Process for producing fertilizer from a biogas stream

A process for producing an organic fertilizer, comprising:

• introducing a stream of sulfur dioxide into a first column;
• routing an ammonia-containing gas stream into the first column, wherein the ammonia-containing gas stream is circulated through an aqueous solution containing bisulfite ions in the first column, and further wherein the ammonia-containing gas stream reacts with the sulfur dioxide and the aqueous solution containing bisulfite ions to produce an aqueous solution comprising ammonium bisulfite and diammonium sulfite;
• wherein the first column contains at least two contact zones, and wherein the sulfur dioxide is introduced near a first contact zone and the ammonia-containing gas stream is introduced near a second contact zone, and
• further comprising maintaining a higher pH in the first contact zone and a lower pH in the second contact zone;
• routing a portion of the aqueous ammonium bisulfite and diammonium sulfite solution to a second column;
• introducing a biogas stream into the second column, wherein the biogas stream comprises hydrogen sulfide;
• and
• contacting the routed aqueous ammonium bisulfite and diammonium sulfite solution and biogas stream in the second column to substantially scrub the hydrogen sulfide from the biogas stream and produce an effluent stream containing aqueous ammonium thiosulfate.