Evaluating the energy and carbon footprint of water conveyance system and future water supply options for Las Vegas, Nevada.

摘要

Water production requires the use of energy to transport water from distant locations, pump groundwater from deep aquifers and treat water to meet stringent drinking water and wastewater regulations. Energy production based on its source involves the emission of greenhouse gases also known as carbon footprint, which is the leading cause of global warming and climate change. Because of growing concerns of global warming due to these emissions, water providers are required to analyze the energy and associated carbon footprint of existing water production facilities and future water supply options. A system dynamics model is developed to estimate the energy requirements and carbon footprint as its consequence to move water in the distribution laterals of the Las Vegas Valley. The model is also used to evaluate the two future supply options for the Las Vegas Valley: seawater desalination and water conveyance from distant locations using water conveyance infrastructures. The simulation results show that it requires significant amount of energy to lift water from water source to water treatment plants (0.3 million megawatt hours per year (MWh/y)) and then to distribute treated water in distribution laterals (0.55 MWh/y) in 2010. It requires more energy to distribute treated water (65%) when compared to lift water from source to treatment plants (35%). Different scenarios including change in population growth rate, water conservation, increase in water reuse, change in the Lake level, change in fuel sources, change in emission rates, and combination of multiple scenarios are tested to evaluate the change in energy requirements and associated carbon footprint. The increase in water conservation resulted to be the most energy efficient option and consequently generated lower carbon footprint. The reduction of per capita water demand to 753 lpcd (199 gpcd) by 2035 lowered the energy requirements and associated carbon footprint by 16.5%. In addition, reuse of wastewater effluent within the Valley can be an excellent way of saving energy. However, reusing only 77 million cubic meters (MCM) (56 mgd) treated wastewater effluent by 2020 results in the decrease of energy consumption by nearly 3.6%. If 20% of the treated wastewater can be reused within the Valley besides status quo reuse (127 MCM or 92 mgd), the energy consumption and associated carbon footprint is lowered by 9% by the year 2035. Of the two water supply options, seawater desalination is more energy intensive (96% higher) as compared to the water conveyance from remote locations and the associated carbon footprint is 47% higher. However, desalination option is cost efficient. The unit cost of seawater desalination is ;Keywords: Water; Energy; Carbon footprint; Desalination; Transport; Cost; Las Vegas, NV; System Dynamics