Reverse Osmosis
REVERSE OSMOSIS Seawater + River Water=Electricity.: An article from: Membrane Separation Technology News [H] [T] [M]
(Digital) Thomson Gale 2006-02-01
Release date: 2006-03-09
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Seawater Reverse Osmosis Using a dedicated ship for Reverse Osmosis Water Treatment can provide coastal communities with needed freshwater with ...
tes there are but $$$ energywise
look at marine stuff. They use that on boats.
Which is cheaper in term of energy cost? Seawater desalination or waste water treatment by RO?
And which one is more environmentally friendly?
Note:
With a reference plz
RO= is reverse osmosis
reverse osmosis is only used as a final stage in waste water treatment so its not a fair comparison. you would have to add in the pumping and agitating energy for the sewage works.
desalination by reverse osmosis takes up less room, but more energy than for the final stage 'polishing' of waste effluent. in fact it is most common to use brackish water where possible, to make the process easier and reduce time between back washes. also you have to add in the energy used to pump the brine back out to sea a good way, you cant just discharge it back into the estuary..
either are only as environmentally friendly as the energy source used.
Note:
With a reference plz
its your homework,
find your own
http://www.google.co.uk/search?hl=en& ;rlz=1B3GGGL_enGB215GB216&sa=X&o i=spell&resnum=0&ct=result&c d=1&q=Seawater+desalination+or+waste water+treatment+by+RO&spell=1
Desalinates 1950 Gallons Per Day (7.38 M3/Day) at 99.4% Stabilized (99.2% Minimum) Salt Rejection
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Converts Seawater to Drinking Water in WaterMakers , Shipboard Applications, Land-and-Sea Based Desalinators.
What is the minimum pressure that must be applied at 25C to obtain pure water by reverse osmosis from seawater which is 2.0 M in sodium chloride? The effective molarity (i) of all particles must be used.
What is the osmotic pressure (at 25°C) of seawater?
You specify that it is 2M in NaCl. This is very high, it is usually taken as ≈0.45M, but let us use your figures.
p = i*n*R*T
p = i (2.0) (0.08206) (298)
i is the van 't Hoff factor. What is its value for NaCl?
We will assume that it is 2.0 because the NaCl dissociates completely to produce Na+ and Cl- ions.
p = (2.0)*(2.0) (0.08206) (298)
p = 97.82 atmospheres This is the osmotic presssure generated by the 2M NaCl solution. A minimum of this pressure must be applied to reverse the flow due to osmotic pressure.
Below are the concentrations of the most abundant ions in seawater.
Ion Molality
Chloride 0.566
Sodium 0.486
Magnesium 0.055
Sulfate 0.029
Calcium 0.011
Potassium 0.011
Bicarbonate 0.002
Use these data to estimate the osmotic pressure of seawater at 25 oC in units of atmospheres.
atm
What is the minimum pressure in atm needed to desalinate seawater by reverse osmosis?
atm
When pure water and salt water are separated by a barrier that allows water but not solute to pass through, the pure water tends to move into the salt water, with a pressure (Π) called the osmotic pressure
When a pressure equal to the osmotic pressure is applied to the salt water, the pure water is no longer able to 'move in'.
When a pressure GREATER than the osmotic pressure is applied, water actually moves out of the salt water, into the fresh water (desalination).
In this question, first you want to calculate the osmotic pressure:
This can be done using the van't Hoff equation:
Π = [S] RT
Where R is the gas constant, T is the absolute temperature, and [S] is the molar concentration of solute.*
Once you know the osmotic pressure, you'll then know that the applied pressure needs to be more than that to desalinate the water.
*Note: Osmotic pressure is a colligative property, so it depends on the amount of solute, but not the type. You can therefore simply sum up the moles for each solute in the sea water to find the total molar concentration of solute, and use that.
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New bug-powered desalination system can remove 90 percent salt ...
London, August 25 (ANI): Researchers have developed a new microbial desalination system that can remove 90 per cent of the salt from a seawater-like solution.
Microbial desalination could offer big advantages over the methods currently used to purify seawater, which require enormous pressure to operate, and gobble up huge amounts of energy.
According to a report in New Scientist, Bruce Logan, an electrical engineer at Pennsylvania State University in University Park, and colleagues at Tsinghua University in Beijing, China, adapted one of these techniques, electrodialysis, in which electricity draws ions from salt water through semipermeable membranes into two chambers.
The negatively charged chlorine ions are drawn in one chamber and positively charged sodium ions into another – leaving the water salt-free.
Logan’s team replaced an external source of electricity with a microbial fuel cell, which transforms bacteria into batteries.
When the bacteria metabolise nutrients – acetate in this case – they generate protons and electrons.
...Eilene Zimmerman - Selling Science – Could We All Be Drinking ...
Another sunny day in southern California, the sun shining down from a cloudless blue sky onto lawns slowly turning brown, pavement baking in 90 degree temperatures and fresh water in short supply. Add to that a growing population and you’ve got a crisis on your hands–and one not limited to California. According to the International Water Management Institute, about 33% of the world’s population will be facing water scarcity by 2025. One solution has been wastewater recycling plants like the one up and running now in Orange County. That facility recycles about 70 million gallons of water a day. Another is desalination–taking seawater, which accounts for nearly 98 percent of the water on earth, and removing the salt, making the water potable.
Early next year, construction will begin on a desalination plant in Carlsbad, California. According to environmental think tank Pacific Institute in Oakland, California, over the last five years an average of 800 new desalination plants have been constructed each year. The global market for desalination could reach a whopping $58 billion a year. According to the industry research group Global Water Intelligence, the world’s desalination capacity grew 43 percent in 2006 and 2007. About 14,400 plants operate worldwide, according to the research group. The U.S. has been slow to adopt the technology–Saudi Arabia, the Middle East, United Arab Emirates, Spain, northern Africa, Australia and other regions have used desalinated water for years.
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