Effect of High Molecular Weight Organics in Bleached Kraft Mill Effluent on the Biological Removal of Chlorinated Phenolics, 1994 Environmental Conference Proceedings

C. M. Bullock, P. A. Bicho, J. N. Saddler

About 20% of the chemical oxygen demand (COD) of the combined effluent from a softwood kraft pulp mill using an XPpoEDED bleach sequence consisted of high molecular weight (HMW > 1000 daltons) material. Growth experiments using microorganisms from a lab-scale activated sludge reactor showed that the HMW material had a significant role in biomass production, and soluble COD and chlorophenol removal. Large decreases in the soluble COD and increases in the biomass were observed with the addition of HMW material to the low molecular weight (LMW) fraction. Although this could be a result of increased biomass growth, it is more likely due to the sorption of HMW material onto the biomass. The addition of mono- and dichlorinated phenolic compounds at concentrations up to 10 mg/L were found to have no effect on the metabolism or growth of the microorganisms in the activated sludge. The presence of the high molecular weight material appeared to improve the removal of the chlorophenolic compounds. While 6-chlorovanillin (6-CV), 2,4-dichlorophenol (2,4-DCP), and 4,5-dichloroguaiacol (4,5-DCG) were found to be stable in uninoculated controls and inoculated LMW effluent over a 160 hour period, these compounds decreased significantly when LMW with three times the original concentration of HMW material (LMW+ 3xHMW) was inoculated with microorganisms. The removal rates of these compounds increased in the order: 6-CV > 4,5-DCG > 2,4-DCP. Although the removal mechanism has not yet been identified, biodegradation seems to be more predominant than biosorption. Sorption of these mono- and dichlorinated phenolics to the HMW material does not seem to be a major factor in their removal.