BERLIN, GERMANY — Recycling mixed plastics has long been expensive and labour-intensive, requiring workers in recycling plants to pick through mountains of items and guess at their composition, separating them into catch-all categories that netted little return.
Indeed, the plastic that consumers can put into their recycling bins is often limited to a few more lucrative types.
Most mixed recyclables that are collected end up being used for fuel or simply incinerated as a better alternative to putting them into landfill.
Technology is changing this, through the use of different types of optical sensors that are becoming faster, cheaper, easier to use and more sophisticated at sorting materials to be recycled.
In a first sorting step, recycled packaging is separated according to size in a drum sieve. Bits of glass and paper are also removed. (DSD)
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With the drive to limit waste, the increasing costs of labour and transportation and the soaring price of petroleum and other commodities that come from recycling — especially those found in packaging — it's important to separate household waste when it gets to the recycling plant.
"It's making more and more sense to sort things out," says Tom Eng, the sales and marketing director for TiTech, based in Norway and Germany, the largest among a handful of global companies that make automated equipment to sort recyclable materials.
Developed over the past 12 years, the nascent field includes sensors that detect objects on fast-moving conveyor belts and targeted air jets that group them according to what they are made of.
One of the most critical of these technologies is near-infrared (NIR) spectroscopy, which exposes each item to a halogen lamp and then senses the quality of reflected light in the infrared wavelength spectrum to determine its molecular composition.
"They all have their fingerprints," Mr. Eng explains.
Much as everyday digital cameras are becoming cheaper and higher in resolution, these spectrometers (which are also used for analysis in food processing and mining) can detect more and more detail with better accuracy to get a purer final product.
"In a world facing a shortage of raw materials, this has enormous growth potential," says Olaf Krenz, marketing director of LLA Instruments, a Berlin company that makes optical measuring systems and was founded by experts of the former East German Academy of Sciences.
"The technology has developed dramatically," says Mr. Krenz, adding that recycling sorting equipment has become robust and mobile in the last couple of years as well as more affordable.
However, a typical scanning unit costs about €100,000, and large plants can employ a dozen or more at a time.
Differentiating between different types of plastics — such as the polyethylene terephthalate (PET) in soft-drink bottles, polypropylene (PP) in yogurt containers and high-density polyethylene (HDPE) in detergent bottles — can improve the value of the end products of recycling and avoid hazards associated with contamination.
The chlorine and bromine found in flame-retardant plastics, for example, can damage equipment and give off toxic gases if it is burned.
New materials and tougher legislation surrounding waste management are driving science in the field, says Thomas Pretz, head of the Department of Processing and Recycling of Solid Waste Material at RWTH Aachen University on Germany's western border.
"Daily life perpetually generates new tasks," Mr. Pretz says. "Industry puts a great deal of intelligence into new materials. We have to keep pace with that."
Nathanael Lortie, a spokesman for Sherbrooke O.E.M. Ltd. and Eagle Vizion, two Canadian companies that specialize in recycling technology, says near-infrared optical sorting is increasingly being adapted and applied to a wide range of products, from plastics to wood and fibre.
Further advances are coming; complete spectral analysis of recyclable materials can be used to compare polymers or discover nuances in products, such as finding a PET bottle that has a problematic chlorine-based PVC label on it, Mr. Lortie says.
One area of research that TiTech is working on, says Mr. Eng, involves analyzing the composition of black plastics, which are difficult to optically sense because they do not reflect light.
Black plastics are especially found in automotive plastics and consumer electronics, which are more lucrative and are targeted by new recycling programs.
Improving the precision of sensing is also key, Mr. Eng says. He notes that machines that once could detect and recover about 90 per cent of metals are now up to 98 per cent accurate, which can amount to thousands of tonnes of additional commodities recovered and new products made. "It pays off to do some more sorting," he says.
Special to The Globe and Mail
