Fabrication Of Rotating Electrochemical Disc Process Setup And Its Application In Organic Wastewater Treatment

Advanced electrochemical oxidation process emerges as a clean technology to operate easily, and it has attracted much attention in wastewater purification. In order to improve the current efficiency, to reduce the cost and to active the electrode, the main research focus on the electrode materials, side reactions, electrode lifetime and mass transfer speed of electrochemical process. This dissertation combines a novel electrode material——boron-doped diamond with an innovative electrolytic setup——micro-array electrode electrochemical rotating disc process together to degrade organic wastewater. The boron-doped diamond electrode has the advantages of high current efficiency and satisfying stability, while micro-array disc electrode electrochemical rotating disc electrode setup has the superiority in the mass transfer speed and the oxidation efficiency. Thus, the current efficiency can be enhanced. The main work of this dissertation includes two parts as the following:The first part of this dissertation,a novel electrochemical method, Cu-C Rotating Electrochemical Disc Process (RECDP), has been developed and employed for wastewater treatment. The anodes and cathodes are distributed alternatively and evenly on a round electrochemical disc. This setup can speed up the mass transfer rate and increase the oxygen transfer from air to the bulk solution when the disc is rotating. As a result, the redox efficiency of cathode can be improved. The main application of the Cu-C RECDP was as the following: First, Cu-C RECDP was applied to degrade simulated dye wastewater. The influence of rotating speed, voltage, current, pH value and treating time on the color and CODCr removal efficiency were investigated by experiments. The mechanism of the reaction was studied by UV-Vis, IR and EPR. For the simulated dye solution containing Reactive Brilliant Orange X—GN, the decolourization efficiency reached as high as 99.5% by 60-min electrolysis (rotate speed: 70rpm, current intensity: 0.15A and pH: 7.03). The results of the UV-Vis experiments indicated a rapid decrease of absorbance during the treatment. The EPR experiment showed the evidence of the free radical formation. For the simulated dye wastewater containing Reactive Brilliant Blue X-BR, the influence of rotate speed, voltage,pH and treatment time on the removal efficiency of color and CODCr was investigated. The degradation mechanism was studied by UV-Vis. The experimental results showed that Cu-C RECDP could efficiently remove the color and CODCr from the simulated dye wastewater. The color removal efficiency reached 96% by 60min electrolysis and CODCr removal efficiency reached 61% by 150min electrolysis respectively (rotate speed: 70rpm, voltage: 10V and pH: 7.02).Then, Cu-C RECDP was used for cutting oil wastewater (COW) treatment. The oil and CODCr removal of COW was experimentally investigated using both developed Cu-C RECDP and traditional electrochemical reactor (TER). The experimental results show that Cu-C RECDP is more efficient than TER and it can efficiently remove the oil and CODCr from COW, the removal efficiency reached 94.9 % and 86%, respectively (rotate speed: 60rpm, voltage: 10V,pH: 7.75 and time: 120min).The second part of this dissertation,Boron-Doped Diamond film (BDD) was prepared on Silicon wafer by Hot-filament chemical vapor deposition (HF-CVD). Its property was investigated by scanning electron microscopy (SEM), Raman spectroscopy, and cyclic voltammetry. Then, BDD was prepared as a micro-array electrode rotating electrochemical disc and applied to degrade simulated dye wastewater and textile effluent. The main work of this part was as the following:First, diamond film was prepared on Silicon wafer by Hot-Filament Chemical Vapor Deposition. The influence of the pretreatment method on the density of the diamond cores was studied. The influence of the carbon concentration and depositing temperature on the quality of the diamond was studied also. The diamond film in good quality was obtained under the experimental conditions: the Silicon wafer is pretreated by diamond particles of 0.5-1.0μm for 45min, the distance between filament and Silicon wafer is about 7mm, the total gas flux is 260 SCCM, the carbon concentration is 0.7%, and the deposited temperature is 700-750℃.Then, the diamond film was patterned by deposited SiOxNy and photoetching, and finally the boron-doped diamond film was deposited on the diamond film under the same preparation conditions of the diamond film. The BDD micro-array disc electrode was finally obtained by eroding the SiOxNy layer in HF solution for about 40min.Third, the BDD micro-array disc electrode is characterized via SEM and Raman spectroscopy. The results demonstrate that the BDD is in good quality and non-diamond particle in it is rare. The electrochemical characterization of the BDD micro-array disc electrode was performed in Na 2 SO4 solution and Fe(CN)6 4-/3- redox couple solution by cyclic voltammetry. Its voltage window is 2.9 V in the former solution and it shows quasi-reversible character in the latter solution. At last, BDD micro-array disc electrode was used to treat the simulated dye solution containing Acid Deep Blue P-2RB, dye solution containing Reactive Briliant Blue X-BR and the real dye wastewater. For the simulated dye wastewater, the influence of rotating speed, voltage, pH value and treating time on the decolourization efficiency were investigated by experiments. The mechanism of the reaction was studied by UV-Vis. The experimental results showed that BDD micro-array disc electrode could efficiently remove the color and CODCr from the simulated dye wastewater. For the simulated dye wastewater containing Acid Deep Blue P-2RB, the color and CODCr removal efficiency reached 90% by 40-min electrolysis and 72% after 3h treatment respectively (rotate speed: 90rpm, voltage: 8V and pH: 7.0). For simulated dye wastewater containing Reactive Briliant Blue X-BR, the color and CODCr removal efficiency reached 95% by 70-min electrolysis and 66% after 3h treatment respectively (rotate speed: 90rpm, voltage: 8V and pH: 7.0). For real dye wastewater, the color and CODCr removal efficiency reached 90% after 90min treatment and 65% after 3h treatment respectively.Conclusion can be made in this paper that the Cu-C RECDP can efficiently remove the color and CODCr from the simulated dye wastewater, and oil from COW. The BDD micro-array disc electrode prepared using HFCVD and photo-etching was in good quality. The BDD RECDP can efficiently remove the color and CODCr from the simulated and real dye wastewater. The BDD RECDP has adavantages in enhancing decolorization efficiency and saving energy.