Hydrogen sulfide oxidation in novel Horizontal-Flow Biofilm Reactors dominated by an Acidithiobacillus and a Thiobacillus species

Hydrogen Sulfide (H₂S) is an odourous, highly toxic gas commonly encountered in various commercial and municipal sectors. Three novel, laboratory-scale, Horizontal-Flow Biofilm Reactors (HFBRs) were tested for the removal of H₂S gas from air streams over a 178-day trial at 10°C. Removal rates of up to 15.1 g [H₂S] m⁻³ h⁻¹ were achieved, demonstrating the HFBRs as a feasible technology for the treatment of H₂S-contaminated airstreams at low temperatures. Bio-oxidation of H₂S in the reactors led to the production of H⁺ and sulfate (SO²⁻ ₄) ions, resulting in the acidification of the liquid phase. Reduced removal efficiency was observed at loading rates of 15.1 g [H₂S] m⁻³ h⁻¹. NaHCO₃ addition to the liquid nutrient feed (synthetic wastewater (SWW)) resulted in improved H₂S removal. Bacterial diversity, which was investigated by sequencing and fingerprinting 16S rRNA genes, was low, likely due to the harsh conditions prevailing in the systems. The HFBRs were dominated by two species from the genus Acidithiobacillus and Thiobacillus. Nonetheless, there were significant differences in microbial community structure between distinct HFBR zones due to the influence of alkalinity, pH and SO4 concentrations. Despite the low temperature, this study indicates HFBRs have an excellent potential to biologically treat H₂S-contaminated airstreams.