In the spring of 2008, Bangor International Airport started conducting experiments with floating treatment wetlands also known as Biohavens® to help improve the quality of the water at the outfalls near the airport property. The islands were created by Floating Islands International and donated to the Airport by the inventor Bruce Kania. These islands “bio-mimic” floating wetlands that are found in nature (ex. Peat bogs),and are composed of fibers made from 100% recycled plastic, the layers of recycled plastic are then bonded with foam to provide buoyancy.
At the airport we are always looking for options that can enhance the quality of the storm water that flows off of the property. We began looking into the floating wetlands as an option to meet three treatment objectives.
The objectives were:
- Remove/reduce nutrient levels in the waterways
- Remove/Reduce trace amounts of glycol in waterways
- Reduce the temperature of the water
After determining the objectives two islands were ordered. The first was a 64 sq. ft. island that would be launched in the waterway. The second island was 1 sq. ft. and would be used for laboratory testing.
The Big Island:
Once we received the big island a spot was chosen in the waterway to launch it. The island was planted with sod, and plants from the surrounding area. The goal for the first year was to observe the island and ensure good growth of the plants and grass and to see if it would survive through the winter.
I have provided photos of the island throughout the past three years.
|June 17, 2008 a few days after the island was launched|
|One month later the island has started to fill in nicely.|
During the same time period that monitoring of the large island was taking place tests were being conducted in the laboratory.
The first test that we completed was a control test to see how long it would take glycol to break down in water without any treatment. Two bins were set up with 10 gallons of water each. Circulation pumps were added to move the water between the two bins. Next 1000mL of glycol (a 50/50 mixture was made with 500mL Type I and 500mL Type IV) was added to the system. Originally we thought that the glycol would break down on its own as the water circulated between the two bins. The system was tested each day with a MISCO hand held refractometer, after 7 days of monitoring there was no change in the concentration of glycol within the bins. Next a bubbler was added to the system to see if aerating the water helped the glycol break down. Again after 7 days there was no change in glycol concentration.
Since no change in glycol content was found it was decided that a new test would be started. The whole system was torn down, cleaned, and put back together. The bins were filled with 20 gallons of clean water and 1000mL of type I glycol. The system was tested and an initial glycol reading of 1.0 was recorded. Once again after a period of 14 days there was no change in the glycol content within the system.
On the third attempt a light was installed above the system to see if this would cause a change in the glycol content. The experiment was completed again and no change was recorded after a 14 day period.
The Small Island:
The next test was to begin using the island to see if it would aid in breaking down glycol at different concentrations. The original system was torn down and cleaned and a new test was started.
The island was planted with Swiss Chard and allowed to grow over a period of time, algae also began to grow along the sides of the bin. Swiss Chard was chosen because it grows relatively quickly and has a generous root system. Shortly after preparing the island it was found to be very unstable due to its small size. The first time the island was “launched” in the bin it rolled over and all the soil and seeds were dumped into the water. A second attempt was tried at planting the island with soil and seeds and re-launching it in the bin, again it rolled over. This problem was resolved by placing the island off to one side of the bin and adding a partition to hold it in place (see photo below). In addition to the partition a glass jar was placed under the island to further stabilization. The light was put on a timer to mimic a natural light cycle. We kept the aerator from the previous tests to continue to provide air flow within the water column. The bin was then filled with approximately 15 gallons of water. In order to estimate a scale for real world application we determined that this island occupies about ½ of the surface area of our little pond.
|The lab all set up|
|Another shot of the lab|
The goal was to see if the biological life growing within the island and the algae growing on the walls of the bin would be able to reduce/remove glycol from the water.
The experiment was started on March 3, 2010. 10 drops of type I glycol were added, with a dropper, to the system each day for (3) days. After the three day period the water was tested for glycol with a CHEMetrics Vacu-vial Glycol test kit, the result after the three day period was 4ppm.
On March 16, 2010 the test was repeated. The amount of glycol was increased to 10 drops of type I glycol each day for (10) days. The purpose of extending the number of days was to attempt to greatly increase the concentration of glycol within the system. After ten days the water was tested again and a result of 3ppm was recorded.
This test continued over a period of approximately one month by continually increasing the amount of glycol each week. Every five days the concentration of glycol in the water was tested. After 30 days the test results continued to be recorded at 3-4ppm of glycol within the system.
Since there was no real change in the concentration of glycol within the system after 30 days, it was decided that a much higher amount of glycol would need to be added in order to obtain a measurable increase.
On April 4th 2010, 2mL glycol was added to the system each day for five days, again a similar result of approximately 2ppm was found after testing.
Next 4mL glycol was added to the system for five days. At this time we also began monitoring Dissolved Oxygen (DO), and pH. After the five day period the results still produced a reasonable glycol content of approximately 21ppm. The DO after this period of time was 4.93mg/L and the pH 7.
The Turning Point
After the first two tests the concentrations did not appear to be reaching a level that would provide a good test of what the system might be capable of.
On April 9th 2010, 10mL of glycol was added to the system. Three days later (4/12/2010) the water was tested, the concentration of glycol was at 30ppm.
On 4/16/2010 the water was retested and the concentration had dropped to 1ppm, DO had risen to 8.33mg/L and pH remained at 7.
This is exactly what we had been looking for; the island system was consuming the glycol and essentially removing everything except the smallest amounts from the water.
Once again the island was put to the test. This time 15mL glycol was added. A glycol test was completed within a few hours of adding the 15mL to see what the glycol concentration starting point was. The result was found to be greater than 65ppm which is the limit of the test kit without dilution. It was decided that it would take considerably longer for the system to consume the glycol at high concentration. After 10 days the concentration was tested and the result was 2ppm Glycol, DO=7.39mg/L, and 5.29pH.
The testing continued over another 30 day period. The amount of glycol added was increased by 5mg/L each week (15mL, 20mL, 25mL, and 30mL). Over this time the concentration was driven up to over 200ppm glycol. Each time the system would consume the glycol bringing it back to 0-1ppm within 7 days.
The final test was completed on June 1st 2010. 30mL of type I glycol was added to the system. The concentration of glycol increased to 500ppm with a DO level of 7.82mg/L and pH of 7.82. On 6/8/2010 the water was retested and the concentration had dropped to 25ppm (95% glycol removal in 7 days). The system was checked again on 6/15 and the concentration had dropped again to 1ppm. Also during this time a population of spring tails was observed on the water’s surface.
These results taken over the 3 month period proved to us that the island systems could effectively reduce glycol concentrations in water. We also believe that increased aeration may improve the islands performance and hope to do more experiments in the future to prove that theory.
I feel that these islands would be a great asset to any airport or other business that may have similar storm water objectives. These systems can improve water bodies by lowering nutrients, providing shade to reduce water temperature, and by reducing or eliminating glycol in the stormwater runoff with the addition of detention and aeration.