Activated Alumina Works To Lower Fluoride to Safe Levels in Drinking Water

Water fluoridation is a double edged sword.  In the U.S. fluoride has been added to most water streams in order to help prevent tooth decay.  (I should mention fluoride naturally occurs in a lot of drinking water sources throughout the world).  However fluoride can be damaging to bones at higher doses and it can even be fatal if you take in large quantities of it.

The desiccant activated alumina plays a very important role in reducing fluoride levels in water.  By doing this activated alumina leaves enough fluoride in water for people to receive its potential health benefits while at the same time it makes sure that health damaging amounts of fluoride do not remain in drinking water.

In 1994 the World Health Organization recommended that fluoride levels in water should be contained from 0.5-1mg/L.  Fluoride levels above 1mg should undergo defluoridation, which can be done three different ways: with chemicals and precipitation, with membrane based technologies, or with ion exchange and adsorption.

A lot of times these methods are used in combination.  For example, when fluoride levels are above 15ppm using lime which falls under the chemicals and precipitation category should be used because they can handle the high levels of fluoride.  Once that level is lowered using lime, activated alumina, which falls under the adsorption category, should be used to reduce to the fluoride content to below 1ppm since activated alumina can purify water up to 99%.

How does Activated Alumina work in removing fluoride from water?

Activated alumina adsorbs fluoride because fluoride is attracted to alumina.  It wants to make aluminum fluoride which it does once it comes into contact with activated alumina.  The alumina fluoride will remain stuck to the alumina beads so long as the pH level of the water remains below 6.  If water’s pH remains lower than a 6 the effectiveness of activated alumina starts to be reduced.  It can also allow aluminum to get in your water, although aluminum does not typically dissolve in water.

Note: Reverse osmosis is used to remove aluminum from water and so can certain distillers.  Aluminum does not typically get into water because water has a difficult time dissolving it.

It’s recommended that you pre-treat activated alumina with aluminum sulfate before you use it in order to improve the first adsorption runs.  After pretreatment it’s important to remember that adsorption reactions with activated alumina are  flow-rate dependent.  Although activated can handle high flow rates and still work, its adsorption capacity is reduced and this could lead to having to do additional cycles.  Doubling the flow rate allowed 33% more fluoride through the activated alumina beds, thus reducing activated alumina effectiveness in adsorbing fluoride.

There is a possibility of other ions interfering with the adsorption process when working with activated alumina, this is due to water in the U.S. containing other ions.  These ions are usually sodium chloride, sodium sulfate, and sodium bicarbonate.  Sodium chloride and sodium sulfate do not interfere with the adsorption process, but sodium bicarbonate can reduce the capacity of activated alumina between 33% and 70%.

Activated alumina like most desiccants can be regenerated.   Sodium hydroxide, aluminum sulfate, or sulfuric acid are applied to a lye solution with the activated alumina, allowing the adsorbent to be regenerated.  Once regenerated activated alumina can continue to be re-used, and when used properly activated alumina can last years.

Activated alumina is essential in removing fluoride in water up to 99% and making water safe for people to drink.

Sources:

http://www.watersanitationhygiene.org/References/EH_KEY_REFERENCES/WATER/Water%20Quality/Fluoride/Defluoridation%20Using%20Activated%20Alumina%20%28UNICEF%29.pdf

http://www.bibliotecapleyades.net/salud/salud_fluor23.htm

World Health Organization: http://whqlibdoc.who.int/trs/WHO_TRS_846.pdf

http://www.tramfloc.com/tf133.html

Double Flow Rate = 33% decrease in adsorption capacity, reverse osmosis, and ions.  http://www.purewateroccasional.net/newnewsletter8.html

Water below pH of 6 reduces effectiveness of Activated Alumina http://greenlivingqa.com/content/fluoride-filtration-using-alum

Part Two of a Two Part Article Dealing with Ethanol Dehydration and Sieve Regeneration and Rotation

Regeneration and rotation of molecular sieve beds is an important part of the dehydration process.  When you rotate your beds you allow ethanol to simultaneously be dehydrated and regenerated. Additionally, regenerating your sieve beads allows the material to remain in use for approximately five to seven years before you would need to change it out.

Using a typical 3-bed dehydration system as an example, rotation works by having one sieve bed adsorbing, one sieve bed depressurizing, and one sieve bed under vacuum for regeneration.  The molecular sieve units operate sequentially, rotating their functions as they’re needed.  This allows ethanol to constantly and simultaneously dehydrate and regenerate. The rotating process is why a 3-bed system has only one bed adsorbing moisture at a time.

Regeneration allows sieve beads to release the moisture they adsorbed in the most efficient manner possible.  After releasing moisture, sieve can continue to be reused for future adsorption cycles.

Regeneration is accomplished by applying vacuum to the bed undergoing regeneration. Once under vacuum adsorbed moisture from the molecular sieves desorbs and evaporates into the ethanol vapor stream.  The sieve that is still left in the tower is now ready to begin the dehydration cycle again.

This mixture of ethanol and water that is removed during the regeneration process is condensed and cooled against cooling tower water in the regeneration condenser. Any condensed vapor and entrained liquid leaving the regeneration condenser enters the regeneration receiver, where it is contacted with cooled regenerated liquid.

The cooled regenerated liquid is weak in ethanol concentration, as it contains all the water desorbed from the molecular sieve beds and contains only traces of alcohol. This low strength liquid is recycled back to the stripper column for recovering ethanol.

Part One of a Two Part Article Dealing with Ethanol Dehydration and Sieve Regeneration and Rotation

Bedded dehydration systems are some of the most frequently used devices for the purification of ethanol.  This article focuses on how bedded dehydration systems distil and purify ethanol to make it over 99% pure.   Ethanol is purified so it can be used as a fuel in automobiles, which currently requires ethanol to be over 99% pure.

The distillation process begins after the fermentation process.  From the beer column, rectified ethanol is pumped into the rectifier column (frequently called the stripper). After distillation occurs in the rectifier column the ethanol mix goes to the condenser.

After ethanol is condensed in the condenser the gaseous ethanol can go to one of two places: the first partial steam of vapors can be sent back to the rectifier column as reflux, or the rest of the vapors are passed through a super-heater before being taken to the molecular sieve units for dehydration.

This part of the process distils the ethanol solution and making it around 95% pure ethanol.  The last 5% of the solution is water still needs to be separated from the mixture in order for ethanol to be use as fuel.  This is done with molecular sieve.

After passing through the super heater the vapor now passes through one of what could be many dehydrating beds of molecular sieve beads. Water in the incoming vapor stream is adsorbed on the molecular sieve material.  Anhydrous ethanol vapor that is now over 99% pure has been created from the sieve loaded dehydration bed, and is now free to be collected.

The process is finalized when the ethanol vapor remaining from the molecular sieve units are condensed in the condenser and cooled down in the product cooler, bringing it closer to its ambient temperature.  The product is then stored in a product tank until it is ready to be sold.

Part two is forthcoming…