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Engineering 183EW: Desalination And It's Place In California (Research Paper Sample)




Desalination and its Place in California
Drought Background
California as a whole is no stranger to drought, or the impact it can have on its people. In the past century, California has experienced 6 major droughts, each averaging over 5 years in length (California Department of Water Resources, 2015, pg.31). Though the people of California have always managed to adapt to these conditions and persevere, the current drought is presenting challenges never before seen in regular drought conditions.
This drought, now in its 4th year, is showing no signs of stopping. As a result of both record low precipitation conditions, and all-time high temperatures driving the evaporation of any residual groundwater, the length of this drought is predicted to exceed any in the recorded history of California. “What we are seeing now is fundamentally different from previous mega-droughts, because they were driven by precipitation.” (Nesbitt, 2015). According to Jeff Nesbitt, the National Science Foundation's director of legislative and public affairs, mega-droughts – droughts lasting 20 or more years – have historically been driven almost exclusively by precipitation. However, with the temperatures of California's rainy seasons rising at an alarming rate, it is predicted that this drought will not follow the established normal timeline, but rather last far longer than California is currently prepared to handle.
This previous winter, California experienced its highest seasonal temperature in 120 years. This increase in seasonal temperatures is not an anomaly, but rather a trend of steadily increasing temperatures that we've seen over the past several decades (CDWR, 2015, pg.24). As a result, the California Snowpack (compacted snow present in the Sierra Nevada Mountain Range) has decreased to dangerously low levels.
10147300Figure 1 – California's Sierra Nevada Snowpack Levels (Erdman, 2015)
Since the initiation of the drought in 2012, the snowpack levels have been steadily decreasing as a result of the abnormally, but steadily increasing, winter temperatures. The snowpack is typically replenished by winter precipitation, and subsequently will evaporate throughout the warmer seasons, providing a replenished source of water for the lakes downstream. However, with the lack of precipitation to increase the snowpack levels, as well as the temperature forcing additional evaporation, the snowpack currently sits at only 5% of the seasonal average. According to Weather Channel's winter weather expert Tom Niziol, this trend is not likely correct itself the coming years, and as a result California's ability to supply its citizens with water is rapidly diminishing.
For the second time in history, California has declared a state of emergency with regards to this situation. The first, being the drought of 2007-2009, was short-lived. Now, this statewide emergency status has already exceeded the first in length, and experts agree that this is no coincidence. In July 2014, 36% of California's population was said to be in a state of exceptional drought, D4, the highest category of drought condition used by the United States Drought Monitor. Today, only 1 year later, the percentage of Californians experiencing exceptional drought has climbed to 46%, with an unprecedented 95% experiencing severe drought, and a total of almost 37 million people being affected (United States Drought Monitor, 2015). California is in dire need of a source of fresh water, and now more than ever it needs to seek a solution to this problem before irreparable damage is done.
Current Desalination Technologies
One such potential solution to the issue of the rapidly diminishing fresh water supply is desalination. Simply put, desalinization is the process in which salt is removed from salt water, rendering the water safe for consumption. With the effectively limitless supply of salt water present in the Pacific Ocean along the coast of California, this would be a clear-cut solution…if it weren't for the problems that desalination poses on a large scale. Desalination has vast power requirements during operation, as well as needing incredibly large processing plants to accommodate the volume of water required, making it a rather expensive endeavor as a whole.
The costly nature of desalinization is directly correlated to the current methods by which we can remove salt from water. There are several means currently available to remove enough salt from water to make it potable, including the use of salt-restrictive membranes, distillation processes, various chemical treatments, and even through the use of solar or geothermal energy. Each process offers unique advantages, but all possess drawbacks that limit their ability to be scaled to accommodate the demand of providing the public with a long-term supply of water.
We will attempt to cover some of the more popular options currently in use, as well as provide detail on some of the technologies being researched that may become viable in the future. When making a decision on whether or not desalination offers a viable solution to supplying fresh water to the population of California, however, only functional technology can be considered.
Membrane Processes
One of the leading candidates for a large-scale desalination solution in California is reverse osmosis. This process uses what is referred to as a semi-permiable membrane, which allows water molecules to flow through, but restricts the flow of salt and other contaminants.
center000Figure 2 – Reverse Osmosis Schematic (HCTI, 2008)
Demonstrated in figure 2, the process is as simple as having water pass through a preinstalled membrane, and the salt present in the ocean water will have been effectively removed. The trouble, however, comes from the pressure required to force the water through the membrane. Since the membrane has holes so small that salt cannot pass, water will still pass through, but not without the application of considerable force. A great deal of pressure is required to ensure the throughput of water through this filter. During normal use, salt will also accumulate in front of the membrane, requiring a means of removing this buildup, as well as even greater pressure to maintain filtration flow. This method of water purification has already been well adopted commercially on a small scale, as it is not uncommon to find reverse osmosis filtration systems in homes across America for personal and family use in removing heavy metals and other contaminants from drinking water. Problematically, when seeking to increase the scale of this system to one that can accommodate an entire state, or a select few cities if multiple plants were used, the power required will scale exponentially with the vol...

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