Recent trends in decentralized wastewater treatment system in developing countries: A critical review of case studies...

The management of wastewater has become a significant environmental and public health concern, especially in rapidly urbanizing developing countries. Traditional centralized wastewater treatment systems often face infrastructural, financial, and operational challenges, leading to inadequate service coverage and inefficiencies. This review explores the potential of Decentralized Wastewater Treatment Systems (DeWTS) as sustainable and context-appropriate alternatives. DeWTS offers localized, 'low-energy, and community-driven' solutions that are particularly suited to diverse environmental and socio-economic conditions in resource-constrained regions. The paper compiles and critically analyzes recent advancements in DeWTS technologies such as constructed wetlands, anaerobic baffled reactors, and integrated modular systems, focusing on their ability to remove both conventional and emerging contaminants through mechanisms including biodegradation, filtration, and sorption. India is used as a representative case study to demonstrate real-world applications, performance metrics, and policy integration of DeWTS. The review highlights the importance of community participation, resource recovery, and system adaptability. By identifying key success factors and existing knowledge gaps, this paper provides a foundation for future innovations, policy frameworks, and the large-scale implementation of DeWTS to support sustainable water management in alignment with the United Nations Sustainable Development Goal (SDG) 6.