is circulated from the tank through the sprayers for several days. By spraying the liquid and by allowing it to drain through the trough the concentration of oxygen in the liquid increases, and this enhances the selection and growth of desirable aerobic microorganisms. 
     Not surprisingly, with the increased awareness that compost teas provide economical and organic alternatives to pesticides and fertilizers, more automated methods of manufacturing teas have been developed. These range from small devices that provide constant stirring and aeration of compost in water-filled tubs, to more complex devices such as the one described in U.S. Pat. No. 6,168,949. The “bioreactor” described in the &#39;949 patent uses a tank having a conical bottom that holds the production liquid. The liquid is circulated through the tank by pumping it through the bottom and spraying it through an atomizing nozzle in the headspace above the liquid—called a vortex chamber. The finely divided spray produced by the atomizing nozzle allows for the introduction of gases in the headspace into the liquid—oxygen for instance. 
     These known methods of making compost tea are useful for making the product. However, there is a need for a compost tea system that is simple and which allows for the manufacture of high quality teas. The present invention provides a compost tea production apparatus that is simply constructed and simple to operate, and which provides a high quality tea rich in aerobic bacteria. 
     The tea system of the present invention uses a production tank that is filled with water that does not recirculate the water through a pump. Compost is introduced into the liquid in filter baskets suspended in the tank. Oxygen is introduced into the liquid through membrane disk diffusers positioned on the bottom of the tank. As air is pumped into the diffusers it is bubbled through the liquid in fine bubbles that have a high surface area to volume ratio. This causes both passive circulation of the liquid to ensure a homogenous blend of nutrients and constant turnover of the liquid, and maintains the concentration of dissolved oxygen in the liquid at a high level to encourage growth of desired aerobic organisms during the production cycle production. The entire production process is accomplished relatively quickly with the system of the present invention, and high quality compost teas may be produced within 24 hours. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood and its numerous objects and advantages will be apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings. 
     FIG. 1 is a top perspective view of an assembled compost tea producing apparatus according to the present invention. 
     FIG. 1A is a top perspective view of the compost tea producing apparatus shown in FIG. 1 with the component parts shown in exploded view and with a portion of the tank cut away to show the tank interior, and with some of the plumbing components shown in phantom lines. 
     FIG. 2 is a partial cross sectional view taken of the compost tea producing apparatus of the present invention showing some of the tank interior and components. 
     FIG. 3 is a top plan view of the compost tea producing apparatus showing the plumbing and air circulation system, and in which the tank and frame components are shown in phantom lines. 
     FIG. 4 is a detailed cross sectional view of a membrane disk diffuser used in the compost tea system 
     FIG.  5 . is an exploded perspective view of the unassembled membrane disk diffuser shown in FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, and more specifically to FIGS. 1 and 1A, it will be seen that compost tea system  10  includes a fluid holding tank  12  that is supported by an external frame  14 . A lid  16  covers the upper opening of tank  12 , and as detailed below, system  10  includes a liquid plumbing system and an air plumbing system. Air is provided to the liquid contained in tank  12  with an air pump  18  that is supported by a shelf  20 , located above the liquid level and connected to frame  14 . The location of shelf  20  shown in the figures is exemplary of one embodiment only, and the shelf may be mounted to the tank itself or at other locations. 
     FIG. 1A shows some of the components of system  10  in an exploded view. Tank  12  may be of any appropriate size and shape, such as 100 gallons or more. It will be appreciated that the system  10  may be of much greater volume and capacity, or much less, depending upon the requirements of the particular user. In the preferred embodiment shown in the figures the tank is circular in cross section, but the tank could be of any cross sectional shape. Moreover, in the preferred embodiment the tank and other components are manufactured of a high quality, strong and easily cleaned ultra-violet resistant plastic. However, the tank and other components may be manufactured from other appropriate materials such as stainless steel and the like. 
