Simultaneous removal of H₂S and NH₃ in biofilter inoculated with acidithiobacillus thiooxidans TAS

H₂S and NH₃ gases are toxic, corrosive and malodorous air pollutants. Although there are numerous well-established physicochemical techniques presently available for the treatment of these gases, the growing demand for a more economical and improved process has prompted investigations into biological alternatives. In biological treatment methods, H₂S is oxidized to SO₄^2- by sulfur-oxidizing bacteria, and then NH₃ is removed by chemical neutralization with SO₄ ^2- to (NH₄)₂SO₄. Since the accumulated (NH₄)₂SO₄ can inhibit microbial activity, it is important to utilize an effective sulfur-oxidizing bacterium that has tolerance to high concentrations of (NH₄)₂SO ₄ for the simultaneous removal of H₂S and NH₃. In this study, a sulfur-oxidizing bacterium with tolerance to high concentrations of (NH₄)₂SO₄ was isolated from activated sludge and identified as Acidithiobacillus thiooxidans TAS. A. thiooxidans TAS could display its sulfur-oxidizing activity in a medium supplemented with 60 g·l^-1 (NH₄)₂SO ₄, even though its growth and sulfur-oxidizing activity were completely inhibited in 80 g·l^-1 (NH₄) ₂SO₄. When H₂S alone was supplied to a ceramic biofilter inoculated with A. thiooxidans TAS, an almost 100% H₂S removal efficiency was maintained until the inlet H₂S concentration was increased up to 900 μl·l^-1 and the space velocity up to 500 h^-1, at which the amount of H₂S eliminated was 810 g·S·m^-3·h^-1. However, when NH ₃ (50-500 μl·l^-1) was simultaneously supplied to the biofilter with H₂S, the maximum amount of H₂S eliminated decreased to 650 g·S·m^-3·h ^-1. The inhibition of H₂S removal by low NH₃ concentrations (50-200 μl·l^-1) was similar to that by high NH₃ concentrations (300-500 μl·l^-1). The critical inlet H₂S load that resulted in over 99% removal was determined as 400 g·S·m^-3·h^-1 in the presence of NH₃.