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The full proceedings paper is at: www.extension.org/72846
Although acid scrubbers can capture ammonia (NH3) in exhaust air from animal facilities, they are not cost-effective because the nitrogen (N) captured has roughly the same value as the acid. The objective of this work was to develop an NH3 scrubber that uses acid-tolerant nitrifying bacteria to generate the acid needed for scrubbing NH3. Nitrification is an acid-forming process, with two moles of acid formed for each mole of ammonium (NH4) nitrified. A laboratory microcosm that held a clay substrate was inoculated with sewage from the aeration basin of a local wastewater plant. A feed solution containing ammonium chloride (NH4Cl) and sodium bicarbonate (NaHCO3) was then pumped through the system. Ammonium, nitrate (NO3) and pH were measured periodically in the influent and effluent. After a few weeks, NO3- analysis indicated >95% of the NH4 was being nitrified to NO3-, at which point the NH4Cl and NaHCO3 concentrations were doubled. This process was repeated until the feed solution contained 4 g NH4Cl/L. Then the NaHCO3 was reduced over time so that the molar ratio of base to potential acidity (from nitrification of NH4) was less than one, causing the effluent pH to decrease. Even though the influent pH was 8.2, the effluent pH was reduced to 4.2 over time, indicating acid-tolerant nitrifying bacteria were at work. Clay substrate from the microcosm was then used to inoculate slats of an NH4 scrubber with these bacteria at a commercial broiler farm in NW AR, by encasing the clay substrate in mesh that was attached to the slats. Within weeks, bacteria slime mats formed on the slats and nitrification of NH3 and acid generation began. Over 20 kg of N were captured in 35 days, about half of which was NO3-. This technology has the potential to make the use of NH4 scrubbers a cost-effective best management practice.