Teen converts water pollutant into a plant fertilizer | Science News for Students

Teen converts water pollutant into a plant fertilizer

A teen designed a way to reduce, reuse and recycle nutrients for plants
Mar 14, 2017 — 10:28 am EST
2011 Lake Erie algae bloom

Excess phosphate fertilizer that washes off of farms can become a water pollutant that fuels the growth of algae. The green swirls near center of this 2011 image of Lake Eric show one such bloom.

Jesse Allen and Robert Simmon/NASA Earth Observatory/Wikimedia Commons

WASHINTON, D.C. — Farmers fertilize their crops to increase the size of their harvests. But when they use too much fertilizer, some of it runs off into nearby rivers and lakes. That can be a danger to the life there. Stefan Wan, 17, developed a method to soak up some of this excess before it can cause harm. And his method doesn’t just soak up those chemicals — it also releases them. That means the fertilizer can be used again.

The senior at Alexander W. Dreyfoos School of the Arts in West Palm Beach, Fla., showed off his fertilizer-recycling technique at the Regeneron Science Talent Search. Each year, this competition brings 40 seniors together from around the country to show off their science projects to the public. The teens also compete for almost $2 million in prizes. The competition is run by Society for Science & the Public and sponsored by Regeneron, a company that develops medicines. (Society for Science & the Public also publishes Science News for Students and this blog.)

Stefan has always had a science-filled life. His mother, Jianchang Cai, is an engineer, and his father, Yongshan Wan, is a scientist who studies soil. But the teen didn’t become passionate about science until 10th grade, when he took chemistry. “I fell in love with the subject and wanted to do more with it,” he says. He wanted to use his newfound love of chemistry to solve an environmental problem. The teen just needed the right problem.

And he found one close by. The farms near his hometown of Wellington, Fla., fertilize their crops with nitrate and phosphate — two chemicals that plants need to grow. When it rains, any excess fertilizer can run off into nearby waterways. There, those nutrients may fuel an explosive growth of algae, known as a bloom. When the blooms later die, bacteria will break down the algae. This will fuel the growth of the bacteria, which need oxygen to do their work. The oxygen they use can leave less for fish and other living things, causing many of them to suffocate and die. This process is known as eutrophication (YU-trow-fih-KAY-shun).

Several blooms occurred in the summer of 2016 on the Caloosahatchee River in Stefan’s home state. The teen thought he might be able to help prevent future blooms by developing a method to absorb some of the fertilizer that runs off farms. His father helped him get in touch with Yuncong Li, a scientist who studies soil and water. Li works at the University of Florida Tropical Research Education Center in Homestead.

After reading some scientific papers that Li recommended, Stefan came up with a plan. He started with biochar. This is a type of charcoal. Farmers add it to the soil to help it retain water and nutrients. Since biochar is made from plants, it won't harm the environment, Stefan notes.

Stefan Wan works in the lab
To make his biochar mix, Stefan Wan had to make very careful measurements.
S. Wan

Biochar has its benefits, but it doesn’t absorb phosphate or nitrate. Layered double hydroxides (or LDHs) are chemicals that contain pairs of positively charged atoms. These may be magnesium and aluminum, for instance, or magnesium and iron. Their positive electrical charge lets LDHs attract negatively charged chemicals, such as phosphate. But LDHs aren’t very efficient at this. On their own, Stefan says, they “form kind of a sludge.” That means the positively-charged sites won't be exposed and able remove the phosphate.

The LDHs can’t spread out on their own into a single layer, which would be needed for them to filter out the phosphate. Biochar, however, does work well in filters. So Stefan hypothesized that if he could get an LDH to stick to biochar, the LDH would spread out in a thin layer. Then it should be able to remove the phosphate.

“By combining the two you kill two birds with one stone,” Stefan says. By that, he means, the biochar will be “making the LDH more viable, by spreading it out.”

To test his idea, the teen began by making combinations of biochar and LDHs. He tested two types of LDH. One contained magnesium and aluminum. The other had magnesium and iron. He put these into solutions of phosphorus and measured how much each mix could remove from the water.

The magnesium and aluminum pairing worked best. And the best recipe was made from 60 percent biochar and 40 percent of this LDH. It soaked up phosphate well. It became 95 percent saturated with phosphate in just one hour.

Stefan was curious whether the biochar mix could later release the phosphate it had taken up. Then that nutrient might be returned to the soil as a plant fertilizer. To test the idea, the teen prepared small cups of sand in which he would grow lettuce seeds. Some cups had only sand. These served as his control. The others also contained his phosphate-loaded mixture. After 12 days, the teen measured how big the lettuce seedlings had grown.

The seedlings grown in cups that also had the phosphate-loaded biochar were 20 milligrams (0.0007 ounce) heavier than those grown in just sand. The biochar had released some of the phosphate, which the lettuce seeds used to grow.

