Water draining a waste dump at the Hartenstein site of the former uranium mining company SDAG Wismut is characterised by an uranium concentration between 1mg/L and 3 mg/L and a nitrate concentration from 30 mg/L to 120 mg/L. A microbiological process was developed between 2001 - 2003 under laboratory conditions and, after this time, the process was scaled up to a technical plant. The water was treated continuously by a controlled microbiological process under anaerobic conditions with methanol as the sole carbon and energy source. The reduction plant is a basin filled with about 540 m³ of gravel and with a free water volume of about 200 m³. The plant was foreseen for the treatment of a drainage water flow rate of 2 m³/h – 5 m³/h. The residence time of the treated water in the plant comprises 40 h– 100 h according to the water flow. The continuous process started in 2004. The Uranium concentration decreased to values lower than 0.5 mg/L. The arsenic concentration varied in a range from 60 to 80 .g/L after reaching stable anaerobic conditions. The plant worked also during deep temperatures in the wintertime.