An economically sustainable process was developed for propionic acid production by fermentation of glycerol using Propionibacterium acidipropionici and potato juice, a by-product of starch processing, as a nitrogen/vitamin source. The fermentation was done as high-cell-density sequential batches with cell recycle. Propionic acid production and glycerol consumption rates were dependent on initial biomass concentration, and reached a maximum of 1.42 and 2.30 g L-1 h(-1), respectively, from 50 g L-1 glycerol at initial cell density of 23.7 g(CDW) L-1. Halving the concentration of nitrogen/vitamin source resulted in reduction of acetic and succinic acids yields by 39% each. At glycerol concentrations of 85 and 120 g L-1, respectively, 43.8 and 50.8 g L-1 propionic acid were obtained at a rate of 0.88 and 0.29 g L-1 h(-1) and yield of 84 and 78 mol%. Succinic acid was 13 g% of propionic acid and could represent a potential co-product covering the cost of nitrogen/vitamin source. (C) 2012 Elsevier Ltd. All rights reserved.