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Inactivation of pathogenic bacteria in sewage by means of various disinfection techniques

Mantzikou Maria

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Summary

One of the most important problems nowadays is the quality deterioration of water resources, making it increasingly difficult to find clean water. Water intended for human consumption must be free from pathogenic microorganisms and therefore, the application of appropriate disinfection techniques is imperative should.Common disinfection methods include UV irradiation, chlorination and ozonation. Although these methods are effective, they have significant disadvantages such as the generation of toxic by-products or high cost. In this context, researchers have turned their attention to the development of alternative sustainable and efficient disinfection techniques like the utilization of solar radiation through photocatalysis.The purpose of the present study was the inactivation of the pathogenic bacteria Escherichia coli, Staphylococcus aureus and Klebsiella pneumoniae secondary treated effluents, applying solar photocatalysis, chlorination and UV-C radiation.Solar photocatalysis was applied using ZnTiO3 as catalyst at the concentration of 50 mg/L. This method was more effective for S. aureus as the recorded reduction of bacterial population was 6 Logs in 2h. E. coli and K. pneumoniae were reduced by 1 and 2 Logs, repectively within the same treatment period.Subsequent disinfection experiments were carried out using UV-C radiation, which proved to be the most effective method since all three bacteria were eliminated over a period of 20 sec.Finally, chlorination was examined with two different chlorine concentrations, namely 1 and 5 mg/L. In the first cycle of experiments the dose of 1 mg/L was effective for E. coli and K. pneumoniae as the reduction of bacterial population was 5 and 4 Logs respectively in period of 1 hour. On the contrary, there was only a 2 Log reduction of S. aureus population in 30 min. In the second cycle of experiments, the dose of chlorine was 5 mg/L, which resulted in the complete removal of all bacterial load over a period of 2 min.Of the three methods used the most efficient for all three bacteria examined was UVC, as complete inactivation of microorganisms was achieved in a short period of time.

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