To centralize or to decentralize? A systematic framework for optimizing rural wastewater treatment planning

Untreated rural sewage seriously affects the universal access to clean water of rural residents. The lack of decision-support tools in rural sewage treatment (RuST) planning makes it difficult for RuST system to achieve the expected results and is not conducive to the optimal allocation of limited funds. Hence, there is an urgent need to develop a decision-support framework for large-scale RuST planning. For the first time, RuST planning decision-support framework was developed using divide-and-conquer strategy based on rural residents' spatial pattern (RESP) and the optimal pattern of RuST. This framework can be transferred to other countries/regions easily by correcting RESP dataset according to the spatial and environmental characteristics. We confirmed that the variation of RESP made the ideal RuST pattern varied significantly under different topography. And community-based pattern could be the optimal pattern for large-scale RuST planning, when spatial obstacle and RESP were fully considered. The price of onsite sewage treatment facility is the most significant factor for RuST planning. In our selected case, requited onsite facility accounted for 65.51%. For the total investment, the cost of sewer systems accounted for 56.01%, and the average investment in plains, hills, platforms and mountains was 1401, 1803, 1903 and 1859 USD/household, respectively. We expect this research could provide reference for RuST planning in other developing countries/regions all around the world.