Abstract:
A method of producing an organic based fertilizer and usable water from animal waste includes the step of separating the animal waste into liquid waste and solid waste. The liquid waste is clarified to produce a supernatant and a sludge which is pressed into a filter cake. Ammonia is extracted from the supernatant to produce ammonium sulfate and an aqueous solution. The aqueous solution is filtered to produce a concentrate and water filtrate. The water filtrate may be used as drinking and washing water. The filter cake, ammonium sulfate, and concentrate may be used to supplement to the solid waste which is pelletized into the organic based fertilizer. In alternative embodiments a portion of the supernatant and aqueous solution may be used as a liquid fertilizer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of provisional application 61/156,375 filed in the United States Patent and Trademark Office on Feb. 27, 2009, the complete disclosure of which is incorporated herein by reference and priority to which is claimed pursuant to 35 U.S.C. section 120. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a method of producing an organic based fertilizer and, in particular, to a method of producing an organic based fertilizer from animal waste in a closed loop system that conserves water. 
         [0004]    2. Description of the Related Art 
         [0005]    In modern agricultural practice, it has become usual to employ an agricultural operation as an intensive feeding operation for raising hundreds or even thousands of livestock, for example swine and bovine animals, at a single location. Consequently, large amounts of animal waste are produced at such locations. The disposal of this waste in a hygienic and inoffensive manner is problematic. 
         [0006]    More particularly, it has been suggested that hogs produce more than four times as much waste as humans. It has, for example, been planned to initiate a hog farm containing 2,000,000 hogs, which will produce an amount of waste equivalent to that produced by the city of Los Angeles. The current pig population of North Carolina is four times that number. Accidents in North Carolina, in which millions of gallons of hog excreta were released into the countryside, have drawn attention to the problems involved in the disposal of such waste. Applications for permits to construct large hog farms have been denied because of concerns about odours and waste disposal. 
         [0007]    Animal waste, including hog waste, has traditionally been disposed of by spreading it over agricultural land as a liquid fertilizer. For sufficiently large cropped land bases this method of disposal can be performed safely. However, in areas of high population density or where multiple farms are closely clustered, and the land base is therefore relatively small, problems arise. For example, excess nutrients cannot be absorbed by crops and leach into ground water and surface water. 
         [0008]    When land application is prevented, for example, because the ground is frozen or saturated with water and/or nutrients, the waste must be stored, usually in large pits, with consequential costs and environmental risk. 
         [0009]    As an alternative to land disposal, it is also common practice to compost the waste. For this purpose, the waste is separated into solid waste and liquid waste through the use of inclined screens, sometimes followed by the use of belt or filter presses. These methods produce an output containing about 30% solid material at best. This is then mixed with a bulking material to facilitate aeration and an appropriate C:N ratio, and deposited in windrows for stabilization, over a period of about 45 to 60 days, by composting. This process may not ensure that pathogens in the waste are killed and the windrows are often odorous and may attract birds, rodents and vermin. The liquid, approximately 90% of the total waste still has to be dealt with through land application. 
         [0010]    The challenges involved in the treatment of animal waste include the destruction of pathogens, the controlled extraction of ammonium and other plant nutrients, and the disposal of organic matter. 
         [0011]    It is known, from U.S. Pat. No. 4,093,544, issued Jun. 6, 1978, to David S. Ross, the full disclosure of which is incorporated herein by reference, to remove ammonium from wastewater by firstly increasing the pH value of the wastewater, then desorbing ammonium by vacuum and subsequently absorbing the desorbed ammonium in liquid having a pH value and temperature substantially less than that of the original wastewater. 
         [0012]    It is further known from U.S. Pat. No. 5,914,040, issued Jun. 22, 1999, to Yvette Pescher et al., the full disclosure of which is also incorporated herein by reference, to purify a medium containing organic waste, for example animal waste, by subjecting the medium to treatment with an oxidizing agent, treatment with a flocculating agent, and treatment with at least one polyelectrolyte. The effluent thus obtained is filtered to provide a filtration cake and a filtrate. 
