The aim of the study was to establish such conditions that would provide high-efficiency aerobic biodegradation of beet molasses vinasse with a mixed culture of thermo- and mesophilic bacteria of the genus Bacillus in batch processes without controlling the pH of the medium. Particular consideration was given to the betaine removal (the main pollutant of vinasse), which accounted for as much as 37.6% of total organic carbon. Biodegradation was performed in a stirred tank reactor at 27-63°C with initial pH (pH₀) of 6.5 and 8.0. Efficiency of biodegradation was expressed in terms of reduction in SCOD_sum, which is a sum of SCOD (soluble chemical oxygen demand, i.e. COD determined after suspended solids separation) and theoretical COD of betaine. The values achieved at 27 and 36°C with pH0 = 8.0 exceeded 77.7%, whereas those obtained at 36 and 45°C with pH₀ = 6.5 were higher than 83.6%. The high biodegradation efficiency obtained in the four processes is attributable to the betaine removal by the bacterial strains used in the study. Maximal extent of reduction in SCOD_sum (85.41%), BOD5 (97.91%) and TOC (86.32%), and also the fastest rate of biodegradation (1.17 g O₂/l∙h) was achieved at 36°C and pH₀ = 8.0