The deicing of airplanes is a process of removing ice from an airplane body. The removing of the ice, snow or frost from an airplane body is vital in order to maintain the shape of an airplane, so the airplane can work in proper way. Thus, deicing of airplanes are important to ensure the safety of air transportation but the deicing chemicals that used in the deicing process bring harm to the environment through ADFs runoff to the receiving water near the airports and the soil. The deicing chemicals impact the human being, animals, aquatic organisms, receiving waters and many more. They are two types of glycols which are propylene glycols and ethylene glycols as part of a composition of deicing chemicals. In addition, there are some other chemicals that made up deicing chemicals. All these chemicals could bring harm to the environment.
This case study concerns the impact of deicing of airplanes to the living things and the environment. This topic is important to be investigated because the deicing process caused many problems to the living things and the environment but at the same time, this process is crucial to be done for a safe take off.
Deicing of airplanes is a process that removes ice from the airplanes bodies. It helps an airplane to function properly during cold weather. In cold weather, the airplanes need to deal with ice, snow, and frost that built upon their bodies. The built-up ice, snow, and frost may change the geometry shape of the wings of an airplane, disrupt the airflow and thus, decrease the lift ability. As we know, each part of an airplane is designed to create lift force. Most of the lift force is generated by the wings and rear tail of an airplane. Both wings and rear tail of an airplane is designed or engineered with a specific shape that crucial for the airplane to have a proper lift to fly. This shape made the lift possible but the built-up ice, snow, and frost due to cold weather might change the shape of those parts and this may lead the parts to function in dangerous and in the improper way. Besides, the built-up ice, snow, and frost may increase the drag and restrict the moving parts of an airplane too.
In order to prevent a dangerous take-off, deicing process is urged to be done. In the deicing process, some chemicals are used. The common one is the de-ice type I. It prevents the ice built up in a short period of time and is used when the temperatures are not very cold or extremely low. This fluid is heated to 80 degrees Celsius before the fluid is sprayed on the surface of an airplane to remove all the built up ice, snow, and frost.
The deicing fluid is applied on the along the centerline of the fuselage at the upper part and then over the side of the fuselage. The fluid is preventing contact with the window. At the wings, the fluid is sprayed starting from the front edge to the trailing edge. The workers in charge have to take precautions to not letting the fluids from getting into the engines and minimize the fluids application at the landing gear and wheel bays areas.
In the United States, the Federal Aviation Administration (FAA) is controlled and managed for the deicing procedures. The FAA put on some criteria for approving the deicing chemicals while the federal and state environmental agencies are those that respond to evaluate the impacts of the deicing chemicals or fluids to the environment and to regulate the discharge of the fluids accordingly. The deicing process has often been done during the winter storms, so the runoff from the storms will transport the deicing chemicals from the airfield into the local receiving waters such as wetlands, rivers, coastal areas, creeks, and lakes. However, most of the federal and state environmental agencies that existed do not include the limits on deicing chemicals in the stormwater discharges. The airports used this advantage to freely discharging the stormwater that contaminated with deicing fluids. This lead to water pollution issue.
As the air travel is increasing over time, the volume of deicing fluids discharged to the environment is increasing too. Thus, the airports are struggling to decrease the impacts of the deicing fluids to the environment while maintaining the safe air transportation.
iii. Literature Review
In history, the airplanes could not fly during the winter. As time flies, the new techniques were started to exist but they need to perform the techniques manually to remove the ice that adhered to the airplanes bodies. Somehow, a series of tragic crash happened in the 80s caused the commercial aviation industry to take more scientific approaches to de-icing.
Deicing of airplanes removes and inhibit the formation of ice, snow, and frost at the bodies of airplanes especially at the fuselage, wings, and rear tail. This practice, remove all the accumulation at the airplanes bodies before take-off.
Based on a research, Logan airport applying deicing fluids on airplanes surfaces as a hot mixture under pressure using a nozzle mounted on a vehicle. During deicing process, in about only 20%-50% of the deicing fluids remained on the airplanes bodies while the rest in about 80% end up as runoff. Besides, an airplane can reach from 10 gallons to thousands gallons usage of deicing fluids. Either airline or the service company is responsible to do this procedure.
There are four types of deicing fluids which are Type I, Type II, Type III and Type IV. These four types of deicers are distinguished by the composition and the holdover over time of deicing fluids application. In this study, the Type I deicers will be focused on because the other three type deicers are actually the anti-icing fluids. The deicing fluids and anti-icing fluids differ in compositions. The composition of deicing fluids is usually ethylene glycol, diethylene glycol or propylene glycol based fluids containing water, corrosion inhibitors, wetting agents and dye while anti-icing has the addition of polymeric thickeners which can prevent the ice formation for a longer period of time compared to deicing.
