instead of a metal containing liquid the process stream 10 fed to the contactor c may also be a liquid which absorbs the hydrogen sulphide in order to transport it to a regeneration column to concentrate the hydrogen sulphide to a higher percentage gas stream gt 90 the hydrogen sulphide gas stream can be used for the different industrial purposes of hydrogen sulphide furthermore the contactor c may also be a membrane unit in which the hydrogen sulphide is selectively removed and concentrated to produce also a more highly concentrated gas stream to be used for different purposes in industry it is also possible to strip the hydrogen sulphide directly from the bioreactor r or from stripper s using a process gas stream instead of using a gas recycle to transport the hydrogen sulphide to a liquid stream in order to achieve high hydrogen sulphide production rates the process has to be controlled carefully an important factor is the control of the ph in the water system the water system comprises the reactor and optional stripper and connecting lines the biological reduction of elemental sulphur using hydrogen gas carbon monoxide or organic compounds as an electron donor results in the production of the acids hydrogen sulphide and carbon dioxide in the bioreactor in principle this would lower the ph in the reactor to low levels which may inhibit the biological reactions as no liquid bleed stream from.