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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

2008-05-11 14:14:22 by Meme S

Great Empress: I do NOT think your answer is brief enough :-P
Besides you did not read very carefully about the part''is used to purify sea water''

Reverse osmosis is the process of pushing a solution through a filter that traps the solute on one side and allows the pure solvent to be obtained from the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute.

The membranes used for reverse osmosis have a dense polymer barrier layer in which separation takes place. In most cases the membrane is designed to allow only water to pass through this dense layer while preventing the passage of the solute (e.g. salt). This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2 - 14 bar (30 - 200 pounds per square inch) for fresh and brackish water, and 40 - 70 bar [(600 - 1000 psig)] for seawater, which has around 24 bar (350 psi) natural osmotic pressure which must be overcome.

This process is best known for its use in desalination (removing the salt from sea water to get fresh water) and has been used in this way since the early 1970s.

2007-03-04 04:35:58 by Mary S

Price: $8.95 $8.95

Thanks heaps

Osmosis is the process whereby if a concentrated solution is seperated from a less concentrated solution by a semi permeable membrane*, then the molecules of solvent from the less concentrated solution will permeate through the membrane to dilute the higher concentrated solution until equilibrium was established with the two solutions having the same concentration. In doing this the solvent molecules develop a high pressure called osmotic pressure.
If you take the above example as sea water on one side of the membrane and pure water on the other, under normal conditions the pure water would cross the membrane in an attempt to dilute the sea water. As above, an osmotic pressure would be formed across the membrane. If a pressure exceeding the osmotic pressure was applied to the sea water side, reverse osmosis would take place and the water in the sea water solution would pass through the membrane to the pure water side. If this process is carried out continuously, pure water is obtained and a concentrated salt solution is discarded.
* a semipermable membrane is like a molecular sieve that allows water molecules to pass through but not the sodium chloride molecules or ions.

2008-06-22 04:35:27 by Sung J

Price: $8.95 $8.95

Inlet Water here may refer to brackish or sea water

The inlet water is kept moving over the membrane to prevent a high local ion concentration (which would impede the process). The flow flushes the ions and other non permeable contamination away, this flow with slightly higher ion concentration is then rejected

2008-09-02 01:45:48 by ShN

Would a global desalination initiative help reduce the threat of rising sea levels from global warming and increase the supply of fresh water for irrigation or human consumption?Renewable energy sources such as solar or wind power and chemical processes such as vaccuum distillation and reverse osmosis can be used make desalination an energy efficient and cost effective option. If all nations with coastlines set up large desalination plants and draw millions of cubic meters of water from the oceans every day, will we be able to thwart the catastrophic effects of global warming?

You raise a number of issues in the additional details that you added.

First: Desalination plants will not reduce sea levels because the water that is desalinated and used will eventually return to the sea.

Desalination is an excellent way to provide fresh water provided the source of the energy is low enough in cost.

With respect to energy sources: some that you mentioned are low cost, but some are also extremely high cost.

For example electricity generated by wind power has a cost of production of about 4 cents per kilowatt hour. The electricity generated by wind power can be used to provide the energy for reverse osmosis or vacuum distillation.

Unfortunately electricity generated by solar photovoltaic cells is very expensive because the capital cost of solar photovoltaic cells is very high. The cost to produce electricity by solar photovoltaic cells is over 40 cents per kilowat hour and is not cost effective for the purpose of desalinazitaion of water.

From a cost standpoint, It makes far more sense to use wind power rather than solar photovoltaic cells to produce the electricity for desalination of water.

With respect to Global Warming there is an enormous amount of hype in the popular media with respect to Global Warming.

Although the scientific literature does show that there is some Global Warming, the popular media has exaggerated the effects of Global Warming to a ridiculous extent.

Global Warming will not produce catastrophic effects. But it will produce some effects.

For example:

It is likely that Global Warming will reduce rainfall in some areas of the world.

Desalination of water will be very helpful to make up for the resuction in rainfall.

Also as our world population continues to grow at the rapid rate that it is growing there will be more demand for fresh water.

Desalination will be a very important tool to meet that increased demand.

.

2007-12-04 09:35:08 by KT