Post-Treatment and Microbial Risk Assessment of Compost for Food Production

Abstract

The compost withdrawn from a composting toilet still contains pathogens and therefore requires a post-treatment unit to treat the compost prior to reuse on an agricultural land. A quantitative microbial risk assessment with Monte Carlo technique was conducted to evaluate the risk of infectious disease and length of time required for the post-treatment. The incidental ingestion of compost (0.5-0.8 g) in a scenario of worst case was evaluated. High temperature was efficient in reducing the risk of pathogens; however, the temperature distribution in the unit (steel box) was not sufficient to reduce pathogens. Therefore, to efficiently reduce pathogens during the post-treatment and also reduce the time of treatment, the steel box needs an insulator to maintain the temperature. The guidelines for the design of the post-treatment facility are: for Ascaris, the steel box and the lower temperature -5, -10 and -15 degrees C, post-treatment requires approximately 295 h to achieve the safe level of 10-4 pppy. For norovirus, post-treatment requires approximately 845 h for the scenarios to achieve a safe level. Salmonella requires 969.5 h, for all scenarios to reach a safe level.