title: Evaluating the contribution to toxicity of weak black liquor in pulp mill effluents
Creators: name: Ragsdale, Renee L.
Publisher: name: Western Washington University
Year: 2011

description: <p>Weak black liquor (WBL) losses in pulp mills may affect effluent treatment efficiencies and may be linked to aquatic toxicity observed in final mill effluents. Best management practices (BMP) for controlling losses of WBL have been effective at reducing WBL from entering the mill effluent treatment system, but it is unclear at what level WBL may contribute to increased toxicity, or whether specific chemical compounds found in WBL may be consistently responsible. The objective of this study was to evaluate the contribution of WBL in biologically-treated bleached kraft pulp mill effluents to toxicity, and to assess effluent chemical parameters that may correlate with biological responses. Weak black liquor and untreated wastewater (as it enters the biological treatment system) were collected from four bleached kraft mills along with mill-treated effluent samples. To simulate a range of potential WBL losses, various concentrations of WBL were added to untreated wastewater from each mill and treated in bench top aerobic reactors to mimic biological treatment (biotreatment). Following laboratory biotreatment, toxicity of the resulting "simulated effluents" (as well as mill-treated effluents) were evaluated using 48-h Mytilus galloprovincialis embryo-larval development and 7-d Ceriodaphnia dubia survival and reproduction chronic toxicity tests. All effluent samples were chemically characterized for pH, color, conductivity, turbidity, total suspended solids (TSS), polyphenols, hardness, alkalinity, salinity, biochemical oxygen demand (BOD), dissolved chemical oxygen demand (DCOD), dissolved organic carbon (DOC), resin acids (RAs), and phytosterols. Correlation analysis was used to determine if there were significant correlations between: 1) WBL solids and simulated effluent chemical parameters; 2) WBL solids and chronic toxicity to M. galloprovincialis and C. dubia; 3) effluent (mill-treated and simulated) chemical parameters and chronic toxicity to M. galloprovincialis and C. dubia; and 4) between the two chronic toxicity tests. Multivariate methods including cluster analysis (hierarchical, kmeans, and non-metric Riffle) and PCA were also used to explore the data for patterns, and to identify effluent chemical parameters that might relate to WBL solids or effluent toxicity. Results were that the 48-h EC50 for M. galloprovincialis embryo-larval development appears to be a more sensitive endpoint than the 7-d C. dubia reproduction with respect to both mill-treated and simulated effluent samples. For the simulated effluent samples, color, DCOD, and polyphenols were positively correlated with WBL solids. For three out of four mills, color and polyphenols were negatively correlated with the 48-h EC50 for M. galloprovincialis embryo-larval development (i.e. as the EC50 decreased (toxicity increased) these chemical parameters increased)). For two out of four mills, DCOD was negatively correlated with the 48-h EC50 for M. galloprovincialis embryo-larval development. Significant negative correlations were also observed between the 48-h EC50 for M. galloprovincialis embryo-larval development and abietic acid (one mill out of four) and between the 48-h EC50 for M. galloprovincialis embryo-larval development conductivity (one mill out of four). None of the measured chemical parameters correlated with chronic toxicity to C. dubia. A significant negative correlation was also observed between the 48-h EC50 for M. galloprovincialis embryo-larval development, and between WBL solids and the 7-d IC25 C. dubia reproduction (i.e. as WBL solids increased the toxicity increased (as indicated by a decrease in EC50/IC25)). A correlation was not found between the two chronic toxicity tests. Consistent across all multivariate methods, simulated effluent samples appeared to group together based on mill rather than on the amount of WBL solids added.</p>