Biological Removal of Methanol from Kraft Mill Condensate, 1999 Environmental Conference Proceedings

Thomas Welander

ANOX AB

Roine Morin

SCA Graphic Sundsvall AB

Björn Nylén

Södra Cell AB

The anaerobic and aerobic biological treatment of kraft mill condensate were studied in laboratory, pilot plant and full scale. High-strength foul condensate containing 3000-6000 mg/l methanol and 5000-10000 mg/l COD was treated in anaerobic and aerobic laboratory scale suspended carrier biofilm reactors. Both anaerobic and aerobic treatment could be operated at volumetric loading rates up to 20-25 kg COD/m3 d achieving a complete elimination of methanol and a soluble COD-removal around 90%. Treatment of evaporator condensate of moderate strength, containing 300-600 mg/l methanol and 800-1200 mg/l COD, in a sequential anaerobic/aerobic system consisting of an anaerobic filter followed by an aerobic suspended carrier reactor was studied on a laboratory, pilot plant and full scale. At volumetric loadings of 3 (full scale), 5 (pilot scale) and 8 (lab scale) kg COD/m3 d, the anaerobic filter removed >95% of the methanol and around 70% of the COD from the condensate. The aerobic posttreatment increased the removal of COD from the condensate to 90%. However, the condensate was found to exhibit an inhibitory effect on the methanogenic microflora, limiting the capacity of the anaerobic process, making it more sensitive to disturbances and causing long recovery times after upsets.