Removal of Cod From Pulp and Paper Industry Effluents Using Suspended Carrier Technology, 1998 Environmental Conference Proceedings

Thomas Welander

Åsa Malmqvist

ANOX AB

Alf Svensson

Bäckhammars Bruk

Christer Torstenson

Nyboholms Bruk

The performance of two full-scale suspended carrier biofilm processes within the Swedish pulp and paper industry has been evaluated. The effluent from the Bäckhammar unbleached kraft mill is treated in a two-stage biofilm process followed by chemical precipitation and clarification. The biofilm reactors are operated without any preceding primary clarifier and primary sludge as well as biosludge and

chemical oxygen demand (COD) at a total treatment time of 1.5 h. Occasional fibre and black liquor spills have proved the process to be tolerant to very high fibre concentrations (>30 g/l) and to recover within a few days after severe disturbances caused by high pH (>12). The effluent from the Metsä Tissue Nyboholm mill, producing tissue from recycled paper, is treated in a process comprising primary clarification, biological treatment and secondary clarification, both clarifiers operated with chemicals to enhance the separation. The biofilm reactor removes 70-80% of the soluble COD at a treatment tune of 3 h. The process has been found to be very little affected by great variations in operating temperature over the year.