Efficacy of an electrochemical flow cell introduced into the electrochemical Fenton-type process using a Cu(I)/HOCl system.

An electrochemical flow cell was introduced into the electrochemical Fenton-type process using a Cu(I)/HOCl system. The effects of the current density and the initial cupric ion (Cu2+) concentration on the process performance were discussed. The current efficiency of the process improved from 6.1% for an electrolytic tank system to 33% for the electrochemical flow cell system at a current density of 5.0 mA/cm2 and an initial Cu2+ concentration of 1.0 mM. The current efficiency increased to 58% for Cu2+ concentrations of 2.0 mM and beyond. The cathodic reduction of Cu2+ to the cuprous ion (Cu+) emerged as the rate-determining step in comparison to the anodic production of free chlorine. The introduction of the electrochemical flow cell enhanced the cathodic production of Cu+ by reinforcing the mass transfer of the Cu2+ to the cathode, and the detachment of micro bubbles generated electrochemically at the cathode surface. A decrease in the current density and an increase in the initial Cu2+ concentration also improved the current efficiency by promoting the cathodic production of Cu+. This involved the prevention of the cathodic reduction of protons to hydrogen gas and the elevation of the electrode potential of the cathodic reaction from Cu2+ to Cu+.

Reusability of iron sludge as an iron source for the electrochemical Fenton-type process using Fe²+/HOCl system.

This paper reports on the reusability and the optimal reuse of iron-rich sludge for an electrochemical Fenton-type process using sequencing batch mode and separation batch mode reuse models. In the sequencing batch mode, processes of electrochemical treatment, neutralization, sedimentation, and re-dissolution of iron sludge were all performed in the same reactor, whereas the neutralization and sedimentation of iron sludge in the separation batch mode was carried out in an iron recovery tank separated from the electrochemical reactor. The effects of iron speciation at different pH levels were discussed. It was found that ferric ions at a pH ≤2.5 were suitable for this electrochemical Fenton-type process where ferrous ions acted as hydroxyl radical scavengers, generating brownish deposits on the cathode at pH 3. When the sequencing batch mode was applied, the current efficiency in the Fenton-type process after the iron recovery declined due to the formation of insoluble deposits on the electrodes, which decreased at lower pH. The deposits were mainly formed during the neutralization and sedimentation steps after the electrochemical process. Fortunately, iron from the sludge could be reused for the electrochemical process when the separation batch mode was used, with 100% iron recovery and no decline in current efficiency.