Organic recycling with metal addition

Abstract

The invention is directed to methods for producing a granular nitrogen fertilizer from an organic material comprising adding a metallic salt to said organic material to form a slurry. Preferably the organic material comprises dewatered biosolids and contains water from a scrubber. Metallic salts that can be used comprise a salt of iron, zinc, or a mixture thereof. Preferred iron salts comprises ferric sulfate or ferric oxide, and preferred zinc salts comprises zinc sulfate or zinc oxide. Preferably, the metallic salt is mixed with an acid such as sulfuric acid to form an acidified metal salt. Slurry pH ranges from approximately 2-2.5. The acidified metal salt is added to the organic material in sufficient quantity to lower viscosity of the slurry such that the resulting fluid does not hinder fluid flow during operation. When the metallic salt comprises acidified ferric sulfate or ferrous sulfate, sufficient iron can be present to produce a fertilizer product with 0.1 weight percent to 10 weight percent iron sulfate calculated on a dry weight basis. The invention is also directed to fertilizer products made by the methods of the invention. Preferred products are granules and the metallic salt increases product hardness. Fertilizer granules preferably contain metal that is bioavailable to a plant when used as a fertilizer. Solubility of the metal of the product in water is enhanced, and the product is low staining.

1 . A method for producing a granular nitrogen fertilizer from an organic material comprising adding a metallic salt to said organic material to form a slurry.  
     
     
         2 . The method of  claim 1 , wherein the organic material comprises biosolids.  
     
     
         3 . The method of  claim 1 , wherein the slurry comprises dewatered biosolids.  
     
     
         4 . The method of  claim 3 , wherein the dewatered slurry of biosolids contains scrubber water.  
     
     
         5 . The method of  claim 1 , wherein the metallic salt comprises a salt of iron, zinc, or a mixture thereof.  
     
     
         6 . The method of  claim 5 , wherein the iron salt comprises ferric sulfate or ferric oxide.  
     
     
         7 . The method of  claim 5 , wherein the zinc salt comprises zinc sulfate or zinc oxide.  
     
     
         8 . The method of  claim 1 , wherein the metallic salt is mixed with an acid to form an acidified metal salt.  
     
     
         9 . The method of  claim 8 , wherein the acidified metal salt is added in sufficient quantity to lower viscosity of the slurry.  
     
     
         10 . The method of  claim 1 , wherein the slurry is mixed at a sufficient concentration and consistency to form a fluid that does not hinder slurry flow during operation.  
     
     
         11 . The method of  claim 1 , further comprising adding sulfuric acid.  
     
     
         12 . The method of  claim 11 , wherein the sulfuric acid is mixed with the metallic salt prior to adding to said organic material.  
     
     
         13 . The method of  claim 11 , wherein the sulfuric acid is mixed with ferrous oxide to produce ferrous sulfate such that said slurry has a resultant pH of approximately 2.0 to 2.5.  
     
     
         14 . The method of  claim 11 , wherein the sulfuric acid is mixed with ferric oxide to produce ferric sulfate such that said slurry has a resultant pH of approximately 2.0 to 2.5.  
     
     
         15 . The method of  claim 11 , wherein the metallic salt comprises acidified ferric sulfate or ferrous sulfate which is mixed with the organic material such that sufficient iron is present to produce a fertilizer product with 0.1 weight percent to 10 weight percent iron sulfate calculated on a dry weight basis.  
     
     
         16 . The method of  claim 15 , wherein the fertilizer product has between 0.5 weight percent and 5 weight percent iron sulfate calculated on a dry weight basis.  
     
     
         17 . The method of  claim 15 , wherein the fertilizer product has between 1 weight percent to 3 weight percent iron sulfate calculated on a dry weight basis.  
     
     
         18 . The method of  claim 11 , wherein the sulfuric acid is added to the organic material prior to reaching a mix tank and at a rate of approximately 1.75 percent of a total feed rate to result in a pH range of 3.0 to 3.5.  
     
     
         19 . The method of  claim 1 , wherein the slurry is pumped into a shear mix tank that contains a high shear rotary agitator which turns at a speed sufficient to produce high shear.  
     
     
         20 . The method of  claim 19 , further comprising passing the slurry from said shear mix tank to a holding or equilibrium tank containing an agitator.  
     
     
         21 . The method of  claim 20 , wherein the holding or equilibrium tank containing the agitator is capable of providing approximately 2 hours of storage for the slurry.  
     
     
         22 . The method of  claim 20 , wherein the holding or equilibrium tank is operated to maintain a pH of 3.0 to 4.0 with a solids content of between 15 percent and 28 percent solids.  
     
     
         23 . The method of  claim 22 , wherein the solids content is from 20 percent to 23 percent.  
     
     
         24 . The method of  claim 1 , wherein the metallic salt chemically bonds with one or more elements of the slurry.  
     
     
         25 . The method of  claim 24 , wherein the metallic salt is an iron salt that bonds with ammonium sulfate or ammonium phosphate present in the slurry.  
     
     
         26 . The method of  claim 1 , wherein the metallic salt comprises acidified ferrous or ferric salts to reduce sulfur compounds in the slurry.  
     
     
         27 . The method of  claim 26 , wherein the acidified ferrous or ferric salts reduce dust formation during operation.  
     
     
         28 . The method of  claim 26 , wherein the acidified ferrous or ferric salts reduce odor during operation.  
     
     
         29 . The method of  claim 1 , wherein adding the metallic salt enhances granulation formation of the slurry.  
     
     
         30 . The method of  claim 1 , wherein the metallic salt initiates chemical hydrolysis of organic molecules in the slurry.  
     
     
         31 . The method of  claim 1 , wherein the metallic salt drives reduced sulfur compounds out of the organic material reducing odorant sources in a fertilizer product.  
     
     
         32 . The method of  claim 1 , wherein the metallic salt is added to said organic material in a pipe-cross reactor.  
     
     
         33 . The method of  claim 32 , wherein the metallic salt enhances reaction kinetics of the pipe-cross reactor.  
     
     
         34 . The method of  claim 32 , wherein the metallic salt lowers viscosity of the slurry such that operation of the pipe-cross reactor is more controllable than without the metallic salt.  
     
     
         35 . The method of  claim 1 , wherein the metallic salt is added in a tubular reactor.  
     
     
         36 . A fertilizer product produced by the method of  claim 1 .  
     
     
         37 . The product of  claim 36 , wherein the metallic salt is acidified ferrous or ferric salts.  
     
     
         38 . The product of  claim 37 , wherein the acidified ferrous or ferric salts increase product hardness.  
     
     
         39 . The product of  claim 36 , which has a crush weight of greater than 6 pounds.  
     
     
         40 . The product of  claim 39 , which has a crush weight of greater than 7 pounds.  
     
     
         41 . The product of  claim 36 , wherein metal of the metallic salt is available to a plant.  
     
     
         42 . The product of  claim 41 , wherein solubility of the metal in water is enhanced.  
     
     
         43 . The product of  claim 36 , which is a low staining product.