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Economic Input-Output Life Cycle Assessment of Water Reuse Strategies in Residential Buildings
Gardels, D., J. Stansbury, S. Killion, T. Zhang, M. Hu, AND J. R. NEAL. Economic Input-Output Life Cycle Assessment of Water Reuse Strategies in Residential Buildings. Presented at ASCE Annual Civil Engineering Conference, Las Vegas, NV, October 21 - 23, 2010.
To inform the public.
This paper evaluates the environmental sustainability and economic feasibility of four water reuse designs through economic input-output life cycle assessments (EIO-LCA) and benefit/cost analyses. The water reuse designs include: 1. Simple Greywater Reuse System for Landscape Irrigation for a Single-Family Residential House (gravity flow of greywater to subsurface irrigation system; no treatment) 2. Indoor Greywater Reuse System for Toilet Flushing and Laundry Washing for a Single-Family Residential House (collect, treat (bio-membrane), and store greywater in basement; pump to laundry and toilets) 3. Hybrid Greywater and Rainwater Reuse System for Landscape Irrigation, Toilet Flushing, and Laundry Washing for a Single-Family Residential House (gravity flow of greywater to subsurface irrigation system; collect and store rainwater and pump to laundry and toilets) 4. Rainwater Reuse System for Toilet Flushing and Laundry Washing for an Apartment Complex (collect and store rainwater; pump to laundry and toilets). Due to regional differences in precipitation and costs, these designs were evaluated and analyzed in four distinct climatic regions including Seattle, Washington; Scottsdale, Arizona; Omaha, Nebraska; and Tampa, Florida. An EIO-LCA was conducted for each design in each location. Phases in the life cycle that were analyzed include the manufacturing of materials phase, construction phase (e.g., excavation for underground cisterns), operation phase (includes both the water savings and the energy costs for pumping and treatment), and the disposal phase. The EIO-LCA included the specific residential buildings as well as changes to the municipal water treatment and distribution systems (e.g., less water use and treatment). The impact categories for this EIO-LCA include greenhouse gas emissions, energy consumption, toxic releases, and water consumption. The results of this analysis were highly dependent on the level of treatment required for the intended use of the water and the cost of the water in the given area. For example, the Indoor Greywater Reuse System was much more energy intensive than the Simple Greywater Reuse System because the simple system used the greywater for landscape irrigation and did not require any treatment. Thus, the indoor greywater reuse system was less favorable from an environmental standpoint (higher greenhouse gas emissions and greater energy consumption) than the simple greywater reuse system. The cost of water also had a large impact on the economics of the designs as the price of water and sewage services were much higher in Seattle and Tampa than Scottsdale and Omaha. The results of the analysis also indicate interesting regional differences. For example, the months with the greatest precipitation coincide with the months of greatest evapotranspiration in Omaha. Thus, harvesting rainwater for landscape irrigation worked very well and had favorable results. However, the harvested rainwater did not meet much of the irrigation demand in Scottsdale. This study also revealed some economies of scale with these designs as the payback periods were less for rainwater harvesting systems on apartment buildings as compared to single family residential houses.