Degradation of Oxytetracycline by Electrochemical, Fenton and Electro-fenton Processes Using SS316 and SS316/β-PbO2 Anodes: Process Optimization Using Rsm-ccd, Bioassay Test and Degradation Pathway

The aim of the present study was to evaluate the efficiency of advanced oxidation processes (electrochemical, Fenton and electro-Fenton) in the removal of oxytetracycline using SS316 and SS316/β-PbO2 anodes. This study was performed experimentally on a laboratory scale in a 250 mL reactor. First, experiments were designed for the electrochemical process using a central composite design, and the optimal conditions for the variables pH(3.53), electric current density(3.85mA/cm2), initial concentration of oxytetracycline (20mg/L) and electrolysis time (42.35min) was obtained; then, under these conditions, the efficiency of Fenton process with FeSO4 variable without the presence of electrodes was evaluated, and its optimal value was 0.3 g/L, and then in the presence of optimal values ​​of the above 5 variables, the efficiency of electro-Fenton process with H2O2 changes were investigated and the optimal value of 0.12 was obtained for H2O2. The removal efficiencies of oxytetracycline in electrochemical, Fenton, and electro-Fenton processes were 84.7%, 73.4%, and 98.2%, respectively. Under optimal conditions, the SS316/β-PbO2 anode electrode enhanced the oxytetracycline efficiency by electron-Fenton process to 100%. The results of bioassay with microorganisms showed that the reduction of toxicity of the effluent treated by electro-Fenton process for Pseudomonas aeruginosa and Staphylococcus aureus was 84.5% and 69%, respectively.

Application of electrochemical plasma on iron electrodes for treating 2,4-Dichlorophenoxyacetic acid (2,4-D) and 2,4,5-Trichlorophenoxyacetic acid (2,4,5-T) in water environment

The herbicide compounds contain aromatic ring and chlorine atom such as 2,4-dichlorophenoxylacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic (2,4,5-T) cause serious environmental pollution. However, it is very difficult to decompose by chemical, physical and biological methods. The high voltage direct current electrochemical method can be control to form plasma on metallic electrodes. Thus, it creates active species like as H 2 , O 2 , H 2 O 2 and free radicals such as: H•, O•, OH•. Especially, OH• free radicals that has a high oxidation potential, so it is possible to oxidize benzene oring compounds more effective. The iron electrode is used in the studing to combine the dissolve process of the iron anode electrode with aims is to create Fe 2+ ions and electrochemical fenton reaction. Besides, the flocculation process by Fe(OH) 2 also happen. The plasma will appear with a voltage of 5 kV on the iron electrode in a solution of 30 mg/L 2,4-D or 2,4,5 T. After a period time of the reaction, the aromatic oring compounds contaning the chlorine was treated, the electric conductivity of the solution increases due to the amount of Cl - ions releasing in the solution. The degradable products of the 2,4-D and 2,4,5-T were analyzed qualitatively by the gas chromatograph mass spectrometer GC-MS 6890-5975 Agilent system. The results described that the straight chain carboxylic acids were formed in the solution. These compounds are easy to oxidize thoroughly under appropriate conditions in solution by OH• free radicals . Moreover, the 2,4-D and 2,4,5-T were also analyzed quantitatively by a calibration curve from GC-MS 6890-5975 Agilent system or high performance liquid chromatograph HPLC 1100 Agilent system. The treatmental process can be controlled to achieve optimum performance by technological factors such as input voltage, distance between anode and cathode electrodes, initial concentration of 2,4-D and 2,4,5-T as well as flowing air through solution. The analysis results showed that the degradation efficiency of 2.4-D and 2,4,5-T reached at 99.98%; 99.83%, respectively.

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+.