Drying Oxygen in Aerobic Digestion

Waste water needs to be treated before it can be released back into the environment.  There are many different processes that are used to accomplish this.  This article focuses on how aerobic digestion works and why drying oxygen with desiccants can be beneficial to you.

Aerobic digestion requires the use of bacteria to digest the sludge, which is the collective contaminate in a water supply.  The key component to making this process work is oxygen and there are two reasons why.

One reason why oxygen is needed is because large volumes of bacteria used in this process quickly eat up all of the oxygen the bacteria need to live, so without oxygen the process would not work and all the bacteria would die.

The second reason again revolves around aerobic bacteria eating up all of the oxygen.  This presents another problem when releasing waste water back into a river or stream.  When all the bacteria is released back into a stream for example they end up taking all of the river’s oxygen, which makes it impossible for plants and fish that are dependent on the stream to survive.  The added oxygen ensures that there is enough for the wildlife.

Aerobic digestion works by using either a PSA oxygen generator or a cryogenic compressor/oxygen generator to aerate oxygen into the bacteria and sludge mixture.  Before oxygen can be added the digestion process moisture needs to be removed from the air.  This is done by using either silica gel or activated alumina in an air dryer.  Once the air has been dried the aerobic bacteria can remove the sludge.

Drying the oxygen with silica gel and activated alumina can increase the efficiency of a PSA unit or cryogenic compressor, and help purify the oxygen thus giving you a higher concentration of it to insert into the digestion process.  More oxygen equals more bacteria, and more bacteria makes sludge go away faster.

The primary advantage of aerobic digestion is that the process is quick and produces a high quality result.  The downside is it uses a lot of energy and the potential to kill the bacteria if you do not use enough energy.  The restart process once the bacteria are killed is very time consuming, and the extra cost from using too much energy to run this operation requires skilled workers and constant supervision.

Purifying and drying oxygen can help to prevent this from happening.

http://www.wastewaterhandbook.com/

What’s the Difference Between Blue, Orange, and White Silica Gel?

Silica gel is a widely used porous material that adsorbs moisture and is frequently used to limit the damaging effects of humidity.  Its widespread use has led to the creation of many different types, colors, and sizes of silica gel.  This article focuses specifically on why silica gel comes in different colors, and the three most frequently seen colors are: blue, orange, and white.  How does the color of silica gel make a difference?

Blue Silica Gel

Blue silica gel is blue because it has cobalt chloride in it.  The reason cobalt chloride is used is because it allows blue silica gel to turn pink once it has reached its adsorption capacity, in other words it’s an indicator for silica gel being full of moisture.  The creation and disposal of blue silica gel is difficult because cobalt chloride is toxic.

Orange Silica Gel

Orange silica gel has methyl-violet in it, which is what gives it an orange color.  Orange silica gel turns green once it has reached its adsorption capacity.  Like blue silica gel orange silica gel is also an indicating type of silica gel, however methyl-violet is not toxic making it safer to create and use.

White Silica Gel

White silica gel is non indicating silica gel.  What this means is as the silica gel adsorbs moisture it does not change colors.  This type of silica gel is most frequently used for preserving items and for reducing humidity for items that are in storage.  White silica gel is the type of gel you find in the little packets you find when you purchase certain products.

A Look Into How Military’s Use Desiccants in Gas Masks and Medical Equipment

Desiccants are used all over the world and military’s around the world are no exception.

The first widespread use of desiccants by any military occurred during the First World War.  This war is famous for the use of chemical gases as a weapon, and armies that were afflicted with a barrage of gas containing shells needed protection in order to avoid being poisoned.

This led to the first gas masks being mass produced.  The material in the gas mask canisters that absorbed potential toxins was silica gel, and this helped to reduce the effects of poisonous gas attacks that opposing armies faced throughout the remainder of the war.

During 1915 ,while World War I was on-going, Russian scientist Nikolay Zelinsky improved upon the gas mask by creating a filter that used activated carbon, another desiccant.  Today activated carbon is the standard desiccant used in most modern gas masks.

The activated carbon filters in gas masks didn’t start getting used until after World War II.  During this war silica gel was replaced as the primary adsorbing material in gas mask by asbestos… which the world learned after the war caused serious illnesses like mesothelioma and malignant lung cancer.