         [0013]    It is still further known from U.S. Pat. No. 6,916,426, issued Jul. 12, 2005, to Van Slyke et al., the full disclosure of which is also incorporated herein by reference, that the extraction of nitrogen, potassium, and phosphorus from animal waste is substantially enhanced if the animal waste is treated promptly after production of the waste by the animals. More particularly, it is known that potassium is present in animal waste material in the form of an insoluble potassium urate, and a substantial amount of the potassium in animal waste material can be extracted in a solid form, as potassium urate, before microbial action breaks down the potassium urate to leave potassium and ammonium in solution. Extracted urates are then available for inclusion in a fertilizer. When the fertilizer is used on land, the microbes in the soil break down these urates, releasing the potassium and ammonia, but at a rate less than that at which these nutrients would be released in the soil if dissolved in water. 
         [0014]    It is yet still further known from U.S. Pat. No. 7,232,036, issued Jun. 19, 2007, to Van Slyke et al., the full disclosure of which is also incorporated herein by reference, that solid waste may be rapidly separated from liquid waste using an inclined conveyor belt system. 
       SUMMARY OF THE INVENTION 
       [0015]    It is an object of the present invention to provide an improved system and method for producing an organic based fertilizer. 
         [0016]    It is a particular object of the present invention to provide a system and method for producing an organic based fertilizer and usable water from swine and bovine waste collected on an agricultural operation. 
         [0017]    In one embodiment of the system and method disclosed herein animal waste is collected at least once daily from a barn or other animal enclosure on an agricultural operation. Preferably solid waste is separated from liquid waste in the barn. The solid waste is directed to a bio-mass fuelled dryer. The dried solid waste may be used as a bio-mass fuel for the system, or supplemented with concentrated by-products of the treatment of the liquid waste and other nutrients, as required, to produce a commercially viable organic based fertilizer. If the solid waste is used as a bio-mass fuel for the system the resulting ash may be added as a supplement to the solid waste prior to pelletizing the solid waste into a fertilizer. If the solid waste is not burned as a fuel for the system other suitable bio-mass fuel may be used. 
         [0018]    The liquid waste is treated with chemicals for coagulation and flocculation to assist the settling of any particulates remaining in the liquid waste. The particulates are then collected and may be added as a supplement to the solid waste prior to pelletizing the solid waste into a fertilizer. After heating and pH adjustments, the liquid waste is passed against a gas transfer membrane to remove ammonia from the liquid waste. Once the ammonia passes through the membrane it is exposed to sulfuric acid to produce ammonium sulfate which may also be added as a supplement to the solid waste prior to pelletizing the solid waste into a fertilizer. The remaining liquid waste is passed through a direct contact distillation membrane to filter water in the liquid waste from the total dissolved solids in the liquid waste. The total dissolved solids may also be added as an additional supplement to the solid waste prior to pelletizing the solid waste into a fertilizer. 
         [0019]    The water filtrate is treated with pH adjustments, cooling, and UV sterilization to produce water which is usable for both barn washing and animal drinking. This may significantly reduce fresh water consumption by over 50%. 
         [0020]    In preferred embodiments the system operates continuously and is designed to process collected animal waste in 24 hours. The system collects a majority of the solid waste and, after any losses from using some the solid waste as a bio-mass fuel, the collected solid waste is pelletized into fertilizer. This produces a commercially viable fertilizer which may be sold to help offset operational costs, i.e nutrient imbalances on other agricultural operations may be rectified by transporting the dry pelletized fertilizers off-site. The resulting water filtrate may be diverted for irrigation at points dictated by the economics of the agricultural operator or recycled back to the barn for animal washing or drinking. 
         [0021]    The system and method disclosed herein provide the advantage of reducing odours by rapidly separating the solid waste from the liquid waste in either the barn or a treatment building connected to, or adjacent, the barn or another enclosure housing livestock. This reduces the contact between urease found in the solid waste and urea found in the liquid waste thereby minimizing release of gases which are harmful to humans, animals, and the environment. Odours and greenhouse gases are also reduced by minimizing anaerobic activity which occurs in longer term storage methods common to other treatment systems currently in use. Agricultural operation can therefore exist closer to urban areas thereby reducing the cost of transporting the livestock to market. 
