Mechanistic investigation and environmental effects of a ferric citrate-activated electrokinetic-persulfate system for remediation of PCB28-contaminated soil.

Highly toxic, persistent polychlorinated biphenyls threaten soil and human health. To overcome low activation efficiency and insufficient free radicals in single persulfate (PS) pollutant degradation, ferric citrate's synergistic boosting effect on electrokinetic-persulfate (EK-PS) systems was studied for PCB28-contaminated soil remediation. In the optimized EK-PS system, ferric citrate was added into the anode chamber as an activator. The removal efficiency of PCB28, as well as the changes in soil physical and chemical properties, including pH, electrical conductivity (EC), soil organic matter (SOM), available nitrogen (NH4+-N, NO3--N), available phosphorus (AP), and cation exchange capacity (CEC)), were analyzed. The degradation mechanism was revealed by quenching experiments, EPR spectroscopy, and gas chromatography-mass spectrometry (GC-MS). The EK-PS system activated by ferric citrate in this study had a voltage gradient of 1 Vcm-1, a PS mass concentration of 10%, and a PCB28 removal efficiency of 87% ± 0.01 after 9 days of operation (p < 0.05, n = 3, reported as mean ± standard deviation). Ferric citrate-activated EK-PS system boosted PS decomposition, SO4·- and HO· radical generation, raising degradation efficiency markedly. This treatment group exerted limited influence on soil physical and chemical properties (pH, EC), and soil nutrients (NH4+-N, NO3--N, AP, SOM, CEC). GC-MS intermediate identification revealed that PCB28 successively underwent dechlorination, biphenyl bond cleavage and hydroxylation, oxidative recombination and aromatic ring opening, complete ring opening and chain saturation processes, and further oxidation during treatment. The EK-PS system activated by ferric citrate can remove PCB28 without damaging the soil, demonstrating practical application potential.