Abstract:
A flush system for processing waste slurry contains animal waste, comprising a primary separator, a primary digester, and a secondary digester. The primary separator separates the waste slurry into a first portion and a second portion. The primary digester digests the first portion. The secondary digester digests at least part of the second portion. A solids content of the first portion is higher than a solids content of the second portion.

Description:
RELATED APPLICATIONS 
       [0001]    This application (Attorney Docket No. P216840) claims benefit of priority to U.S. Provisional Application Ser. No. 61/417,387, filed Nov. 26, 2010. 
     
    
       [0002]    The contents of the patent application(s) listed above are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0003]    The present invention relates to manure processing systems and methods for use in dairy operations and, more specifically, to improved waste processing systems and methods for use with dairy facility flush systems. 
       BACKGROUND 
       [0004]    Dairy and similar livestock operations generate animal waste. The present invention is of particular significance in the field of dairy operations, and the invention will be described in the context of a dairy operation. The present invention may, however, have application to other environments. 
         [0005]    In a dairy operation, cows are often held for periods of time in contained locations. Over time, cow waste collects in such contained locations and must be removed. Dairy systems thus typically use a flush system to remove cow waste from contained locations where the waste has collected. A flush system employs a pressurized liquid that is flushed onto the contained locations to remove the waste. The flush liquid and animal waste form a waste slurry that is collected and removed from the contained location. 
         [0006]    The flush system thus requires both a continuous supply of flush liquid and a way to handle the waste slurry. To deal with both problems, processing systems have been developed that process the waste slurry generated by the flush system to obtain useable manure and to extract from the waste slurry a liquid suitable for use as the flush liquid. 
         [0007]    Systems and methods of processing waste slurry generated by flush systems are described in U.S. Pat. No. 7,306,731 to DeWaard, and the contents of the DeWaard &#39;731 patent are incorporated herein by reference. The waste processing system described in the DeWaard &#39;731 patent employs an arrangement of settling and storage tanks and liquid/solid separators to obtain useable flush liquid and also to provide a supply of material suitable for use in a digester. The flush liquid may be re-used by a conventional flush system, while the digester process yields manure material that may be safely spread directly on soil as fertilizer and/or liquid that may be used as fertilizer. 
         [0008]    A problem with the waste slurry processing system described in the &#39;731 patent is that the amount of liquid volume that can economically be processed by the digester limits the size of the digester. To extract all of the latent energy from the waste, the digester must be significantly over sized. Typically, it is not cost effective to install a digester of sufficient size to process all of the waste slurry. Accordingly, in a typical implementation of the system described in the &#39;731 patent, a portion of the waste slurry is not processed by the digester, and the energy latent in this unprocessed portion of the waste slurry is not recovered. 
         [0009]    The present invention may be implemented as improved waste processing systems and methods for optimizing the processing of waste slurry arising from use of a dairy flush system. 
       SUMMARY 
       [0010]    The present invention may be embodied as a flush system for processing waste slurry contains animal waste, comprising a primary separator, a primary digester, and a secondary digester. The primary separator separates the waste slurry into a first portion and a second portion. The primary digester digests the first portion. The secondary digester digests the second portion. A solids content of the first portion is higher than a solids content of the second portion. 
         [0011]    The present invention may also be embodied as a method of processing waste slurry containing animal waste comprising the following steps. The waste slurry is separated into a first portion and a second portion, and a solids content of the first portion is higher than a solids content of the second portion. The first portion is digested in a primary digester. The second portion is digested in a secondary digester. 
         [0012]    The present invention may also be embodied as a flush system for processing waste slurry containing animal waste, comprising a first vessel, a second vessel, a low-rate digester, and a high-rate digester. The first vessel separates the waste slurry into a first thick fraction and a first thin fraction. The second vessel separates the second portion of the waste slurry into a second thick fraction and a second thin fraction. The low-rate digester digests the first thick fraction and at least a portion of the second thick fraction. The high-rate digester digests at least a portion of the first thin fraction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic view of a first example manure processing system of the present invention; 
           [0014]      FIG. 2  is a schematic view of a second example manure processing system of the present invention; 
           [0015]      FIG. 3  is a schematic view of a third example manure processing system of the present invention; 
           [0016]      FIG. 4  is a schematic view of a fourth example manure processing system of the present invention; and 
           [0017]      FIG. 5  is a schematic view of a fifth example manure processing system of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    The principles of the present invention can be implemented in any number of different forms depending upon the nature of the particular operating environment, including available storage and disposal facilities and quantity and/or characteristics of the waste to be processed. Several example implementations of the present invention will be discussed separately below. 