         [0022]    Furthermore, water consumption may be significantly reduced on the agricultural operation through the recycling of water filtrate to the barn or another installation on the agricultural operation. Large scale agricultural operations will also not require disposal acreage for the storage and disposal of liquid manure slurries now used in the production of fertilizer. 
         [0023]    Additional advantages of the system and method disclosed herein will be apparent to a person skilled in the art. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0024]    The invention will be more readily understood from the following description of preferred embodiments thereof given, by way of example only, with reference to the accompanying drawings, in which: 
           [0025]      FIG. 1  is a schematic diagram showing a first embodiment of an improved system and method for producing an organic based fertilizer and usable water from animal waste collected with in-barn conveyors on an agricultural operation; and 
           [0026]      FIG. 2  is a schematic diagram showing a second embodiment of an improved system and method for producing an organic based fertilizer and usable water from animal waste collected by scraping or flushing on an agricultural operation. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    Referring to the drawings and first to  FIG. 1  this is a schematic diagram showing a first embodiment of an improved system and method for producing an organic based fertilizer and usable water from animal waste collected on an agricultural operation. In this example, animal waste is collected in a barn  100  but in other embodiments animal waste may be collected anywhere on the agricultural operation. Preferably the animal waste is removed from the barn  100  using a conveyor system  190  similar to the type disclosed in U.S. Pat. No. 7,232,036, issued Jun. 19, 2007, to Van Slyke et al., the full disclosure of which is incorporated herein by reference. This allows for the rapid separation of solid wastes from liquid wastes. 
         [0028]    In the example shown in  FIG. 1 , the conveyor system  190  disclosed by Van Slyke et al. is used to rapidly separate solid waste  102  from liquid waste  104  in the barn  100 . The solid waste  102  is collected in a solid waste storage tank  106  and the liquid waste  104  is directed to a liquid waste storage tank  108 . The solid waste  102  is directed from the solid waste storage tank to a dryer  110 . Some of the dried solid waste may be used as a bio-mass fuel to power the system. However, in this example, a majority of the solid waste  102  is pelletized into a fertilizer while other available bio-mass fuels are used to power the system by fuelling the burners of dryer and heaters disclosed herein. 
         [0029]    The liquid waste  104  is agitated in the liquid waste storage tank  108  to avoid settlement of any particulates in the liquid waste  104 . The liquid waste  104  is then treated with a first polymer  112  as it is directed to a first clarifier  114 . The first polymer  112  is a standard coagulating and/or flocculating agent readily available from chemical supply companies. For example, the first polymer  112  may be a polyacrylamide or polyamine. The purpose of the first polymer  112  is to accumulate suspended particulates in the liquid waste  104  so they can be more easily settled in the first clarifier  114 . Sludge  116  from the first clarifier  114  is directed to a sludge storage tank  118  from which it is then directed through a first heater  120  to a filter press  122 . Filter cake  124  from the filter press  122  is dried in the dryer  110  and used to supplement the solid waste material being pelletized into a fertilizer. In this example, the filter press  122  should be capable of producing a filter cake with a solid matter content of at least 30%. Filtrate  126  from the filter press  122  may be re-introduced into the first clarifier  114  for further processing. 
         [0030]    Supernatant  128  from the first clarifier  114  may be released for irrigation as will be discussed in greater detail below. However, in this example, most of the supernatant  128  is treated with lime  130  (to increase pH) and a second polymer  132  as it is directed to a second clarifier  134 . The second polymer  132  is a standard coagulating and/or flocculating agent readily available from chemical supply companies. For example, the second polymer  132  may be a polyacrylamide or polyamine. Lime sludge  135  from the second clarifier  134  is directed to the sludge storage tank  118  from which it is directed to the first heater  120  and filter press  122 . As disclosed above, filter cake  124  from the filter press  122  is used to supplement the solid waste material being pelletized into a fertilizer. Filtrate  126  from the filter press  122  may be re-introduced into the first clarifier  114  for further processing. 
