Biological removal of H2S gas in a semi-pilot scale biotrickling filter: Optimization of various parameters for efficient removal at high loading rates and low pH conditions

•Semi-pilot scale biotrickling filter (BTF) successfully removed high level of H2S gas.•Elimination capacity increased almost linearly with loading rates up to 38.5 g/m3 h.•H2S at inlet concentrations of 2000 ppm could be removed with >99% efficiency at 15 min retention time.•Acidithiobacillus caldus was enriched at all portions of BTF during H2S removal. In this study, a semi-pilot scale biotrickling filter (BTF) was operated in a continuous co-current mode to remove high concentration of hydrogen sulfide (H2S) at optimum operational conditions. The early startup period of 6 days was needed, and then stable removal of H2S gas at inlet concentrations up to about 2000 ppm was successfully obtained at gas retention time (GRT) of 15 min and liquid recirculation rate (LRR) of 120 ml/min. The elimination capacities (ECs) increased linearly with increase in H2S loading rates (HLRs up to 38.5 g/m3 h), but a gradual decrease in removal efficiency was observed from a volumetric HLR of 18.1 g/m3 h. The LRR was further decreased from 120 to 30 ml/min, and the minimum liquid–gas ratio of 0.24 was found without decrease in removal efficiency. The MiSeq analysis revealed the presence of sulphur oxidizing bacteria (SOB) dominated by Acidithiobacillus caldus (>97%) at all portions of BTF.