H₂S removal and microbial community composition in an anoxic biotrickling filter under autotrophic and mixotrophic...

Removal of H₂S from gas streams using NO₃^--containing synthetic wastewater was investigated in an anoxic biotrickling filter (BTF) at feed N/S ratios of 1.2-1.7 mol mol^-1 with an empty bed residence time of 3.5 min and a hydraulic retention time of 115 min. During 108 days of operation under autotrophic conditions, the BTF showed a maximum elimination capacity (EC) of 19.2 g S m^-3 h^-1 and H₂S removal efficiency (RE) >99%. When the BTF was operated under mixotrophic conditions by adding organic carbon (10.2 g acetate m^-3 h^-1) to the synthetic wastewater, the H₂S EC decreased from 16.4 to 13.1 g S m^-3 h^-1, while the NO₃^- EC increased from 9.9 to 11.1 g NO₃^--N m^-3 h^-1, respectively. Thiobacillus sp. (98-100% similarity) was the only sulfur-oxidizing nitrate-reducing bacterium detected in the BTF biofilm, while the increased abundance of heterotrophic denitrifiers, i.e. Brevundimonas sp. and Rhodocyclales, increased the N/S ratio during BTF operation. Residence time distribution tests showed that biomass accumulation during BTF operation reduced gas and liquid retention times by 17.1% and 83.5%, respectively.