A review of ammonia emission mitigation techniques for concentrated animal feeding operations

Several approaches have been suggested and evaluated for reducing ammonia emissions from excreted animal manure: reducing nitrogen excretion through dietary manipulation, reducing volatile ammonia in the manure to stop ammonia loss, and segregating urine from faeces to reduce contact between urease and urine. When urine–faeces segregation is not an option, urease inhibitors can also be used to reduce or eliminate the hydrolysis of urea into ammonia. Methods for reducing the more volatile ammonia in manure include the reduction of pH, which shifts the equilibrium in favour of ammonium over ammonia; use of other chemical additives that bind ammonium-N; and the use of biological nitrification–denitrification to convert ammonium into non-volatile N-species such as nitrite, nitrate, or gaseous nitrogen. Other methods for mitigating ammonia emissions target emitting surfaces, and include capturing air (using physical covers) and treating the captured air to remove ammonia (using bio-filters or bio-covers, and scrubbers), and direct manure injection or incorporation into the soil. Manure collection facility designs and appropriate facility management are also essential for abating ammonia emissions. This paper provides a review of these approaches in the context of concentrated animal feeding operations (CAFOs).