A water quality improvement with financial model was developed to investigate total benefits over costs and relative competency of different wastewater management approaches for recovering pollution overloaded canals in the center of Bangkok, Thailand. Implementation of centralized and decentralized wastewater treatment systems was evaluated within five different scenarios. Three major improvement mechanisms for open-canal water quality were considered including removal of wastewater loads, dilution by reclaimed water, and self-purification. Percent improvement of water quality within each canal is ranging from 40-84 % if centralized system was implemented vs. 41-88% if decentralized system was implemented. Estimated benefit/cost ratio from water improvement in centralized system, centralized with redistribution/reuse water system, and decentralized system are 2.28, 2.05, and 2.30 respectively. The results show that decentralized approach provides no significant difference in the benefit over cost ratio compared to centralized system, but offer slightly better in canal quality improvement. Therefore, decentralized wastewater management can be a promising alternative to promote sustainable uses of water and can work in help with centralized system. In the future, co-existing of large-scaled centralized and small-scaled decentralized systems may increasingly need to improve net efficiency of wastewater management where there are site specific problems with financial and political constraints.

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