THE operators of composting facilities face a dilemma - on the one hand, customers demand compost of increasingly higher quality while on the other, organic waste contains a steadily rising amount of foreign particles.


The STEINERT UniSort Black serves as a supplemental quality assurance element when processing compost.

However, the sorting process does not begin at the composting facility but in people’s homes as they decide what to put into the organic waste bin. That’s why municipalities in particular have to do more to educate citizens and counteract people’s ‘sorting fatigue’.

The UniSort Black from STEINERT serves as a supplemental quality assurance element in processing facilities.

A case study from Germany

According to the RAL quality assurance method for compost (RAL-G2-251), only 25 square centimetres of foreign particles are permitted per litre of fresh substance in fresh and finished compost. This will be reduced to 15 sqcm beginning on July 1, 2018. The proportion of foreign particles in compost is also restricted by the Fertiliser Ordinance.

The entire materials cycle is threatened if a company is unable to adhere to the quality criteria and standards for compost because the organic waste it is supplied with contains too many impurities that prevent the operator from achieving the required purity level.

To address this situation, processing companies are working together with the sorting specialist STEINERT on one of the many components of a comprehensive solution. Among other things, the UniSort Black ejects foreign particles out of the structural material and creates a pure intermediate product.

Removing foreign particles

In the first step of processing, magnets above the belt remove all of the iron components. Later on, during the pre-processing stage, sieves and wind sifters pre-condition the material for processing in the UniSort Black.

Once this process is finished, conveyor belts transport the material to the UniSort Black, which separates out all plastics, including all dark-coloured and black plastics, as well as the remaining foils and metals.

Overall, the technologies remove more than 98% of the foreign particles and during this process, the technology can also sort out broken glass, stones and ceramics.

Ensuring quality

The UniSort Black sorting system consists of an NIR (near infrared) sensor for recognising NIR-detectable plastics as well as objects that are normally not detectable by means of NIR, such as dark-coloured and black plastics. Both types of material are sorted out during the same run-through.


The type of impurities that can contaminate compost.

“The UniSort Black helps us ensure quality in the current situation. However, it cannot be the sole solution — municipalities also bear a responsibility, because they have to supply us with organic waste that is largely free of impurities,” says Olpe composting plant head of operations Klaus Remm.

The use of hyper spectral imaging (HSI) technology enables the UniSort Black to recognise both types of material simultaneously, which sets it apart from standard technologies. Moreover, it also detects broken glass, stones and ceramics. A metal sensor can be installed optionally in order to detect and separate residual metals. Depending on the application, this technology has a throughput rate of 6 to 10 t/h at a working width of 2.8m; the grain sizes range from about 10 to 70mm and from 70 to 350mm.

“The UniSort Black enables us to purify the structural material so well that it doesn’t have to be incinerated. This reduction of incineration costs by up to 90%, the return of the material into the composting process as a structural material, and the marketing of the quality-assured products pay off for the operator,” says STEINERT business development manager Patrick Lindweiler.

UniSort Black specifications

Application: Removal of plastics, foils, metals, ceramics, stones and broken glass from organic material.

Technology: Hyper spectral imaging (HSI), NIR sensor and metal sensor. Application-related analysis software.

Spectral resolution: <3 nm

Spatial resolution: HSI chip with 320 measuring points

Number of detections per second: > 27 million

Light source: Halogen

Grain size: adjustable, eg 10 to 70mm and 70 to 350mm

Valve distance: 12.5mm and 31mm available

Working widths: 1000mm, 1400mm, 2000mm and 2800mm

Resource Center Whitepapers, Videos, Case Studies

Conferences & Events

No events