Experiments on Disinfection with Monochloramine and Free Chlorine in Hot Spring Water- Application to Geochemical Research -

Abstract

Japan has developed a world-class hot spring culture by utilizing hot spring water as a geochemical resource. In order to provide hot springs for bathing, it is a prerequisite that the hot springs are properly disinfected. However, there have been scattered cases of pathogens including Legionella pneumophila causing infectious diseases under improper sanitation. Conventional disinfection of hot spring water has widely used free chlorine disinfection by the addition of sodium hypochlorite. It has become clear that some hot spring waters including high pH have chemical inhibitors to free chlorine disinfection. Therefore, the Ministry of Health, Labor and Welfare of Japan (MHLW) research group led by the National Institute of Infectious Diseases has been conducting research and development of monochloramine as an alternative to free chlorine disinfection, and it is expected to be widely used in the future. As a member of this MHLW research group, we have been conducting both field and in vitro studies on monochloramine disinfection. In this presentation, we will outline a series of research results and discuss the interface between geochemistry and hygiene engineering. As a result of field use of monochloramine disinfection at a facility using highly alkaline hot spring water with a pH of 9.5 in Mie Prefecture, it was observed that heterotrophic bacteria in the hot spring water were proliferating. Therefore, an experiment was conducted to compare the disinfection effects of free chlorine and monochloramine on this hot spring water and L. pneumophila, Mycobacterium phlei, Escherichia coli, and Bacillus subtilis. The results showed that L. pneumophila and E. coli were rapidly inactivated by both monochloramine and free chlorine disinfectants, while M. phlei and B. subtilis required considerable contact time. This suggests that biofilm formation by highly disinfection-resistant bacteria such as M. phlei may also induce the growth of L. pneumophila. The findings on disinfection of hot springs could be applied to geochemical research, such as proper preservation of samples. This study was partially supported by a Research Grant (25LA1003) from the MHLW.