O-2-limiting/microaerobic conditions were applied in order to control the H2S content of biogas. The S-0-rich deposits found all over the headspace of two pilot reactors (R1 and R2) as a result of operating under such conditions for 7 and 15 months (respectively) were sampled and removed. After restarting micro-oxygenation, H2S-free biogas was rapidly obtained, and the O-2 demand of R2 decreased. This highlighted the need for a cleaning interval of less than 14 months in order to minimise the micro-oxygenation cost. The H2S removed from R2 after approximately 1 month was recovered from its headspace as S-0, thus indicating that the biogas desulphurisation did not take place at the liquid interface. Denaturing gradient gel electrophoresis indicated that the composition, species richness and size of the sulphide-oxidising bacteria population depended on the location, and, more specifically, moisture availability, and indicated increasing species richness over time. Additionally, a possible succession was estimated. (C) 2014 Elsevier Ltd. All rights reserved.