Water: What are some ways to obtain safe drinking water?

Mercer University School of EngineeringProfessional Practices, Dr. DavisJ. Walsh

What’s wrong with our water today?Some contaminants of our water today:

LeadRadonNitratesParasites

Traditionally, chlorine has been used to eliminate these contaminantsProblems with chlorine:

It reacts with decaying organic matter This causes cancer causing chemical byproducts

One way the Army is providing water to its soldiersNew technology being tested by the ArmyTurns exhaust in Humvees to drinking waterFive part system:

1. Catalytic converter-device in all modern vehicles that oxidizes the toxic organic compounds not combusted by the engine

The army has enlarged its surface area so it takes longer for the fumes to pass through it

This makes it cleanse the fumes more2. Heat exchanger

Refrigerates fumes and causes them to condense3. Treatment tanks

Bed of six activated-carbon and ion-exchange filters the liquid goes through

Exhaust to drinking water4. Water-Quality Sensor

• Checks cleanliness of the water5. Storage Tank

• Chlorine is added to purify water• Held in a 5 gallon tank on rear• Water comes through a spigot• Water goes through air conditioning unit to chill and

remove chlorine taste

Two ways to purify water: UV and desalinationUV lightCurrently 3000 to 5000 systemsUseful in wastewaterFew official regulations exist for performance-related

criteria for UV units for drinking water

UV light continuedHow it works:

Proteins, phenols and humic material that contaminate water absorb the rays and die

Destroys all bacteria and virusesMade of multiple standard high-quality UV lamps,

sealed within quartz tubes or sleeves

Photo courtesy of Islandnet.com

Two methods of desalination: reverse osmosis and electro dialysisReverse Osmosis-membrane process for desalting water

Uses hydrostatic pressure to drive water through a semi permeable membrane, which means only selected things can go through the membrane

Pure water comes out at near atmospheric pressureWaste is at original pressureThe figure below illustrates how this system works

Desalination techniques continued: Electro dialysisElectric energy is used to transfer ionized salts from feed water

through membranes, leaving behind purified product waterSalts are ionic, so cation and anion-selective membranes are

placed, alternately between two electrodes This means the salt particles have a charge and they are

attracted to the electrodes so they can be removedThree elements:1. Supply of pressurized water2. Membrane stack3. DC power supply

• A rectifier converts alternating current to direct current• Used on membrane stack• Energizes ions and causes them to move through selective

membranes

How can UV light and desalination be useful?UV light

It is an environmentally safe, nonchemical, physical process that produces no toxic side effects

The equipment is easy to operate and maintainThere can be no overdosingNo residue leftVery quick; only a few seconds while chlorine takes ¼ to ½

and hourDesalination

Uses no chemicalsEnables salt water to be harvested for fresh drinking waterAlso no overdosing or residue left

Referenceshttp://www.islandnet.com/~tiger/Tiger/UV/UV_pics/Trojan/

diagram.jpgKeats, J. (2006, January 16). Converting tailpipes into water

fountains. Popular Science. Retrieved March 16, 2008, from http://www.popsci.com/scitech/article/2006-01/converting-tailpipes-water-fountains

Masschelein, W. J. (2002). Ultraviolet light in water and wastewater sanitation. Boca Raton: CRL Press LLC.

Montgomery, J. M. (1985). Water treatment principles and design. Canada: John Wiley & Sons, Inc. 225-235.

Spellman, F. R. (1999). Choosing disinfection alternatives for water/wastewater treatment. Lancaster, PA: Technomic Publishing Company, Inc. 108-113.

Worshop, R. L. (1994, February 11). Water quality: should safety standards for drinking water be tougher in the US? CQ Researcher, 4, (6).