Economic and Social Evaluation of Decentralized Sanitation Systems

Economic and Social Evaluation of Decentralized Sanitation Systems J. Vieira*, E.C. Francisco**, P. D. M. Lima*** and P.L. Paulo* * Programa de Pós-Graduação em Tecnologias Ambientais, UFMS, Federal University of Mato Grosso do Sul. ** Department of Energy and Technology, SLU, Swedish University of Agricultural Sciences. *** Unit Closed Loop Engineering II, RISE, Research Institutes of Sweden. (E-mail: en[email protected]om; [email protected]; priscila.de.mo[email protected]; paula[email protected]) Abstract Decentralized sewage treatment systems are a viable solution for universal basic sanitation, providing technologies that meet discharge and reuse standards while benefiting the environment. This study applied Social Life Cycle Assessment (S-LCA) and Life Cycle Cost Analysis (LCC) to evaluate nine treatment scenarios for single-family homes in peri-urban Brazil. Scenarios included rudimentary septic tanks, septic tanks with soakaway, and source-separation technologies like evapotranspiration tanks (TEvap), compostable dry toilets, constructed wetlands for greywater, and urine storage tanks. Indicators assessed included economic factors (CAPEX, OPEX, TC, NPV) and social factors (health, monetization, living conditions, and development). The TEvap system for blackwater with greywater reuse (EvaTAC) ranked highest in economic and social sustainability, while rudimentary septic tanks performed poorly socially but moderately economically due to lower costs. These findings provide valuable insights into sustainable decentralized sewage technologies for peri-urban areas in Brazil, supporting informed decisionmaking to improve economic and social outcomes. Keywords: Economic impacts, reuse, social impacts, sustainable depletion. INTRODUCTION In 2010, the UN General Assembly recognized access to potable water and sanitation as a fundamental human right essential for poverty reduction, quality of life, economic growth, and environmental sustainability. However, 46% of the global population lacks safely managed sanitation, and only 20% of wastewater is treated (WHO/UNICEF, 2021; UN, 2016). In Brazil, 62.5% of the population has sewage access, leaving 49 million reliant on inadequate solutions (IBGE, 2022). The Basic Sanitation Legal Framework (Law 14.026/2020) sets a goal for 90% sewage access by 2033. Achieving this requires decentralized treatment systems, particularly in rural and peri-urban areas where centralized networks are infeasible. Sustainable sanitation systems, as defined by SuSanA (2017), must promote health, environmental protection, and economic viability while being socially and culturally appropriate. Although advancements in wastewater treatment technologies enable resource recovery and meet environmental standards, economic and social inclusion remain critical. Research on the economic and social sustainability of decentralized systems is limited, often overlooking the holistic integration of social life cycle assessment (S-LCA) and life cycle cost analysis (LCC). This study aims to evaluate decentralized wastewater treatment systems through economic and social criteria, providing indicators for sustainability and aiding decision-makers in selecting the most viable solutions. MATERIAL AND METHODS This study analysed nine decentralized wastewater treatment scenarios tailored for rural, remote, and peri-urban areas in Brazil. The scenarios included various practices, ranging from rudimentary latrines to advanced resource-recovery systems. Each was designed for a single-family household of four people, considering a 15-year lifespan and assessing the potential for water and nutrient reuse. The daily water consumption was assumed to be 150 L/person, generating 120 L/person of wastewater, with 30 L from toilets (blackwater) and 90 L from greywater. The scenarios considered were: • Scenario 1A: Rudimentary pit latrine, the least sustainable option, requiring a new pit every six months. • Scenario 1B: Similar to 1A, with greywater discharged untreated into the soil. Filling time extended to one year. • Scenario 1C: Includes a septic tank and soakaway system, following technical standards, with a grease trap for kitchen effluent. • Scenario 2A: Segregates grey and blackwater, using constructed wetlands (EvaTAC) and infiltration trenches for treatment, with no reuse of treated water. • Scenario 2B: Similar to 2A but incorporates treated greywater reuse and evapotranspiration tanks (TEvap) for blackwater treatment. • Scenario 3A: Adds urine storage for fertilizer, greywater reuse, and a septic tank for blackwater. • Scenario 3B: Uses TEvap for blackwater and greywater reuse with urine storage. • Scenario 3C: Connects black and kitchen greywater to municipal sewer systems while treating other greywater with EvaTAC. • Scenario 3D: Employs a dry composting toilet, urine storage, and greywater treatment through EvaTAC. The scenarios are the same analysed by de Simone Souza, et al. (2023) in terms of the environmental impacts. The technologies proposed for scenarios 1C to 3D are illustrated in Figure 1. dry composting toilet Septic tank Soakaway EvaTAC TEvap Figure 1. Technologies used for the different scenarios (Paulo et al, 2021). Life Cycle Cost Analysis (LCCA) The economic analysis evaluated i) CAPEX (Capital Costs): Includes materials, labour, and system construction costs and; ii) OPEX (Operating Costs): Includes maintenance, energy, sludge removal, and material replacements. Using the National System of Civil Construction Costs (SINAPI), costs were calculated for a 15year lifespan. Additionally, the Net Present Value (NPV) was estimated under 2% and 14.25% annual interest rates. Social Life Cycle Assessment (S-LCA) The S-LCA methodology followed UNEP guidelines, evaluating impacts on the three stakeholder groups: workers (health, safety, and labour conditions), users (risks of contamination, odour, and benefits like reduced water and fertilizer use), communities (contributions to safe living conditions, environmental protection, and local economic development). The data was collected through a survey with 11 experts in sanitation and decentralized wastewater systems. Economic