Development of New Disinfection Indicator in Chlorine Contact Tanks

Abstract

Although alternative methods for evaluating disinfection performance have been developed recently, the conventional CT value has been widely used due to its simplicity. This research proposes a simple, nondimensional variable chlorine disinfection index (CDI), which is derived from a chlorine decay constant, an inactivation rate constant, the initial dosage of chlorine, and the deadzone volume percentage, and investigates its possibility as a new disinfection indicator. To assess disinfection performance using CDI, 75 cases were created from each factor's value, based on previous research, and simulated using the computational fluid dynamics model. Results showed that CDI is linearly correlated with log inactivation of microorganisms, but that the relation varies with the value of the chlorine decay constant. Although the CT value is also correlated with log inactivation by linear regression, the relationship of the CT value to log inactivation is different with the inactivation rate being constant. Statistical values, such as the determination coefficient, p-value, and root mean square error value, showed that CDI is statistically more reliable, especially in the condition of less than five log. Although improvement with CDI is slight, CDI can be simply derived from steady-state simulation. Moreover, the CDI value is composed of independent values, and CDI is more convenient for design engineers when evaluating disinfection performance and calculating log inactivation due to its greater simplicity and the elimination of confusion regarding use.