Design and Fabrication of a Laboratory Scale Hydromechanical Surface Floating Waste Collector Using River Flow

Rivers are the arteries of our planet, carrying water from the mountains to the sea. But they also carry the unwanted byproducts of human life: plastic bottles, foam packaging, and tangled debris. When this waste floats on the surface, it threatens fish, birds, and the water quality itself. For decades, engineers have tried to build machines to scoop this trash out of the water. Many of these machines rely on electricity or fuel to run their motors, which means they need power cables, batteries, or generators. This creates a problem for remote rivers where no power grid exists, and it adds cost and complexity to the cleanup effort. The challenge, then, is to create a device that can clean the river using only the energy already present in the water: the current itself.

A team of researchers in Iran set out to solve this problem by designing a floating waste collector that runs entirely on the power of the river flow. They built a laboratory-scale prototype to test whether a simple mechanical system could intercept trash, lift it out of the water, and deposit it into a storage bin without any external power source. The device works like a water wheel. As the river current pushes against blades attached to a large rotating wheel, the wheel turns. This rotation is mechanically linked to a conveyor belt that sits at an angle, rising out of the water. As the wheel turns, it drives the belt, which acts like a ramp to carry floating debris up and out of the river and into a holding tank. The researchers wanted to find the perfect combination of parts to make this system work as efficiently as possible. They tested different shapes for the blades, different numbers of blades, different types of conveyor belts, and different angles for the ramp, all while observing how the machine performed in a real river with varying speeds.

The team constructed a sturdy metal frame that could be adjusted to sit at the right depth in the water. At the front, a large wheel with blades waited for the current. Behind it, a conveyor system was ready to lift the catch. To ensure the trash actually reached the machine, they attached long guiding arms that acted like fences, funneling floating debris toward the intake. They also built a smart stopping mechanism: if the trash bin filled up, a sensor would detect the level and automatically stop the machine to prevent overflow, signaling that it needed to be emptied. The researchers took this device to the Safarood River in Iran. They tested it under different conditions, releasing various types of waste—ranging from badminton shuttlecocks and pinecones to plastic bottles and foam pieces—into the water upstream to see if the machine would catch them.

The experiments revealed that not all designs worked equally well. The researchers found that a rigid, straight guiding arm was far superior to a flexible one, which tended to flop around in the current and let trash escape. They also discovered that a conveyor belt made of modular segments worked better than a chain system, likely because the segments provided better grip for the wet, slippery trash. When it came to the angle of the conveyor belt, a gentle slope of 30 degrees proved more effective than a steep 60-degree slope, allowing the waste to slide up more easily without falling back. The most critical factor, however, was the design of the rotating wheel. While flat blades generated more torque (the turning force), the researchers found that curved blades with twelve of them spinning together created the best overall performance. This configuration allowed the wheel to spin faster and catch more items in a given time.

When the team ran the machine with its optimal settings, the results were encouraging. At a river flow speed of 0.4 meters per second, the device successfully collected 83 percent of the floating waste it encountered. It performed exceptionally well with certain materials, capturing 100 percent of the polyethylene terephthalate (PET) bottles and expanded polystyrene (EPS) foam, which are common in river trash. It also caught 93 percent of high-density polyethylene (HDPE) and 84 percent of low-density polyethylene (LDPE). However, the study also highlighted a clear limitation: as the river flowed faster, the machine became less efficient. At a speed of 1.1 meters per second, the collection rate dropped to 71 percent. The researchers explained that at higher speeds, the water moves too quickly for the guiding arms to steer the trash effectively, and the debris often slips past the machine before it can be lifted.

This study demonstrates that a self-powered, hydromechanical system is a viable solution for cleaning rivers, particularly in areas where electricity is unavailable or expensive. The device proved it could operate continuously using only the kinetic energy of the water, offering a sustainable alternative to fuel-powered boats or electric scooters. While the machine struggled in very fast currents, its high efficiency in moderate flows suggests it could be a valuable tool for managing waste in many natural waterways. The researchers concluded that by carefully tuning the mechanical parts—specifically the blade shape, the number of blades, and the angle of the conveyor—it is possible to create a robust, energy-independent cleaner. This approach offers a promising path forward for reducing the amount of plastic that travels from rivers into the oceans, relying on the river's own power to heal itself.