Treatment of phenol-contaminated streams using iron-based persulfate activation process: The effect of coexisting Ions.

Over last decades, the treatment of phenol-contaminated streams has invariably been as top-priority. In this paper, electropersulfate (EPS) process was investigated for the phenol degradation. In EPS, persulfate ions are electrochemically activated using iron electrodes as a continuous low-cost Fe2+ source. In addition, the effect of wide range of coexisting cations and anions on the phenol removal were demonstrated. The study was undertaken at the optimal operating conditions obtained by previous literature review. In this regard, at different concentrations, cations (Ca2+, Mg2+, Mn2+, NH+4) and anions (HCO−3, CO2−3, SO2−3, SO2−4, NO−3, SCN−) were chosen as common ions presenting along with phenolic species in water/wastewater sources. The results indicated that the introduce of coexisting cations and anions exerted a significant role, leading to a reduction in the removal efficiency of phenol. The order of the coexisting cations from significant effect to the neglectable was Ca2+>NH+4 >Mg2+> Mn2+. The presence of Ca2+, Mg2+, and Mn2+ caused formation of passivation layer on the electrodes leading to decline the phenol removal. Besides, the negative effect of NH+4 was due to its oxidation by the sulfate radicals (SO•−4) or its transformation to nitrophenolic byproducts. The coexisting anions had serious harmful effect more than the cations on the phenol degradation. The results revealed that the presence of thiocyanate (SCN−) or sulfite ions (SO2−3) could completely prevent the removal of phenol a result of simultaneous consumption of the generated SO•−4 by them. However, the other anions (HCO−3, CO2−3, and SO2−4) had lesser effect due to banishing the alkalinity at acidic condition and also because of the reduction of anodic dissolution. [ABSTRACT FROM AUTHOR]