Process for the treatment of a waste liquor produced in the agri-foodstuffs industry, containing both inorganic salts consisting predominantly of potassium sulphate, and organic matter, so as to obtain, on the one hand, a solid fraction consisting chiefly of inorganic salts and, on the other hand, a concentrate of organic matter with a low potassium content, the waste liquor to be treated feeding a plant comprising at least two concentration stages (21, 22) in series and at least two separators, the first separator (41) being fed by the last concentration stage (22) and producing the concentrate of organic matter, and the second separator (29) being fed by any concentration stage (21) other than the last stage and producing the inorganic salts, into which sulphuric acid and an aqueous solution of ammonium sulphate are introduced into the treated liquid stream so as to make the pH in the concentration stage (21) feeding the second separator (29) between 3.5 and 5.5. <IMAGE>
