Electrolysis of Weak Black Liquor and Bleach Effluent, 1996 Engineering Conference Proceedings

A. membrane-assisted electrolysis (MAE) cell capable of recovering chemicals from streams that normally foul anodes and membranes such as weak black liquor and bleach effluent has been developed and tested at the pilot-plant scale. In the electrolysis of weak black liquor, the pH of the liquor drops as caustic soda is recovered from the liquor. As the pH drops, the lignin precipitates and is recovered as a solid powder. The decreased solids content of the weak black liquor allows incremental pulp production at a recovery-boiler-limited mill. The lignin byproduct can be burned in the lime kiln or in a power boiler or sold as a byproduct. In the electrolysis of bleach effluent, caustic is recovered and the chemical oxygen demand (COD), biological oxygen demand (BOD), and color of the effluent are significantly reduced. The results of lab and pilot plant testing at the Boise Cascade Wallula, WA Paper Mill are reported. Pilot testing on weak black liquor processing has proven that MAE provides cost effective incremental capacity.