Life-cycle air emission effects of supplying water are explored using a hybrid life-cycle assessment. For the typically sized U.S. utility analyzed, recycled water is preferable to desalination and comparable to importation. Seawater desalination has an energy and air emission footprint that is 1.5-2.4 times larger than that of imported water. However, some desalination modes fare better; brackish groundwater is 53-66% as environmentally intensive as seawater desalination. The annual water needs (326 m 3 ) of a typical Californian that is met with imported water requires 5.8 GJ of energy and creates 360 kg of CO 2 equivalent emissions. With seawater desalination, energy use would increase to 14 GJ and 800 kg of CO 2 equivalent emissions. Meeting the water demand of California with desalination would consume 52% of the state's electricity. Supply options were reassessed using alternative electricity mixes, including the average mix of the United States and several renewable sources. Desalination using solar thermal energy has lower greenhouse gas emissions than that of imported and recycled water (using California's electricity mix), but using the U.S. mix increases the environmental footprint by 1.5 times. A comparison with a more energy-intensive international scenario shows that CO 2 equivalent emissions for desalination in Dubai are 1.6 times larger than in California. The methods, decision support tool (WEST), and results of this study should persuade decision makers to make informed water policy choices by including energy consumption and material use effects in the decision-making process.
This letter describes a comprehensive modeling framework and the Wastewater-Energy Sustainability Tool (WWEST) designed for conducting hybrid life-cycle assessments of the wastewater collection, treatment, and discharge infrastructure in the United States. Results from a case study treatment plant which produces electricity using methane offgas are discussed. The case study system supplements influent with 'high-strength organic waste' to augment electricity production. The system balance is 55 kg of greenhouse gases per million liters of wastewater. Sensitivity analysis confirms that reusing biogas from anaerobic digestion for electricity reduces life-cycle greenhouse gas emissions by nine times. When biogas is captured and reused for electricity, material production (e.g., chemicals and pipes) and the corresponding supply chains, rather than energy production, are responsible for most of the environmental effects. When biogas is flared, the material and energy production contributions are similar.
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