Scaled Decentralization Approach for Urban Sewerage Infrastructure Planning: Lessons from Life-Cycle Costing

Rapid investments are taking place in wastewater treatment and management in developing countries, focused on the construction of sewer networks. Decentralized wastewater treatment systems in networked infrastructure are suggested alternatives for achieving sustainability and resilience; however, determining the appropriate scale of implementing decentralized systems is a case-specific decision. A combination of centralized and decentralized infrastructure has been reported to achieve the advantages of both systems, and is regarded as a scaled decentralization approach. Several modeling studies comparing the technoeconomic benefits of centralized and decentralized infrastructure lack the representativeness of ground conditions. The present research adopted a fieldwork-based approach for analyzing a spectrum of decentralized configurations using primary data based on field surveys. Additionally, the scope of economic analysis was expanded to include sewage conveyance costs, treatment costs, and revenue generation across all scales of decentralization, thereby providing insights for holistic economic assessment from a life-cycle perspective. The trade-offs between various cost components were analyzed considering economies of scale for three sewage treatment approaches. The study systematically identified optimal number of zones for the case city based on life-cycle cost analysis. Furthermore, the study identified the potential of natural treatment systems in implementing decentralized sewage treatment plants in small-scale cities, which also provides intangible benefits such as climate change adaptation and resilience. Moreover, recognizing the vital role of local factors such as topography and population density, this work discusses the implications of scaled decentralization for infrastructure planning in large-sized cities. The research shows that for the study area in a small Indian city, the life-cycle costs of sewerage infrastructure decrease with an increasing degree of decentralization.