| With the development of industry and the improvement of people’s living standard, surfactant products have become an essential part in daily life. However, wastewater containing surfactants is highly harmful to environment, and even endangers the aquatic life. In recent years, electrochemical oxidation appears to be a most promising technology for the treatment of wastewater containing organic pollutants for its distinct advantages including energy efficiency, environmental compatibility, cost effectiveness and amenability to automation. As a kind of electrochemical method, the three-dimensional electrochemical reactor, which derived from traditional two-dimensional reactor, can produce a higher current density, better effect of mass-transfer and higher space time yield, and therefore offer a wide application prospect.In this work, the degradation of sodium dodecyl benzene sulphonate (SDBS), a member of anionic surfactants family, was investigated with graphite as the main anode and cathode, and modified kaolin as the particle electrodes. The main research content and results include:(1) Particle electrodes were prepared by modifying kaolin with cetyl trimethyl ammonium bromide (CTAB), a kind of cationic surfactants. Some parameters, such as CTAB concentration, initial SDBS concentration, initial pH and dosage of particle electrodes on SDBS removal were investigated. Then orthogonal method was used to determine the optimum operating conditions. The results showed that the SDBS removal reached96.83%when CTAB concentration was O.lg/L and initial SDBS concentration500mg/L at pH5, particle electrodes dosage was11g.(2) A series of particle electrodes were prepared by modifying kaolin with the cationic surfactant, anionic surfactant and nonionic surfactant, respectively. Effective electrochemical oxidation was achieved with nonionic surfactant (polyvinyl alcohol, PVA), so PVA was chosen as the modifier. In this part, the effect of PVA concentration, dosage of particle electrodes, initial pH and SDBS concentration on SDBS removal were investigated. And the degradation kinetics of the reaction process was analyzed. The results showed that the SDBS removal reached80.85%under the condition that PVA concentration was0.1g/L, particle electrodes dosage was13g, initial SDBS concentration300mg/L, current density was100mA/cm2, Na2SO4was10g/L, and pH was not adjusted. Kinetics analysis showed that particle electrodes dosage was the parameter that affect SDBS removal most. (3) Particle electrodes, M-kaolin, were derived from kaolin cation exchanged with s-block (s-kaolin), d-block (d-kaolin) or p-block (p-kaolin) metal ions. Results showed that p-kaolin presented relatively higher removal efficiency, while s-kaolin showed the lowest removal, and d-kaolin showed the moderate removal efficiency.(4) It was observed that the addition of M-kaolin could change the pH of solution. The changed pH was signed as pHM-kaolin.It seemed that SDBS removal was determined by the pHM-kaolin to some extent. To further investigate the relationship between pHM-kaolin and SDBS removal, regression analysis was carried out in this study. Results showed that pHM-kaolin has a significant impact on SDBS removal and a predictive value for degradation effect.(5) From M-kaolin, we selected Al-kaolin as the representative particle electrodes to investigate the effect of some important operating parameters and the kinetics of the reaction process. It was showed that when the initial concentration of SDBS was500mg/L, particle electrodes dosage was13g, support electrolyte (Na2SO4) was10g/L, current density was126.98mA/cm2, pH was not adjusted, SDBS removal and COD removal can reach87.78%and88.49%in10min, respectively. Additionally, the data of SDBS degradation agree well with the pseudo-second-order kinetics, and the rate constant k=0.60000/(min-%).(6) The particle electrodes were characterized by SEM, XRD, BET, FT-IR and XRF. |
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