Effect of Copper and Other Trace Metal Addition to Pulp and Paper Wastewater

Porous pots were used to mimic, on a laboratory scale, an industrial activated sludge plant from a thermomechanical pulp and news print paper mill. Trace metal additions of Ca, Co, Cu, Fe(III), and Mg were found to improve chemical oxygen demand removal from 82% to 86 to 87%. Copper (0.1 to 1.0 mg/L) was also found to be beneficial in significantly inhibiting the growth of filamentous bacteria, contributing to a reduction of 20 to 45% in sludge volume index (SVI) with improved settle ability and decreased bulking. However, at levels of 1.0 mg/L and higher, the concentration of Cu in the porous pot effluent would potentially exceed guidelines for receiving waters. The fate and impact of Cu was affected by the presence of other trace metals, in particular Mg and Ca. The addition of Mg or Ca along with 0.5 mg/L Cu increased the amount of Cu in the aqueous phase to levels that would potentially exceed government environmental guidelines. Calcium addition was also found to inhibit the effect of Cu in reducing filamentous bacteria and SVI.