Degradation of sulfamethoxazole by persulfate assisted micrometric Fe0 in aqueous solution

Persulfate (PS) chemical activation using micrometric Fe0 particles (MIPs) was tested on sulfamethoxazole (SMX) solution (39.5 μM). MIPs load (0.89-17.85 mM), PS content (0.4-1.0 mM), pH (5.50-8.30) and alkalinity (bicarbonate) were investigated for the improvement of SMX degradation. Optimum conditions for the enhancement of the reaction stoichiometric efficiency (RSE = 5.2%) were developed. HPLC-MS results confirmed that SMX was converted into its reduced form through cleavage of the isoxazole N-O bond by two routes: (i) electron abstraction upon sulfate radicals (SRs) attack yielding non stable radical cation SMX+ or (ii) electron addition through Fe0 oxidation yielding unstable radical anion SMX−. In both cases, the final transformation product was identified as b-aminoenone after acceptance of electrons originated from the MIPs surface and protons present in the acidic medium. This suggested that PS activated into SRs was responsible of the rapid degradation of SMX and its transformation product as well in contrast to Fe0 alone. Different water matrices were evaluated in order to understand the role that dissolved ions play on the reaction degradation rate. Successive experiments (n = 3) of 1 h each conducted on remaining Fe0 showed complete SMX degradation. The extent of SMX mineralization under the experimental conditions reached 37% making from Fe0/PS system an excellent source of SRs able to sustain oxidation reactions in aqueous media of slightly acidic pH.