Fate of pharmaceuticals during varying redox treatment environments

The purpose of this study was to examine the relationship between low DO treatment conditions and transformation of environmentally relevant concentrations of pharmaceuticals. The compounds sulfamethoxazole (SMX), atenolol (ATE), desvenlafaxine (DVF), trimethoprim (TMP), and Dilantin (DLT) were detected in local primary effluent, and transformation was measured in lab-scale sequencing batch reactors operating concurrently with 10 day SRT and either anoxic/aerobic, fully aerobic, or microaerobic (DO < 1 mg/L) conditions. Endpoint reactor samples revealed that DVF, TMP, and DLT were recalcitrant in all redox conditions investigated; only ATE and SMX showed significant transformation. Transformation of ATE was greatest in the aerobic reactor (87 ± 13%), followed by the microaerobic reactors (74 ± 9 %) and anoxic/aerobic reactor (62 ± 19%). The microaerobic reactors showed the best performance for SMX transformation (55 ± 25%), followed by the aerobic reactor (38 ± 15%) and anoxic/aerobic reactor (30 ± 21). Cross-cycle sampling revealed different patterns of removal for ATE and SMX. Transformation of ATE appears to occur rather consistently across the reaction cycle independent of redox environment, whereas transformation of SMX appears to be influenced by nitrification. An increase in SMX was observed during anoxic conditions, consistent with previous studies that show human metabolites deconjugate back to the active compound in bioreactors. Operation and nutrient removal performance of the sequencing batch reactors is also discussed.