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Project Phosphogypsum: The Effect of Phosphogypsum on the Water-retaining Properties of St. Augustine Grass

Annika Intro

My project was designed to test whether applying phosphogypsum to St. Augustine grass is effective during drought conditions. Polk County, Florida, could directly benefit from this project because my county has been under water restrictions as a result of the drought we have been experiencing for several years. There is a large amount of sod farming in our area, and farmers can use less water by using phosphogypsum. Central Florida is also a tourism area, and there are many golf courses that could benefit from the water-retaining properties of phosphogypsum. All over the world, people are running into the problem of what to do with useless phosphogypsum stacks piling up, and the world could benefit from the use of the substance on outdoor lawns. For years, people across the globe have tried to find a use for this growing problem. I thought that this might be the answer—using phosphogypsum on grass to help it retain water.

Preparing the metal pans for the grass

Preparing the metal pans for the grass


Checking the grass for establishment

Checking the grass for establishment


Sprinkling PG on the grass

Sprinkling PG on the grass


Watering the grass

Watering the grass


Average Weight Change of Pans (weight lost)

Average Weight Change of Pans (weight lost)


Placing pans on the scale

Placing pans on the scale


Weighing pans on the scale

Weighing pans on the scale


Placing a pan on a water collection pan

Placing a pan on a water collection pan


Data Chart: Weight of Pan in Kilograms

Data Chart: Weight of Pan in Kilograms


Before starting the experiment, I collected research from two main websites: the Florida Institute of Phosphate Research (FIPR) website and the Environmental Protection Agency (EPA) website. Based on my research, I hypothesized that pans of St. Augustine grass with the most amount of phosphogypsum applied would retain the most water. I observed that if phosphogypsum can be used for water retention, we can use less water to irrigate sod farms, golf courses, and our lawns. Also, if people are able to sprinkle phosphogypsum on their lawns to help retain water, precious water in our aquifers would be saved and water bills would be lowered. My county has a water shortage problem, and county officials are not sure where the public water supply will come from in the next 20 years. I observed that if the county can use this byproduct from phosphate mining, we could clean up our environment and save the water my state is running out of.

I drew up a plan for the project. The metal pans I used measured 20 inches by 13 inches, and had holes for drainage. A paper towel and thin layer of sand/soil mixture were layered on the bottom, and pieces of St. Augustine sod were cut to fit the pans. I labeled each pan with a popsicle stick. Pans 1A, 1B, 1C, and 1D were the control pans of grass, and received no phosphogypsum. Pans 2A-2D received 6.63 grams of phosphogypsum, Pans 3A-3D received 33.17 grams, and Pans 4A-4D received 66.34 grams.

After planning for the experimentation process, I went to the Florida Institute of Phosphate Research (FIPR) and set up the pans, weighing the pans on a laboratory scale to measure the change in weight of the grass, and using aluminum pans underneath the grass to measure the amount of water released. The grass was established for two weeks, and then I sprinkled the corresponding amounts of phosphogypsum into the pans. Before simulating a complete drought, I watered each pan evenly with 300 mL of water twice a week for two weeks, and then 400 mL for one week. By the end of that week, the grass looked very dry, but the pans with the most phosphogypsum did look greener than the control pans. I watered the grass with 1,000 mL of water to revive it, and the next week put it into complete drought and did not water the pans at all, measuring the weight change each day. After gathering my data and organizing it into data charts, I analyzed the data.

As shown in the graph, Pan Group 4A-4D performed the best and retained the most water (partially supporting my hypothesis). From a line graph, it is easy to see that there is a trend, except for the Pan Group 3A-3D. Based on previous research tested on bahiagrass by the FIPR researchers, the amount of phosphogypsum sprinkled on Pans 3A-3D was the optimum amount—but in my experiment, this did not prove to be the case. After Pans 4A-4D, Pans 2A-2D retained the most water, followed by Pans 1A-1D and then 3A-3D. The reduction in weight from the baseline to the end point for Pans 4A-4D averaged 0.295 kg, followed by Pans 2A-2D with 0.416667 kg, Pans 1A-1D with 0.78 kg, and lastly, Pans 3A-3D with 0.9175 kg.