         [0031]    Alternatively, the first clarifier  114  may be bypassed or even removed from the system all together. Liquid waste  104  from the liquid waste storage tank  108  would then be treated with lime  130  and the second polymer  132  as it is directed to the second clarifier  134 . This would occur in situations where supernatant  128  from the first clarifier  114  will not be released for irrigation. In other embodiments, the clarifiers  114  and  134  may be provided with a skimmer for collecting any floating materials in the liquid waste which will not settle in the clarifiers  114  and  134 , for example, spilled feed or diarrhea which comprises undigested feed. The collected floating materials are directed to the sludge storage tank  118  for further processing. Other means to collect floating materials may also be employed such as dissolved air flotation or charged air flotation. 
         [0032]    Supernatant  136  from the second clarifier  134  is passed through a second heater  138  before being passed through an ammonia extractor  140 . In some cases, the supernatant  136  may be subject to filtration prior to being passed through the ammonia extractor  140 , particularly; if the supernatant  136  contains solid particulates. The solid particulates would then be returned to the sludge storage tank  118  for further treatment. In this example, the ammonia extractor  140  includes a series of gas transfer membranes  142   a ,  142   b  and  142   c  which allow the ammonia gas to transfer and make contact with sulfuric acid  150  on the other side of the membranes and combine to make ammonium sulfate  146  and an aqueous solution  148 . In other embodiments other methods of ammonia extraction may be used and other ammonium salts, such as ammonium nitrate, may be produced. The ammonium salts may be used to supplement the solid waste material being pelletized into a fertilizer. The aqueous solution  148  may be released for irrigation as will be discussed in greater detail below. However, in this example, most the aqueous solution  148  is treated with sulfuric acid  150  for pH normalization and both the aqueous solution  148  and ammonium sulfate  146  are passed through a third heater  152 . 
         [0033]    After being heated the aqueous solution  148  is passed through Direct Contact Distillation Membranes  154   a  and  154   b , or any other system such as a nanotube filtering system, that allows drinking water to pass through the membrane. Such systems typically heat a solution causing water vapour from the warm side to pass through the membrane and condense with a colder solution on the cold side. An example of a suitable Direct Contact Distillation Membrane is disclosed in United States Patent Application Publication Number 2006/0076294 A1 which was filed by Sirkar et al. on Jul. 26, 2006 and the full disclosure of which is incorporated herein by reference. The Direct Contact Distillation Membranes  154   a  and  154   b  separate the aqueous solution  148  into concentrated dissolved solids or concentrate  156  and a drinking water filtrate  158 . The concentrate  156  is used to supplement the solid waste material being pelletized into a fertilizer. The drinking water filtrate  158  is exposed to UV light in a sterilizer  160  and passed through a cooler  162  prior to being recycled back as return water  164  into the barn  100  for washing or drinking. It is desirable for the return water  164  to have less than 3,000 ppm total dissolved solids. 
         [0034]    Referring back to the solid waste  102 , the dryer  110  lowers the moisture level of the solid waste  102 , filter cake  124 , and concentrate  156  to a suitable level to pelletize. Dryer exhaust of warm moist air and dust is directed to a dust collector  166  which separates the dust for return to the solid wastes for pelletizing while directing the air stream to a bio-filter  168  to further condense moisture and reduce odours before being released as air  170 . Condensate  172  from the bio-filter may be re-introduced into the second clarifier  134  for further treatment. 
         [0035]    If any of the dried solid waste is used as a bio-mass fuel to power the system, the ash  174  may also be used to supplement the solid waste material being pelletized into a fertilizer. Likewise ash from any bio-mass fuel may be used to supplement the solid waste material being pelletized into a fertilizer. Other foreign supplements  176  may also be used to supplement the solid waste material being pelletized into a better balanced fertilizer for the market. The supplemented dried solid waste is pelletized and cooled in a pelletizer  178 . The pelletized fertilizer may be kept in an on-site storage  180 . 
