Effect of biological treatment on halogenated organics in bleached kraft pulp mill effluents studied by molecular weight distribution analysis

The removal potential of different biological treatments of organohalogen compounds in kraft pulping and bleaching effluents was studied by nonaqueous size-exclusion chromatography and grouping the compounds by solubility and adsorption characteristics. Organohalogen compounds of waste waters from five pulp mills with different processes exhibited similar molecular weight distributions, ranging from 100 to 4000. The anaerobic/aerobic lagoon system removed 58-66% of the organochlorine compounds from the water phase and the fullscale activated sludge plants removed 19-55%. Both biotreatments removed all size classes of organochlorine molecules and slightly changed the relative size distribution of the compounds remaining in the water phase toward the larger molecular weights. The organic chlorine compounds were divided into three categories on the basis of extractability to organic solvent and adsorption to activated carbon, one of the categories being recalcitrant to the biotreatments studied.