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.