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

Abstract

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. © 2005, The Society for Biotechnology.