Clever sorting system removes foreign particles from compost

The operators of composting facilities are faced with a dilemma. On the one hand, customers are demanding compost of increasingly higher quality. On the other, organic waste contains a steadily rising amount of foreign particles. Furthermore, 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.

To address this situation, processing companies are working together with the sorting specialist STEINERT on one of 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.

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 precondition the material for processing. Once this process is finished, conveyor belts transport the material to the UniSort Black, which separates out all plastics as well as the remaining foils and metals. All in all, the technologies remove more than 98% of the foreign particles. During this process, the technology can also sort out broken glass, stones and ceramics.

The 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, with the use of hyperspectral imaging (HSI) technology enabling the system to recognise both types of material simultaneously. Moreover, it also detects broken glass, stones and ceramics. A metal sensor can be installed optionally in order to detect and separate residual metals.

The system features a halogen light source and application-related analysis software. It has spectral resolution of <3 nm and can conduct over 27 million detections per second. Depending on the application, the technology has a throughput rate of six to 10 t/h at a working width of 2.8 m; the grain sizes range from about 10 to 70 mm and from 70 to 350 mm. Valve distances of 12.5 and 31 mm are available, while working widths include 1000, 1400, 2000 and 2800 mm.

“The UniSort Black enables us to purify the structural material so well that it doesn’t have to be incinerated,” said a spokesperson for STEINERT. “This reduction of the 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.”

“The UniSort Black helps us to ensure quality in the current situation,” added Klaus Remm, Head of Operations at the Olpe composting plant, Germany. “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.”