Dose-dependent effects of acetate on the biodegradation of pharmaceuticals in moving bed biofilm reactors

Moving bed biofilm reactors (MBBR) are promising as a post-treatment for removing pharmaceuticals from wastewater. However, the effect of easily degradable carbon sources on the degradation of pharmaceuticals is unclear. This study shows the influence of acetate on the degradation of 26 pharmaceuticals in an MBBR was dose- and compound-dependent: while the degradation of venlafaxine, tramadol and ciprofloxacin was promoted (increase of reaction rate constant (k) by 133%, 212%, 55%) by acetate, its presence caused negative effects on the removal of ibuprofen, citalopram and diclofenac (decrease of k by 76%, 57%, 44%). The deconjugation of acetyl-sulfadiazine was clearly slowed down (decrease of k by 75%) by the dosed acetate, probably due to feedback inhibition by abundant acetate. 17 out of 25 tested compounds were found to be independent of the acetate dosage, which suggested dosing acetate induced minor effects on most of pharmaceuticals' removal. Enrichment of S- or first eluted enantiomer of 4 β-blockers and the metabolite metoprolol acid was observed. Both non-enantioselective (rapid at elevated compound concentration) and enantioselective enzymes (slower and predominant at lower compound concentration) played a part in the biodegradation. High doses of acetate slowed down the enantiomeric enrichment of atenolol, metoprolol, propranolol and metoprolol acid, which demonstrated that the acetate is able to up- or down-regulate enzymes involved in the enantioselective degradation of β-blockers and thus reveals a complex co-metabolism relationship between transformation pathways of pharmaceuticals and carbon source.