Aerobic biodegradation of potato slops under moderate thermophilic conditions: Effect of pollution load Edmund Cibis * , Małgorzata Krzywonos, Tadeusz Mis ´kiewicz Department of Bioprocess Engineering, Wroclaw University of Economics, ul. Komandorska 118/120, 53-345 Wroclaw, Poland Received 16 March 2004; received in revised form 14 December 2004; accepted 17 March 2005 Available online 31 May 2005 Abstract The effect of the pollutant load on the efficiency of aerobic biodegradation of potato slops with a mixed population of thermo- and mesophilic bacteria of the genus Bacillus was examined. Batch biodegradation processes were carried out at 45 °C, using slops with the initial chemical oxygen demand (COD) totalling 11.3, 18.0, 42.6, 58.0 and 74.0 g O 2 /l. The extent of COD removal ranged from 80.4% (with COD of 11.3 g O 2 /l) to 88.7% (with COD of 58.0 g O 2 /l). With potato slops of higher initial COD levels (58.0 and 74.0 g O 2 /l), the first 24 h of growth were characterised by a deficiency of oxygen and a considerable rise in the content of acetic acid, which was then removed. In the first 48 h of the process, irrespective of the initial COD level, the biodegradation of the pollutants removed in the course of the entire process exceeded 91%. The rate of COD removal calculated for that period was a linearly increas- ing function of the initial pollution load. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Potato slops; Thermophilic and mesophilic bacteria; High strength wastewater; Aerobic biodegradation; Batch cultures 1. Introduction The activated sludge process is the most popular aerobic method of sewage treatment, but recently references to the use of meso- and thermophilic microor- ganisms in the aerobic treatment of wastewater have become increasingly frequent (Ginnivan et al., 1981; Perttula et al., 1991; Malladi and Ingham, 1993; Couil- lard and Zhu, 1993; Zvauya et al., 1994; LaPara and Al- leman, 1999; Skjelhaugen, 1999; Pagilla et al., 2000; Kosseva et al., 2001; Lasik et al., 2002). Aerobic biodeg- radation with thermophilic and mesophilic bacteria offers a variety of benefits. From the investigations re- ported so far it can be inferred that this method applies well to the treatment of both cold and hot waste- waters. There is no need for heat supply to provide appropriately high temperatures, because aerobic bio- degradation at elevated temperatures is an autostable process (Su ¨ru ¨cu ¨ et al., 1976; Loll, 1976; Jewell and Kab- rick, 1980). Potato slops, a troublesome effluent from distilleries, create serious problems with further processing and util- isation. Until recently, they have been utilised in Poland primarily as a fodder. Unfortunately, Polish farmers are no longer interested in breeding their cattle or pigs on that kind of fodder (Kotarska et al., 1996) and therefore new ways of using or degrading potato slops are desired. A novel approach to the biological decomposition of potato slops was proposed by Cibis et al. (2002) and Krzywonos et al. (2002). In this method, potato slops were used as a substrate for aerobic biodegradation under thermophilic and thermotolerant conditions using a mixed population of thermo- and mesophilic bacteria of the genus Bacillus. The publications mentioned concerned temperature and pH optimisation. Studies presented in this paper 0960-8524/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.03.035 * Corresponding author. Tel.: +48 71 3680285; fax: +48 71 3680753. E-mail address: cibis@credit.ae.wroc.pl (E. Cibis). Bioresource Technology 97 (2006) 679–685