This paper compares cost and environmental evaluation methods of sewer collection systems and proposes that a combined cost and environmental evaluation method should be used. The model area is 20ha (500m×400m), flat, with good soil conditions and with a groundwater level of 2.0m
below ground. The systems compared in this study are 1) Gravity-only (G-1), 2) Gravity with pumping stations (G-2), 3) Pressure Sewer System (PSS), and 4) Vacuum Sewer System (VSS). The methods used to evaluate the systems are a) Installation and Operation / Maintenance Costing, b) Life
Cycle Costing, c) Life Cycle Energy Assessment and d) Life Cycle C-CO2 Emission Assessment. Construction cost is calculated based on the standard of construction cost estimation of Japan1). The maintenance cost model was developed using data derived from the manual and
investigation. Installation and Operation / Maintenance Costing evaluation shows the ranking as G-2, G-1, VSS and PSS. For LCC, discount rate is set at 2.8%. All costs are converted into present-worth value using the declining balance method. The ranking by LCC is VSS, G-2, PSS
and G-1. Initial energy consists of product energy and construction energy. Maintenance energy is calculated from exchanged parts, fuels and materials. Operating energy is estimated as electricity consumption. Energy unit values are derived from a paper2). LCE evaluation shows the
ranking as PSS, VSS, G-2 and G-1. The Life Cycle C-CO2 emissions are calculated based on the data collected. The evaluation result is similar to that of LCE and the ranking is also the same as that of LCE. It is shown that rankings by costing methods and by environmental factors
are different. So in selecting both a cheaper and environmentally friendly system, the combined evaluation method is recommended to find the most suitable collection system for us. Each maximum value is set at 1.0 and other lower values are calculated proportionally. It shows that VSS is the
No.1 followed by PSS, G-2 and G-1 in this case study.
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