NOVELTY - Purifying glycerin derived from biodiesel production involves: (A) acidifying glycerin; (B) treating with base; (C) feeding glycerin to electrodialysis unit having cation and anion exchange membrane(s), to define diluted and concentrated compartment(s), where glycerin is fed to diluted compartment and sodium chloride solution is fed to concentrated compartment; (D) applying potential difference, so that ions in glycerin migrate through anion and cation exchange membranes from diluted to concentrated compartments, where they are trapped, purifying glycerin; and (E) extracting glycerin.    USE - For purifying glycerin derived from biodiesel production (claimed). The purified glycerin is useful in foods, cosmetics, and pharmaceuticals.    ADVANTAGE - The process provides purification of glycerin derived from biodiesel production by economically viable treatment adaptable to small-and medium-sized enterprises for purifying glycerin, in which the process is based on membrane technology i.e. electrodialysis; whereas when higher degree of purification of glycerin is desired, it requires phases of bleaching, deodorizing, and ion exchange for removing trace impurities and salts, which are expensive and generally not within economic capacity of small- and medium-scale plants. After neutralization with base, glycerin is diluted with water up to 50% to improve electrodialysis. The process starts with acidifying glycerin with inorganic acid, which allows removing of soaps, and fats from glycerin. In electrodialysis, after applying potential difference between anode and cathode, anions migrate through anion exchange membranes, from diluted compartments to concentrated compartment, where they are trapped, due to ion barrier formed by cation exchange membrane(s) placed in their path. Analogously, cations migrate through cation exchange membranes, from diluted compartments to concentrated compartment, where they are concentrated since anionic membranes prevent their migration towards cathode. The glycerin produced by the method is suitable for use in pharmaceuticals, as it has chloride ion concentration of (less than 10 ppm) i.e. achieves elimination of chlorides close to 100%.    DETAILED DESCRIPTION - Purifying glycerin derived from biodiesel production, involves:    (A) acidifying the glycerin;    (B) treating the acidified glycerin with a base;    (C) feeding the glycerin into an electrodialysis unit comprising at least one cation exchange membrane and at least one anion exchange membrane separated between an anode and a cathode, such that they define at least one diluted compartment and at least one concentrated compartment, located between the anode and the cathode, where glycerin is fed into the diluted compartment and NaCl solution is fed into the concentrated compartment;    (D) applying a potential difference between the anode and the cathode, so that the ions present in the glycerin migrate through the anion and cation exchange membranes from the diluted compartments to the concentrated compartments, where they are trapped, purifying glycerin; and    (E) extracting the purified glycerin from the electrodialysis unit.