Inactivation of pathogens by a novel composting toilet: bench-scale and field-scale studies
Keim, Erika Karen
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Pathogen transmission is a major concern when implementing sanitation systems in resource poor areas. Multiple studies have shown that ecological sanitation systems are an effective means for improving health in areas where standard systems cannot reach disparate populations. Emerging designs of ecological sanitation systems provide needed access to hygiene but they still require confirmation of their effectiveness in reducing pathogen loads in the waste and transmission of disease. "The Earth Auger" is a novel composting toilet design that has incorporated critical elements to accelerate pathogen die off and has proven to be popular among recipients. A subset of active composting toilets were monitored for 2 months, taking samples at different points in the treatment line to determine the presence and quantity of total coliforms, E.coli, helminth ova and Salmonella. In addition, two scaled composting units were inoculated with Ascaris suum, Salmonella enterica, poliovirus 1, and MS2 bacteriophage. Over a period of two months tested for E.coli and inoculated pathogens for die-off. Samples were used to determine pathogen die-off through the treatment line according to time, pH, temperature and moisture content. Multi-variable linear regression compared E.coli levels in the treatment line with community as a modifying variable, statistically significant reductions were observed from the bowl to the receiving tank (avg. log10 reduction: -1.27; 95% CI: -2.22 to -0.32), and from the bowl to into storage (avg. log10 reduction: -2.71; 95% CI: -3.55 to -1.87). There were no statistically significant differences seen between communities (p-value=0.566) or from the bowl to the end of the horizontal reaction tube (p-value=0.120). Additionally, sample sizes in study were too small to see statistically significant differences between communities and between different points along the treatment line. Helminths were found in some endpoints during field work, increasing in numbers through treatment line, but prevalence was low and die-off patterns could not be established. Tested environmental factors did not significantly contribute to indicator reduction. At the endpoints for this study, however, indicator levels in compost directly out of treatment system were still above acceptable values delineated by EPA biosolids class B and below WHO guidelines for excreta reuse in agriculture. Salmonella were not found in samples throughout the treatment line. Experimental composting units did not yield useful die-off results but suggested modest decreases in Ascaris suum ova and bacteriophages. Additional human subject participation would have greatly benefited bench-scale experiments and elicited more information about the system. Under the current deployment and usage practices, these composting toilets do not strongly reduce indicator organisms after initial treatment, which will limit the use of post-treatment compost and extend storage time.
- Environmental health