The conversion of glycerol to 1,3-propanediol (PDO) using Klebsiella pneumoniae M5al under anaerobic condition was scaled up from scale 5 to 5000 1 in series. A simple strategy for scale-up was to transfer the optimized conditions of a lab scale bioreactor to pilot-scale fermentation. Multistage inocula were developed and their fermentation abilities were assessed in a small-scale fermenter. The experimental results showed that inoculum development in the early steps of a scale-up process could influence the outcomes of a large scale fermentation. Through three-stage liquid inoculum development and a pulse addition of (NH4)(2)SO4 and yeast extract at 30 h of fermentation, the best results in a 5000 1 fermentation were achieved leading to 58.8 g l(-1) 1,3-propanediol with a yield of 0.53 mol mol(-1) glycerol and productivity of 0.92 g l(-1) h(-1). This is the first report on pilot-scale 1,3-propanediol production using K. pneumoniae. (c) 2007 Elsevier Ltd. All rights reserved.