| Summary: | 碩士 === 國立高雄大學 === 土木與環境工程學系碩士班 === 99 === It was expected that the electrochemical oxidation combined with electrokinetic process will enhance the degradation of pollutants. It is possible that this new idea will create a more effective and efficient method. For removing of BPA, binary metallic oxide electrode (BMOE) was first prepared. Then cyclic voltammetry (CV) and surface metal quantification were conducted to identify the stability of the prepared electrode. Effects of parameters such as electrode, processing fluid(type and concentration), potential gradient, operating duration, contacting area of electrode, etc. were adopted in the discussion about mechanism and efficiency of electrochemical geooxidation (ECGO).
At first, changes of electrode potential versus electric current of BMOE were measured in order to determine BPA,s red-ox potentials. It is useful in the evaluation of effectiveness. Peak potentials were measured at various operation conditions with various fluids and they were applied in electrochemical geooxidation (ECGO) operating at 2 V/cm. The peak potentials measured are 0.27V, -0.31V, 0.12V, 0.47V, and 0.2V. for DI Water (ph=6.7) and -0.2V, 0.45V, 0.5V, 0.2V, and -0.6V for NaOH (pH=11.9). These indicate that stronger electrochemical reactions are apt to be brought out in basic conditions, owing to ionization of BPA at high pH.
Surface characteristics of electrodes prepared by deposition and electroplating were analyzed with SEM-EDS. The results show that target metal is present in the electrodes, indicating that target metal has been successfully coated on Ti electrodes. The amounts of coated metal on electrodes of PT, ST, MT, RT and PCT were found to be 1.53±0.08%, 1.43±0.34%, 1.82±0.27%, 1.36±0.09 %, and 1.5±0.16 %, respectively. by hydrofluoric acid digestion test. These data show that the electrodes have been essentially homogeneously coated with target metals.
It was shown that processing fluid 0.1 M sodium chloride (67.3 %) > 0.1 M citric acid (60.4 %) > sodium hydroxide (60.2%) > sodium sulfate (55.3 %) > DI Water (52.2 %) were established when BPA 30 mg/kg samples were treated at 2 V/cm for 5 days by RT electrode. The datum of citric acid might be due to a strong electrochemical reaction in acidic condition. The datum of sodium sulfate and sodium hydroxide might be due to a large dissolution of BPA in acidic condition, which can bring more BPA out of soil. Sodium hydroxide as a fluid has pH (11.9) higher than that (9.4) of sodium sulfate. In addition, sodium hydroxide has efficiency higher than sodium sulfate. It is sodium chloride which has the highest efficiency, owing to strong oxidative OCl- ion from electrolysis.
Five day tests with RT as anode were made on various fluids. The potential gradient was set at 2 V/cm. The result indicates that although acidic conditions favor electrochemical reaction but they give little promotion in efficiency. Surfaces of the electrode were stripped. Basic conditions elevate efficiency at higher concentrations. This is due to higher dissolutions of BPA at the concentrations. Efficiency decreases from 67.3 % to 61.3 % as NaCl increases from 0.1M to 0.4M, indicating a competition between Cl-¬ and BPA. 0.2 M NaCl is the optimal fluid because it creates an efficiency of 66.8% and a degradation of 63.1 %.
BPA treatment efficiencies of 60.1 %, 66.8 %, and 55.8 % were reached with RT anode and 0.2M of NaCl at 1, 2, and 3 V/cm, respectively for the duration of five days. Lower potential gradient did not created good performance.The lower effiency at 3 V/cm is due to large power consumption.It was shown that 2 V/cm is the best potential drop at which power consumption is 509.5 kwh/m3.
BPA treatment efficiencies of 37.3, 49.4, 66.8 %, and 68.3 % were made with RT anode and NaCl 0.2 M at 2 V/cm for 1, 3, 5, and 7 days, respectively. The corresponding power consumptions are 168.4, 381.4, 509.4, and 699.1 kwh/m3. It shows that five days is the optimal duration. Treatments based on RT,s contacting areas 6.03 cm2 and 8.04 cm2 at 2 V/cm were carried out for the optimal duration. It was found that larger areas favor efficiency and degradation. This is due to that larger areas bring out stronger electrochemical reactions. The corresponding treatment efficiencies are 72.3 % and 73.5 %. The treatment based on the optimal parameters: RT, contacting area 8.04 cm2, 2 V/cm, NaCl 0.2 M, five days, yields efficiency, 73.5 %, and degradation, 66.3 %.
In summary, treatment of BPA present in soil by ECGO method can give better efficiencies by suitable choose of parameters.
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