Effect of oxygen dosing point and mixing on the microaerobic removal of hydrogen sulphide in sludge digesters

► Microaerobic removal of H2S achieved an efficiency higher than 98%. ► Headspace was found the optimal dosing point. ► Dissolved sulphide was removed with biogas recirculation. ► The main result of H2S oxidation was S0, partly accumulated in the headspace. ► Sulphide-oxidising bacteria developed in the headspace.