Biodegradation of main carbon sources in vinasse stillage by a mixed culture of bacteria: influence of temperature and pH of the medium

Efficiency of aerobic biodegradation of sugar beet distillery stillage under dissolved oxygen tension-controlled conditions

The efficiency of aerobic biodegradation of distillery wastewater using various microbial cultures is intricately linked to process conditions. The study aimed to examine the aerobic biodegradation by a Bacillus bacteria under controlled dissolved oxygen tension (DOT) conditions as a novel approach in the treatment of sugar beet distillery stillage. The processes were conducted in a 2-L Biostat®B stirred-tank reactor (STR), at a temperature of 36°C, with aeration of 1.0 L/(L·min), and uncontrolled pH of the medium (an initial pH of 8.0). Each experiment was performed at a different DOT setpoint: 75%, 65% and 55% saturation, controlled through stirrer rotational speed adjustments. The study showed that the DOT setpoint did not influence the process efficiency, determined by the pollutant load removal expressed as COD, BOD5 and TOC. In all three experiments, the obtained reduction values of these parameters were comparable, falling within the narrow ranges of 78.6-78.7%, 97.3-98.0% and 75.0-76.4%, respectively. However, the DOT setpoint did influence the rate of process biodegradation. The removal rate of the pollutant load expressed as COD, was the lowest when DOT was set at 55% (0.48 g O2/(L•h)), and the highest when DOT was set at 65% (0.55 g O2/(L•h)). For biogenic elements (nitrogen and phosphorus), a beneficial effect was observed at a low setpoint of controlled DOT during biodegradation. The maximum extent of removal of both total nitrogen (54%) and total phosphorus (67.8%) was achieved at the lowest DOT setpoint (55%). The findings suggest that conducting the batch aerobic process biodegradation of sugar beet stillage at a relatively low DOT setpoint in the medium might achieve high efficiency pollutant load removal and potentially lead to a reduction in the process cost.

Continuous process of aerobic biodegradation of beet molasses vinasse: focus on betaine removal

We analyzed the effect of hydraulic retention time (HRT) and pH control of beet molasses vinasse on the efficiency of its continuous aerobic biodegradation with a mixed culture of Bacillus bacteria. Two experimental series were conducted in a 2-L stirred-tank reactor, at an aeration rate of 1 vvm, stirrer speed of 900 rpm, and temperature of 36 °C. The first series was run without medium pH control, whereas the other with pH maintained at 8.0. In both series, HRTs were 26, 47, and 78 h, whereas vinasse pH was raised to 8.0. The extent of its treatment via aerobic biodegradation depended on betaine assimilation phenomenon. High removal of pollutants (over 84%) expressed by the SCODsum index (SCODsum = soluble COD determined with the dichromatic method + theoretical COD of betaine) was achieved at HRTs of 47 and 78 h, whereas medium pH control had no explicit effect on biodegradation efficiency.