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

Abstract

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 initial nominal 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) above 99%. Excess biofilm growth reduced the HRT from 115 to 19 min and decreased the desulfurization efficiency of the BTF. When the BTF was operated under mixotrophic conditions by adding organic carbon (43.2 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 consumed 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.