Degradation of emerging pharmaceutical micropollutants in municipal secondary effluents by low-pressure UVC-activated HSO5- and S2O82- AOPs

The degradation of six representative emerging pharmaceuticals (PhACs) (carbamazepine (CBZ), crotamiton (CRMT), N,N-diethyl-meta-toluamide (DEET), gemfibrozil (GEM), ibuprofen (IBP) and trimethoprim (TMP)) mixture in municipal secondary effluents by UVC-activated HSO5- and S2O82- were investigated and compared to UV/H2O2 process. The results showed that the PhACs degradation efficiencies by UV/HSO5- were typically smaller than those obtained by UV/H2O2. In contrast, UV/S2O82- offered larger degradation efficiencies of CBZ, GEM, IBP and TMP in comparison to UV/H2O2, which however was less effective in degrading CRMT and DEET. The electron spin resonance (ESR) and radical scavenging tests indicated that hydroxyl radical (HO center dot) was the major reactive species responsible for the degradation of PhACs by UV/HSO5-, while both sulfate radical (SO4 center dot-) and HO center dot contributed to PhACs degradation by UV/S2O82-. The rate constants of PhACs reacting with HO center dot/SO4 center dot- were determined on the basis of their degradation kinetics. All PhACs have large rate constants with HO center dot over the range of (7.66-9.86) x 10(9) M-1 s(-1). Among of them, CBZ, GEM, IBP and TMP have large rate constants with SO4 center dot- at (1.48-4.59) x 10(9) M-1 s(-1). However, CRMT and DEET have smaller rate constants with SO4 center dot- at 2.84 x 10(8) and 2.95 x 10(8) M-1 s(-1), respectively, thereby resulting in limited degradation efficiencies by UV/S2O82-. The degradation intermediates of PhACs were investigated and tracked by LC-QTOF-MS. Evolution of effluent organic matters (EfOM) was investigated by means of excitation-emission fluorescence matrices (EEFM), indicating successful destruction of EfOM by HO center dot/SO4 center dot-. The reaction stoichiometric efficiencies (RSE) of Delta dissolved organic carbon (DOC)/Delta oxidants were compared, suggesting high oxidant utilization efficiencies for UV/HSO5- and UV/S2O82- at 66.8% and 52.0%, respectively.