Calcium carbonate was evaluated as a replacement for the base during the fermentation of glycerol by a highly productive strain of 1,3-propanediol (PDO), viz., Clostridium butyricum JKT37. Due to its high specific growth rate (mu(max) = 0.53 h(-1)), 40 g/L of glycerol was completely converted into 19.6 g/L of PDO in merely 7 h of batch fermentation, leaving only acetate and butyrate as the by-products. The accumulation of these volatile fatty acids was circumvented with the addition of calcium carbonate as the pH neutraliser before the fermentation was inoculated. An optimal amount of 15 g/L of calcium carbonate was statistically determined from screening with various glycerol concentrations (20-120 g/L). By substituting potassium hydroxide with calcium carbonate as the pH neutraliser for fermentation in a bioreactor, a similar yield (Y-PDO/glycerol = 0.6 mol/mol) with a constant pH was achieved at the end of the fermentation. (C) 2017 Elsevier Ltd. All rights reserved.