This work aimed to investigate the interactive effects of empty bed retention time (EBRT), specific hydraulic loading rate (q) and initial pH (pH(i)) of the aerated recirculating liquid to remove H2S in extreme acidic biofiltration. Biogas containing H2S 6395 +/- 2309 ppm and CH4 79.8 +/- 2.5% was fed to the biofilter as pH of the high dissolved oxygen recirculating liquid swung between pH(i) to 0.5. Response surface methodology was employed that gave the H2S removal relationship model with R-2 0.882. The predicted highest H2S removal within the studied parameter ranges was 94.7% at EBRT 180.0 s, q 4.0 m(3)/m(2)/h and pH(i) 3.99. Results from separate runs at a random condition were not statistically different from the model prediction, signifying a validity of the model. Additionally, CH4 content in the exit biogas increased by 4.7 +/- 0.4%. Acidithiobacullus sp. predominance in the consortia of this extreme acidic condition was confirmed by DGGE. (C) 2012 Elsevier Ltd. All rights reserved.