     The tank is supported and surrounded by frame  14 , which includes shelf  20  for holding air pump  18 . The frame  14  shown in the figures is not necessary on all designs and is illustrated in herein as being representative of one model and size of system  10 . For example, the tank may be designed to be self-supporting. Frame  14  supports tank  12  above a floor member  22  that is spaced apart from the bottom of tank  12  to provide room for various air and fluid plumbing fittings. A basket tray  24  covers the open upper end of tank  12  and includes plural openings  26 , each of which receives a compost basket  28  such that the basket is suspended into the tank interior. Plural vents  30  are formed in basket tray  24  to ensure that the system is open to the atmosphere. Lid  16 , which is sized to fit snugly over and cover basket tray  24  also includes plural vents  32  to ensure open circulation of atmospheric air into the interior of tank  12 . 
     Turning now to the interior of tank  12 , system  10  includes membrane disk diffuser modules  34  that are spaced around the interior bottom of the tank and around a central drain opening  36 . Each of the membrane disk diffuser modules is fluidly plumbed to a source of air—air pump  18 , and central drain opening  36  is fluidly plumbed to the liquid plumbing system. These connections are detailed below. 
     Various components of system  10  are detailed in FIG.  2 . The tank preferably has a flat bottom fitted with a drain that allows for all fluid to drain from the tank. The tank itself, as noted, in the embodiment shown in the figures is supported by frame  14 . Basket tray  24  includes an outwardly extending annular flange  38  that is sized to fit over the upper edge  40  of tank  12  and frame  14  to support the basket tray. Inwardly of annular flange  38  basket tray  24  has a downwardly extending annular side wall  42  that fits within the interior circumference of tank  12 . In this way, basket tray  24  fits snugly onto tank  12  but is easily removed for cleaning and maintenance. Similarly, lid  16  includes an outwardly extending annular flange  44  that fits over annular flange  38 . 
     Compost basket  28  comprises an annular flange  46  that is larger in size than opening  26  so that when the basket is assembled with tray  24 , the basket is suspended into the tank interior. The basket includes an inner layer of mesh screen  48  and outer layer mesh screen  48 , each of which has relatively large mesh openings, and an inner filter media  50  that has relatively smaller mesh openings sandwiched therebetween. The bottom plate of basket  28  is also open with holes that define a larger mesh opening than the mesh openings of filter medial  50 . Filter media  50  is preferably a punched plastic material having appropriately sized openings (such as 20 mesh) for containing compost yet allowing rapid flow of water through the compost basket and easy cleaning. Filter media  50  is cylindrically shaped with a bottom so that it is sized to fit within the outer layer of mesh screen  48 . Once filter media  50  is inserted into the basket, the inner layer of mesh screen  48  is inserted into the basket. Mesh screen  48  may be made from plastic or metal such as stainless steel. The inner layer of mesh screen  48  defines primary filter media for the compost, which is contained with the compost basket, and retains larger pieces of compost material. Filter media  50  defines a secondary filter media to retain relatively smaller pieces of compost particulate matter in the compost basket. The open bottom of basket  28  allows oxygen and agitation to occur through the bottom as well as the sides of the filter basket. 
     Plural membrane disk diffuser modules  34  are spaced around the interior of tank  12  and each is fluidly connected to air pump  18  through an air line  52 . The number and placement of disk diffuser modules  34  is not critical and should be determined by the volume of the tank and by the amount of air that flows through the system. The liquid and air plumbing connections and systems are detailed in FIG.  3  and reference is now made to that figure. Beginning with the air plumbing connections, air line  52  extends from the outlet  54  on air pump  18  to a T-header  56  located near the bottom edge of the tank where the air line branches into four separate lines, one running to each of the diffuser modules. The air line is preferably fabricated from rigid tubing, such as PVC schedule 80 tubing or other appropriate materials. The air line preferably extends from pump  18  to individual diffuser module inlets on the outside of the tank. 