       I. First Example 
       [0019]    Referring initially to  FIG. 1  of the drawing, depicted therein is a first example waste processing system  20  adapted to be used with a flush system  22 . The example flush system  22  is or may be conventional and comprises a dairy flush facility  30  and a reception pit  32 . The flush facility  30  comprises an inlet  34  through which flush fluid is introduced and an outlet  36  through which waste slurry is collected. During use of the flush system  22 , the flush liquid is mixed with the animal waste to form waste slurry. The waste slurry flows through the outlet  36  and is collected in the reception pit  32 . 
         [0020]    The first example waste processing system  20  comprises a storage facility or structure  56 , a primary digester  80 , and a secondary digester  82 . The primary digester  80  and the secondary digester  82  are configured to process digester mixtures having different characteristics. 
         [0021]    The first example waste processing system  20  operates basically as follows. A solids portion, or first digester mixture or thick fraction, of the waste slurry collected by the reception pit  32  flows into the primary digester  80 . A liquid portion, or second digester mixture or thin fraction, of the waste slurry collected by the reception pit  32  flows into the secondary digester  82 . 
         [0022]    In practice, when a given slurry material containing liquids and solids is separated into a thick fraction and a thin fraction, the thick fraction will comprise a high percentage of settleable solid material relative to the given material, while the thin fraction will comprise a relatively low percentage of settleable solid material relative to the given material. Both the thick fraction and the thin fraction contain biodegradable solid material, but the thick fraction will typically contain a higher percentage of biodegradable material than the thin fraction. Further, the ratio of unsettleable solid material to settleable solid material in the thin fraction will be typically be higher than the ratio of unsettleable solid material to settleable solid material in the thick fraction. 
         [0023]    The primary digester  80  breaks the biodegradable material in the first digester mixture or thick fraction down into a first digested material. In the example first waste processing system  20 , the first digested material is allowed to flow into the storage facility  56 . In addition to processing a portion of the waste slurry, the primary digester  80  may further be configured to release useable energy from the solids portion processed thereby. 
         [0024]    The secondary digester  82  breaks the biodegradable material in the second digester mixture or thin faction down into second digested material. In addition to processing a portion of the waste slurry, the secondary digester  82  may further be configured to release useable energy from the second digester mixture. In the example first waste processing system  20 , the second digested material is allowed to flow into the example storage facility  56 . A portion of the liquids collected by the reception pit  32  may be fed back into the dairy flush facility  30  as depicted in  FIG. 1 . 
         [0025]    In a waste processing system constructed in accordance with the principles of the present invention, the ratio of the percentage of solids in the first digester mixture to the percentage of solids in the second digester mixture is within a first range of approximately 5:1 to 10:1 and in any event should be within a second range of approximately 2:1 to 15:1. In the first example waste processing system  20 , the ratio of the percentage of solids in the first digester mixture to the percentage of solids in the second digester mixture is approximately between 7:1 and 8:1. 
         [0026]    The primary digester  80  may be characterized as a low-rate digester, while the secondary digester  82  may be characterized as a high-rate digester. In particular, in a waste processing system constructed in accordance with the principles of the present invention, the primary digester  80  should completely process the first digester mixture in a first range of approximately 10 to 100 days and in any event should be within a second range of approximately 15 to 40 days. In the first example waste processing system  20 , the primary digester  80  processes the first digester mixture in approximately 20 days. On the other hand, the secondary digester  82  should completely process the second digester mixture in a first range of approximately 6 hours to 8 days and in any event should fully process the second digester mixture within a second range of approximately 12 hours to 5 days. In the first example waste processing system  20 , the second digester  82  processes the second digester mixture in approximately 1 day. 
         [0027]    The ratio of the digestion rates of the first and second digesters of a waste processing system of the present invention should be within a first range of approximately 1.5:1 to 5:1 and in any event be within a second range of approximately 1.5:1 to 3:1. The ratio of the digestion rates of the example primary digester  80  and the example secondary digester  82  is approximately 2:1. 
         [0028]    The first digester mixture fed into the primary digester  80  should have a solid content of within a first range of approximately 6% to 10% and, in any event, the solid content of the first digester mixture should be within a second range of approximately 4% to 20%. In the first example waste processing system  20 , the first digester mixture has a solid content of approximately 7% to 8%. The second digester mixture should have a solid content of within a first range of approximately 0.5% to 2% and, in any event, the solid content of the second digester mixture should be within a second range of approximately 0.25% and 4%. In the first example waste processing system  20 , the second digester mixture has a solid content of approximately 1%. 
