Liquid-liquid extraction, perhaps by using tert-amyl alcohol, could possibly be considered to extract some of the glycerol from the aqueous phase.The ternary phase diagram (with tie lines) for the glycerol―water―tert-amyl alcohol can be found at: Alfred W. Francis, "Liquid-Liquid Equilibriums", Interscience Publishers (John Wiley & Sons), New York and London, 1963, p. 36.