NOVELTY - Gas is provided to a main process tank, gas comprising hydrogen sulfide and main process tank comprising sulfur-oxidized bacteria, a clean scrubber liquid containing sulfate ion is supplied to the main process tank, provided in the presence of oxygen and desulfurized gas and at least a portion of used scrubber liquid is supplied to a sedimentation tank. The used scrubber liquid is contacted in the sedimentation tank with water and precipitation is allowed to form in the tank providing a precipitation and the cleaned scrubber liquid.    USE - Desulfurization of gas e.g. biogas desulfurization process (claimed).    ADVANTAGE - The gas is economically and efficiently desulfurized with reduced energy consumption.    DETAILED DESCRIPTION - Gas is provided to a main process tank, gas comprising hydrogen sulfide and main process tank comprising sulfur-oxidized bacteria, a clean scrubber liquid containing sulfate ion is supplied to the main process tank, provided in the presence of oxygen and desulfurized gas and at least a portion of used scrubber liquid is supplied to a sedimentation tank. The used scrubber liquid is contacted in the sedimentation tank with water and a precipitation comprising oxidized sulfur compounds is allowed to form in the tank providing a precipitation and the cleaned scrubber liquid. The water is not demineralized or deionized. INDEPENDENT CLAIMS are included for the following:    (1) preparation of liquid substrate, which involves providing an acid liquid containing sulfate to a sedimentation tank supplied with wastewater and optionally raw water, allowing sulfate to react with compounds and/or organic material contained in wastewater and/or raw water such as to form a precipitation and a liquid substrate, and separating the liquid substrate from the precipitation;    (2) usage of precipitation as liquid fertilizer; and    (3) usage of wastewater and/or raw water for precipitation of sulfate derived from gas desulfurization process, as substrate for sulfur-oxidized bacteria and as scrubber liquid.