         [0029]    The use of two separate digesters having different characteristics optimizes the overall digestion rate of the first example waste processing system  20 . The first example waste processing system  20  thus yields improved rates at which the waste slurry is processed into flush liquid appropriate for use by the flush system and dry solids appropriate for storage and/or disposal. 
       II. Second Example 
       [0030]    Referring now to  FIG. 2  of the drawing, depicted therein is a second example waste processing system  120  adapted to be used with a flush system  122 . The example flush system  122  is or may be conventional and comprises a dairy flush facility  130  and a reception pit  132 . The flush facility  130  comprises an inlet  134  through which flush fluid is introduced and an outlet  136  through which waste slurry is collected. During use of the flush system  122 , the flush liquid is mixed with the animal waste to form waste slurry. The waste slurry flows through the outlet  136  and is collected in the reception pit  132 . 
         [0031]    The second example waste processing system  120  comprises a reception pit pump  140 , a first separator  142 , a first separator pump  144 , a first settling tank  150 , a buffer tank  152 , a flush reserve tank  154 , a long term storage facility  156  such as a lagoon, a second separator  170 , a batch tank  172 , a batch tank pump  174 , a make-up tank  176 , a primary digester  180 , a secondary digester  182 , a reception pit  190 , a reception pit pump  192 , and a third separator  194 . 
         [0032]    The second example waste processing system  120  operates basically as follows. The reception pit pump  140  pumps waste slurry from the reception pit  132  into the first separator  142 . The first separator  142  causes a first portion of the waste slurry (first thick fraction) to flow into the batch tank  172 , and the first separator pump  144  pumps a second (effluent) portion of the waste slurry (first thin fraction) into the first settling tank  150 . 
         [0033]    The first settling tank  150  causes a third portion of the waste slurry (second thick fraction) to flow into the buffer tank  152  and a fourth portion of the waste slurry (second thin fraction) to flow into the flush reserve tank  154 . If used, the second buffer tank  152  causes a fifth portion of the waste slurry (second thick fraction) to flow into second separator  170 . 
         [0034]    The second separator  170  causes a sixth portion of the waste slurry (third thick fraction) to flow into the batch tank  172  and a seventh portion of the waste slurry (third thin fraction) to flow into the make-up tank  176 . The make-up tank  176  uses part the seventh portion of the waste slurry to form a digester pre-mixture (fourth thick fraction) and allows the digester pre-mixture to flow into the batch tank  172  to mix with the contents of the batch tank  172  (i.e., first and sixth portions of the waste slurry) to form a first digester mixture. The batch tank pump  174  forces the first digester mixture into the primary digester  180 . 
         [0035]    The primary digester  180  breaks the biodegradable material in the first digester mixture down into first digested material. The first digested material is allowed to flow into the reception pit  190 . In addition to processing a portion of the waste slurry, the primary digester  180  may further be configured to release useable energy from the first digester mixture. 
         [0036]    The make-up tank  176  further uses part of the seventh portion of the waste slurry to form a second digester mixture (fourth thin fraction) and allows the second digester mixture to flow into the secondary digester  182 . The secondary digester  182  breaks the biodegradable material in the second digester mixture down into second digested material. In addition to processing a portion of the waste slurry, the secondary digester  182  may further be configured to release useable energy from the second digester mixture. The second digested material is allowed to flow into long term storage  156  such as a storage lagoon. 
         [0037]    The first digested material within the reception pit  190  forms a final digested material. The reception pit pump  192  forces the final digested material into the third separator  194 . The third separator  194  allows a liquid portion of the final digested material to flow into one or both of the settling pond  156  and the flush reserve tank  154 . The third separator  194  further yields dry solids that may be disposed of (e.g., spread directly on soil or used as bedding material). 
         [0038]    The liquids stored in the flush reserve tank  154  are appropriate for use as the flush liquid used by the flush system  122 . Accordingly, the inlet  134  of the flush facility  130  is operatively connected to the flush reserve tank  154 . 
         [0039]    The primary digester  180  and the secondary digester  182  are configured to process digester mixtures having different characteristics. 
         [0040]    In a waste processing system constructed in accordance with the principles of the present invention, the ratio of the percentage of solids in the first digester mixture to the percentage of solids in the second digester mixture is within a first range of approximately 5:1 to 10:1 and in any event should be within a second range of approximately 2:1 to 15:1. In the second example waste processing system  120 , the ratio of the percentage of solids in the first digester mixture to the percentage of solids in the second digester mixture is approximately between 7:1 and 8:1. 
