Thermo- and mesophilic aerobic batch biodegradation of high-strength distillery wastewater (potato stillage) – Utilisation of main carbon sources Małgorzata Krzywonos a, * , Edmund Cibis a , Małgorzata Lasik b , Jacek Nowak b , Tadeusz Mis ´ kiewicz a a Department of Bioprocess Engineering, Wrocław University of Economics, Komandorska 118/120, 53-345 Wrocław, Poland b Institute of Food Technology of Plant Origin, Poznan ´ University of Life Science, Wojska Polskiego 31, 60-624 Poznan ´, Poland article info Article history: Received 2 September 2008 Received in revised form 2 December 2008 Accepted 4 December 2008 Available online 9 January 2009 Keywords: Aerobic biodegradation Thermophilic and mesophilic Bacillus Distillery stillage Organic acids High-strength wastewater abstract The aim of the study was to ascertain the extent to which temperature influences the utilisation of main carbon sources (reducing substances determined before and after hydrolysis, glycerol and organic acids) by a mixed culture of thermo- and mesophilic bacteria of the genus Bacillus in the course of aerobic batch biodegradation of potato stillage, a high-strength distillery effluent (COD = 51.88 g O 2 /l). The experiments were performed at 20, 30, 35, 40, 45, 50, 55, 60 and 63 °C, at pH 7, in a 5 l working volume stirred-tank bioreactor (Biostat Ò B, B. Braun Biotech International) with a stirrer speed of 550 rpm and aeration at 1.6 vvm. Particular consideration was given to the following issues: (1) the sequence in which the main carbon sources in the stillage were assimilated and (2) the extent of their assimilation achieved under these conditions. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction When high-strength wastewater is treated in the presence of microorganisms under aerobic thermophilic conditions, both or- ganic and inorganic pollutants are transformed into environ- ment-friendly by-products. The majority of the organic compounds are oxidised to carbon dioxide and water, and the heat produced during industrial-scale degradation in the bioreactors ac- counts for a rise in temperature to 50–70 °C(Kurisu et al., 2002). That is what enables the treatment processes to be conducted by the aerobic method with no temperature control (Kelly et al., 1993). The commonest treatment systems, however, work at ambi- ent temperature (5–20 °C), and, not surprisingly, the effect of tem- perature on the kinetics of the process has only been examined over that temperature range (Droste and Sanchez, 1983). As yet, there is no satisfactory explanation regarding the effect of temper- ature on the metabolism of mesophilic and thermophilic bacteria that participate in wastewater treatment. Although there have been attempts to examine this phenomenon, they have concen- trated primarily on the contribution of temperature to the effi- ciency of biodegradation achieved with high-strength effluents. In those studies use was made of both pure (Becker et al., 1999) and mixed bacterial cultures (LaPara and Alleman, 1999; Lim et al., 2001). The catabolic capacity of mixed bacterial cultures used for the biodegradation of wastewaters with a high chemical oxy- gen demand (COD) was examined by our research team (Cibis et al., 2002, 2006; Krzywonos et al., 2002, 2008), as well as by some of the researchers collaborating with our team under UE V Frame- work Programme, who are working on the bioremediation of cheese whey (Kosseva et al., 2001, 2003), and on the treatment of wastewater from potato processing (Lasik and Nowak, 2007). The literature contains only a few reports on the issue of how tem- perature contributes to the sequence in which the microorganisms assimilate the carbon sources that are found in the wastewater being biodegraded, or to the extent of assimilation achieved under this conditions (LaPara et al., 2000; Ugwuanyi et al., 2005a,b; Voge- laar et al., 2002). This is what prompted us to examine the influ- ence of a wide range of temperature, from 20 to 63 °C, on the course of the biodegradation of potato stillage, a hot industrial effluent of a high COD, which in some instances exceeds 100 g/l (Cibis et al., 2002). Particular consideration was given to the se- quence in which the main carbon sources in the stillage, i.e. reduc- ing substances, glycerol and organic acids, were assimilated by the mixed culture of thermo- and mesophilic bacteria of the genus Bacillus used in the present study. Such knowledge offers possibil- ities of enriching the mixed culture with other bacteria of Bacillus sp. that will utilize those substances at a faster rate. This will en- hance not only the rate of biodegradation but also the efficiency of the process. The understanding of the mechanisms is a prerequi- site not only for modelling the biodegradation process or comput- ing the kinetic and dynamic process parameters, but also for ascertaining how this method of establishing the efficiency and the course of the biodegradation process compares with alterna- tive methods. 0960-8524/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2008.12.008 * Corresponding author. Tel.: +48 71 368 08 72; fax: +48 71 368 07 53. E-mail address: malgorzata.krzywonos@ue.wroc.pl (M. Krzywonos). Bioresource Technology 100 (2009) 2507–2514 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech