NOVELTY - Preparation of salt- and glycerin-containing composition, comprises: (a) preparing a raw-glycerin-phase comprising 40-99 wt.% of glycerin, 0.1-30 wt.% of water, 0.1-15 wt.% of salt and 0.1-15 wt.% of impurities other than glycerin, water and salt; (b) distilling the raw-glycerin-phase to give a pure-glycerin-phase and a residual product comprising salt and glycerin; and (c) contacting the residual product with 1-50 wt.% of water and 0.1-10 wt.% of acid, whose pKa value is greater than 5 to obtain the salt- and glycerin-containing composition.    USE - The salt- and glycerin-containing composition is useful as biomass for preparing methane containing gases and fatty alkyl ester. The combination of water and acid (preferably citric acid) is useful for treating the salt- and glycerin-containing residue (all claimed).    ADVANTAGE - The cost-effective method allows for the treatment of saline residues so that they can be easily used as biomass in the biogas plant.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) the salt- and glycerin-containing composition obtained by the method;    (2) a method-1 for preparing methane containing gases through fermentative decomposition of an organic phase comprising (i) preparing the salt- and glycerin-containing composition, (ii) optionally mixing the salt- and glycerin-containing composition with further organic material, and (iii) anaerobically fermenting the glycerin in the composition or in the mixture from the salt- and glycerin-containing composition and the further organic material to form the methane containing gases;    (3) the methane containing gas obtained by the method; and    (4) a method-2 for preparing fatty acid alkyl ester comprising preparing the salt- and glycerin-containing composition, transesterifying mono-, di- or triglyceride with alcohol to form glycerin phase and fatty acid alkyl ester phase, reprocessing the glycerin phase to obtain raw glycerin and reprocessing the raw-glycerin to obtain the salt- and glycerin-containing composition.