Comparison of autotrophic and mixotrophic biofilters for H ₂ S removal

We demonstrate that the facultative chemoautotroph Thiobacillus novellus CH 3 removes hydrogen sulfide (H ₂ S) gas in continuous reactors under nutrient-limiting conditions. Extensive tests including removal characteristics, metabolic products, and removal efficiencies of H ₂ S by T. novellus CH 3 were conducted in autotrophic and mixotrophic environments. The optimal pH value and temperature required to remove hydrogen sulfide are found to be pH 7 and 26°C. The biofilter had an H ₂ S removal efficiency greater than 99.5% under the mixotrophic condition after 10-day operation. The results show that the maximum removal rate and saturation constant were 1.9 g S/d per kg bead and 69.2 ppm, respectively. The main metabolic product of H ₂ S oxidation was determined to be sulfate, but the conversion ratio was dependent on the growth environment. These results suggest that the mixotrophic potential of T. novellus CH 3 biofilter provides a significant advantage in H ₂ S removal over autotrophic biofilters.