Treatment of Packaging Board Whitewater in a Combined Anaerobic and Aerobic Bio-Kidney, 2002 Environmental Conference Proceedings

T. Welander, T. Alexandersson, Å. Dahl and Å. Malmqvist

Trials were carried out in a pilot scale that combined anaerobic/aerobic bio-kidney with whitewater from a recycling packaging board mill in order to study the start-up time and process stability towards natural variations in water composition.

After a long start-up time the process showed high efficiency and stable operation, despite a highly variable load. The organic loading rate (OLR) on the anaerobic step varied between 5 and 44 kg COD/m3*d while the OLR on the aerobic step was between 2 and 25 kg COD/m3*d.

The removal of organic matter, as soluble COD, at the lowest OLR was 78% in the anaerobic step and 87% after the combined process. An OLR of 20 kg COD/m3*d resulted in the removal of 65% soluble COD and 80% soluble BOD7 in the anaerobic step. The OLR on the subsequent aerobic step was 11 kg COD/m3*d and the removal efficiency over the combined process around 80% on soluble COD and 90-95% on soluble BOD7. The removal efficiency remained high even at the highest loading where the removal of soluble COD was 67 and 85% in the anaerobic and combined process respectively.

Filtration tests showed that the filterability of the water varied significantly depending on the amount and fate of biosolids in the treated whitewater. Water treated at a moderate organic load, with a slight excess of nutrients and with some separation of biosolids, showed to have a shorter filtering time than the untreated whitewater. In comparison, aerobically treated water containing a high amount of biosolids with poor separability showed very long filtering times.