Social, Environmental, and Economic Wastewater Decision Support Tool for Small Systems

Abstract

Small wastewater systems serving less than 10,000 population equivalents (p.e.) face a wide range of challenges due to technical and managerial capacity issues, limited resources, and the need to reduce environmental impacts. Based on the wide range of challenges of small systems, the authors of this manuscript developed the social, environmental, and economic wastewater decision support tool (SEE WWDST) to aid decision makers in comparing the sustainability of treatment alternatives. The tool uses multi-criteria decision analysis to produce a single SEE impact score that assesses 12 sustainability metrics across three larger categories: economic performance (e.g., net present worth of costs, affordability), environmental performance (e.g., carbon footprint, eutrophication, water reclaimed), and social performance (e.g., maintenance time, employee training, degree of automation, operator certification requirement, system intrusiveness, daily, and seasonal resilience). This paper compares the performance of three onsite wastewater treatment systems in Florida. The three systems evaluated include: (1) a passive septic tank effluent biofilter (STEB) system, (2) a mechanized aerobic treatment unit (ATU) system, and (3) a passive clay, sulfur, and shell biofilter (CSSB) system. The passive CSSB system was found to be the preferred system due to its lower present worth of cost, lower carbon footprint and eutrophication potential, and better performance for various social factors (e.g., maintenance time, degree of automation, system intrusiveness). The passive STEB system was the second preferred alternative, despite having a worse social performance and the highest present worth of cost. The systems were then assessed using even, social, environmental, and economic weighting preferences and a sensitivity analysis was conducted. In spite of shifts in weighting preference and changes to input data parameters to assess sensitivity, the passive CSSB system was found to be the preferred alternative. This paper highlights the importance of using triple bottom line sustainability metrics to assess small wastewater treatment alternatives using a novel decision support tool.