First in Sweden: Near-infrared technology sorts out plastic and metal

In fact, the more precise term is post-sorting, and it cuts down CO2 emissions by 75%

The post-sorting facility located in Brista, near Stockholm (Sweden), counts on a pioneering technology to ensure that more plastic gets recycled rather than incinerated. The name of that technology – near-infrared (NIT), an application tech that has been used more widely in the field of medicine and diagnostics.

The post-sorting plant is the first of its kind in Sweden. It has been operating there since 2021 helping to reduce CO2 emissions from plastic and metal incineration by 75%.

Making the planet’s resources last longer

The facility is a collaborative project between Stockholm Exergi (the capital’s energy provider) and Sörab and is part-financed by Klimatklivet (Sweden’s national green financing scheme).

A total of 11,000 tonnes of plastic and 2,500 tonnes of metal are sorted out there each year. This means that the directives from the EU on recycling are met, offering Stockholm a sustainable solution in terms of prolonging the lifecycle of materials.

The near-infrared sorting technique means that the machine identifies different types of plastic and sorts the ones that can be recycled, such as plastic packaging.

Here’s how it works

There are in fact two separate steps where NIT is used in the post-sorting process, once to separate organic waste from the rest and then again to separate plastic from metal.

A diagram showing the post-sorting process, Source: Stockholm Exergi

1. Incoming household waste is emptied on one of four walking floors. A vibrating sieve sorts out ordinary garbage bags, while larger items are sent onto a crusher.
2. (a) Optical sorting, NIT: In a first scan, green bags with food waste are identified via Near Infrared scanning technology and sorted out from other residual waste bags using compressed air. The bags are opened in a bag opener. The bags are separated from the food waste in a drum sieve and the food waste is transported to containers. (b) Biogas plant: Food waste is sent away to become biogas, a renewable fuel, and biofertilizer. Biofertilizers contain nutrients such as nitrogen, potassium and phosphorus. 
3. Bag opener and atomizer: All residual waste bags are opened. The large fractions returned from the drum sieve are finely divided.
4. Drum sifter: The residual waste is divided according to fraction size for more efficient sorting. Larger parts are sent back to the crusher while smaller parts go on.
5. Optical sorting (NIT): Plastic is identified and sorted out. No distinction is made here between different types of plastic, but technically it is possible to divide it into different fractions.
6. Metal separation: Magnets and eddy current separators sort out all magnetic and non-magnetic metals.
7. Material recycling: Sorted plastic and metal go to external partners for further processing before it becomes raw material for new products.
8. (a) Treatment of residual waste: The waste which cannot be recycled, goes via a conveyor belt into Stockholm Exergi's intermediate storage station at the incineration plant, alternatively into containers. (b) Energy extraction from heat and electricity: Energy is extracted in the process and heat and electricity are produced.