A sequential stage physico-chemical refining of crude glycerol, derived from a waste used-oil utilizing biodiesel (methyl ester) production plant, was performed by acidification, polar solvent extraction and activated carbon adsorption at a laboratory scale and ambient temperature. The effect of varying the acid type (H3PO4, H2SO4 and CH3COOH) and pH (1-6), the type of polar solvent (CH3OH, C2H5OH and C3H7OH) and their ratio to glycerol (3:1-1:3 v/v), and adsorption with activated carbon at different ratios of activated carbon to glycerol (40-200 g/l) on the purity of crude glycerol was explored. The highest glycerol purity (95.74 wt.%) was obtained with the sequential acidification to pH 2.5 with H3PO4 and phase separation, followed by extraction with C3H7OH at a solvent:crude glycerol ratio of 2:1 (v/v). Finally, adsorption with commercial activated carbon at 200 g/l also achieved a 99.7% color reduction. (C) 2010 Elsevier B.V. All rights reserved.