     The liquid plumbing connections include central drain opening  36 , which is fluidly connected to a drain pipe  60  (FIG.  2 ). A first isolation valve  62  is positioned in drain pipe  60 . Downstream of isolation valve  62  the drain pipe connects to an in-line filter (not shown) such as a 20 mesh glass bowl-type filter, which is removable for cleaning. The discharge piping then splits at a T-connection  64  into two fluid paths. The first fluid path is a passive discharge path is through pipe  66  and includes a valve  68 . The second fluid path is an active discharge path through an water pump  72 . Downstream of isolation valve  62 , pipe  70  includes a valve  71  (such as a ball valve) and is connected to the water pump  72 , the outlet of which is plumbed to a valve  74 . Water pump  72  is a preferably an electric pump, but could be another type of pump if needed. It will be appreciated that the active discharge system is optional and is provided on systems having relatively large volume tanks and/or where a source of electric power is readily available. In all cases the passive discharge system is provided. The first fluid path allows for draining of the fluid from tank  12  by gravity when valves  62  and  68  are open and valve  74  is closed. The second fluid path allows for draining of fluid from tank  12  by action of pump  72  when valves  62  and  74  are open and valve  68  is closed. Each of the fluid paths for draining the tank includes an outlet  76  that may be fluidly connected with appropriate fittings to hoses and the like. 
     The membrane disk diffusers  34  provide a means for introducing oxygen to the liquid and agitation within the tank and are detailed in FIGS. 4 and 5. Each diffuser  34  includes a main body member  78  that has a downwardly depending nipple  80  that is fitted through an opening formed in the bottom of tank  12  and is fluidly sealed thereto. The manner in which main body member  78  is connected to the tank is not of particular importance provided there is a fluid seal at the connection. The body member could thus be threaded through an opening in the tank or glued in place. Appropriate seals may be used as necessary. The portion of nipple  80  external to tank  12 , and which extends below tank  12  includes an internally threaded opening  82  for a sealed connection to a threaded end connector on air line  58 . A centrally bored orifice  84  extends completely through nipple  80 . On the interior of tank  12 , main body member  78  includes a flattened disk portion  86  inwardly of a threaded edge  88 . A retaining ring  90  has is threaded to match threaded edge  88  such that ring  90  may be screwed onto body member  78  with a diffuser membrane  92  sealed therebetween. Diffuser membrane  92  is a flexible rubber material having plural small openings  94  such as slits formed completely through the rubber membrane material. When the diffuser modules  34  are assembled as shown in FIG. 4, diffuser membrane  92  is fluidly sealed in the module between the retaining ring  90  and threaded edge  88  by a crushing action between the retaining ring and the flattened disk portion  86 . 
     Membrane disk diffusers suitable for use with the present invention are available from US Filter Company, headquartered in Palm Desert, Calif., and on the web at www.usfilter.com, and are sold under the brand name FLEXDISC™. 
     In operation, valve  62 , and preferably valves  68  and  74  are closed and tank  12  is filled with water from an external source. Depending upon the water source and the requirements of the particular application, the water may be purified and, again depending on the application, additives such as carbohydrates and other nutritional supplements for microorganisms may be added to the water. Basket tray  24  is then fitted over the upper opening into tank  12  and high quality compost is added to each of the compost baskets  28 . The baskets are then inserted into openings  26  in basket tray  24  such that the compost baskets are suspended in the tank interior. The water level  96  in tank  12  (FIG. 2) is such that the compost baskets  28  and the compost contained therein are immersed in the water. Lid  16  is then placed over basket tray  24 . 
     Air pump  18  is connected to a source of electric power and is switched on at a switch  98 . Air pump  18  is sized to pump a quantity of air appropriate to the size of the tank and the number of membrane disk diffuser modules. In the preferred embodiment disclosed herein with a tank capacity of about 100 gallons and four membrane disk diffuser modules, and appropriately sized air pump moves about 22 gallons of air per minute and at a working (open) pressure of about 0.15 pounds per square inch. The closed pressure is about 6.5 pounds per square inch. It will be appreciated that these figures are exemplary only, and that many other air pump sizes will be appropriate in a given circumstance. Numerous commercially available air pumps are adequate for use with the present invention. One exemplary model is manufactured by Rolf C. Hagen, Inc. of Montreal, Quebec and sold under the model number A-814. There are many other comparable pumps available on the market. Moreover, while in the preferred embodiment compressed air is supplied from air pump  18 , other sources of air may be used such as compressed air from pressurized tanks and the like. 
