Abstract: The application relates to an anaerobic digestion system for production of biogas with a reduced hydrogen sulphide content. The system comprises an airtight reactor vessel comprising: —sludge comprising a surface layer and a volume underneath the surface layer comprising bio-matter and micro-organisms that are able to anaerobically digest the bio-matter, thereby producing biogas comprising hydrogen sulphide, —a headspace above the surface layer of the sludge into which biogas migrates out of the sludge, —a spraying system for spraying an aqueous nitrate containing solution in the headspace using a carrier gas stream to form a nitrate containing interphase layer between the surface layer of the sludge and the headspace, with the proviso that the reactor vessel does not comprise a membrane or fabric positioned in the headspace.