(JP9187793-A)      Cleaning a waste water stream or the like comprises: (a) a desulphurisation step whereby a desulphurising agent is added and a buffer; (b) a biodenitrification step using micro-organisms which feed on the buffer in the waste-water stream. The sulphur contaminants and the like are removed in the desulphurisation step. Nitrate contamination and the like, as well as the buffer, are removed in the bio-denitrification step. Also claimed, (1), use of a buffer to enhance the desulphurisation of a flue gas stream or the like with a desulphurising agent such as lime or limestone suspension. (2), use of microorganisms for removing buffer from a waste-water stream which has been subjected to the desulphurisation step of part (a). (3), apparatus for cleaning a waste-water stream or the like which, comprises: (a)' a desulphurising unit where the sulphur components are removed from the stream via a buffer enhanced desulphurising agent; (b)' a biomass reservoir contg. microorganisms. (c)' a means for supplying the desulphurised waste-water stream and the buffer into the biomass reservoir where the waste water is denitrified; and (d)' an outlet for guiding the denitrified waste water stream away from the reservoir.    USE -   A process to clean a waste water stream, e.g. from a flue-gas cleaning installation.    ADVANTAGE -    The process is environmentally friendly and does not release harmful sulphur cpds. i.e. sulphur dioxide, into the atmos. Biological denitrification is effectively carried out at a chloride concn. of 44 g/dm3.    (US5830357-A)      Cleaning a waste water stream or the like comprises: (a) a desulphurisation step whereby a desulphurising agent is added and a buffer; (b) a biodenitrification step using micro-organisms which feed on the buffer in the waste-water stream. The sulphur contaminants and the like are removed in the desulphurisation step. Nitrate contamination and the like, as well as the buffer, are removed in the bio-denitrification step. Also claimed, (1), use of a buffer to enhance the desulphurisation of a flue gas stream or the like with a desulphurising agent such as lime or limestone suspension. (2), use of microorganisms for removing buffer from a waste-water stream which has been subjected to the desulphurisation step of part (a). (3), apparatus for cleaning a waste-water stream or the like which, comprises: (a)' a desulphurising unit where the sulphur components are removed from the stream via a buffer enhanced desulphurising agent; (b)' a biomass reservoir contg. microorganisms. (c)' a means for supplying the desulphurised waste-water stream and the buffer into the biomass reservoir where the waste water is denitrified; and (d)' an outlet for guiding the denitrified waste water stream away from the reservoir.    USE -   A process to clean a waste water stream, e.g. from a flue-gas cleaning installation.    ADVANTAGE -    The process is environmentally friendly and does not release harmful sulphur cpds. i.e. sulphur dioxide, into the atmos. Biological denitrification is effectively carried out at a chloride concn. of 44 g/dm3.