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GOT WATER?

FACTS ABOUT WATER

Did you know that more than one billion people on earth lack access to fresh clean drinking water?

By the year 2030, two-thirds of the population will be suffering from severe water shortages.

The demand for fresh water is increasing for two reasons:

1. Population growth

2. Technological advancements

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90% of planet's fresh water goes to global industry.

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In 2000, U.S. withdrew about 408 bg/d

–85% fresh water

–15% saline water

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In 2000, 96% of saline water withdrawals in the U.S. was for thermoelectric-power use

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In 2000, 52% of fresh water withdrawals in the U.S. was for thermoelectric-power use http://ga.water.usgs.gov/edu/pictures/powerplant.jpg

What is salt water?

Salt water contains by definition about 3.5% total dissolved solids. These total dissolved solids include chlorine, sodium, potassium, magnesium, and calcium. Fresh water, by definition, contains less than 0.1% total dissolved solids. Water that is considered fit for human consumption contains about 0.2-0.3% total dissolved solids.

How much water is on Earth?

The Earth is covered with 30% land and 70% water.

The majority of the water, 97%, is salt water found in the oceans.

Approximately 3% of the earth's water is fresh water.

The problem is that only 1% of the earth's fresh water is usable, because the other 2% is locked away in glaciers. This 1% of fresh water comes from lakes, rivers, and aquifers.

The Earth maintains this percentage of water through recycling.

http://ga.water.usgs.gov/edu/watercycle.html

•WATER DESALINATION

Water desalination is a proposed solution to the growing problem.

The abundance of water on the Earth can be utilized if the salt could be removed to the desired purity.

There are five major desalination processes:

1. Reverse Osmosis

2. Multi-Stage Flash

3. Electrodialysis

4. Multi-Effect

5. Vapor Compression

History of Desalination

The first large scale facilities began in the Middle East following World War II due to the necessity of fresh water.

The popularity of water desalination increased in the 1960s when the reliability of reverse osmosis membrane was proven.

Currently, reverse osmosis is the most popular method for water desalination.

REVERSE OSMOSIS

Reverse osmosis operates off of the principal of normal osmosis.

http://www.visionengineer.com/env/reverse_osmosis.shtml

When two salt water solutions are separated by a semi-permeable membrane, the solution of lower concentration will diffuse through the membrane to dilute the solution of higher concentration. The force behind this phenomena is termed osmotic pressure.

In order for reverse osmosis to occur, a pressure greater than the osmotic pressure must be applied to the solution of higher concentration to force the water through the membrane, while leaving the salt behind.

Diagram of Reverse Osmosis Plant

Source: O.K. Buros, et. Al., The USAID Desalination Manual, Englewood, N.J., U.S.A., IDEA Publications.

The membranes used in reverse osmosis are delicate and can foul and clog easily. Hence, the sea water must be pretreated before it is forced through the membrane. The suspended solids are removed and the pH is adjusted to reduce the alkalinity of the solution. Once the water has been sufficiently pre-treated, it is passed through a high pressure pump and then the water is forced through the membrane and the fresh water is collected, and the brine (highly concentrated salt water) water is disposed.

Inland brine disposal

–Deep well injection - These are wells that are typically several hundred to several thousand feet deep. One major problem is that the ability to drill these wells depends greatly on the geography of the region.

–Evaporation ponds - These are large shallow concrete ponds where the brine is pumped to let the water evaporate. The left over solids can be harvested and turned into commercial products that can be resold.

–Solar ponds - These are large concrete ponds where the brine is pumped. Then, brine is heated and pumped into the bottom of the pond. This creates a convection current and a small amount of energy can be harvested from this process.

The main problem with evaporation and solar ponds is that the concrete can crack, which allows the brine to escape into the surrounding soil. This can cause contamination to the aquifer.

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•Other possibilities:

– Irrigation of salt tolerable plants

–Brine shrimp harvesting

What is the output of Reverse Osmosis?

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More than 300 million gallons per day is produced in the U.S.

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The output of each plant varies with plant size.

Cost of Reverse Osmosis

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•Cost

–$1.50-3.00/1000 gal for brackish

–$3.00-8.00/1000 gal for seawater

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Operating pumps

–$0.01/kwh in 1977

–$0.05/kwh currently

Ultra Low Pressure Reverse Osmosis

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Ultra low pressure reverse osmosis has become increasingly popular due to the decrease in energy requirements. Below is a comparison of an ULPRO membrane and a traditional membrane. Although the cost for replacing the membrane is higher, the ULPRO energy requirements are much lower, making this new advancement more desirable than traditional reverse osmosis.

	ULPRO Membrane	Traditional Membrane
O&M, US$/yr
Energy	224,003	296,659
Labor	153,600	153,600
Chemicals	72,686	70,969
Membrane Replacement	65,620	58,800
Total O&M	515,909	580,028
Difference:	64,119

Energy Alternatives

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Photo-Voltaic Cells

Reverse osmosis has a lower power requirement compared to many other processes, so PV cells are an option for small-scale desalination.

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Wind Turbines

http://www.hawaii.edu/wrrc/research/project_liu/desalination.html

Coconut Island was created in 1997 by Drs. Liu and James Moncur, in association with the University of Hawaii at Manoa.

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Located off the coast of Oahu, Hawaii.

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More effective in areas with supplies of brackish water.