Risk assessment of a septic tank variant used for the blackwater treatment

The reuse of wastewater in agriculture on a single-family scale presents a series of challenges regarding operation, maintenance, and sanitary safety. The present study therefore aimed to assess the potential microbiological risks to which users of a variant of septic tank (biodigester septic tank, BST) are exposed when using this system for treating blackwater (wastewater from toilets) and to propose control measures using the quantitative microbiological risk assessment (QMRA) methodology. This methodology entailed mapping the routes of exposure and calculating the probabilistic infection risk of E. coli. The results indicated that there is a microbiological health risk associated with the BST maintenance and usage. It was proposed that the fresh bovine feces addition for system maintenance should be stopped and that the reuse of the effluent for agricultural purposes should be reused via subsurface irrigation. It is therefore vital to exercise caution and implement a risk management strategy in order to ensure the safe dissemination of this technology in Brazil and Latin America.