Problems in waste treatment
In most cases, available sorting technology limits the amount of material that can be recycled. Typical waste recycling process includes collection to the recovery facility, separation to different waste streams, basic cleaning and final sorting to classes. The resulting product is then either burned, recycled based on type and purity or placed to landfill. At the moment these recovery or recycling plants use different technologies from barcode readers, RGB cameras to x-ray and eddy current systems. These are capable technologies to some extent but not perfect solutions as they cannot recognize the material itself. For example, in case a plastic bottle is missing its label with printed barcode it is not possible to say if it is PET or HDPE. So-called multispectral technology is helping but is limited to a few basic materials in each sorting location.
It is also a fact that human labor must be used due to inadequate detection technologies. Waste is shipped to lower cost countries where people are manually sorting materials from conveyor belts. Although this creates jobs, it is by far not the safest and most desirable of professions. It would be beneficial to have robots or other sorting machinery in most places – but a robot needs “visual” aid for material detection.
Spectral camera – state of the art solution
Spectroscopy is the art of measuring the interaction between light and matter. In all matter around us this interaction, absorption, and reflection, is different. All different plastic types, wood, paper etc. have different spectra that we can measure using a spectrometer. As an analogy to visual interpretation, we can say that materials have different “colors” in the infrared region of light. This makes sorting based on actual material type possible just by measuring their spectrum.
A spectroscopy instrument is called spectral if it is capable of aerial imaging. The camera is placed above a conveyor belt and, while the material is passing by, it gives information on the exact material type, position in belt and size. Information is then passed to the sorter for proper action.
When used together with other technologies, spectral cameras make sorting more accurate as they provide true information on material type. The latest generation of hyperspectral cameras can increase the purity of recycled materials to close to 100%. This is important since the possibility to recycle plastic polymer for example generally depends on the material purity. Increasing the purity of recycled material by even a few percents can double its value. Extracting more recyclable material also means that we are disposing less waste to landfill.
Very recent advances in spectral camera technology further to infrared spectrum has made it possible to develop a camera that is also capable of separating black plastics, which has been a huge, unsolved problem hindering recycling efficiency for many years.
Recycling and sorting systems will continue to evolve and become more accurate and easier to implement. At the same time, these systems become completely automated and use different sensors and robotics. One thing is certain: the spectral camera is one key element for improving recycling success.