Stefan and three University of Florida scientists have just published the new findings in the March Journal of Industrial and Engineering Chemistry.

The next test will be to see if the biochar mix works as well on farms. “I still think more research needs to be done,” Stefan says. Another mix of LDH and biochar might work even better. Also, he only tested one kind of biochar. It had been made from bamboo. He would like to also test biochars made from sugarcane or hickory.

Once he’s done that, Stefan hopes to improve his water treatment. “[Phosphate] is a big contributor to eutrophication,” he explains. “But it’s not the only one.” He’d like to made a pollutant treatment that also can soak up nitrate.

This project shows that even teens can do research offering potentially important, real-world benefits.

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Power Words

(more about Power Words)

agriculture     The growth of plants, animals or fungi for human needs, including food, fuel, chemicals and medicine.

algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

aluminum     A metallic element, the third most abundant in Earth’s crust. It is light and soft, and used in many items from bicycles to spacecraft.

atom     The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and uncharged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

biochar     A type of charcoal often used in agriculture to improve soil for plant growth. It can help plants take up nutrients, improve soil drainage and increase crop yields.

bloom     (in microbiology) The rapid and largely uncontrolled growth of a species, such as algae in waterways enriched with nutrients.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical can also be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemistry     The field of science that deals with the composition, structure and properties of substances and how they interact. Chemists use this knowledge to study unfamiliar substances, to reproduce large quantities of useful substances or to design and create new and useful substances. (about compounds) Chemistry also is used as a term to refer to the recipe of a compound, the way it’s produced or some of its properties. People who work in this field are known as chemists.

control     A part of an experiment where there is no change from normal conditions. The control is essential to scientific experiments. It shows that any new effect is likely due only to the part of the test that a researcher has altered. For example, if scientists were testing different types of fertilizer in a garden, they would want one section of it to remain unfertilized, as the control. Its area would show how plants in this garden grow under normal conditions. And that gives scientists something against which they can compare their experimental data.

eutrophication     The process by which a body of water becomes full of nutrients, which then stimulates the excessive growth of plants and algae. When these organisms die, bacteria break them down. But this bacterial activity can temporarily use up much of the water’s dissolved oxygen. With too little oxygen, animals can suffer — even suffocate. In short order, a eutrophic ecosystem can collapse.

fertilizer     Nitrogen, phosphorus and other plant nutrients added to soil, water or foliage to boost crop growth or to replenish nutrients that removed earlier by plant roots or leaves.

filter     (in chemistry and environmental science) A device or system that allows some materials to pass through but not others, based on their size or some other feature. 

iron     A metallic element that is common within minerals in Earth’s crust and in its hot core. This metal also is found in cosmic dust and in many meteorites.

journal     (in science) A publication in which scientists share their research findings with the public. Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

magnesium     A metallic element that is number 12 on the periodic table. It burns with a white light and is the eighth most abundant element in the Earth’s crust.

nitrate     An ion formed by the combination of a nitrogen atom bound to three oxygen atoms. The term is also used as a general name for any of various related compounds.

nitrogen     A colorless, odorless and nonreactive gaseous element that forms about 78 percent of Earth's atmosphere. Its scientific symbol is N. Nitrogen is released in the form of nitrogen oxides as fossil fuels burn.

nutrient     A vitamin, mineral, fat, carbohydrate or protein that a plant, animal or other organism requires as part of its food in order to survive.

oxygen     A gas that makes up about 21 percent of Earth's atmosphere. All animals and many microorganisms need oxygen to fuel their growth (and metabolism).

phosphate     A chemical containing one atom of phosphorus and four atoms of oxygen. It is a component of bones, hard white tooth enamel, and some minerals such as apatite.

phosphorus     A highly reactive, nonmetallic element occurring naturally in phosphates. Its scientific symbol is P. It is an important part of many chemicals and structures that are found in cells, such as membranes, and DNA.

recycle     To find new uses for something — or parts of something — that might otherwise be discarded, or treated as waste.

runoff     The water that runs off of land into rivers, lakes and the seas. As that water travels over land, it picks up bits of soil and chemicals that it will later deposit as pollutants in the water.

Science Talent Search     An annual competition created and run by Society for Science & the Public. Begun in 1942, this event brings 40 research-oriented high school seniors to Washington, D.C. to showcase their research to the public and to compete for awards. In 2016, Regeneron Pharmaceuticals became the program's new sponsor.

seedling     The initial plant that sprouts leaves and roots after emerging from a seed.

Society for Science and the Public    A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: the Regeneron Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

solution     A liquid in which one chemical has been dissolved into another.

suffocate     To be unable to breathe, or to cause a person or other organism to be unable to breathe.

viable     Able to survive. (in engineering) Something that should work or operate according to plan, as in a “viable concept.”


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