Transformation of paracetamol into 1,4-benzoquinone by a manganese oxide bed filter.

This study investigates the transformation of paracetamol (PRC) by a granular manganeseoxide in a column bed reactor. Paracetamol was quantitatively transformed into p-benzoquinone(BZQ) for empty bed residence times (EBRT) <5 min at pH 6.0. For 5mM MOPS (3-morpholinopropane-1-sulfonic acid) and pH 7.0, the mean removal yield of PRC was 77% for initial PRC concentrations ranging from 0.1 to 50 µM. Conversion of PRC and formation of BZQ decreased when pH increased from 6 to 8. Dimer of PRC was observed at pH 7.0, which could explain the lower conversion into BZQ when pH increased. The presence of organic buffer MOPS and natural organic matter (NOM) reduced the oxidation of PRC because of competition reactions for active sites. The formation of the toxic BZQ metabolite was reduced in presence of NOM because of cross-coupling reactions between phenoxyl radicals and NOM. Results suggest that manganese oxide bed filter can be used to remove pharmaceutical compounds including phenolic moiety in their structure.

Oxidative decarboxylation of diclofenac by manganese oxide bed filter.

Diclofenac (DCF) was eliminated by fast chemical oxidation on natural manganese oxide in a column reactor. Identification of transformation by-products of DCF by HPLC-UV-MS(n) gave evidence of decarboxylation, iminoquinone formation and dimerization. The fast oxidation of DCF is also accompanied by a strong adsorption of organic carbon that was explained by the sorption of dimer products on the surface of manganese oxide. Decarboxylation and dimerization increased the hydrophobic interactions with manganese oxide and reduced the presence of potentially toxic by-products in the effluent. The rate of oxidation was first order with respect to DCF and was slowed down by the presence of organic buffer MOPS (3-morpholinopropane-1-sulfonic acid). The first order rate constant in absence of MOPS was extrapolated by considering a surface site-binding model and MOPS as a co-adsorbate. The rate constant was 0.818 min(-1) at pH 7 and 10 mM NaCl corresponding to empty bed residence time of 50 s only for 50% removal of DCF. Rate constants increased when pH decreased from pH 8.0 to 6.5 and when ionic strength increased. Manganese oxide bed filter can be considered as an alternative treatment for polishing waste water effluent or for remediation of contaminated groundwater.