Mechanism of o-cresol polymerization and its carbon recovery from aqueous solution by a cathode/Fe2+/H2O2 process

Abstract

Converting organic pollutants into easily recyclable solid polymers has the advantages of saving oxidants and recovering organic carbon, compared to degrading them into smaller organic molecules. Taking o-cresol as a representative phenolic pollutant, this study realizes the dominant reaction of organic polymerization and the recovery of organic carbon from wastewater via a cathode/Fe2+/H2O2 process. With HO• initiation, 53 % of chemical oxygen demand is removed in the form of suspended solid polymers and equivalent organic carbon is recovered. At the same time, the dissolved organic carbon (DOC) removal reaches 64 %, and the H2O2 consumption is only a quarter of that in an ideal degradation process. The recovered solid polymers are oligomers derived from o-cresol and its derivatives, with the molecular weight ranging from 400 to 2500 Da. The polymerization pathway involves repeated HO• oxidation and coupling of intermediate organic radicals. The energy consumption is 26.7 kWh/kg DOC, significantly lower than that of previous Fenton-like processes in the literature. This study broadens the scope of polymerization-based technologies for organic wastewater treatment, and demonstrates that HO• has the potential to simultaneously reduce organic pollution and recover organic carbon by generating suspended solid organic polymers, which may provide new avenues for H2O2-based Fenton processes toward resource recovery and water purification.