Biogenic metals for the oxidative and reductive removal of pharmaceuticals, biocides and iodinated contrast media in a polishing membrane bioreactor

Pharmaceutical and personal care products, biocides and iodinated contrast media (ICM) are persistent compounds, which appear in ng to μg L−1 in secondary effluents of sewage treatment plants (STPs). In this work, biogenic metals manganese oxides (BioMnOx) and bio-palladium (Bio-Pd) were applied in lab-scale membrane bioreactors (MBR) as oxidative and reductive technologies, respectively, to remove micropollutants from STP-effluent. From the 29 substances detected in the STP-effluent, 14 were eliminated in the BioMnOx-MBR: ibuprofen (>95%), naproxen (>95%), diuron (>94%), codeine (>93%), N-acetyl-sulfamethoxazole (92%), chlorophene (>89%), diclofenac (86%), mecoprop (81%), triclosan (>78%), clarithromycin, (75%), iohexol (72%), iopromide (68%), iomeprol (63%) and sulfamethoxazole (52%). The putative removal mechanisms were the chemical oxidation by BioMnOx and/or the biological removal by Pseudomonas putida and associated bacteria in the enriched biofilm. Yet, the removal rates (highest value: 2.6 μg diclofenac L−1 d−1) need to improve by a factor 10 in order to be competitive with ozonation. ICM, persistent towards oxidative techniques, were successfully dehalogenated with a novel reductive technique using Bio-Pd as a nanosized catalyst in an MBR. Iomeprol, iopromide and iohexol were removed for >97% and the more recalcitrant diatrizoate for 90%. The conditions favorable for microbial H2-production enabling the charging of the Pd catalyst, were shown to be important for the removal of ICM. Overall, the results indicate that Mn oxide and Pd coupled to microbial catalysis offer novel potential for advanced water treatment.

Research highlights
► Oxidative properties of biologically precipitated manganese oxides.
► Reductive properties of nanosized palladium particles.
► Removal of recalcitrant trace compound from wastewater effluent.