Environmental Impact of Acidic Shower Water Usage on the Final Stage of a Brownstock Washing System, 1995 Environmental Conference Proceedings

William Josephson

Harry T. Cullinan

Gopal A. Krishnagopalan

Auburn University

Using an acidic shower stream on the last stage of pulp washing is a method of increasing the level of chemical recovery in the Kraft process. This effect occurs because the lowered pH environment causes sodium ions to desorb from the pulp fibers and thus become available for removal through washing. However, the effects of the acidic shower on the washing of organic materials are largely unknown. There are grounds for believing that an acidic shower would adversely affect the washing efficiency of organic materials (lignin). Since these organic materials are a source of aqueous pollutants, use of acidic shower streams may increase the need for wastewater treatment in a typical Kraft mill. The effects of using acidic showers were investigated using a laboratory displacement cell washing apparatus. Experiments were conducted where pulp was washed using neutral shower water, acidic showers or 50/50 split applications of neutral and acidic showers. The results indicate that, while acidic showers make possible increased chemical recovery, they also increase the retention of bound organic materials with the pulp. Although the total amount of lignin leaving with the pulp is not changed, a greater proportion of lignin is bound to the fibers as the last washing stage is exited. These increased levels of bound organic materials may increase bleach plant chemical demand and the load on a mill’s effluent treatment system. The bound organic materials will affect the economics of the process. Thus, the behavior of organic materials must be accounted for when considering using an acidic shower system...