The aim of the study was to optimise the parameters (temperature and pH) of potato slops biodegradation with a mixed population of thermophilic and mesophilic aerobic bacteria of the genus Bacillus. Temperature and pH were optimised during 93-hour growth in the shake-flasks at 30 to 60ºC and pH 3.88 to 9.0. The course of the biodegradation process at optimal temperature and pH, and with increased oxygen supply, was investigated in an aerated stirred-tank bioreactor. During cultivation in shake-flasks, the following phenomenon was observed: the higher was the process temperature, the sooner the maximal number of cells was achieved. Taking into account the need of maximising the extent of the COD reduction, the optimal temperature and pH values (calculated on the basis of experimental data) were 44.6ºC and 7.40. With such parameters, a 22.5% reduction in COD was obtained. The highest number of cells (2.3x10⁹/mL) was achieved at 30ºC and pH 5.96.n The biodegradation of potato slops in the stirred-tank bioreactor yielded an 86.5% reduction in COD. The process was carried out for 53 hours but most of the pollutants were degraded at the initial stage (21 h). Of the compounds which were utilised as carbon sources and occurred in the highest amounts, lactic, propionic and acetic acids were removed completely (100%), while the removal of reducing substances and glycerol exceeded 90%.