     With air pump  18  switched on, air is pumped into and flows through air line  52 , into distribution module  56  and into air lines  58 , each of which is fluidly connected and sealed to a membrane diffuser module  34  as detailed above. With reference to FIG. 4, air enters the diffuser through nipple  80  and flows in the direction of arrow A through orifice  84  and to the underside of diffuser membrane  92 , between the membrane and the flattened disk  86 . The air pressure causes diffuser membrane  92  to deflect upwardly as illustrated with phantom lines in FIG.  4 . Stated otherwise, the pressure of the air flowing into the diffuser module causes the membrane to inflate. The space defined between the interior surface of the membrane and the disk  86  thus defines a plenum for receiving air from air pump  18 . The size of the plenum increases as the amount of air flowing into the plenum increases, and/or the pressure of the air in the system increases. As the membrane inflates, slits  94  open very slightly—enough so that air begins to bubble out of the openings and into the liquid in very small bubbles. Each diffuser membrane  92  includes hundreds of openings  94 . As a result, many thousands of small air bubbles are constantly rising through the liquid. This results in efficient mixing action of the liquid. 
     It will be appreciated that the combination of an air source and the membrane diffuser modules define a highly efficient bubble generator to introduce air bubbles into the liquid, and thus maintain the concentration of dissolved oxygen in the liquid at a desirable high level. It will also be appreciated that there are other equivalent apparatus for introducing air bubbles into tank  12 , such as perforate air lines and the like installed in the tank. 
     Because the bubbles are small and have a high surface area to volume ratio, a high level of dissolved oxygen is maintained in the water. And because the water flows readily through the compost baskets and the filter media the compost is agitated by the bubbling action. This results in efficient extraction of microorganisms from the compost into the water. 
     Air pump  18  is kept on for a set time period during which bubbles are generated in the tank so that the liquid in the tank is constantly circulating and oxygen is constantly being dissolved into the water. During this period the microorganisms in the liquid, and particularly the aerobic bacteria are reproducing rapidly. The microbial load of the liquid thus increases during this production period due to rapid reproduction of bacteria and other microbes. Because the oxygen concentration in the water is high, desirable aerobic organisms are favored and the growth and reproduction of anaerobic microorganisms is inhibited. 
     When the production period is complete—typically between about 15 to 30 hours and more preferably about 24 hours, but varying with specific circumstances, the air pump is switched off at control switch  98 . With air pump  18  off and the flow of air to the membrane diffuser modules stopped, the diffuser membranes  92  deflate to the flat condition shown in FIG.  4 . This causes the slits  94  to close, thereby stopping the backflow of liquid into the air plumbing system. 
     The finished compost tea is drained off through one or both of the two fluid paths and into appropriate hoses and the like that are attached to outlets  76 . If the tea is drained off through the second fluid path, the water pump  72  is switched on at control switch  98 . The tea may be filled into appropriate application apparatus for direct application as a foliar spray or for application to soil. 
     The tea system is easily cleaned and/or sanitized by removing lid  16 , basket tray  24  and compost baskets  28 . The interior of tank  12  may thus be sprayed out with clean water and sanitizers or soaps as needed. The other components may similarly be cleaned and sanitized. Spent compost is removed from the compost baskets  28  and they are sprayed out and cleaned as needed. 
     In view of the many possible embodiments to which the principles of our invention may be applied, it should be recognized that the detailed embodiments are illustrative only and should not be taken as limiting the scope of our invention. Rather, we claim as our invention all such embodiments as may come within the scope and spirit of the following claims and equivalents thereto.