and Social Sustainability The Analytic Hierarchy Process (AHP) was used to compare scenarios based on economic and social indicators, creating a hierarchical framework to evaluate sustainability. Indicators were normalized using a min-max approach to ensure comparability. RESULTS Economic Assessment This section evaluates the economic performance of the nine decentralized wastewater treatment scenarios based on four key indicators: CAPEX, OPEX, CT, and NPV. These indicators were calculated for a 15-year operation period for a household of four people. The cost overview is shown in Table 1. Table 1. Cost Overview. Scenario Technology CAPEX (€) OPEX (€) CT (€) Savings from Reuse Revised CT (€) 1A Rudimentary pit 74.53 2,235.98 2,310.51 - 2,310.51 1B Pit + soil discharge 74.53 1,118.00 1,192.52 - 1,192.52 1C Septic tank + soakaway 744.84 436.36 1,181.21 - 1,181.21 2A Septic tank + EvaTAC (no reuse) 1,746.59 448.91 2,195.50 - 2,195.50 2B EvaTAC + TEvap (with reuse) 2,257.96 322.12 2,580.09 1,653.94 926.15 3A Septic tank + EvaTAC + urine tank 2,129.43 2,022.31 4,151.74 1,806.97 2,344.77 3B EvaTAC + TEvap + urine tank 2,316.21 1,598.49 3,914.70 1,806.97 2,107.73 3C ETE + EvaTAC + urine tank 1,499.16 4,134.35 5,633.51 1,806.97 3,826.55 3D EvaTAC + dry toilet + urine tank 2,117.36 3,364.01 5,483.01 1,806.97 3,676.05 In the CAPEX analysis, the lowest construction costs were observed in Scenarios 1A and 1B (€74.50), though these are environmentally inadequate as untreated sewage is discharged directly into the soil, posing health and environmental risks. Intermediate CAPEX levels (€744.84– €1,746.59) were seen in Scenarios 1C, 3C, and 2A, with Scenario 1C (septic tank and soakaway) being the most cost-effective compliant option. Scenarios involving TEvap and EvaTAC technologies, such as 2B and 3B, reached the highest CAPEX levels (€2,316.21), reflecting material and construction demands. In terms of OPEX and CT, Scenario 2B (€322.12) was the most economical, benefiting from low maintenance and greywater reuse, while Scenario 3C (€4,134.35) had the highest costs due to municipal treatment fees and urine stabilization. When resource reuse was factored in, Scenario 2B further reduced its total cost to €926.15, driven by savings from greywater reuse and fertilizer production. Resource reuse significantly improved economic sustainability; for instance, Scenario 2B achieved a positive cash flow of €1,331.81, with other reuse-based scenarios like 3B and 3A also showing better performance. Despite these benefits, none of the scenarios achieved a positive NPV over 15 years, even at a 2% interest rate. Scenario 2B came closest but required 36 years to break even. Strategies such as reducing construction costs (e.g., alternative materials for EvaTAC) or implementing government subsidies for reuse could enhance the economic feasibility of decentralized wastewater treatment systems. Social Assessment The social sustainability assessment identified Scenario 2B (TEvap for blackwater and EvaTAC for greywater reuse) as the best-performing option due to its health benefits, reduced contamination risks, and environmental improvements. Scenario 1C (septic tank and soakaway) ranked moderately well, being widely used and compliant with technical standards but lacking resource reuse features. In contrast, Scenarios 1A and 1B (rudimentary pits) performed poorly, posing significant health and environmental risks. Overall, systems with resource recovery and reuse were found to deliver the most social benefits. Economic and Social Sustainability The combined economic and social sustainability analysis of nine decentralized wastewater treatment scenarios revealed that Scenario 2B (TEvap for black water and EvaTAC for gray water reuse) achieved the highest overall score. Its economic viability, driven by cost savings from greywater reuse, and its strong social performance, including health and environmental benefits, made it the most sustainable option. Scenario 1C (septic tank and soakaway) ranked second overall. It was the most economically viable after 2B, with low costs and widespread adoption in Brazil, but its limited resource recovery reduced its social sustainability. Scenarios 1A and 1B (rudimentary pits) were the least sustainable due to significant environmental and health risks, despite their low initial construction costs. Conversely, higher-cost scenarios with resource recovery, like 3B (EvaTAC + TEvap + urine tank), performed well in sustainability rankings due to water and fertilizer reuse benefits. Overall, systems incorporating resource recovery and reuse outperformed those relying on traditional or rudimentary methods, emphasizing the importance of integrating environmental, social, and economic considerations in decentralized wastewater solutions. CONCLUSIONS This study assessed nine decentralized wastewater treatment scenarios, emphasizing economic and social sustainability through a multi-criteria decision-making approach considering regional factors, stakeholder needs, and implementation goals. Results showed that social assessments are influenced by subjectivity, while economic outcomes depend on regional costs and inflation. Scenario 2B, combining TEvap for black water and EvaTAC for greywater reuse, emerged as the most sustainable option due to water savings and stakeholder approval, followed by Scenario 1C, a costeffective septic tank and soakaway system widely used in Brazil. The findings provide valuable guidance for selecting sustainable wastewater technologies. ACKNOWLEDGMENTS Funding for this research was provided by CNPq (National Council for Scientific and Technological Development), CAPES (Coordination for the Improvement of Higher Education Personnel), Fapemig (Minas Gerais State Agency for Research and Development) and, INCT Sustainable ETEs. REFERENCES de Simone Souza, H. H., de Morais Lima, P., Medeiros, D. L., Vieira, J., Magalhães Filho, F. J. C., Paulo, P. L., ... & Boncz, M. Á. (2023). Environmental assessment of on-site source-separated wastewater treatment and reuse systems for resource recovery in a sustainable sanitation view. Science of the Total Environment, 895, 165122. 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