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Chloride-assisted electrochemical disinfection : bacteria and bacteriophage inactivation and disinfection by-product formation

Authors Fang, Qian
Issue Date 2004
Summary Electrochemical (EC) disinfection is applied as an alternative to chlorination because of its main advantage of in situ production of disinfectants. Despite the fact that the inactivation of bacteria by some EC systems has been documented in the literature, the effectiveness of EC processes on inactivation of viruses is unknown. In addition, the kinetics of EC disinfection is not well understood and the mechanisms have never been clarified. Furthermore, few researches investigated the formation of disinfection by-products (DBPs) from EC systems, which constitutes another important concern for adopting this disinfection alternative. Thus, this research is largely directed to explore the solutions to these unknowns and to comprehensively evaluate and characterize the EC disinfection process. This study comprised three phases. In the first phase, synthetic solutions were subjected to EC disinfection in a well-mixed reactor under different combinations of various operation parameters, i.e., contact time, current applied and salt content. Pictures depicting time-dependent inactivation performance were constructed, from which the effects of different factors were evaluated directly. Furthermore, comparison between EC disinfection and chlorination was also made in this phase. In the second phase, kinetic models were established based on the data obtained in the first phase. The relative importance of the operation parameters on EC disinfection was evaluated mathematically and different surrogates (bacteriophage MS2 and fecal coliform bacteria) were compared in their responses to EC disinfection. The third phase studied the impacts of several factors on the DBP formation during EC disinfection and also compared the DBPs formed from the EC system and chlorination. Results showed that compared to chlorination, EC process could achieve similar or even higher inactivation of bacteriophage MS2. Though better disinfection efficiency could be achieved with the increases of salt concentration, contact time, and applied current, the influences of these three parameters on EC disinfection were not even. The effect of contact time was the most significant parameter in MS2 inactivation, while its influence on the fecal coliform inactivation was less remarkable. The inactivation data of MS2 and fecal coliform were regressed to fit the modified Chick-Watson (n≠1) model and the modified Hom model, respectively, indicating different patterns of responses of these two microorganisms to EC disinfection. Though the formation of THMs and HAAs in the EC and chlorination systems followed the similar trends, apparent discrepancy existed between the two systems in the concentrations of these two organic DBPs, with the yields of THMs and HAAs in the EC system being less, especially with longer incubation time. Among the inorganic DBPs studied, only chlorate ion was detectable and chlorite did not appear in any sample. The relatively high concentration of chlorate ion in the chlorination system was due to the decomposition of the stock hypochlorite solution. The occurrence of chlorate ion in the EC system was characterized by a fast formation rate even after the system was shut off, which might indicate the generation of other potent oxidants. This research work presented valuable data concerning the inactivation achieved and the DBPs formed in the EC system. Furthermore, this study opened up prospects for the further elucidation of the mechanisms of EC disinfection because the results indicated that certain difference existed between the species generated in the EC and chlorination systems.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2004
Language English
Format Thesis
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