Advanced effluent treatment with ozonation and biofiltration at the paper mill SCA-Graphic Laakirchen AG - Austria: Design and operation experience

The paper mill SCA GRAPHIC LAAKIRCHEN AG is situated in Austria and produces 486,000 to of graphic paper per year. A yearly amount of 6,923,000 m(3) of wastewater with a COD-load of 7,819,000 kg is treated on site (2005). The trend towards brighter paper grades requires more intense bleaching of mechanical pulp and increased usage of chelating agents and optical brighteners. These chemicals are difficult to degrade with biological waste water treatment. Higher bleaching dissolves more lignin, which is hard to degrade as well. As a result the COD removal efficiency in the biological stage of the wastewater treatment plant drops and additional measures for enhanced COD reduction have to be implemented in order to maintain given discharge limits.