Biotrickling filters for biogas desulfurization still must prove their stability and robustness in the long run under extreme conditions. Long-term desulfurization of high loads of H2S under acidic pH was studied in a lab-scale aerobic biotrickling filter packed with metallic Pall rings. Reference operating conditions at steady-state corresponded to an empty bed residence time (EBRT) of 130s, H2S loading rate of 52gS-H2Sm-3h-1 and pH 2.50-2.75. The EBRT reduction showed that the critical EBRT was 75s and the maximum EC 100gS-H2Sm-3h-1. Stepwise increases of the inlet H2S concentration up to 10,000ppmv lead to a maximum EC of 220gS-H2Sm-3h-1. The H2S removal profile along the filter bed indicated that the first third of the filter bed was responsible for 70-80% of the total H2S removal. The oxidation rate of solid sulfur accumulated inside the bioreactor during periodical H2S starvation episodes was verified under acidic operating conditions. The performance under acidic pH was comparable to that under neutral pH in terms of H2S removal capacity. However, bioleaching of the metallic packing used as support and chemical precipitation of sulfide/sulfur salts occurred. © 2014 Elsevier B.V.