Abstract: A process for purifying waste water containing sulphide, comprises oxidizing the sulphide to elemental sulphur in a reactor with sulphide-oxidizing bacteria in the presence of oxygen, and separating from the waste water at least a part of the sulphur formed during the oxidation, while recycling a part of the elemental sulphur separated from the reactor effluent into the reactor in such a way that a concentration of elemental sulphur of at least 1 g/l is maintained in the reactor. The sulphur, in the form of aggregates, is used as a carrier material for the sulphide-oxidizing bacteria.

Abstract: The invention provides a method for removing sulphur compounds from water which contains low levels of organic matter, by anaerobic reduction of the sulphur compounds to sulphide, followed by partial oxidation of the sulphide to elementary sulphur.

Abstract: The invention provides a method for removing sulphur compounds from water by anaerobic reduction of the sulphur compounds to sulphide, followed by a partial oxidation of the sulphide to elementary sulphur. The anaerobic reduction is carried out at elevated temperature, either continuously at a temperature of 45.degree.-70.degree. C., or periodically at a temperature of 55.degree.-100.degree. C. If the reduction is carried out periodically, a single rise in temperature for a few hours to several days over a period of 3-6 months can suffice. The method is particularly applicable to the removal of sulphate, sulphite and thiosulphate.

Abstract: A process for the removal of sulphur compounds from a gaseous effluent, comprising the steps of: a) contacting the gaseous effluent with an aqueous solution wherein sulphur compounds are dissolved; b) adjusting the concentration of buffering compounds such as carbonate and/or bicarbonate and/or phosphate in the aqueous solution to a value between 20 and 2000 meq/l; c) subjecting the aqueous solution containing sulphide to sulphide-oxidizing bacteria in the presence of oxygen in a reactor wherein sulphide is oxidized to elemental sulphur; d) separating elemental sulphur from the aqueous solution; and e) recycling the aqueous solution to step a). This process is suitable for removing H.sub.2 S from biogas, ventilation air etc. It can be used for removing SO.sub.2 from combustion gases by introducing the additional step, after step a) and before step c), of subjecting the aqueous solution containing the sulphur compounds to a reduction of the sulphur compounds to sulphide. H.sub.2 S and SO.sub.

Abstract: The invention provides a process for the removal of sulfur dioxide from waste gas, comprising the steps of:a) contacting the waste gas with a basic aqueous solution wherein sulfur dioxide is dissolved as sulfite;b) subjecting the aqueous solution containing sulfite to sulfur reducing bacteria in an anaerobic reactor wherein sulfite is reduced to sulfide;c) subjecting the aqueous solution containing sulfide to sulfur oxidizing bacteria in the presence of a limiting amount of oxygen in a reactor wherein sulfide is oxidized to elemental sulfur;d) separating the elemental sulfur form the aqueous solution; ande) recycling the aqueous solution to step a).