Around 2,500 households across the Swiss city of Bern have reduced the amount of residual waste they produce by a fifth in a new pilot scheme.

The Optibag scheme tested a ‘bag-in-bin’ system which uses six different coloured bags so people can separate their waste depending on what type of material it is, making it easier to process and recycle.

Colour-sorting technology scans the bags to identify what kind of waste they contain so they can be processed appropriately.

The six different waste streams are separated and collected in different bags: glass bottles and containers, plastic bottles, mixed plastic waste, aluminum and small metal packaging and paper and cartons.

The firm said the trial saw a very high purity of material in each separate waste stream and noted more than 90% of the participants were satisfied or very satisfied with the colour sorting.

Paper and carton collections are gathered in paper bags so it can all be recycled in one go, simplifying the process.

Optibag has also helped the Swedish town of Eskilstuna introduce optical sorting – within a few months the region’s target of recycling 50% of its waste was accomplished, totalling around 18,000 tonnes a year.