Degradation of nitrogen-containing pharmaceuticals by anammox bacteria: Inhibition and nitrogen removal

Anaerobic ammonium-oxidizing (anammox) bacteria effectively remove nitrogen from wastewater and are widely used in sidestream processes, such as the treatment of centrate, which contains high concentrations of pharmaceuticals. To evaluate the role that anammox bacteria play in degrading nitrogen-containing pharmaceuticals, we exposed biomass from an anammox enrichment reactor to a synthetic wastewater mixture containing caffeine, carbamazepine, sulfamethoxazole, trimethoprim, and fluoxetine. These compounds were introduced at elevated concentrations, typically observed in agricultural wastewater or in municipal sludge and sidestream processes. Despite significant reduction in the ammonium removal efficiency upon exposure, total dissolved nitrogen removal efficiencies remained high. 16S rRNA gene sequencing showed that pharmaceutical exposure changed the microbial community, causing a reduction in the relative abundance of anammox species, including Candidatus Brocadia sinica and Ca. Brocadia fulgida , but an increase in denitrifiers. Incubations containing anammox reactor biomass showed higher pharmaceutical removals than abiotic controls and heat-treated samples, but the removals were only significant for caffeine and trimethoprim. Fluoxetine and sulfamethoxazole unfortunately could not be quantified due to analytical constraints and are therefore not included in the removal analysis, which presented a limitation of this study. Heterotrophs Zeimonas arvi and Aggregatilinea lenta increased in abundance and may have contributed to pharmaceutical removal through co-metabolism. This research leads to a better understanding of both the resilience of anaerobic consortia containing anammox and the effect that mixtures of pharmaceuticals have on systems that rely on biological removal of nitrogen.