Life cycle analysis for water and wastewater pipe materials

A life cycle analysis (LCA) was performed for six commonly used types of water and wastewater pipe materials: polyvinyl chloride (PVC), ductile iron, cast iron, high density polyethylene (HDPE), concrete, and reinforced concrete. The objectives were to (1) compare the six pipe materials in terms of global warming potential (GWP) through four LCA phases: pipe production, transport, installation, and use; (2) determine the primary source(s) of differences in LCA results; and (3) examine the effectiveness of currently used pipe size selection criteria when LCA GWP is considered. The results for unit lengths of discrete pipe sizes were used to generate functions relating GWP per kilometer of pipe to diameter and material selections. The LCA results were monetized using an emission penalty of 25/equivalent ton of CO2. For pipe diameters ≤61 cm (24 in.), GWP due to pipe manufacture, transport, and installation of ductile iron pipe was the largest among the six materials. At diameters ≥76 cm (30 in.), the GWP of PVC was highest. Concrete pipe resulted in the lowest GWP across the entire range of pipe sizes investigated. The GWP for pipe production, transport, and installation in a high-growth planning area in southeast Tucson, Arizona, was approximately one-tenth of the GWP derived from pipe network operation. The lifetime GWP from production, transport, and installation increased monotonically with pipe diameter for all materials analyzed, whereas, for a given flow, GWP from energy loss due to friction in flow simulations was inversely related to pipe diameter. The tradeoff suggests that there is an optimum diameter that minimizes lifetime GWP. However, optimum pipe sizes based on GWP were similar to pipe diameters selected based on economic cost alone, suggesting that LCA of water distribution and wastewater collection systems will not yield major changes in criteria for selection of pipe size.