Abstract
The high consumption of salt reagents and strict pH control are still bottlenecks for the full-scale application of the Fenton reaction. In this work, a novel eco-friendly iron cathode electrochemical Fenton (ICEF) system coupled with a pH-regulation divided electrolysis cell was developed. In a pH-regulation divided electrolysis system, the desired pH for an effective Fenton reaction and for a neutral treated media could be obtained by H2O splitting into H+ and OH− at the anode and cathode, respectively. In an ICEF system, an iron plate was used as the cathode to inhibit the release of iron ions and promote the reduction of Fe3+ to Fe2+. It was found that when a potential of 1.2 V/SCE was applied on the iron cathode, 98% of p-nitrophenol was removed in the combined system after 30 min with continuously adding 200 mg/L of H2O2. Meanwhile, a COD and TOC removal efficiency of 79 and 60% was obtained, respectively. In this case, the conductivity just slightly increased from 4.35 to 4.37 mS/cm, minimizing the increase of water salinity, as compared with the conventional Fenton process. Generally, this combined system was eco-friendly, energy-efficient, and has the potential of being a promising technology for the removal of bio-refractory organic pollutants from wastewaters.
Highlights
Over the past few decades, advanced oxidation processes (AOPs) have attracted increasing interests for wastewater treatment since the highly oxidative hydroxyl radical (OH, E0 2.80 V/SHE) was generated in situ and found to be capable of degrading any refractory organic molecules present in the aqueous solution until total mineralization at the kinetic constant values as high as 108∼1010 M−1s−1 (Andreozzi et al, 1999; Oturan and Aaron, 2014; Gao et al, 2018)
A neutral solution containing 100 mg/L of PNP and 3 g/L of Na2SO4 electrolyte was pumped into the electrolysis device at a flow rate of 20 ml/min by a peristaltic pump, where the residence time was 1 min
It could be clearly observed that as the cathodic potential decreased from −1.0 to −1.2 V/saturated calomel reference electrode (SCE), the ratio of chemical oxygen demand (COD) removal to produced Fe and H2O2 consumption was increased from 3.9 to 5.7 and 0.61 to 0.63, while the value significantly decreased to 4.4 and 0.45 at a higher cathode potential of 1.4 V/SCE. These results demonstrated that -1.2 V/SCE was the optimal cathodic potential with suitable Fe production for the electroFenton reaction, which exhibited slightly higher COD removal/Fe and COD removal/H2O2 consumption for the traditional Fenton reaction system
Summary
Over the past few decades, advanced oxidation processes (AOPs) have attracted increasing interests for wastewater treatment since the highly oxidative hydroxyl radical (OH, E0 2.80 V/SHE) was generated in situ and found to be capable of degrading any refractory organic molecules present in the aqueous solution until total mineralization at the kinetic constant values as high as 108∼1010 M−1s−1 (Andreozzi et al, 1999; Oturan and Aaron, 2014; Gao et al, 2018). Among various AOPs, the conventional Fenton reaction process has been most widely applied for the treatment of wastewater streams because it exhibits the advantages of fast reaction rates, mild operating conditions, and simplicity to control (Bello et al, 2019). The second stage is characterized by a slow reaction between Fe3+ and H2O2 for the regeneration of Fe2+ (Eq 2), maintaining the continuous Fenton reaction (Babuponnusami and Muthukumar, 2014; Bello et al, 2019).
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