Paul, a 25-year-old product designer, was bothered by all the deposit bottles he saw being thrown away, so he came up with a brilliant idea that's been catching on, not only in Cologne, but across Germany.
Germany may be known for having a strong social welfare system, but there are still plenty of people who rely on the extra bit of cash they get by collecting discarded deposit bottles from public trash cans.
Paul Ketz's creative invention makes it easier for collectors to locate the unwanted bottles, worth between 8 and 25 cents a piece. He not only invented the so-called "deposit ring" - an attachment for public waste bins - he also welds them himself in his own workshop.
The rings have caught on so well that a number of cities in Germany have commissioned them. In the video above, DW reporter Carl Nasman filmed Cologne's very first deposit rings. Listen to the Generation Change radio report for the whole story.