Induction of microbial oxidative stress as a new strategy to enhance the enzymatic degradation of organic micropollutants in wastewater

Organic micropollutants (OMPs) are pervasive anthropogenic contaminants of fresh and marine waters with known potential to adversely affect aquatic life (e.g. endocrine disruption). Their ubiquitous environmental occurrence is primarily attributed to wastewater treatment plant discharges following their incomplete removal by common biological treatment processes. This study assesses a new strategy for promoting the degradation of six model OMPs (i.e. sulfamethoxazole, carbamazepine, tylosin, atrazine, naproxen and ibuprofen) by stimulating microbial oxidoreductase production to counter the effects of oxidative stress caused by oxygen perturbation. Microbial cultures from dairy farm wastewater were exposed to a cyclical ON-OFF perturbations of oxygen supply, ranging from 0.16 to 2 cycles per hour (i.e. 2, 1, 0.5, 0.25 and 0.16 cycles/hour), in laboratory bioreactors. The activity and relative abundances of microbial oxidoreductases (such as peroxidases, cytochromes P450) were upregulated by oxygen perturbation. In comparison to controls subjected to constant oxygen levels, OMP concentrations in perturbed cultures decreased by 70{+/-}9% (mean {+/-} SD). A distance-based linear model confirmed strong positive correlations between the relative abundance of the bacterial families, Rhodocyclaceae, Syntrophaceae and Syntrophobacteraceae, and oxygen perturbations. Our results confirm that intentional perturbation of oxygen supply to induce microbial oxidative stress can improve OMP removal efficiencies in wastewater treatment bioreactors.