Inactivation Mechanisms of E. coli in the Sawdust Used in Composting Toilet

Abstract

A composting toilet, using sawdust as a matrix, has the potential to trap pathogens that might occasionally be contained in human feces. High temperature, low water content and high pH conditions are effective in reducing the pathogen content. However, it is not clear which parts or functions of pathogens are damaged under these conditions. Therefore, the present study investigates the inactivation mechanisms of pathogenic bacteria in a composting toilet, focusing on which parts and/or functions were damaged. Escherichia coli (E. coli) was used as a model of pathogenic bacteria, and its inactivation mechanisms were estimated by multiple detection methods. Differences in detection principles among the 3 types of growth media and the polymerase chain reaction method (PCR) were used as a method to investigate the damages caused by each. In addition, damage to the outer membrane was distinguished by using a propidium monoazide (PMA) treatment. The results indicated that E. coli was rapidly inactivated due to metabolic function and slight outer membrane damage under high pH conditions. In dry conditions, E. coli was inactivated by damage to metabolic function and slight outer membrane damage. High temperature treatment damaged the outer membranes effectively, and inactivated them rapidly.