Diclofenac Oxidation by Biogenic Manganese Oxides

Diclofenac, a nonsteroidal anti-inflammatory drug, is one of the most commonly detected pharmaceuticals in sewage treatment plant (STP) effluents. In this work, biologically produced manganese oxides (BioMnOx) were investigated to remove diclofenac. At neutral pH, the diclofenac oxidation with BioMnOx was 10-fold faster than with chemically produced MnO2. The main advantage of BioMnOx over chemical MnO2 is the ability of the bacteria to reoxidize the formed Mn2+, which inhibits the oxidation of diclofenac. Diclofenac-2,5-iminoquinone was identified as a major transformation product accounting for 5-10% of the transformed diclofenac. Except for 5-hydroxydiclofenac, which was identified as an intermediate, no other oxidation products were detected. Diclofenac oxidation was proportional to the amount of BioMnOx dosed, and the pseudo first order rate constant k was 6-fold higher when pH was decreased from 6.8 to 6.2. The Mn2+ levels remained below the drinking water limit (0.05 mg L-1), thus indicating the efficient in situ microbiological regeneration of the oxidant. These results combined with previous studies suggest the potential of BioMnOx for STP effluent polishing.