Oxyethylated acetals

A surface active compound comprises a lipophilic alkyl group linked to a hydrophilic oxyethylated group through an acetal linkage so that, on acidification of an aqueous medium containing such a surface active compound, rupture of such acetal linkage permits separation of said lipophilic alkyl group, possibly with lipid material associated therewith, from the aqueous medium in which the oxyethylated groups remain so in turn permitting recovery of such lipophilic groups and any such lipid material, and effective elimination of active surface active compound from the aqueous phase.