Fe(II)-activated persulfate oxidation to degrade iopamidol in water: parameters optimization and degradation paths

Removal mechanism of Microcystis aeruginosa in Fe2+/sodium percarbonate and Fe2+/sodium persulfate advanced oxidation-flocculation system

Advanced oxidation process (AOPs) can be used for the treatment of harmful algal blooms (HABs). In this study, two systems of Fe²⁺/sodium percarbonate (Fe²⁺/SPC system) and Fe²⁺/sodium persulfate (Fe²⁺/PS system) were established to explore the removal mechanism of Microcystis aeruginosa (M. aeruginosa). The results indicated that the Fe²⁺/SPC system catalyzed H₂O₂ to generate a large amount of [Formula: see text] for oxidation by Fe²⁺ and formed Fe³⁺ to promote the flocculation of M. aeruginosa. The persulfate was activated by Fe²⁺ to generate [Formula: see text] with super-oxidizing properties, and Fe³⁺ was generated to realize the oxidation and flocculation of M. aeruginosa in the Fe²⁺/PS system. Compared with the traditional method in which the pre-oxidation and flocculation processes are carried out separately, the method in this study effectively improves the utilization rate of the flocculant and the removal effect of M. aeruginosa. The absolute value of zeta potential of Fe²⁺/PS system (|ζ|= 0.808 mV) was significantly lower than that of Fe²⁺/SPC system (|ζ|= 21.4 mV) (P < 0.05), which indicated that Fe²⁺/PS system was more favorable for the flocculation of M. aeruginosa cells than the Fe²⁺/SPC system.

Arsenic removal in aqueous solutions using FeS2

This study tested the technical feasibility of pyrite and/or persulfate oxidation system for arsenic (As) removal from aqueous solutions. The effects of persulfate on As removal by the pyrite in the integrated treatment were also investigated. Prior to the persulfate addition into the reaction system, the physico-chemical interactions between As and the pyrite alone in aqueous solutions were explored in batch studies. The adsorption mechanisms of As by the adsorbent were also presented. At the same As concentration of 5 mg/L, it was found that As(III) attained a longer equilibrium time (8 h) than As(V) (2 h), while the pyrite worked effectively at pH ranging from 6 to 11. At optimum conditions (0.25 g/L of pyrite, pH 8.0 and 5 mg/L of As(III) concentration), the addition of persulfate (0.5 mM) into the reaction promoted a complete removal of arsenic from the solutions. Consequently, this enabled the treated effluents to meet the arsenic maximum contaminant limit (MCL) of <10 μg/L according to the World Health Organization (WHO)'s requirements. The redox mechanisms, which involved electron transfer from the S₂^2- of the pyrite to Fe³⁺, supply Fe²⁺ for persulfate decomposition, oxidizing As(III) to As(V). The sulfur species played roles in the redox cycle of the Fe³⁺/Fe²⁺ of the pyrite by giving its electrons, while the As(III) oxidation to As(V) was attributed to the pyrite. Overall, this work reveals the applicability of the pyrite as an adsorbent for water treatment and the importance of persulfate addition to promote a complete As removal from aqueous solutions.