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Separating seawater through desalination Essay

Chemistry assignment:

The mixture selected in this assignment is seawater obtained from the hydrosphere.

The seawater can be separated through out several processes, both chemically and physically. The separation process is known as desalination. This name is getting more common everyday, as the Australian water demand grows with population we can no longer ignore the salinity problem. Desalination process could take use of the salt concentrated water, turning them into fresh water.

Industrial Separation Procedure:

1. The seawater is inputted through pre-treatment. During the physical separation process of pre-treatment it involves mostly of filtration (physical separation) removing larger solids in seawater.

2. Next, when the water travels through a pipe, its ph rate has been adjusted, if the water is too acidic it can damage the membrane permanently, the cost for recovery is also very high.

3. The filtered seawater now enters a pump, which compresses and puts pressure onto the filtered seawater. The high-pressure pump releases the seawater, sends it towards the RO (Reverse Osmosis) Membrane. (Physical pressure) The procedure is vital to the product freshwater, if the pressure is low, the salt cannot be fully separated from the water by the membrane, so the quality of the water really depends on the pressure applied when entering membrane.

4. The RO Membrane is a semipermeable membrane that separates the salt particles from the water. The membrane also separates ions, large organics, bacteria and even small particles such as sodium, chlorine, calcium and magnesium. In reality usually around 1% of the salt does get through due to leaks or around seals. The water is not completely pure, but it is still drinkable in normal Australian standards. But if it is used for other industrial purposes, distillation of the water might be needed to guarantee security. The membrane removes as high as 99% of bacteria’s and 90% of simple inorganic ions. (Physical separation, simple in applying pressure to seawater pushing the seawater through the membrane)

5. The water is then near pure freshwater, passed to post treatment also known as stabilization. Where the water’s pH levels are been change usually from around 5 to neutral, which is 7

The separation method of desalination involves basic physical separation of applying pressure through membrane and filtration. There is other process of distillation, which involves high cost in energy usage (due to the fact that heat has to be constantly produced). It is not usually used for the desalination purpose in reality. There is no chemicals involve when separating the seawater apart from pH adjustments and when chemicals such as chlorine is used to clean the pipes, system etc. The properties of the mixture that allowed the physical separation include the pre-treatment filtration, where there is a difference in particle size E.g sand, metals, algae, smaller marine life and water

From the pressurized process, it uses to water’s liquid property by pressuring it, the seawater is then ready to be expel powerfully towards the membrane making it easier to separate the salt from water under the pressure.

The membrane acts similarly to the filter process (pre-treatment) except the membrane is much more sophisticated filtering systems it can get rid of even simple ions. The properties of the seawater that allowed this separation is the difference in size of particles in mixture.

The Post-Treatment process is not considered separation because nothing is extracted from solution.

~Products of Production~

Pre-treatment: This process’s produce is the filtrate containing mostly of saltwater and small particles of bacteria, ions. The filtrate will be sent towards further treatment. The Particles left on the filter paper will be discarded it has no purpose.

pH adjustments: This procedure does not separate any of the mixture.

Pressuring: no product

Membrane separation: The product left within the membrane system is mostly salt particles, ions and bacteria. The excess of ‘water’ from membrane will be carried out to further treatment, this ‘water’ is almost pure.

Post-treatment: The product from this last process is the water itself, pH adjusted on 7.

Wastes product and the distribution of waste

The pre-treatment process’s wastes include the mixture of particles trap on filter paper containing mostly of sands and solids (metals, organic waste). It is cleaned every few day, the process of cleaning it would including back washing to clear build up waste of sand and solids. The waste are usually discarded back into the sea, or in some countries it is filtered again, only this time, using filtering equipment that allowed larger grains such as sand to pass through, the wasted is then send to sewage treatment plant, dehydrated then dispose into the landfills.

There are issues arising with the amount of waste produced. The desalination plant in City of Santa Barbara has the capacity of 7.16 MGD and produced 1.7 MGD waste from filter backwash only. That is 1.7 to 5.1 cubic yards of solid waste generated. So far there has been no better solution thought of about the disposal of this filter backwash waste problem. The desalination plant has not been commonly used enough to cause of serious nationally concerning problem.

Next separation process’s wastes contain mostly salt, some bacteria and small metals. The waste is so concentrated in salt that it becomes highly acidic, therefore corrosive to pipes; it has 1.8 times greater salinity then normal seawater hance when release it would kill marine organisms when released. Another problem include how to release the brine, it cannot be release via pipe unless it is treated before it enters into any system with metals (highly corrosive). The solution to this is to mix the brine with other solution or source of water, adjusting its pH then pumping it out. Other desalination plant management official propose using better water source such as beach wells.

Post-treatment process does not include any extraction of waste, but only to add chemicals to balance the pH level.


Water treatment premier: http://www.cee.vt.edu/program_areas/environmetal/teach/wtprimer/desalt/desalt.htm#EFF

Titled: Membrane separation, last updated 2001, may

California coastal commission: http://www.coastal.ca.gov/desalrpt/dchap1.html

Titled: Process description, last updated 1999, April

World Wide Water: http://www.world-wide-water.com/Desal.html

Titled: Desalination, last updated 2003 (month not mentioned)

OAS: www.oas.org/usdepublications/unit/oea59e/cu20.htt

Titled: RO Desalination 2.1, last undated 2003, January

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