I finally finished this bitch...
It's long, but I know some of you are dorks so I figured I'd post it.
It's long, but I know some of you are dorks so I figured I'd post it.
Follow the Liter:
Tampa Bay’s Foray into Desalination
By Shawn Reynolds
“Water, water, every where, nor any drop to drink,” laments Samuel Taylor Coleridge in The Rime of the Ancient Mariner. “More than ninety-seven percent of the water on Earth is saltwater” (Swichtenberg, 2003). Sadly, this enormous resource is not potable. If ingested, our cells urgently endeavor to equalize our system. They release fresh water to dilute the salts, which subsequently forces the body into a state of dehydration. Cells then transport the salt to the kidneys. The salt overcomes the kidneys, the kidneys shut down, and then we die. With fresh water stores dwindling worldwide, the Earth’s vast oceans seem our most likely targets. We need only figure out a viable means of harnessing them. How then might we derive fresh water from the sea? The solution is desalination. But what is desalination?
The obvious definition is the removal of salts from a solution or compound. A more focused explanation, for the sake of this essay, pertains to the removal of salts from the world’s most abundant resource - seawater. There are two commercial techniques for seawater desalination: the membrane process and the thermal process. The first utilizes various forms of osmosis; the second relies on an assortment of phase-change processes, such as distillation (Hamdan, Zarei, Chianelli, & Gardner, 2008).
Reverse osmosis (RO) forces seawater through a semipermeable membrane. This permits fresh water to pass through and traps the salts on one side. Thermal procedures separate fresh water from saltwater through the evaporation of water out of a solution. One then collects the distillate for consumption, irrigation, and other uses. (Hamdan, Zarei, Chianelli, & Gardner, 2008).
A Brief History of Reverse Osmosis
Since the early 1900s, scientists sought the utilization of a membrane with which to divide salt from seawater. They base this concept on the “osmotic nature” of cell walls, which asserts, “certain semipermeable membranes, such as animal and plant cell walls, allow water to pass through, creating an equilibrium between a highly concentrated solution on one side of the membrane and a diluted concentration on the other.” Scientists postulate that sufficient pressure against the proper membrane will reverse this process, thus leaving a higher concentration of dissolved solids on one side (Graber 2006).
In the 1960s, industrial researchers realize that membranes they have created might well be suited for desalination (Graber 2006). In order to do such, these units remove very minute particles - in the Angstrom range - with a molecular weight in excess of two hundred (Hafez, Khedr, & Gadallah, 2007). By the 1970s, developers put these membranes to use in the first desalination plants of this kind (Graber 2006).
Originally, the high costs associated with the massive amounts of energy necessary for desalination processes were a huge factor in the consideration of a plant. As technology progresses, advancements greatly reduce the amount of energy essential to the process. In fact, over the last three decades, the requisite energy for desalination decreases by nearly seventy-five percent (Graber, 2006). The years between 1994 and 2004 witness the total volume of worldwide seawater desalination increase from 17.3 to 35.6 million cubic meters per day. Current desalination efforts generate one percent of the world’s drinking water (Yermiyahu, Tal, Ben-Gal, Bar-Tal, Tarchitzky, & Lahav, 2007).
In late 2005, Israel opens the world’s largest RO desalination facility. This plant churns out one hundred million cubic meters of fresh water per year. An ideal example of the advances in technology, this is the first time any desalination facility has produced potable water for less than fifty-five cents per cubic meter (Yermiyahu et al, 2007). Juan Maria Galtes, director of special projects for Inima, a Spanish corporation that specializes in desalination, emphasizes, “We are very close to the minimum energy for desalination. There’s a point where it’s impossible to go any further” (Graber, 2006).
New Technologies
There are a couple technologies on the horizon worthy of mention. In one example, the University of Florida’s John Klausner pushes saltwater through a heat source into a diffusion tower where it mists down into an upward surge of warm air and evaporates. It then blows into a condenser that extracts the fresh water (Jennings, 2005).
In another, Yale University’s Menachem Elimelech has a new approach he calls forward osmosis desalination. Where reverse osmosis uses high pressure to force seawater through a semipermeable membrane and this pressure fights the predisposition of the fresh water to dilute the salt. Forward osmosis has fresh water act as the higher concentrate through the addition of NH3 and CO2. Water now flows from the saltwater solution to the higher-concentrate “draw solution.” Elimelech then heats the draw solution to evaporate NH3 and CO2 to obtain fresh water – no pressure necessary. The only obstacle in the way is the development of a membrane that will consistently remove ninety-nine percent of the salts. Elimelech’s current membrane removes only about ninety-five percent (Patel-Predd, 2006).
Why desalination?