Pans 1A-1D, 2A-2D, and 4A-4D showed that as the amount of added phosphogypsum increased, the weight reduction declined, leading to the conclusion that increasing the phosphogypsum helped the grass retain more water. However, Pans 3A-3D did not follow that trend. The amount of phosphogypsum in Pans 3A-3D was greater than that in Pans 2A-2D, but Pans 3A-3D had a greater average reduction in weight, meaning that they retained less water than Pans 2A-2D. In fact, they even had a greater reduction in weight than the control pans (1A- 1D) that had no phosphogypsum. This was surprising because the amount of phosphogypsum applied to Pans 3A-3D was supposed to be the optimum amount for water retention based on previous research. I may have made an error in the experimentation process.

An unexpected problem I encountered was controlling the amount of sunlight received by the grass in the greenhouse. Although steps were taken to ensure control of weather conditions by placing the pans in a greenhouse, there were areas of the greenhouse that received more sunlight than others. This problem was overcome by rotating the pans at every visit to the greenhouse.

Also, the aluminum pans placed under the metal pans with sod did not collect the water; either the water had evaporated a few hours later when they were checked, or all of the water was absorbed by the St. Augustine grass and none of it drained out, so the experiment measurement system will have to be modified. In the future, I will also look for better water collection pans.

To spread the word and present my results to the community, I created a PowerPoint presentation explaining what phosphogypsum is and the research I am currently working on. This presentation was presented to 600 students enrolled at Lawton Chiles Middle Academy. Students today are the future tomorrow.

Because applying the phosphogypsum worked well, I would like to take the grass and phosphogypsum outside of the laboratory and use it in a real-world situation. I am currently waiting for permission from EPA to spread the phosphogypsum outside on the lawn. As the weather begins to warm up again, I would like to continue the outside experiment, with the EPA's consent. I will have to wait to see if my work in the lab and my presentation interests the EPA, and they may potentially release the phosphogypsum for outdoor research.

Phosphogypsum is a waste product of the phosphate fertilizer industry. Accumulation of phosphogypsum is a growing environmental problem in Florida and all over the world. As more man-made fertilizer is produced to meet the agricultural needs of a growing world population, phosphogypsum stacks continue to rise and pose an environmental hazard in areas where phosphate is mined. Spreading phosphogypsum over grass in small quantities may be beneficial for water retention and therefore grass growth. This use has the potential to allow for spread and disposal of phosphogypsum. An added benefit would be conserving water during periods of drought. Finding a safe and environmentally friendly use for this waste byproduct is imperative.

Bibliography

"About Phosphogypsum." Environmental Protection Agency, 9 Feb 2009. Retrieved from the World Wide Web on 29 Jul 2009. http://www.epa.gov/rpdweb00/neshaps/subpartr/about.html

"Intel International Science and Engineering Fair: The International Rules and Guidelines." Society for Science and the Public, Intel. 2008. Retrieved from the World Wide Web on 4 Aug 2009. http://www.societyforscience.org/isef/about/rules_regulations.asp

Parsons, Victoria. "Down a Gypsum-Based Road?" Bay Soundings, 2005. Retrieved from the World Wide Web on 16 Jul 2009. http://www.baysoundings.com/sum05/phosphate8.html

"Phosphate Primer." Florida Institute for Phosphate Research. Retrieved from the World Wide Web on 29 July 2009. http://www1.fipr.state.fl.us/PhosphatePrimer/0/E5D15C19BBC6697C85256F800074C32A

"Phosphogypsum." Environmental Protection Agency, 27 May 2009. Retrieved from the World Wide Web on 29 July 2009. http://www.epa.gov/rpdweb01/phosphogypsum.html

Richardson, Steven. "Establishing Vegetation Cover on Phosphogypsum in Florida." Florida Institute of Phosphate Research, Dec 1995. Retrieved from the World Wide Web on 21 Aug 2009. http://www1.fipr.state.fl.us/FIPR/FIPR1.nsf/a1380a2dc3df745f85256b4b006398eb/
ae2a08e8c94683f985256b2e00654471!OpenDocument  

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