Efficient degradation of sulfamethoxazole by the Fe(II)/HSO5− process enhanced by hydroxylamine: Efficiency and mechanism

[Display omitted] •Efficiency and mechanism of degradation of SMX by HA/Fe(II)/PMS were studied.•Role of HA in the HA/Fe(II)/PMS process was explored.•Hydroxyl radical oxidation dominated SMX degradation.•Degradation pathways of SMX were proposed.•HA/Fe(II)/PMS process was effective in removal of SMX and TOC in real wastewater. Fenton or Fenton-like processes have been regarded as feasible methods to degrade a wide variety of contaminants by generating reactive species, but the efficiency is still challenged by the slow transformation from Fe(III) to Fe(II) and pH. This study employed hydroxylamine (HA) to improve the oxidation efficiency of Fe(II)/HSO5− (Fe(II)/PMS) process, by selecting sulfamethoxazole (SMX) as the target compound. The degradation efficiency and mechanism of SMX by the HA/Fe(II)/PMS process were elucidated for the first time. Compared with Fe(II)/PMS process, the HA/Fe(II)/PMS process showed about 4 times higher degradation efficiency of SMX at pH 3.0. The analysis of steady-state concentration of Fe species indicated that HA enhanced the transformation of Fe(III) to Fe(II), sustaining the rapid Fenton-like reactions. Both sulfate radicals and hydroxyl radicals accounted for the degradation of SMX, with the latter regarded as the dominant reactive species. Degradation intermediates of SMX were further analyzed, and three main transformation pathways were thus proposed. The HA/Fe(II)/PMS process was also effective in the removal of SMX and total organic carbon from real pharmaceutical wastewater. This work would broaden the scope of application of Fenton and Fenton-like processes enhanced by HA in contaminants treatment.