         [0041]    The primary digester  180  may be characterized as a low-rate digester, while the secondary digester  182  may be characterized as a high-rate digester. In particular, in a waste processing system constructed in accordance with the principles of the present invention, the primary digester  180  should completely process the first digester mixture in a first range of approximately 10 to 100 days and in any event should be within a second range of approximately 15 to 40 days. In the second example waste processing system  120 , the primary digester  180  completely processes the first digester mixture in approximately 20 days. On the other hand, the secondary digester  182  should completely process the second digester mixture in a first range of approximately 6 hours to 8 days and in any event should fully process the second digester mixture within a second range of approximately 12 hours to 5 days. In the second example waste processing system  120 , the second digester  182  completely processes the second digester mixture in approximately 1 day. 
         [0042]    The ratio of the digestion rates of the first and second digesters of a waste processing system of the present invention should be within a first range of approximately 1.5:1 to 5:1 and in any event be within a second range of approximately 1.5:1 to 3:1. The ratio of the digestion rates of the example primary digester  180  and the example secondary digester  182  is approximately 2:1. 
         [0043]    A make-up tank of a waste processing system of the present invention should generate the digester pre-mixture such that the first digester mixture has a solid content of within a first range of approximately 6% to 10% and, in any event, the solid content of the first digester mixture should be within a second range of approximately 4% to 20%. In the second example waste processing system  120 , the example make-up tank  176  creates a digester pre-mixture such that the first digester mixture has a solid content of approximately 7% to 8%. On the other hand, the make-up tank of a waste processing system of the present invention should generate a second digester mixture having a solid content of within a first range of approximately 0.5% to 2% and, in any event, the solid content of the second digester mixture should be within a second range of approximately 0.25% and 4%. In the second example waste processing system  120 , the example make-up tank  176  creates a second digester mixture having a solid content of approximately 1%. 
         [0044]    The use of two separate digesters having different characteristics optimizes the overall digestion rate of the second example waste processing system  120 . The second example waste processing system  120  thus yields improved rates at which the waste slurry is processed into flush liquid appropriate for use by the flush system and dry solids appropriate for disposal by spreading directly on the soil. 
       III. Third example 
       [0045]    In the second example waste processing system  120  described above, gravity will cause the solids within the waste slurry or material within the first settling tank  150  to settle towards the bottom of the first settling tank  150 , and removal of the solids portion is performed by allowing material to flow from the bottom of the tank (i.e., bottom removal). Removal of the liquid portion is performed by skimming or otherwise removing liquids off of the top of the tank. 
         [0046]    One problem with such settling tank type separators is that the waste slurry collected by the first settling tank  150  will tend to stratify over time if the removal of the solids and liquid portions of the waste slurry is not properly managed. In particular, if the rate at which the waste slurry is removed from the bottom of the first separator (i.e., solids portion) is too low, a layer or zone of heavy and/or emulsified solids may collect towards the bottom of the first settling tank  150 . However, if the rate at which the waste slurry is removed from the bottom of the first separator (i.e., solids portion) is too high, the level of liquids in the material removed from the bottom of the first settling tank  150  may be too high for proper functioning of the primary (low rate) digester  180 . 
         [0047]    A mechanical rake or other means of collecting the solids within the first settling tank  150  may be used but requires significant capital investment and operational and maintenance costs. More typically, then, the second separator  170  and/or make-up tank  176  are used instead of a mechanical stirring system to allow the solids portion of the material in the first settling tank  150  to be removed at a sufficiently high rate to prevent build-up of solids within the first settling tank  150 . The optional second separator  170  and/or optional make-up tank  176  remove liquids from the solids portion removed from the first settling tank for processing by the secondary (high rate) digester  182  yet maintain the level of the removed solids within the range necessary for satisfactory functioning of the primary (low rate) digester  180 . 
         [0048]    An alternative to the second example waste processing system  120  is depicted in  FIG. 3  of the drawing. In particular,  FIG. 3  depicts a third example waste processing system  220  incorporating the principles of the present invention. The third example waste processing system  220  operates in the same basic manner as the second example waste processing system  120  but does not use a second separator or make-up tank upstream of the secondary digester. 
         [0049]    In particular, the third example waste processing system  220  is also adapted to be used with a flush system  222 . Again, the example flush system  222  is or may be conventional and comprises a dairy flush facility  230  and a reception pit  232 . The flush facility  230  comprises an inlet  234  through which flush fluid is introduced and an outlet  236  through which waste slurry is collected. During use of the flush system  222 , the flush liquid is mixed with the animal waste to form waste slurry. The waste slurry flows through the outlet  236  and is collected in the reception pit  232 . 