According to the United Nations, one third of the world’s population exists in areas lacking ample fresh water. Projections suggest this number will increase to sixty percent by the year 2025 (Patel-Predd, 2006). The decade between 1993 and 2003 ushers in drastic reductions in the costs of maintaining and operating a desalination plant. In 2003, the United States Desalination Coalition looks to Congress for legislation that will provide incentives and grant money for the evolution and improvement of desalination treatment facilities. (Swichtenberg, 2003).
Florida feels the pain. Not since 1895 has the Sunshine State suffered such a drought (Arrandale, 2007). The preponderance of evidence suggests the time is at hand to devise drought-proof water sources. The Tampa Bay region has been relying on groundwater from the Florida Aquifer for too many years. The demand on the dozen well fields, in 2001, was two hundred and forty-seven million gallons-per-day. Nature has been able to meet these demands sufficiently until recent indicators of stress surfaced (Brown, 2001). Florida typically receives between fifty-two and fifty-four inches of rainfall per year. The period between 1988 and 1994 saw precipitation dip to the thirties and forties. Swift population elevations compound the strain on regional stores. This six-year drought forces many outside entities to take notice, among them, developers, agricultural interests, the Florida Department of Environmental Protection, and the Southwest Florida Water Management District (SFWMD) (Wright, 2002). Tampa Bay Water (TBW), the supplier of fresh water for 2.4 million residents, with the help of Hillsborough, Pinellas, and Pasco counties and the cities of Tampa, St. Petersburg, and New Port Richey, is desperate for an answer (“Tampa Bay seawater,” 2008; Arrandale, 2007; Wright, 2002). TBW executive director Jerry Maxwell suggests there are “four D’s” that control the region’s water strategy: “drought, drainage, development, and drawdown.” Though nearly impossible for TBW to control the first three, “We can,” Maxwell offers, “attack the drawdown” (Wright, 2002). The consortium recognizes two necessary solutions: first, increase the capacity to maintain pace with the demand; second, lower the region’s dependence on ground sources. TBW immediately lowers the permitted groundwater pumping capacity from one hundred and ninety-two to one hundred and fifty-eight million gallons-per-day. That figure drops to one hundred and twenty-one million gallons-per-day by 2003 and to ninety million gallons-per-day by 2008 (Brown, 2001). “We had to do something,” Maxwell asserts, “We had over-permitted the system. We were extracting more groundwater than we could replenish” (Wright, 2002). Through this new “Master Water Plan,” TBW devises various methods to meet existing water demands while preserving groundwater stores. First, and most significant, the region will cull supplies from surface water sources - the Hillsborough River, the Alafia River, and the Tampa Bypass Canal. As a precautionary measure, TBW monitors flows at each location to insure they sustain downstream estuaries without harm (Brown, 2001). A sixty-six million gallon-per-day surface water plant comes online in September of 2002 for the processing of this surface water (Wright, 2002).
Back in October of 1996, the forerunner to TBW, the West Coast Regional Water Supply Authority, set in motion a visionary plan for Tampa Bay’s future. Requests went out for proposals for the construction of a desalination plant (“Tampa Bay seawater,” 2008). The employment of such a facility eases the stress on groundwater stores as well as to area rivers (“Applause,” 2007). “Without the plant’s twenty-five million gallons a day,” says Maxwell, “Tampa Bay Water will be hard-pressed to meet wellfield withdrawal reductions in 2008 required by Swiftmud” (Johnson, 2006a). In August of that same year, contractors begin work on an eleven hundred acre reservoir capable of storing fifteen billion gallons of water. This basin connects to the desalination plant via seventy miles of large transmission pipelines (Wright, 2002).
So why, then, is desalination necessary? In Tampa Bay’s case, at least, there exist few other options. With the rate of growth as it is and the current strain on groundwater sources, action is essential.
Desalination Around the World
More than 15,000 desalination plants - most in the Middle East - operate worldwide today (Graber 2006). Until quite recently, the process was rife with inefficiency, prohibitive costs, and frequent breakdowns. Initial facilities employed a distillation system. This setup is cost prohibitive for most environments given the need to generate an enormous amount of heat to enable vast quantities of seawater to boil. (Jennings, 2005). The first such facility churned out fresh water in Saudi Arabia in 1938 (Arrandale, 2007). In the 1950s and 1960s, the first significant desalination facilities came to life in desert regions primarily in the Middle East. Though these locales are devoid of water, most do possess access to substantial quantities of fuel for heating the water (Graber 2006). As of October 2003, twenty-seven desalination plants exist in Saudi Arabia that supply the country with twelve million cubic meters of fresh water daily; this is seventy percent of the nation’s drinking water. The United Arab Republic manufactures five and a half million cubic meters and Kuwait approximately three million (Ayres, 2003).