Enhancement of the electro-Fenton degradation of organic contaminant by accelerating Fe3+/Fe2+ cycle using hydroxylamine

Abstract

The Electro-Fenton process can generate reactive oxygen species capable of oxidizing refractory organic contaminants. However, low regeneration efficiency of Fe2+ restricts its application. Herein, hydroxylamine (HA) was added into the Electro-Fenton (HA/Electro-Fenton) process to accelerate the transformation of Fe3+ to Fe2+. Using dimethyl phthalate (DMP) as target contaminant, the HA/Electro-Fenton system alleviated the two-stage reaction process and accelerated the removal of DMP in the pH range of 2.0–6.0. With improving DMP concentration from 5 mg L-1 to 50 mg L-1, their degradation rate increased in the HA/Electro-Fenton system, while decreased in the Electro-Fenton system. The addition of HA had negligible effect on electro-generation of H2O2, but facilitate the redox cycle of Fe3+/Fe2+ and the generation of hydroxyl radicals, thus improving the degradation of DMP. The final transformation products of HA were N2, N2O, and NO3−. The presence of PO43− improved DMP degradation, while Cl− and organic matters inhibited DMP removal in varying degrees. This study provided useful reference to solve the low efficiency of Fe3+/Fe2+ cycle and expand the pH application range in the Electro-Fenton process.