Metropolitan Taipei located in north Taiwan uses a hybrid sewer system consisting of mostly separate sewer for the populated regions, and partly combined sewer for less populated regions. This study used the concept that Marginal Cost of Control (MCC) equals to Marginal Benefits of Control (MBC) to establish the method for studying the optimal household connection percentage, and the most cost-effective construction of the separate sewer in the hybrid sewer system. Results indicate the improvement of the receiving water quality in a cost-effective analysis manner. The most cost-effective sanitary sewer construction can be reached when the stream Biochemical Oxygen Demand (BOD5) meets the river quality standard, which can be applied in other cities and existing systems.
Keywords: household connection percentage, hybrid sewer system, marginal benefits of control, marginal cost of control, separate sewer