Treated domestic effluents for non-potable reuse: microbial risk assessment and economic viability

Abstract

Although water quality can be ensured for various pollutant removal processes, concerns regarding microbial pathogens can set very high-quality standards for treated wastewater rendering the practice financially unfeasible. In this study, we applied quantitative microbial risk assessment and net present value methodologies to evaluate the economic viability and safety of wastewater treatment to produce water for reuse. Under the evaluated conditions, even though applying tertiary treatments (such as chlorination, ozonation, or UV radiation) for non-potable reuse purposes presents higher investment costs, it could offer a faster return on investment as a result of the greater income derived from the sale of the treated wastewater, and consequently, reduce the risk of exposure to pathogens. An economic viability analysis revealed payback periods of three to over 15 years for investment in the universalisation of sanitation services in the selected municipalities, wherein the most feasible scenarios were those in which water reuse was carried out at its maximum potential. We evaluated the reuse potential of treated wastewater in terms of reduced concentrations of Escherichia coli and observed that effluents treated by six wastewater treatment plant configurations (involving secondary treatment processes) could be used for restricted crop irrigation, with disability-adjusted life years (DALYs) of 9.20E03 ± 4.59E05 related to the risk of infection to the farmers. The application of additional disinfection procedures indicated that treated wastewater could be reused for unrestricted and restricted urban and agricultural uses, with corresponding DALYs of 1.35E05 ± 6.73E08 for the same group.