Biological oxidation of sulfide was studied to remove toxic hydrogen sulfide ($H_2S$) gas from various air pollution sources as an alternative to the conventional physico-chemical methods that can not eliminate $H_2S$ to a level of air pollution standards. In this study we employed photoautotrophic Chlorobium thiosulfatophilu to compare the performances of two-dimensional air-lift reactor with the conventional fermentors and also studied chemoautotrophic Thiobacillus ferrooxida as a model for non light-utilizing bacteria.
C. thiosulfatophilum has several advantages over other microorganisms ; it growth and sulfide removal rate are faster than other sulfide utilizing bacteria ; inhibition concentration of substrate sulfide was higher than others; sterilization processes of substrate solution is not required. Since it is a photosynthetic bacterium, it requires light energy instead for the conversion of $H_2S$ to elementary sulfur or sulfate. Thus economical light energy supply plays a key role in determining the success of industrial application of these photosynthetic microorganisms. Light emitting diode (LED) of 710 nm was used as an alternative light source to incandescent light to save energy although only 60% of light intensity emitted at 710 nm is picked up by the bacteriochlorophyll that has a peak absorbance at 760 nm. This changes in light source gives 99% light energy savings and two-dimensionaal air-lift reactor functioned 2.5 times better in the $H_2S$ removal per unit biomass than the conventional fermentors.
T. ferrooxidans has an ability to oxidize ferrous ion to ferric ion as well a sulfides. The oxidation of aqueous acidic ferrous sulfate by the cells was studied over the initial ferrous sulfate concentration of 5-90 g $Fe^{2+}$/L in the shake flasks. The ferrous ion oxidation rate decreased with increased ferrous ion concentration. The inhibition concentration of ferrous ion was 20 g/L and sulfur oxidation rate of T. ferrooxidans was higher under pH 2.1 and aerobic conditions than under pH 3.1 and anaerobic conditions.