This paved the way for modern gas masks which use activated carbon filters in combination with aerosol filters to keep soldiers safe.  Activated carbon has a larger surface area than silica gel and can adsorb more potentially dangerous airborne chemicals, thus making it more effective filter.

Besides being used in gas masks, desiccants have recently found a new use in military medical technology.

Zeolites have been attached to gauze and recently been used by the U.S. military to help reduce the blood flow in wounded soldiers and civilians.  The pores in the zeolites are small enough to adsorb the water out of the bloodstream leaving only cells and platelets.

Platelets circulate throughout our blood stream looking to clot blood.  With all the water absorbed out of the bloodstream, thanks to the zeolites, the blood is allowed to clot a lot faster.  This has helped save many lives because it greatly speeds up the time for a wound to close and stop bleeding and it also reduces the chance of wound becoming infected.

The success of zeolites in gauze has allowed this product to be used in the commercial medical market and it is now being used by law enforcement and emergency response units.

…and Oxygen and Carbon Compound Adsorbents?

Absorption and adsorption are two natural occurring processes that are similar, but are not the same.  Here is a basic breakdown of how they are different:  absorption occurs when one material’s physical state is absorbed into another material’s physical state, while adsorption occurs when one material physically sticks to another material without changing it’s physical state.

Absorption occurs when a gas turns into a liquid, or a liquid into a solid, etc.  This is what separates it from adsorption, the physical state of the molecules have changed.  For example if you were to drink a glass of milk, your body would absorb it into your digestive system and eventually into your bloodstream.  The earth absorbs the suns rays and has converted its energy into the life sustaining planet we live on today.  The roots of plants absorb water when it rains converting into the energy it needs to survive.  All of these examples feature one material’s phase being turned into another.

Adsorption occurs when liquid or gas molecules stick to the side of surface, preserving their physical state.  This is useful for separating certain molecules from one another.  Adsorbents are most commonly found as carbon compounds or oxygen compounds.

Oxygen compound adsorbents are used to make products like silica gel which works to absorb moisture and reduce humidity levels or zeolites which can be tailored to specifically remove certain molecules from the air like carbon dioxide.

Carbon compound adsorbents like activated carbon can be effectively used to treat waste water and gas.  Contaminates will get stuck to the pores that are found all over the surface area of activated carbon while the water filters through.

Absorption and adsorption are both sorption processes, they both take in a substance or hold it in place and that is how they are related and why the are so similar, the process, however, is different.

Differences Between Glycol Treatment and Desiccant Treatment

Water removal from a natural gas stream (drying) is an important step in processing natural gas, it prevents corrosion in pipelines and also prevents plugging of pipelines by removing free water and hydrates.  Natural gas drying is preceded by the removal of oil and condensate from the natural gas stream.  Currently there are two common processes which see to the removal of water from gas streams: glycol treatment and desiccant treatment.

Glycol treatment primarily uses triethylene glycol , diethylene glycol, or tetraethylene glycol to adsorb and remove the water from the natural gas stream.  Glycol will adsorb water from liquid gas streams in a dehydrator.  As glycol adsorbs water it becomes heavier and sinks to the bottom of the dehydrator.  After the glycol has adsorbed the water it is boiled out of the dehydrator leaving behind liquid natural gas.

Desiccant dehydration requires the use of adsorption towers, which contain desiccant usually molecular sieve, activated alumina, or silica gel.  Wet natural gas is passed through the top of the tower which contains thousands of pounds of sieve or alumina beads and by the time it reaches the bottom of the tower the water will be removed from the gas stream.  Multiple adsorption towers are used during this process to allow over saturated desiccant to be regenerated.  In other words while one tower has gas running through it another tower is regenerating the previously used (and now over-saturated) desiccant.

The advantage of using dry desiccants is their ability to adsorb and reduce the water from natural gas streams to lower concentrations than glycol.  Pipelines require that water content in gas streams not exceed 7lb/MMSCF (million standard cubic feet) and dry desiccants can achieve this level easily (up to 2lb/MMSCF).  Glycol dehydrators can achieve this level but usually at the bare minimum and sometimes they don’t make the requirement and have to go through the treatment process again.  Although glycol treatment is more popular right now, dry desiccants appear to be more effective at drying natural gas.

http://www.kwintl.com/glycol-dehydrators.html