De/Anti Ice Experience and Experiment

With the Fall freeze approaching in less than half a month in Chicago, the airlines have been working full speed to prepare their anti/de-icing programs.  I've finally put this science degree to use by going on a special assignment to help with the deicing plan which the FAA just approved.

Institutional memory of how to change the dilutions of Type I deicing fluid has been lost.  It had been held by two very senior baggage handlers, who kept their secret closely guarded for years as it allowed them to avoid much manual labor.   One retired and the other was out on long term medical leave.  The FAA requires the freezing point of the deicing fluid to be greater or equal to10C colder than the outside air temp (OAT).  This because the temperature on any given day tends to fluctuate, so that 10C buffer keeps the deicing fluid usable in colder temps.   The airline tries to keep that freezing point as high as possible because it is achieved by mixing the deicing fluid with water and economizes deicing fluid ($5-$7/gal).   However each day the OAT changes, so the Type 1/water ratio should be raised or lowered.  Nobody knew how to do this.   So I taught them how to convert freezing point (which they determine with a refractomitor which operates on the basis of Snell's Law) into a mixture ratio if it is unknown.  From that I taught them how to use a formula to convert any original dilution and quantity to any desired dilution and quantity.  For example a deicing truck with 1000 gallons of 40% Type I to 1600 gallons of 50% with scientific precision.  By the end all the guys were acing my quizzes.  I trust my life to their math, well that and the (tested daily) refractomitors they'll use to confirm the final freezing point.  :)

While researching for this assignment I looked up the MSDS for the deicing fluid.  The BOD made my jaw drop!

Pure propylene glycol has a BOD5 concentration of approximately 1,000,000 mg/L. A typical diluted propylene-based deicing fluid could therefore have a BOD5 concentration of approximately 500,000 mg/L. In comparison, raw sewage typically has a BOD5 concentration of approximately 200 mg/L. [source]

Many organic contaminants in water get broken down by microbes who use it as food, just about every water treatment plant has a stage where microbes and other microflora are fed swage water to decompose it.  In the process the  aerobic bacteria consume oxygen.  The five day BOD test measures how much oxygen those microbes consume in that five day period at 20C, and is used to measure the effectiveness of water treatment.  There are over a thousand flights a day out of O'Hare, each plane on snow events will need deicing.  1,000 to 4,000 gallons of deicing fluid may be needed for larger jets during severe weather conditions. If it is snowing, a jet requires approximately 35 gallons of fluid for anti-icing after deicing.  My fears are that some fluid will leak into the groundwater where it won't be decomposed quickly due to the cold, and will end up in our drinking water.  I also fear that some will flow into local lakes where it can deplete the oxygen and kill the life in it.  

The EPA proposed regulations on de/anti icing fluid effluent in 2009 after very careful study, but nothing came of it.  One of the proposals was to have the airline monitor the COD of what they are discharging into the sewers.  COD is like BOD but monitors the oxygen depletion by chemical reactions. Since it's not being done, I feel a personal responsibility to monitor this.  I can't do a COD test because I don't have a photospectrometer.  I can do the BOD5 test on a couple bodies of water for about $160 for the season.  By writing it here for others to see, it will force me to make good on my commitment. :-)

Update: There is a group of concerned residents and airline workers who have been complaining about the impact of de/anti-icing use at O'Hare Airport and a report was written in 1997 by Paula F. Cowan, M.D. Clinical Asst. Professor of Family Medicine, University of Illinois at Chicago.   Her recommendations for action:

1. An investigation needs to be conducted to determine why these problems were allowed to exist without solutions for so many years.
2. Since there were past abuses, we need methods to see if the airport is adhering to the Clean Water Act.  We need independent scientists and experts to monitor periodically to see if problems are being solved.
3. We also need waterways and water tables tested on a regular basis, looking for specific chemicals when deicing/anti-icing operations are in progress.