UBC Theses and Dissertations
The influence of the high molecular weight fraction of bleached kraft mill effluent on the biological activity of activated sludge Bullock, Christopher Mark
Bleached kraft mills have reduced the environmental impact of their effluent discharges by investing in biological treatment processes such as activated sludge treatment. Since the high molecular weight (HMW) fraction of bleached kraft mill effluent (BKME) represents a significant fraction of the adsorbable organic halide (AOX) and chemical oxygen demand (COD) load on biological treatment systems, the influence of this material on activated sludge activity was studied. Initially, we used ultrafiltration to fractionate the BKME from a mill producing elemental chlorine free softwood pulp. The HMW material (> 1000 Da) fraction contained 20% of the chemical oxygen demand and 75-85% of the AOX. Most of the nitrogen present in the effluent from the pulping and bleaching process was detected in the HMW fraction. Transition metals were associated with the BMW material to a greater extent than the less charged alkaline earth metals. Batch growth trials with microorganisms from a laboratory-scale activated sludge reactor were performed using the low molecular weight (LMW) fraction as the substrate and supplementing it with varying amounts of the HMW material. While both the LMW and HMW fractions alone supported little microbial growth, the HMW material stimulated microbial activity in the LMW fraction, by apparently providing the limiting nutrient, nitrogen. The addition of the BMW material to the LMW effluent increased the removal of various chlorinated phenols (6-chiorovanillin (6-CVa), 4,5-dichloroguaiacol (4,5-DCG), and 2,4-dichiorophenol (2,4-DCP)), which had been added (1.0 mgIL) to the effluent fractions. Supplementing the LMW effluent with nutrients also stimulated chlorinated phenol removal. The relative removal rates of the chlorophenols decreased in the order 6-CVa > 4,5-DCG > 2,4-DCP. Spiking the unfractionated effluent with up to 10 mgfL of 6-CVa, 4,5-DCG, and 2,4-DCP had no effect on the biomass production or substrate removal. These results seemed to demonstrate that the BMW material in the BKME had a stimulatory effect on the microorganisms present in the activated sludge by providing the limiting nutrient, nitrogen.
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