Effect of Tertiary Coagulation and Flocculation Technologies on Bleached Kraft Mill Effluent Quality, 1997 Environmental Conference Proceedings

Crestbrook Forest Industries Ltd. operates a 650 tpd kraft pulp mill in Skookumchuck (near Cranbrook) BC. In addition to primary and secondary effluent treatment, the mill is the first in Canada to implement tertiary wastewater treatment in the form of a coagulation/ flocculation system for colour removal. Since January 1995, the process has removed an average of 60 +7% of effluent colour. Coagulation and flocculation technologies are relatively non-specific. Therefore, in addition to removing the chromophores of concern, tertiary treatment of kraft effluent may also significantly reduce the levels of other major parameters such as chemical oxygen demand, chlorinated organic compounds, and target contaminants such as TCDF. In addition, there is potential for reduction in the compounds responsible for sub-lethal toxic effects such as “Compound X”, the putative inducer of detoxification enzymes in fish. In this way, coagulation/flocculation technologies may prove a cost effective means to dramatically reduce the environmental impact of pulp mill effluent discharge. This paper reports on a number of aspects of a study which we have undertaken at Crestbrook Forest Industries Ltd. pulp mill. First, we will report on the impact of a range of operating parameters (pH, temperature, effluent BOD) on performance of the system. Second, we examine the impact of a full scale coagulation/floculation process on the overall effluent quality at the mill. Third, we will examine the potential for application of such systems to segregated C and E stage process filtrates.