         [0036]    Referring now to  FIG. 2 , this is a schematic diagram showing a second embodiment of an improved system and method for producing an organic based fertilizer and usable water from animal waste collected on an agricultural operation. In  FIG. 2  like components have been given like reference numerals as in  FIG. 1  with the expectation that the reference numerals are in the  200  series as opposed to the  100  series, i.e. the barn is given reference numeral  100  in  FIG. 1  and reference numeral  200  in  FIG. 2 . Similarly the dryer has been given reference numeral  110  in  FIG. 1  and reference numeral  210  in  FIG. 2 . 
         [0037]    In the example shown in  FIG. 2 , animal waste is collected by scraping or flushing the gutters of a barn  200 . This results in slurry  201  of solid waste and liquid waste which may contain bedding or stringy components. The slurry  201  is passed through a chopper pump  203  to promote homogeneity. The collected slurry  201  is stored and agitated in a slurry storage tank  205  to avoid the settlement of any particulates. The slurry is then passed through a heater  207  and treated with a polymer  209  as it is directed to a filter press  222 . The polymer  209  is a standard coagulating and/or flocculating agent readily available from chemical supply companies. For example, the polymer  209  may be a polyacrylamide or polyamine. The purpose of the purpose of the polymer is to accumulate suspended particulates in the slurry  205  so they can be more easily processed by the filter press  222 . 
         [0038]    Filter cake  224  from the filter press  222  is directed to a dryer  210  and is treated in a manner substantially similar as described above for the solid waste  102  in the first embodiment of the system and method disclosed herein. 
         [0039]    The filtrate  226  from the filter press  222  is directed to a first clarifier  214  or alternatively re-introduced into the slurry storage tank  205  to assist filter press operation or returned to the barn  200  as a replacement for flushing volumes. If the filtrate is directed to the first clarifier  214  it is treated in a substantially similar manner as described above for the liquid waste  104  in the first embodiment of the system and method disclosed herein. 
         [0040]    In both embodiments disclosed herein the supernatant  128  or  228  may be released from the system for irrigation through an outlet port  182  or  282  after passing through the first clarifier  114  or  214 . This results in a liquid fertilizer with low suspended solids and a nitrogen content that is desirable for some crops. The aqueous solution  148  or  248  may also be released for irrigation after passing through the ammonia extractor  140  or  240 . Heat levels of the aqueous solution  148  or  248  can be altered by varying the position of an outlet port  184  or  284  to a point after the third heater  152  or  252 . This also results in a liquid fertilizer with low suspended solids and a nitrogen content that is desirable for some crops. 
         [0041]    The system disclosed herein accordingly provides a multistep substantially closed loop system that provides flexibility to an operator of an agricultural operation. Nutrients from solid waste may be packaged in a form that may be easily transported and sold. However, the system also allows for varied uses of liquid wastes as well. 
         [0042]    If the operator desires irrigation water with all dissolved nutrients and minimal suspended solids then the supernatant  128  or  228  is drawn off after passing through the first clarifier  114  or  214 . 
         [0043]    If the operator desires irrigation water with ammonia and some dissolved nutrients withdrawn then the aqueous solution  148  or  248  is drawn off after pH normalization with sulfuric acid  150  or  250 . In this situation the dosages of the sulfuric acid  150  or  250  as well as the lime  130  or  230  and the second polymer  132  or  232  may be varied to meet the operator&#39;s pH requirements. This would provide a liquid fertilizer by-product of ammonium sulfate which may be used by the operator or sold off-set operational costs. 
         [0044]    If the operator desires drinking and washing water for animals the filtrate  158  or  258  from the Direct Contact Distillation Membranes should have acceptable pathogen levels. However, as a precaution, further sterilization of the filtrate  158  or  258  is done using UV light in the sterilizer  160  or  260 . Also, since animals prefer cool drinking water the filtrate  158  or  258  is also passed through the cooler  162  or  262  prior to being return to the barn  100  or  200  as return water  164  or  264 . 
         [0045]    In the embodiment of  FIG. 1 , by-products of the treatment of the liquid waste  104  are re-introduced into the system during the treatment of the solid waste  102  in order to preserve nutrients and avoid other disposal methods. 
         [0046]    It will be understood by a person skilled in the art that many of the details provided above are by way of example only, and are not intended to limit the scope of the invention which is to be determined with reference to following claims.