Activated persulfate by chelating agent Fe·/complex for in situ degradation of phenol: intermediate identification and optimization study

Due to its high toxicity, phenol is classified as a priority. In this paper, the removal of phenol from aqueous solutions was investigated using EDTA and activated persulfate (PS) with nano zerovalent iron (Fe· or nZVI). The influence of operational parameters such as initial pH, Fe·/EDTA ratio, iron species, chemical additives, and the presence of chloride ion on the efficiency of the process was investigated. An artificial neural network (ANN) model was applied to predict the chemical degradation efficiency. The intermediate compounds produced during the mineralization process in addition to the removal of phenol were also investigated. The decomposition products were analyzed using gas chromatography–mass spectrometry analyzer. The highest removal efficiency was 93.98%, which was obtained at pH = 6.0, Fe·/EDTA = 1 and persulfate (PS) = 7 mM. The main intermediates included phenol, 2-chloro-2-nitro-trimethylphosphine oxide, 4-ethylbenzoic acid, oxalic acid, hexadecanoic acid, succinic acid and benzoquinone. Upon application of the ANN model, a good correlation was obtained with training and test data. In conclusion, our results implied that Fe· along with EDTA as a chelating agent can effectively activate the PS and enable the oxidation process to degrade priority pollutants from contaminated wastewater.