Unraveling different mechanisms of persulfate activation by graphite felt anode and cathode to destruct contaminants of emerging concern

The electro-activation of persulfate (PS) by graphite felt (GF) electrode is a novel advanced oxidation process applied for the degradation of contaminants of emerging concern (CECs). Both GF anode and cathode can electro-activate PS to degrade CECs, including atrazine (ATZ), bisphenol S, ethinylestradiol, and ibuprofen. The study examines the removal performance of ATZ in sulfate, nitrate, and perchlorate electrolyte. The degradation of ATZ followed the order of sulfate (36.3 L (Ah)(-1)) > perchlorate (22.2 L (Ah)(-1)) > nitrate (5.8 L (Ah)(-1)) in GF anode/PS system, while electrolytes had little influence on the degradation of ATZ (15.8-21.3 L (Ah)(-1)) in GF cathode/PS system. The mechanisms of PS electro-activation by GF anode and GF cathode were compared and investigated for the first time, through kinetic experiments, radical identification, and products analysis. Quenching experiments demonstrated that O-2(center dot-) and O-1(2) were generated in GF cathode/PS and GF anode/PS systems respectively, besides HO center dot and SO4 center dot-. Degradation pathways of ATZ in these two systems showed slight difference, and a total of eight transformation products of ATZ were identified. Acute toxicity of the treated ATZ solution decreased at the beginning and then increased in both systems at electric charge of 0.11 Ah L-1. Furthermore, both GF electrodes/PS systems exhibited satisfactory performance for actual effluent from wastewater treatment plants in the presence of 30 mM perchlorate (with ATZ removal of 78% at electric charge of 0.11 Ah L-1), leaving a potential possibility for its practical application.