NOVELTY - Separation of suspended solids from a fermentation liquor involves solid-liquid separation of the liquor assisted by a treatment system. The treatment system comprises an anionic polymer with the provision that the system does not include a cationic polymer having an intrinsic velocity (IV) of at least 4 dl/g. The fermentation liquor is produced in a fermentation process for the production of a fermentation product and comprises lignin.    USE - For separating suspended solids from a fermentation liquor to obtain a fermentation product (e.g. ethanol, glycerol, acetone, n-butanol, butanediol, isopropanol, butyric acid, methane, citric acid, fumaric acid, lactic acid, propionic acid, succinic acid, itaconic acid, acetic acid, acetaldehyde or 3-hydroxypropionic acid, glyconic acid and tartaric acid and amino acid (preferably L-glutamic acid, L-lysine, L-aspartic acid, L-tryptophan, L-arylglycine or salts of these acid)).    ADVANTAGE - The treated liquor from which suspended solids have been removed are recycled and used as washed water. The separated solids are dewatered and then dried to provide a dry solid material that is used as a solid fuel, a nutrient source for further fermentation or a source of chemicals. The yield and/or efficiency of the process can be improved by effecting a rapid but efficient solids-liquid separation of the solid residues from an aqueous fermentation liquor containing lignin and that the liquor can be recycled to the fermentation process. The treatment system allows a significantly improved separation of liquors from the solid residues and by-products. The process induces more effective flocculation and the separation process is found to be significantly faster. In addition the solid residues, which contain mainly lignin, resulting from the separation process have higher cake solids than the conventional separations. Such a solid product would take less time and energy to dry and thus can be for instance used more efficiently as a solid fuel.