Degradation of aqueous 3-tertbutyl-4-hydroxyanisole with co-existing propyl gallate by zero-valent iron activated persulfate: Kinetic study and products identification

3-tertbutyl-4-hydroxyanisole (3-BHA) and propyl gallate (PG) are commonly mixed-used typical synthetic phenolic antioxidants (SPAs) and they were considered as environmental pollutants because of their adverse effects of biology. In this work, the degradation of 3-BHA with and without PG by zero-valent iron activated persulfate (ZVI-PS) system were investigated in detail. The effects of PS dose, Fe-0 content, solution pH, humic acid (HA), ions, and water matrix on the removal of 3-BHA with and without PG were evaluated by kinetic experiments. Results showed that increase in the dosages of Fe-0 and PS, and decrease in the pH value and the addition of 0.5 mg/L HA could improve the 90 min-degradation efficiency of 3-BHA to at least 62 %. Some typical ions i.e., Fe3+, NH4+, Cu2+, Cl-, and HCO3-, had positive effects on the degradation of 3-BHA (increase by 28.1 %similar to 70.2 % after 20 min of reaction). Different water matrix gave different observations and the degradation rate of substrate from high to low was ordered as: secondary clarifier effluent (0.1128 min(-1)) > ultrapure water (0.0763 min(-1)) > phosphate buffer solution (0.0342 min(-1)) > tap water (0.0147 min(-1)) > river water (0.011 min(-1)). The addition of PG strongly inhibited the above effects, especially at pH 3.0 (the current inhibition factor reached 14 times), but did not change their conversion trend. Under the optimal conditions of [Fe-0](0) = 2 mM, [PS](0):[SPAs](0) = 25:1 (molar ratio), and pH = 5.0, 19.06 mu M of 3-BHA were degraded after reaction for 90 min; while only 73.4 % of 3-BHA were oxidized with PG. Therefore, more Fe-0 and PS amounts were needed with co-existing PG. O-1(2), O-2(center dot-), and center dot OH and SO4 center dot- in especial triggered mixed SPAs undergoing hydroxylation, sulfate addition, and mixed polymerization to yield 22 possible byproducts. These findings reveal that combined organic pollution is largely distinguished with single system from the perspective of both transformation kinetics and pathways, and researchers should pay more attention on combined pollution. These results provide a theoretical basis for the removal of 3-BHA and PG by ZVI-PS technology, and may contribute to the development of effective treatment methods for the removal of mixed pollution of synthetic phenolic antioxidants in water environment.