Binding due to recalcitrant organic material in pulp mill effluent and its effect on biotreatability of bound pollutants.

摘要

Biological treatment of kraft mill effluents is characterized by the presence of a residual dissolved portion resistant to biodegradation and referred to as recalcitrant organic material (ROM). Recalcitrant organic material in biotreated kraft mill effluent comprises of a predominantly high molecular weight (HMW) fraction and is commonly quantified as chemical oxygen demand (COD) and colour. This research is motivated by the limitations of existing biotreatment systems in degrading ROM and a lack of understanding of the impact of ROM on the performance of biotreatment systems.; Batch biodegradation tests performed on the low molecular weight (LMW) and HMW fractions of ROM under optimized microbiological conditions showed the ROM to be resistant to further biodegradation over the time frames of conventional biological treatment.; Three experimental protocols, namely equilibrium dialysis, headspace analysis and MicrotoX™ toxicity assay were evaluated for their ability to demonstrate and quantify binding due to HMW ROM. Both model hydrophobic pollutants, namely benzo(a)pyrene and toluene, and pollutants found in mill effluents, namely dehydroabietic acid (DHA) and camphor were studied for binding onto HMW ROM. The ROM was also compared with dissolved humic acids for its binding characteristics.; Equilibrium dialysis, the most successful technique, demonstrated and quantified the binding of benzo(a)pyrene, toluene and dehydroabietic acid onto HMW ROM. This binding, which was not readily reversible, decreased with increasing concentration of HMW ROM and was not affected by solution pH or ionic strength. This was further confirmed by the headspace analysis technique conducted with camphor.; At the concentrations studied, batch biotreatability studies with dehydroabietic acid indicated no significant impact on biotreatability of DHA bound onto HMW ROM. Biotreatability studies with 14C-toluene enabled measurements at lower pollutant concentrations and demonstrated a decrease in toluene biodegradation in the presence of HMW ROM. This decrease in biotreatability was of the order of 10–5%.; It is concluded that HMW ROM binds other hydrophobic pollutants in the effluent and this binding affects biotreatability. Although this effect is not substantial for pollutants existing at high concentrations, it is suggested that the impact might be significant for those pollutants in the effluent that are highly hydrophobic and exist at very low concentrations.