Destruction of propyl paraben by persulfate activated with UV-A light emitting diodes

Abstract

UV-A light emitting diodes (LEDs: 10 W of nominal power, 7.9 × 10−7 einstein/(L.s) photon flux) were employed as the radiation source to activate sodium persulfate (SPS) for the degradation of endocrine disruptor propyl paraben (PP). Experiments in ultrapure water (UPW) were conducted varying SPS concentration between 0 and 500 mg/L, PP concentration between 100 and 800 μg/L, initial solution pH between 3.2 and 9.2, as well as adding various organic (alcohols and humic acid) and inorganic (bicarbonate, chloride), non-target species. Besides UPW, experiments were performed in two actual matrices, i.e. secondary treated wastewater and bottled water. Degradation was found to increase with increasing SPS concentration and decreasing PP concentration, while it was favored as near-neutral, inherent solution pH. The addition of methanol and t-butanol, known radical scavengers, partly restricted the reaction, thus implying that both sulfate and hydroxyl radicals are formed and participate in PP degradation. The addition of humic acid in UPW completely quenched the reaction and so did the use of wastewater as the water matrix. Less significant were the effects of bicarbonate and chloride. SPS can also be activated by the UV-A part of simulated solar radiation (7.3 10−7 einstein/(L s) photon flux), potentially improving process sustainability.