Abstract

The colour of sugar beet stillage is produced mainly by two groups of colorants: melanoidins (from the Maillard reaction of sugars (carbohydrates) with proteins (amino groups)), and caramels (from overheated sugars). With its high coloured matter content and high chemical oxygen demand (COD), distillery stillage cannot be treated by conventional biological methods. The aim of this study was to investigate the effect of temperature and medium supplementation on the decolorization of sugar beet stillage. Two mixed bacterial cultures of the genus Bacillus (C1 and C2) were tested for colour removal ability. Sugar beet stillage (W) was enriched with glucose (GLU), salts (S), and yeast extract (YE). Three temperatures were tested: 25, 35 and 45°C. Only at 25°C was a decrease in colorant content observed regardless of culture used and medium supplementation. At 25°C, the highest colorant removal was obtained with culture C2 when media W+S+YE and W+S+GLU+YE were used (34 and 35%, respectively). Melanoidins were degraded at 25 and 35°C, but not at 45°C. Moreover, at 45°C with all the media used, an increase in caramel content was observed. Spectrophotometric and high performance liquid chromatography (HPLC)analyses of treated wastewater demonstrated that the colorants underwent biotransformation.

Key words: Colorant, melanoidins, distillery wastewater, aerobic bacteria, decolorization, Bacillus.