Biochemical Engineering Journal 49 (2010) 1–6 Contents lists available at ScienceDirect Biochemical Engineering Journal journal homepage: www.elsevier.com/locate/bej Aerobic biodegradation of wheat stillage (distillery wastewater) at an elevated temperature—Effect of solids separation Małgorzata Krzywonos ∗ , Edmund Cibis, Agnieszka Ryznar-Luty, Tadeusz Mi´ skiewicz, Daniel Borowiak Department of Bioprocess Engineering, Wroclaw University of Economics, Komandorska 118/120, 53-345 Wroclaw, Poland article info Article history: Received 16 November 2008 Received in revised form 3 November 2009 Accepted 6 November 2009 Keywords: Aerobic digestion Bacillus Distillery Stirred-tank reactor Waste treatment Wheat stillage abstract The aim of the study was to determine how the separation of solids affects the course and efficiency of the batch process of wheat stillage (distillery wastewater) biodegradation using meso- and thermophilic bacteria of the genus Bacillus. The processes with and without solids separation were conducted for 144 h in a 5-L bioreactor, with aeration at 1.6 vvm, stirrer revolutions of 550/min, at a constant pH (pH = 6.5) and the temperature of 45 ◦ C. The results have shown that the separation of solids is superfluous, because it had only a minor effect on the reduction in the chemical oxygen demand determined in the substrate upon solids separation (SCOD). The extent of SCOD reduction amounted to 88.25% for non-filtered and 92.85% for filtered stillage. Moreover, during biodegradation of the non-filtered stillage the bacterial consortium was able per se to remove more than 50% of the suspended solids present in the stillage in the amount of approx. 50 g/L (the biomass produced being neglected). © 2009 Elsevier B.V. All rights reserved. 1. Introduction The persistent rise in the prices of fossil fuels has triggered the trend towards substituting them by renewable natural energy sources. Among those substitutes is ethanol, a product obtainable from vegetable feedstock. Admittedly, this gave rise to a remark- able worldwide increase in ethanol production at the turn of the 21st century [1]. Take for example the overall ethanol volume of 29.2 billion liters produced in the year 2000, which rose to 79.01 billion liters in 2008, thus becoming more than 2.7-fold as high as in 2000 [2]. Changes were also observed in the structure of the feedstocks used for the production of ethyl alcohol. Until recently, preference had been given to sugar-based feedstocks. In 2006, 53% of the world’s alcohol production was based on starch feedstocks, which means that the use of sugar substrates accounted solely for 47% [3]. In Europe the main feedstock used for the production of ethanol as fuel additive is crops, and this includes starch-based substrates, e.g. wheat. The point is that the rise in the production of ethanol is concomitant with the increase in the quantity of stillage, which is a troublesome by-product, the more so as the volume of the stillage produced can be twenty times as high as that of ethanol [4]. A conventional method of utilizing wheat stillage because of its nutritional value includes its direct use as fodder without any pro- cessing [5,6]. This is, however, technically feasible only in the case of small-sized rural distilleries that are combined with farms, since ∗ Corresponding author. Tel.: +48 71 368 08 72; fax: +48 71 368 07 53. E-mail address: malgorzata.krzywonos@ue.wroc.pl (M. Krzywonos). liquid stillage fails to have a long shelf life [7]. In order to overcome that shortcoming, the stillage is made subject to drying, which sub- stantially extends its durability and at the same time reduces the transport charges. It should be noted, however, that in the case of wheat stillage the drying cost largely assets the value of the dried product [8]. One of the available methods for the management of the gener- ated stillage is disposal by classifying it as an industrial waste and making it subject to aerobic or anaerobic biodegradation, depend- ing on the microorganisms applied. A comprehensive account of researches into biological biodegradation of stillage has been pre- sented by Pant and Adholeya [9]. From the review, it can be inferred that the use of thermophilic processes for the biodegradation of distillery effluents has not been sufficiently considered. Aerobic biodegradation at elevated temperature has been used with suc- cess by some of the authors of the present paper for the treatment of other types of starch stillage [10–15]. In those studies, biodegra- dation was conducted solely for the liquid phase of the stillage, using filtration paper. The aim of the present study was to assess the effect of solids separation from wheat stillage on the course and efficiency of its biodegradation performed at elevated temperature (45 ◦ C), using a mixed culture of bacteria of the genus Bacillus. 2. Materials and methods 2.1. Microorganisms The microorganisms used in the experiments (a mixed culture of bacteria of the genus Bacillus) were obtained from an industrial 1369-703X/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.bej.2009.11.003