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Chlorine Cycling in Electrochemical Water and Wastewater Treatment Systems

Chen, Linxi
http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397466841

Abstract Details

2014, PhD, University of Cincinnati, Engineering and Applied Science: Environmental Science.
In this study, phenol was used in a sodium chloride or sulfate matrix as a representative pollutant to systematically study which operating conditions have the largest impact on chlorine forms in an electrochemical treatment system. Initially, an HPLC method was developed and validated to simultaneously determine phenol and potential intermediates from hydroxylation and hypochlorination pathways during electrooxidation in the presence of chloride. In a combined-reactor configured with a boron-doped diamond (BDD) anode, samples were analyzed to identify and quantify organic intermediates and inorganic chlorine species generated during the electrooxidation of phenol. Ionic strength was kept constant at 50 mM and the applied current density was 12 mA/cm2. The effects of chloride-to-phenol ratio on contaminant removal efficiency and byproduct formation were studied. Experimental results showed that phenol was removed faster at higher chloride-to-phenol ratios but more chlorinated intermediates and chlorate were produced. The impact of initial chloride concentration on the chlorate formation rate was stronger than its impact on phenol removal rate. Analysis of variance (ANOVA) was used to evaluate the statistical significance of operational factors in a full 24 factorial design. Factors studied were anode type (BDD vs. graphite), initial phenol concentration (0.25 – 0.5 mM), initial chloride concentration (5 – 50 mM) and applied current density (12 – 25 mA/cm2), on responses such as phenol removal rate and chlorate production rate. Results showed that anode type and chloride concentration had the most significant effects either individually or interactively on the phenol removal rate, and that chloride concentration had a considerable effect on the chlorate production rate. Additionally, applied current density had a significant effect on the free chlorine production rate after breakthrough if and when it occurred with BDD in the presence of excess chloride. A 23 factorial design with a given reactor configuration with either BDD or graphite anode was optimized using response surface methodology (RSM) with respect to phenol removal and control of chlorate production. Linear regression results showed that the phenol removal rate was highest at low phenol concentration and high chloride concentration, whereas low chloride concentration minimized chlorate production. In addition to the ANOVA analyses, kinetics of the electrochemical oxidation of phenol and intermediates formed in the presence of chloride were explored for the different anodes at various chloride-to-phenol ratios. Comparison of rate constant k values of the first-order reactions showed that hypochlorination and hydroxylation pathways were in competition and hypochlorination pathway was more favored and 2-chlorophenol was the most dominant species in most cases. Mass balances around carbon and chlorine for measured species were also considered. Lack of closure for both indicated possible formation of other by-products that were not identified by HPLC. LC-QTOF-MS was used to qualitatively investigate the unknown by-products formed during phenol electrooxidation in the presence of chloride at two levels (5 mM and 50 mM) using the BDD anode. Results showed formation of chlorinated dimers and trimers of phenol, including potential formation of polychlorinated dibenzo-p-dioxins (PCDDs).
Margaret Kupferle, Ph.D. P.E. (Committee Chair)
Woo Hyoung Lee, Ph.D. (Committee Member)
Dionysios Dionysiou, Ph.D. (Committee Member)
George Sorial, Ph.D. (Committee Member)
142 p.
Environmental Engineering
electrooxidation; phenol; chloride; BDD; kinetic modeling; LC-QTOF-MS

Recommended Citations

Citations

  • Chen, L. (2014). Chlorine Cycling in Electrochemical Water and Wastewater Treatment Systems [Doctoral dissertation, University of Cincinnati]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397466841

    APA Style (7th edition)

  • Chen, Linxi. Chlorine Cycling in Electrochemical Water and Wastewater Treatment Systems. 2014. University of Cincinnati, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397466841.

    MLA Style (8th edition)

  • Chen, Linxi. "Chlorine Cycling in Electrochemical Water and Wastewater Treatment Systems." Doctoral dissertation, University of Cincinnati, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1397466841

    Chicago Manual of Style (17th edition)

ucin1397466841
411
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This open access ETD is published by University of Cincinnati and OhioLINK.