Disclosed are methods to convert nitrogen in a wastewater stream to an arginine-enriched polypeptide, which includes supplying a nitrogen-enriched wastewater stream; culturing an organism in the waste stream that produces an arginine-enriched polypeptide to produce the arginine-enriched polypeptide; and removing the produced arginine-enriched polypeptide from the wastewater stream to create a processed wastewater stream. The methods also include a method to make an arginine-enriched polypeptide enriched fertilizer by flowing the effluent from the culturing step over a cation exchange material to allow binding of the arginine enriched polypeptide to the cation exchange material; and collecting arginine-enriched polypeptide to form the arginine-enriched polypeptide enriched fertilizer. The method also includes enhancing the growth or production of a plant using the fertilizer containing the arginine-enriched polypeptide.
