Homogeneous Fenton processes are widely used for chemical industrial wastewater treatment. However, the impact of radical contenders (e.g., most aliphatic hydrocarbons) on hydroxyl radical (●OH) quenching caused inefficient removal of target pollutants (aromatic/heterocyclic hydrocarbons) in refractory wastewater, leading to excess energy consumption. A chelation-modified Fenton process relying on additional polycarboxylic acids could ameliorate this problem but also increase the total organic carbon (TOC) level, thus aggravating the treatment burden. Herein, an extra-chelator-free Fenton process assisted by electrochemical-induced in situ organic carboxylation (electrochemical-assisted chelation-Fenton, EACF), is proposed to significantly enhance target refractory pollutant (pyrazole as representative) removal in the presence of high ●OH contender (glyoxal) level. In alkaline solution, the EACF system achieved ~43-fold pyrazole degradation upon traditional Fenton process, mainly because of the electrochemical-induced glyoxal-to-oxalate transition that stabilized the free Fe2+ and promoted continuous ●OH generation at high pH. Radical detection indicated that superoxide radical ( ) dominated the glyoxal carboxylation process, while hydroxyl radical (●OH) was the main reactive species for pyrazole removal. Additionally, density functional theory simulations proved that the electrochemical process effectively converted the strong ●OH competitor (glyoxal) to a weak radical involver (oxalate), promoting Fe2+ complexation and therefore increasing radical utilization for pyrazole degradation. Compared to traditional Fenton processes, the electrochemical-assisted chelation-Fenton process had 2-folds higher oriented oxidation capability and ~78% lower effective operation costs, demonstrating promising potential for future practical applications.

Extra-chelator-free Fenton process assisted by electrochemical-induced in situ pollutant carboxylation for efficient chemical-industrial wastewater treatment

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