A process for a stream of substances containing at least one valuable substance including (A) amino acids, (B) carboxylic acids, and (C) inorganic salts includes: (1) treating the stream by nanofiltration to obtain a retentate enriched with valuable substance (A); (2) treating the permeate of step (1) by electrodialysis in order to obtain a concentrate enriched with valuable substance (C); (3) treating the diluate of step (2) using a system (3) of two stages (4) and (5) which are directly or indirectly interconnected, wherein (4) one treatment is performed by reverse osmosis and (5) one treatment is performed by electrodialysis, whereby a concentrate enriched with valuable substance (B) is obtained, (6) at least a portion of the retentate of step (4) is directly or indirectly supplied to step (5) and (7) at least a portion of the diluate of step (5) is directly or indirectly supplied to step (4).