Heightening effects of cysteine on degradation of trichloroethylene in Fe3+/SPC process

The development of an efficient and environmentally friendly method for remediating groundwater contaminants under neutral conditions has been a significant challenge. Herein, a natural organic ligand cysteine (CYS), was introduced to improve the redox cycling of iron species for improved degradation of trichloroethylene (TCE) in a ferric ion (Fe3+) catalyzed sodium percarbonate (SPC) process. The Fe3+/CYS/SPC presented pH adaptability around a neutral environment and enriched degradation for TCE compared to other organic ligands (EDTA, BA, and TA) in the Fenton system. The addition of only 0.9 mM CYS in Fe3+/SPC promoted the generation of vital Fe2+ ions from 0.02 mM to 0.85 mM resulting in increased TCE removal from 67 % to about 92 %. The inorganic cations (Ca2+, Na+, K+, and SO42-) showed negligible effect while anions Cl-, and HCO3- inhabited the TCE degradation to 67 % and 25 % respectively at higher concentrations (50 mM). The electron paramagnetic resonance (EPR) and scavenging experiments affirmed the generation of OH center dot and O-2(-center dot) radicals responsible for TCE removal. Through dechlorination, possible degradation mechanisms with intermediate and final products were hypothesized. The CYS can promote contaminant remediation in groundwater by enhancing the reduction of Fe3+ to Fe2+ and forming a complex with Fe3+. Overall, this research will provide a long-term solution for the practical treatment of hazardous contaminants in groundwater.