Decreasing the Load on an ASB System by Pretreatment of TMP Effluent in a Suspended Carrier Biofilm Process, 1999 Environmental Conference Proceedings

R. Hunter

Tasman Pulp and Paper Co Ltd

T. Wellander

ANOX AB

Fletcher Challenge Paper Tasman Mills (Tasman) in Kawerau, New Zealand operates an integrated kraft pulp and mechanical printing paper mill using forest residue pinus radiata as a fibre source. The company has recently commissioned a new Thermo-mechanical pulp mill and as a part of the project installed a suspended carrier biofilm reactor to pretreat the TMP wastewater. This reactor was installed with the aim of decreasing the load from the new plant to the existing aerated stabilisation system (ASB) and avoiding any increase in the BOD load discharged from the mill to the Tarawera River.

The process that has been installed consists of a 1500m 3 reactor 40% filled with carrier elements, into which the raw TMP wastewater is fed without the need for initial clarification. The reactor is therefore required to deal with suspended solids loadings of up to 2000mg/l and BOD loads of around 1500mg/l. The initial startup of the reactor was very rapid with the goal of 50% BOD removal being achieved in 3 days, with process efficiencies continuing to improve and have stabilised at 90 and 80% for BOD and COD respectively. The plant runs trouble free with little operator input and has proven very tolerant of changes in the incoming wastewater, shut downs and other process variation.