Impact of anaerobic zone on biodegradation of micropollutants: Comparison of micropollutants’ removal efficiencies in lab-scale anaerobic bioreactor and in full-scale anaerobic zone

Abstract

To predict the fate of micropollutants (MPs) in the anaerobic zone at the lab and full-scale levels, anaerobically biological removal (adsorption and biodegradation) of 40 MPs was performed. Among the 40 MPs in the full-scale anaerobic tank, estriol and acetaminophen showed the highest total removal efficiencies in the anaerobic zone (∼100 %). In batch tests, five MPs belonging to estrogens (estriol and 17b-estradiol), parabens (ethyl paraben and propyl paraben), and iopromide were completely removed within 12 h. Meanwhile, MPs belonging to perfluorinated compounds and nitrosamines were infrequently removed (<20 %) within 12 h. The obtained solid-water distribution coefficient (Kd) and biodegradation rate constants (Kbiol) values were used for predictive modeling of residual MPs’ concentrations in the full-scale anaerobic zone and were compared with Kbiol obtained from the oxic zone. Most MPs had similar Kbiol values regardless of redox conditions (oxic or anaerobic); however, caffeine, ibuprofen, naproxen, trimethoprim, and iopromide showed different values depending on the redox conditions. Differences in the efficiencies of total MP’ removal were noted between that predicted via modeling and actually observed (-37 % [iopromide] to 49 % [caffeine]) under altered conditions such as levels of dissolved oxygen (DO) and introduction of the primary or returned sludge. This implies that strictly anaerobic conditions are required for the degradation of specific MPs. The Kd and Kbiol values obtained in this study could help predict changes in the concentration of MPs in the anaerobic zone.