IV. Method (Findings)
i) Types of Deicing Chemicals
Deicing chemicals divide into two major types which are the organic chemical with potassium acetate and the other one is chlorate which contains NaCl, CaCl2, MgCl2, KCl, and others. The organic chemical is effective and almost non-corrosive but it is quite expensive, so it is usually used in the airport only. The other kind is generally called deicing salts. It is much cheaper but the breakage by the salts is quite serious.
ii) Working Principle
The salty water is not easy to ice up because of its ability to absorb heat and it has a lower freezing point. That is why the deicing chemicals can decrease the melting point of snow and ice. Thus, make it easier for the ice and snow to turn from solid phase to liquid phase.
Recently, a new deicing chemical named “new type” is produced which is mainly CaCl2 but it still could bring harm to the environment.
iii) The Impacts of Deicing Chemicals on The Environment
a) Biological Oxygen Demand (BOD)
According to Wikipedia, BOD is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a specific time period. A high BOD means there is a large amount of oxygen dissolved in a water body is used up by the substances which are the deicing chemicals fluids, thereby decrease the amount of oxygen available for aquatic organisms to breathe. Thus, many aquatic organisms kill because of deicing chemicals and other environmental effects such as algal blooms, odors and contaminated surface water and groundwater drinking system.
Throughout the time of the deicing process, some of the deicing chemicals which can be up to 80% have a high chance to fall down onto the pavement surfaces. This may happen due to overspray or during taxi and takeoff. In deicing chemicals, there are two type of glycols used which are ethylene glycol and the other one is propylene glycol. Both types of glycol are different by their physical and chemical properties as shown in table 1 below.
Other than that, glycols are biodegradable substances. As glycols absorbed in the soil, the biodegradation is significance in removing the glycols from the soil. According to a source, at concentration of less than 6000 mg/kg in soil, ethylene glycol was found to have biodegradation rate of 3.0 mg/kg in soil/day at -2 degree Celsius and 19.7 mg/kg soil/day at 8 degrees Celsius while in propylene glycols, the rate of biodegradation are 2.3 mg/kg soil/day at -2 degree Celsius and 27.0 mg/kg soil/day at 8 degrees Celsius.
The result of spills, runoff, and discharge of these glycols can reach to nearby groundwater and surface waters of the airports. U.S Toxic Release Inventory (TRI) estimated that 1.2 million pounds of ethylene glycol released to surface water throughout the whole nation.
Based on laboratory experiments, in surface water, glycols undergo rapid biodegradation. In surface water, ethylene glycols have a half-life of 2-12 days under aerobic conditions and 8-48 days under anaerobic conditions. The propylene glycols have a half-life in about 1-4 days in surface waters under aerobic conditions and 3-5 days under anaerobic conditions. Ethylene glycol undergoes complete biodegradation in surface water in 14 days at 8 degrees Celsius.
From this table, it shows that glycols are very soluble in water and thus make biodegradation as a significant process to break down these glycols. In addition, these glycols have high oxygen demand. It had been reported that ethylene glycol required in about 400,000-800,000 mg/L of oxygen in freshwater and in about 260,000 mg/L of oxygen in marine organisms. For propylene glycol in both marine and freshwater, its requirement for oxygen can exceed up to 1,000,000. As a result, these glycols can affect the aquatic life by consuming the large amount of oxygen that available.
2) Formulated Products and Additives of Propylene and Ethylene Glycol
The formulated products and additives of propylene and ethylene glycol present in small amount only in deicing chemicals. They are less concentrated compared to the glycols. This substance may not increase the oxygen demand but it may be toxic to the microorganism that biodegrades them, inhibit the biodegradation of the Aircraft Deicing Fluids (ADFs). As biodegradation required oxygen, the oxygen demand will be decreased results from the inhibition of biodegradation by the additives. The table below shows the biological oxygen demand (BOD) of 5 types of formulated deicers.
There is only a very small component of urea in deicing chemicals. It is not volatile due to low Henry’s constant, even though it drains away from the soil into the surface water and groundwater. In receiving waters, the urea acts as the fertilizer and it triggers the algal blooms due to nitrogen present in urea. Algal blooms happen as the result of excess phosphorus and nitrogen in water. Algal blooms will consume a large amount of oxygen in water lead to eutrophication in still water such as lakes. This leads to the death of aquatic plants and animals that require the high level of dissolved oxygen.
