Anaerobic-aerobic treatment of chemical industrial effluents

Several chemical industries in Canada discharge untreated effluents containing substantial amounts of organic pollutants. Environmental concern regarding the pollution of water bodies has led the authorities to issue stringent regulations with respect to the quality and quantity of wastewater that can be discharged. Chemical characterization and biotreatability of some waste streams generated by a chemical industry in Quebec was therefore undertaken. The study showed that two highly concentrated effluents were amenable to biological treatment. The first effluent, "plastifiant", was generated from the production of plastics, while the second, "colonne", was the product of a resin distillation column. Batch assay tests, including biochemical methane potential (BMP) and anaerobic toxicity assay (ATA), showed a moderate degree of anaerobic treatability with soluble COD removals of 45 to 61% and 11 to 67% for the colonne and plastifiant, respectively. Percentage COD removal was found to vary depending on the source of seed sludge. A mixture of biomasses from different sources was shown to be preferable for the anaerobic degradation of both effluents. The colonne effluent did not exhibit any toxicity to methanogenic bacteria. Inhibition of anaerobic microorganisms from the plastifiant effluent was found to be directly proportional to the increase in concentration, indicating that this effluent should be diluted. Continuous flow studies revealed that the selected effluents could be treated by anaerobic, aerobic or sequential anaerobic-aerobic techniques with soluble COD removals of 58, 80 and 89%, respectively. A significant impact of the type of anaerobic sludge and operating parameters with respect to the extent of biological treatment was noted, suggesting that the treatment efficiencies can be further improved. The one-step anaerobic or aerobic process was found to be applicable as a pre-treatment, while for a full treatment and direct discharge into receiving water bodies, a two-step sequential anaerobic-aerobic process should be implemented.