Relationships among effluent constituents in bleached kraft pulp mills

Effluent constituents in a complete ClO2-substituted bleached Kraft mill were monitored in process lines and sewers for an extended period to determine the transport of these constituents through the mill and its treatment system. The end-of-pipe AOX/COD ratio was constant indicating that both COD and AOX at this location are lignin residuals that are not degraded in the treatment system. The ratio was higher for another mill that included Cl2 in its bleaching sequence. Conductivity at the recovery sewer was a good indicator of black liquor upsets. Significant BOD-COD correlations were found at the pulp mill and evaporator sewers, suggesting that COD from this source is biodegradable. Color and COD correlated well at the end-of-pipe, indicating that color originates from carbon that is not removed during treatment. Color also increased across the pond, suggesting that much of the organic material in the lagoon is not mineralized, but converted into smaller more chromophoric units. No trisubstituted or higher chlorophenols or chlorinated dioxins or furans were found in any of the bleach line filtrates.