Urea consumed in about 20,000 mg/L of oxygen. However, when it breaks down into ammonia, the oxygen demand of urea can increase up to 2,000,000 mg/L. In addition, the breakdown of ammonia cause odors.
4) Potassium Acetate
Potassium acetates are readily biodegradable. It can degrade well at low temperatures. It has a very low biological oxygen demand compared to other deicing chemicals. All potassium acetate will degrade in 20 days at 2 degrees Celsius.
5) Calcium Magnesium Acetate (CMA)
CMA is also readily biodegradable posses BOD5 of 540,000 mg/L.
6) Sodium Acetate
Sodium Acetate is readily biodegradable too at low temperature and has BOD5 of 580,000 mg/L.
7) Sodium Formate
This deicing chemical is highly biodegradable with BOD5 of 120,000 mg/L. (Placeholder1) (Norman)
Toxicity exhibited by deicing chemicals due to the presence of glycols and additives. The glycols in airplanes and airfields are never been the pure substances make the glycols to bring toxicity too.
1) Propylene and Ethylene Glycol
These both types of glycols have same aquatic toxicity characteristics. When these glycols were tested on freshwater and marine organisms, 50% of sample population killed in a short period of time. The standard method then of comparing toxicity among chemicals is to compare the LC50 values for a common species. The increase in the amount of LC50, the decrease or lower the toxicity is. Any substances with LC50 above 1000 mg/L are considered harmless.
The table above is summarized in the LC50 of 4 freshwaters and marine aquatic life.
There are three main exposures of ethylene and propylene glycol to mammalian which are through inhalation, oral and dermal (skin absorption).
Based on some data, both ethylene glycols and propylene glycols do not lead to toxic effects. When a human accidentally or intentionally consumed ethylene glycols, the glycol will quickly break down in the body form chemicals, preventing any crystallization that can affect kidney function. The acidity of the chemicals alters the body’s normal chemical balance.
In addition, the propylene glycols also do not cause any side effects of toxicity. The glycols break down in the body and somehow did not cause any crystal formation or acidic chemicals formation.
2) Formulated Products and Additives of Propylene and Ethylene Glycol
Formulated glycol deicers are a way more toxic compared to pure glycols by order of magnitude. This is because of the additives that were added to the formulated glycols. For little mammalian, the tolytriazoles, a type of additive is harmful if swallowed and also can cause irritation on contact.
Urea is non-toxic to aquatic organisms but it can irritate the nose and throat, causing a sore throat, sneezing or coughing and shortness of breath in humans. If the concentration of urea is high in exposure, it can cause eye damage, skin redness or rash, or emphysema.
However, when urea forms into ammonia, this may affect the aquatic organisms.
In summary, the deicing of airplanes has many impacts on the environment such as:
1. The effects on aquatic life
2. Effects on human health
3. Aesthetic effects such as odor, color, and foaming.
4. Effects on quality of receiving
Deicing chemicals have many impacts to the environment such as to the aquatic organisms, human health, aesthetic effects and water receiving quality, so to overcome these problems several alternatives are invented to minimize the usage of the deicing chemicals.
Alternative to Deicing Chemicals:
1) Infrared Deicing
Instead of using deicing chemicals, we can use infrared (IR). Airplanes are towed under a canopy that directs IR energy at the surface of airplanes that need to deice. The ice, snow or frost that accumulated on the surface of the airplanes will absorb the heat and they will melt, without the airplanes being heated. However, the IR is quite costing as to build an IR system for aviation craft can be up to 1.2 million dollars. Larger system construction for commercial airplanes cost 2.5 million dollars. An IR system can deice airplane with cost 500 dollars.
2) Force Air Blast Deicing
This system uses compressed air combined with a fine spray of glycols. This is to blow off snow and ice from the airplane’s wings. This system decreased the usage of glycols by 70% and save time by half compared when using conventional spray trucks. In addition, this alternative operated from a mobile truck mounted and the cost to retrofit the truck cost in about 100,000 dollars.
3) Clean Wing Detection
This system uses sensors mounted flush on the aircraft skin, helps to detect and measure the thickness of accumulated ice on the surfaces of airplanes wings. It controls the amount of deicing chemicals needed. Therefore, this system can prevent the excess use of deicing chemicals.
4) Upper Wing Heater System
In this system, thin pad heaters are attached to the upper wings surface at the in front of the airplane’s engines. The pad encloses the heater with aluminum sheets with an insulator to prevent the heat loss to the wings and it has heat sensors. The heat sensors will activate the cockpit light if the temperature of the panel reaches 5 degrees Celsius and above as indicated the ice is completely melting.