The concentration stage of the Autonomous River Cleanup (ARC) system aims at blocking and concentrating plastic particles at a specified location to facilitate collection of the plastic waste. To this end, bubble curtains or bubble barriers represent a promising tool for particle concentration using flow shaping techniques.
The basic idea is simple! Air is pumped through a perforated tube lying at the bottom of the river, which induces bubbles at the orifices rising to the surface. This induces a vertical upward current and symmetric horizontal surface currents away from the bubble curtain. These currents are responsible for lifting submerged plastic particles and for blocking them at the surface.
The greatest advantages of bubble barriers are their promising ability to tackle submerged plastic beneath the surface next to floating waste and that they are unlikely to harm fish and allow the passage of boats.
As simple as the basic idea sounds, bubble curtains for plastic particle concentration are not well investigated. This makes designing such a system very challenging, but also very interesting, as many parameters must still be investigated and tested to understand how it can be used most efficiently. The current main challenge is to adjust all possible and interdependent system configurations by testing the bubble barrier in the water channel using standardized plastic particles.
Further work on bubble barriers includes scaling up the system to the real-life application for testing in the Limmat and the Danube river including investigation of the interaction with all other ARC subsystems. Hopefully, bubble barriers are soon helping the Autonomous River Cleanup project working towards a cleaner tomorrow!