A laboratory-scale study was conducted on a two-stage fermentation reactor system and an upflow anaerobic filter system at several loading rates and hydraulic retention times. Feed substrate was wastewater from yeast production plant. The hydraulic residence time for first-stage fermentation reactor was 7 days and loading rate was in the range of 1.1-2.3 kg COD m−3d−1. The hydraulic residence time for second-stage fermentation reactor was 3.5 days and loading rate was 0.8-1.0 kg COD m−3d−1. Upflow anaerobic filter was operated at hydraulic retention time ranging from 5 to 2 days and loading rates ranging from 0.5 to 4.5 kg COD m−3 d−1. Despite shorter residence time, higher purification effects have been achieved for upflow anaerobic filter than for I-stage digestion reactor. For anaerobic upflow filter 61%-68% of COD reduction has been achieved at loading rates 3.5-4.0 kg COD m−3 d−1 and retention time of 2 days. For both systems in comparison the relationship between purification effects and volumetric organic load has been established. Amount of generated fermentation gas has been measured and composition of that gas has been analysed. Methane content in fermentation gas was in the range of 6l%-64%, hydrogen sulfide content was 0.5%-1.9%. Laboratory experiments were carried out at the temperature 33°C.