Abstract
The overall photoelectro-Fenton (PE-Fenton) process for water treatment with neutral initial pH includes three steps of pH reduction, PE-Fenton reaction, and pH elevation. Reaction-controlled pH adjustment (RCpA), which utilizes the intrinsic electrochemical reactions instead of chemical addition, has been employed to lower the pH, maintain the lowered pH for the Fenton reaction, and recover the pH for final effluent discharge. This study demonstrated that the overall efficiency of this sustainable PE-Fenton process was improved by rapidly recycling the iron substance. Nanosized iron oxide was prepared and employed to ensure such rapid recycling. SEM and XRD results showed that the as-prepared iron oxide wasα-FeOOH with 20 nm in size. The experimental results of dimethyl phthalate (DMP) degradation showed that diatomite-supportedα-FeOOH (N-α-FeOOH/diatomite) could efficiently reduce the DMP concentration and total organic carbon. Furthermore, compared with Fe3+, the N-α-FeOOH/diatomite saved 160 min for iron settlement at 20 mg L−1DMP concentration. Also, with the increment in the initial DMP concentration, extra energy consumed by the individual step of PE-Fenton reaction using the N-α-FeOOH/diatomite became negligible compared with that using free iron ions with the increment in the initial DMP concentration. This development is expected to be a major step of the PE-Fenton process with RCpA towards actual water treatment.
Highlights
The cathodic electro-Fenton reaction (E-Fenton) with electrogenerated H2O2 and added Fe2+ as an advanced oxidation process (AOP) has recently been developed on the basis of a well-established Fenton’s reagent [1,2,3,4] for the degradation of recalcitrant organic pollutants in aqueous media
The experimental results of dimethyl phthalate (DMP) degradation showed that diatomite-supported α-FeOOH (N-α-FeOOH/ diatomite) could efficiently reduce the DMP concentration and total organic carbon
With the increment in the initial DMP concentration, extra energy consumed by the individual step of PE-Fenton reaction using the N-α-FeOOH/diatomite became negligible compared with that using free iron ions with the increment in the initial DMP concentration
Summary
The cathodic electro-Fenton reaction (E-Fenton) with electrogenerated H2O2 and added Fe2+ as an advanced oxidation process (AOP) has recently been developed on the basis of a well-established Fenton’s reagent [1,2,3,4] for the degradation of recalcitrant organic pollutants in aqueous media. The medium pH for the Fenton reaction must be maintained within the narrow range of 2.0–4.0 to preclude the iron precipitate This pH limitation obviously requires chemical addition of an acid and a base to obtain the desired pH, essentially hampering the realistic application of the PEFenton reaction. Any measure that serves to separate the nanosized iron oxide rapidly for recovery is desirable in the PE-Fenton process with RCpA for sustainable water treatment. Dimethyl phthalate (DMP), which is representative of dialkyl phthalate esters (DPEs), belongs to the family of endocrine-disrupting chemicals [21,22,23,24] It was used as a model organic substrate in the study to assess the efficiency of the PE-Fenton process rapidly. The efficiency of the iron settlement was evaluated through the settling time
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