Rising Bubbles Help Collect Trash

By Iva Fedorka

The creek behind Dakota Perry’s house often contains plastic bags, bottles, cups, and other waste. She presented her idea for cleaning up the creek at the 2022 Regeneron International Science and Engineering Fair (ISEF) held in Atlanta, Georgia. Perry is a sophomore at W.P. Davidson High School in Mobile, Alabama.

Perry was one of more than 1,100 high school finalists who attended the 2022 ISEF. Another 500 students competed virtually. Regeneron ISEF, sponsored by the Society for Science, awarded nearly $8 million in prizes at this year’s science fair.

How the Bubble Barrier Works

Perry was inspired by the Great Bubble Barrier in Amsterdam. The Dutch system uses a curtain of bubbles rising from the water bottom to gather and move floating trash to the side of the waterway.

Perry’s curtain of bubbles would span the creek diagonally to stop the trash from escaping and move it back toward the shore. She made her system greener by incorporating hydropower and a solar-powered battery-operated conveyor belt to collect and transport the debris to a dumpster.

Tweaking the System

First, Perry focused on fine-tuning the bubble curtain, using her father’s garage as her workshop.

“That was the most important part to figure out,” Perry explained to Science News Explores. “For the bubble system to actually work and actually collect the trash, I have to know how much pressure the air compressor is supposed to push out.”

Then, Perry measured the flow of the creek water after a rainstorm, when more trash typically washed downstream, to test whether the bubbles would be affected by heavier currents. The creek water moved at about 1.3 meters per second.

To mimic the water flow conditions in her test environment (her backyard pool), she rented a water pump from a hardware store. Then she drilled rows of small holes (1.5 millimeters in diameter) into a plastic pipe that she connected to an air compressor. Perry adjusted the air pressure, gradually increasing it until the bubbles rose consistently as a vertical curtain.

Trash Testing

To test the curtain’s ability to collect plastic bottles and other trash, Perry added empty, water-filled, and rock-weighted bottles to the pool water. All of them were stopped by the curtain and then moved along the bubble barrier to its end.

Although she was sure the technique would work, she didn’t expect it to work so well. The current created by the bubbles also pulled leaves and other pool debris to the surface, implying that trash from the creek bottom would also move upwards.

What’s Next?

Perry plans to add a water wheel to the system to power the air compressor, connecting them by pulley systems. The concept has had real-world success and doesn’t interrupt traffic flow or harm wildlife.