Mitigation of ammonia and hydrogen sulfide emissions by stable aqueous foam-microbial media

Stable aqueous foam-microbial media consisting of protein-based foams and odor-degrading bacteria were developed to control the emissions of odorous compounds. The optimum foam formulation was determined based on foam characteristics including 50% drainage time, foam lifetime, and foam expansion ratio. When only the aqueous foam was applied onto the surface of a test odor source (i.e., swine manure), ammonia emission was completely suppressed for about 177, 225, 265, 297, and 471 min when the height of foam barrier was 2.5, 5, 10, 15, and 30 cm, respectively. According to the increasing foam height, ammonia emission rates after breakthrough points decreased to 0.16, 0.13, 0.09, 0.07, and 0.02 mg/m³/min, and thus volatilized ammonia concentrations decreased significantly after 600 min. Hydrogen sulfide was similarly suppressed. Ammonia emission was better controlled by incorporating odor-degrading bacteria into the aqueous foam. The odor suppression capacity of the 5-cm foam barrier with microbes was more than eight times greater than that of the barrier only and was similar to that of 30-cm foam barrier without microbes after 1440 min. A significant amount of dinitrogen gas was evolved by the foam-microbial media, indicating a successful biological transformation of ammonia.