Production of Ammonium Sulfate Fertilizer Using Acid Spray Wet Scrubbers

Abstract

Significant nitrogen loss as ammonia emissions from animal facilities is resulting in severe environmental problems while supply of nitrogen (N) fertilizer for crop production becomes a challenge due to the fact that commercial nitrogen productions use unsustainable natural gas as the primary feedstock. This study investigates an alternative method for production of ammonium sulfate (AS) fertilizer using acid spray wet scrubbers. Ammonium sulfate is produced as a byproduct of mitigation of ammonia emissions from animal production facilities using acid spray wet scrubbers, in which dilute sulfuric acid (H₂SO₄) reacts with ammonia-laden air from exhaust fans of animal facilities. Effluents of two scrubbers: one installed at a deep-pit swine facility and one at a commercial poultry manure composting facility, were analyzed for their characteristics and AS fertilizer contents. Short-term batch operation of the swine and poultry scrubbers resulted in effluents with maximum AS concentrations of 18.7% (w/v) and 36.3%, respectively. Aside from AS, other essential elemental contents were also found in the scrubber effluent, such as Na, Mg, Al, P, K, Ca, Fe, and Mn. Production rates of AS were calculated based on nitrogen mass balance analyses of air streams and were compared to actual production observed during the scrubber operations. The maximum AS production rates were estimated as 1.53 kg d^-1 and 60.96 kg d^-1 for swine and poultry operations, respectively.  However, only 18% and 32% were obtained from actual operation. This discrepancy is primarily due to errors in the estimation and liquid losses from leakage, salt precipitation inside the scrubber during short-term batch operation, and air entrainment. The estimated production costs for both swine and poultry scrubber operations at the estimated production rates are $5.74 and $1.46 per kg AS, respectively. Further study to improve the scrubber design to eliminate leaks and to operate continuously is needed to increase AS yield and profitability of the process.