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Application of advanced oxidation processes for disinfection purposes

Chatzi Anna-Maria

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Year 2023
Type of Item Diploma Work
Bibliographic Citation Anna-Maria Chatzi, "Application of advanced oxidation processes for disinfection purposes", Diploma Work, School of Chemical and Environmental Engineering, Technical University of Crete, Chania, Greece, 2023
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Water forms a fundamental and integral source for all living organisms on the planet. Its role is versatile as it contributes to the preservation of ecosystems, human societies and it also maintains the planet’s balance. Despite this fact, water pollution from pollutants and pathogenic microorganisms is a problem that torments present time and jeopardizes public health. The lack of access to clean water may lead to waterborne diseases which are easy to spread globally. For all the above reasons, the problem asks for special attention and thus the development of ecological techniques, such as Advanced Oxidation Processes (AOPs), is of major importance in order to inactivate pathogenic microorganisms. Considering all of the above, this diploma thesis, examines the potential of inactivating bacterial indicators of fecal contamination via Advanced Oxidation Processes in various water matrices. More specifically, the activation efficiency of sodium persulfate (Na2S2O8) or hydrogen peroxide (H2O2) was first tested using biochars of various origins. Subsequently, disinfection experiments were performed by activation of persulfate radicals with different types of biochar/UVA irradiation and finally, solar photocatalysis experiments with three photocatalysts. Deionized water, tap water, bottled water and secondary effluent waste were selected as aqueous matrixes and the performance of the disinfection methods was tested on the bacterial strains Escherichia coli and Enterococcus sp. The initial concentration of bacterial indicators in all experiments was 106 CFUs/mL. According to the experimental results, it can be seen that not every type of Advanced Oxidation Process has the same effect on bacteria. In particular, in the first cycle of experiments, activation of Na2S2O8 or H2O2 individually by biochar were not considered to be particularly effective methods as they did not bring about any reduction in the population of the two bacterial indicators. Their inactivation occurred only in the presence of persulfate radicals in combination with UV radiation during the second cycle of experiments. However, also in this cycle, only specific type of biochars contributed to the disinfection, depending on the bacterium used each time. In most cases different conditions were required, dictated by the microorganism under study. Despite this, a particularly effective method for the removal of both bacteria from deionized water was found to be the one where S2O82- 1400mg/L was activated by 30W UVA radiation and BSG850 biochar (brewery residues pyrolyzed at 850ºC) 1g/L. Regarding the method of disinfection by heterogeneous solar photocatalysis, during the third cycle of experiments, the kill rates were higher. The photocatalyst TiO2 doped with the transition metals Mo and W had a better effect than that of BiVO4 photocatalyst, on the disinfection of bacterial strains in deionized water. In particular, W-TiO2 showed the best photocatalytic efficiency for the inactivation of E. coli, while for Enterococcus sp. ,Mo-TiO2 photocatalyst. It was shown that reduced solar irradiance decreased the photocatalytic efficiency. When attempting to remove E. coli from waste by S2O82-/UVA/biochar and solar photocatalysis methods, it was shown that this aqueous matrix contributes negatively to disinfection. In general, E. coli showed higher susceptibility during solar photocatalysis while Enterococcus sp. during the UVA/biochar activated persulfate method in deionized water. In summary, Advanced Oxidation Processes and in particular this methodology, as an innovative and environmentally friendly method was found to be effective for the inactivation of the two bacterial indicators under specific conditions, which depends on the variety of their structural characteristics and physiology and the operating conditions in each case.

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