In an assignment for Welcome to the village festival, me and my team members have found a solution for the waste problem at festivals. When you drinks are empty, you put it in a hole of the organ and the organ will make sound when it passes the distance sensor.

Each hole has its own sound. In order to stimulate people it will  make as whole a music piece, if it's completely full. So don't throw your cups on the ground, but make together a music piece with the drinking organ. Fun for young and old.