         [0050]    The third example waste processing system  220  comprises a reception pit pump  240 , a first separator  242 , a first separator pump  244 , a first settling tank  250 , a flush reserve tank  254 , a long term storage facility  256  such as a lagoon, a batch tank  272 , a batch tank pump  274 , a primary digester  280 , a secondary digester  282 , an optional reception pit  290 , a reception pit pump  292 , and a third separator  294 . 
         [0051]    In the third example waste processing system  220 , careful management of the removal of the first portion of the waste slurry from the first settling tank  250  is used as an alternative to the subsequent removal of excess liquids using the separator systems such as the second separator  170  and/or make-up tank  176 . In particular, if first settling tank is managed with sufficient care, the first portion of the waste slurry may be removed from the first settling tank  250  such that build up of solids within this first settling tank  250  is prevented and such that the level of liquids within the removed solids portion does not exceed the level that might inhibit proper functioning of primary digester  280 . In this case, the removal of the first portion of the waste slurry from the first settling tank  250  may be controlled manually or may be performed automatically by a combination of sensors, controllers, and valves. In this case, a portion of the thin portion from the first settling tank  250  would go to the secondary digester  282 . 
       IV. Fourth Example 
       [0052]    Additionally, a waste processing system of the present invention may be implemented entirely as a continuous rather than a patch processing system. In particular, depicted in  FIG. 4  of the drawing is a fourth example waste processing system  320  constructed in accordance with the principles of the present invention. The fourth example waste processing system  320  operates in the same basic manner as the third example waste processing system  220  but does not use a batch tank upstream of the primary digester. 
         [0053]    The fourth example waste processing system  320  is adapted to be used with a flush system  322 . Again, the example flush system  322  is or may be conventional and comprises a dairy flush facility  330  and a reception pit  332 . The flush facility  330  comprises an inlet  334  through which flush fluid is introduced and an outlet  336  through which waste slurry is collected. During use of the flush system  322 , the flush liquid is mixed with the animal waste to form waste slurry. The waste slurry flows through the outlet  336  and is collected in the reception pit  332 . 
         [0054]    The fourth example waste processing system  320  comprises a reception pit pump  340 , a first separator  342 , a first separator pump  344 , a first settling tank  350 , a flush reserve tank  354 , a long term storage facility  356  such as a lagoon, a primary digester  380 , a secondary digester  382 , an optional reception pit  390 , a reception pit pump  392 , and a third separator  394 . In the example depicted in  FIG. 4 , the solids output of the first separator  342  flows or is pumped directly into the primary digester  380 , while the solids output of the first settling tank  350  flows or is pumped directly into the secondary digester  382 . Careful management of the removal of the solids portion of the material in the first separator  342  and in the first settling tank  350  allows the fourth example waste processing system  320  to operate in a continuous manner. Again, the removal of the solids portions of the materials in first separator  342  and in the first settling tank  350  may be controlled manually or may be performed automatically by a combination of sensors, controllers, and valves. 
       V. Fifth example 
       [0055]    Another alternative to the second example waste processing system  120  is depicted in  FIG. 5  of the drawing. In particular,  FIG. 5  depicts a fifth example waste processing system  420  incorporating the principles of the present invention. The fifth example waste processing system  420  operates in the same basic manner as the second example waste processing system  120  but does not use a buffer tank upstream of the secondary digester. 
         [0056]    In particular, the fifth example waste processing system  420  is also adapted to be used with a flush system  422 . Again, the example flush system  422  is or may be conventional and comprises a dairy flush facility  430  and a reception pit  432 . 
         [0057]    The flush facility  430  comprises an inlet  434  through which flush fluid is introduced and an outlet  436  through which waste slurry is collected. During use of the flush system  422 , the flush liquid is mixed with the animal waste to form waste slurry. The waste slurry flows through the outlet  436  and is collected in the reception pit  432 . 
         [0058]    The fifth example waste processing system  420  comprises a reception pit pump  440 , a first separator  442 , a first separator pump  444 , a first settling tank  450 , a flush reserve tank  454 , a long term storage facility  456  such as a lagoon, a second separator  470 , a batch tank  472 , a batch tank pump  474 , a make-up tank  476 , a primary digester  480 , a secondary digester  482 , an optional reception pit  490 , a reception pit pump  492 , and a third separator  494 . 
         [0059]    The fifth example waste processing system  420  operates in the same basic manner as the second example waste processing system  120  described above, but no buffer tank is arranged between the first settling tank  450  and the second separator  470 .