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

Abstract

Lignocellulosic bioreactors use solid-phase substrates 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 environmentally relevant pharmaceuticals associated with treated municipal 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 dominated 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.

Persistent Trace Organic Contaminants Are Transformed Rapidly under Sulfate- and Fe(III)-Reducing Conditions in a Nature-Based Subsurface Water Treatment System

“…In the past few decades, subsurface flow treatment systems, such as constructed wetlands, riverbank filtration, and managed aquifer recharge systems have increasingly been applied as a means of removing trace organic contaminants from treated wastewater and river water. − Although many contaminants are removed in these systems under aerobic conditions, removal of certain recalcitrant compounds, like sulfamethoxazole and carbamazepine, has only been observed to an appreciable degree under more reducing conditions in riverbank filtration systems and anaerobic membrane bioreactors. − Anaerobic microorganisms employ different enzymes and metabolic strategies than the aerobes that dominate carbon processing during wastewater treatment (e.g., activated sludge) and may promote biotransformation of trace organic contaminants that are more slowly biotransformed under aerobic or nitrate-reducing conditions. , …”