1994 Volume 31 Pages 137-148
Progress in urbanization has caused water-related problems such as large expenditure for water resource exploitation, floods in urban rivers and natural flow rate reduction. Indirect potable reuse of treated wastewater and rainwater infiltration systems are part of major artificial water recycle technologies for solving these problems. In this study, the two systems mentioned above were evaluated in several indices: flow rate, water quality, cost, CO2 emission, energy consumption and others. The case of the Tama River in the Tokyo metropolitan area was examined.
Indirect potable reuse proved to flatten the flow rate and preserve upstream water environment, while water quality in the lower course became worse than a case without reuse. However, the cost, CO2 emission and energy consumption were 10% smaller because of diminution of waterworks sizes. The rainwater infiltration systems resulted in 8% increase in the natural flow rate for the main river part and the maximum 80% increase was achieved in a downstream region of the branch rivers. Therefore, 10-20% reduction in terms of CODmn was obtained in the region, indicating an improvement of the water environment. The rainwater infiltration systems accounted for approximately 10% of the total cost, whereas only 4-5% of the total CO2 emission and energy consumption was due to the infiltration systems. Thus, they are expected to have environmentally low impact.
