Pharmaceutical Attenuation Differs within Woodchip-Based Lignocellulose Bioreactors across Nitrate- and Sulfate-Reducing Conditions

Lignocellulosic bioreactors use solid-phase sub-strates such as woodchips to sustain microbial respiration and have been applied to treat agricultural runoff, stormwater, and other impaired waters. Here, we query how respiration of different soluble electron acceptors impacts the degradation of environ-mentally relevant pharmaceuticals associated with treated munic-ipal wastewater discharge. Laboratory-scale columns containing a mixture of woodchips and alfalfa were manipulated across nitrate-and sulfate-reducing conditions using residence time and influent composition. Under steady-state conditions, bioreactors domi-nated by nitrate reduction harbored a distinct phylogenetic profile containing the genera Denitratisoma and increases in the denitrification gene nirS. In contrast, bioreactors where sulfate reduction dominated exhibited increased relative abundance of fermenters (e.g., Obscuribacteriales) and putative sulfate reducers (e.g., Desulfobulbus). Atenolol attenuation and biotransformation to carboxy-metoprolol accelerated under nitrate-reducing conditions; in contrast, trimethoprim attenuation and biotransformation to desmethyl trimethoprim was nearly an order of magnitude faster under sulfate-reducing conditions. Modest sulfamethoxazole attenuation occurred under all tested conditions. Denitrification-associated rate constants for atenolol were comparable to those reported in constructed wetlands and aquifer recharge, suggesting commonality in biotransformation mechanisms. Collectively, results suggest that manipulation of biogeochemical gradients during nature-based treatment can be applied to attenuate nitrate and trace quantities of pharmaceuticals.