Effect of Post-treatment Conditions on the Inactivation Rate of Pathogenic Bacteria after the Composting Process

Abstract

ABSTRACTA urine diverting composting toilet system is modified for rural areas of Burkina Faso from the system that is commercially available in Japan. The rural model does not have a heat source. It still has some pathogens in the compost after three months of operation and hence requires a post-treatment. In this study, the kinetics inactivation of Enterococcus and Escherichia coli, selected as an indicator for pathogenic bacteria, was determined during post-treatment at different temperatures (37, 50, and 70°C) with varying moisture contents (50, 60, and 70%). Additionally, the fate of pathogenic bacteria under different lime doses (1.0, 0.5, and 0.1 g) at 60% of moisture content were determined. As a result, bacteria decreased as temperature increased, moisture reduced, and the length of time increased. However, under high temperature the effect of moisture was not significant. With regards to relative resistance of bacteria, Enterococcus was the most resistant to temperature. For 6 log reduction target to reduce the concentration of E. coli in compost, post-treatment conditions of 50°C, 50%, and a contact time over 4.5 h are needed or post-treatment conditions of 70°C, 50%, with a contact time of over 20 min are required. For Enterococcus, to achieve a 6 log reduction, post-treatment conditions of 50°C, 50%, with a contact time of 15 h or 70°C, 50%, with a contact time of over 2.5 h are required. The addition of the higher dose of Ca(OH)2 to increase the pH of compost to ≥8.1 was capable of reducing the concentration of pathogenic bacteria.