Modulation of crude glycerol fermentation by Clostridium pasteurianum DSM 525 towards the production of butanol R. Gallardo 1,2 , M. Alves 2 , L.R. Rodrigues * CEB - Centre of Biological Engineering, University of Minho, 4710-057 Braga, Portugal article info Article history: Received 25 November 2013 Received in revised form 17 September 2014 Accepted 23 October 2014 Available online 13 November 2014 Keywords: Butanol Clostridium pasteurianum Crude glycerol Butyrate 1,3-Propanediol abstract High production yields and productivities are requisites for the development of an in- dustrial butanol production process based on biodiesel-derived crude glycerol. However, impurities present in this substrate and/or the concentration of glycerol itself can affect the microbial metabolism. In this work, the effect of crude glycerol concentration on the production of butanol and 1,3-propanediol (1,3-PDO) by Clostridium pasteurianum DSM 525 is studied. Also, the effect of acetate and butyrate supplementation to the culture medium and the culture medium composition are evaluated. The results showed a marked effect of crude glycerol concentration on the product yield. The competitive nature of butanol and 1,3-PDO pathways has been evident, and a shift to the butanol pathway once using higher substrate concentrations (up to 35 g l 1 ) was clearly observed. Butyrate supplementation to the culture medium resulted in a 45% higher butanol titre, a lower production of 1,3-PDO and it decreased the fermentation time. Acetate supplementation also increased the butanol titre but the fermentation was longer. Even though glycerol consumption could not be increased over 32 g l 1 , when the concentrations of NH 4 Cl and FeCl 2 were simulta- neously increased, the results obtained were similar to those observed when butyrate was supplemented to the culture medium; a 35% higher butanol yield at the expense of 1,3-PDO and a shorter fermentation. The results herein gathered suggest that there are other fac- tors besides butanol inhibition and nutrient limitation that affect the glycerol consumption. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction Glycerol is an attractive substrate for anaerobic fermentation that has interesting advantages over simple sugars such as glucose. From the technical point of view, the highly reduced nature of this compound results in twice the amount of reducing equivalents when it is converted to glycolytic in- termediates such as pyruvate, which leads to higher yields of reduced compounds such as butanol [1]. On the other hand, glycerol is a by-product in the production of biodiesel and ethanol, representing approximately 10% and 6% (w/w) of the * Corresponding author. Tel.: þ351 253 604401; fax: þ351 253 604 429. E-mail address: lrmr@deb.uminho.pt (L.R. Rodrigues). 1 Current address: Escuela de Ingenierı´a Bioquı´mica, Pontificia Universidad Cat olica de Valparaı ´so, Valparaı´so, Chile. 2 Tel.: þ351 253 604401; fax: þ351 253 604 429. Available online at www.sciencedirect.com ScienceDirect http://www.elsevier.com/locate/biombioe biomass and bioenergy 71 (2014) 134 e143 http://dx.doi.org/10.1016/j.biombioe.2014.10.015 0961-9534/© 2014 Elsevier Ltd. All rights reserved.