Treating wastewater in plastics recycling applications

Recycling lines for plastics are essential to the circular economy, but they also consume resources, particularly water.

The sustainability of recycling technology should not be assessed by the quality of its end-product alone — the processes used to make the end product play an equally important role.

A manufacturer of recycling lines, Krones sees itself as bearing a particular responsibility for meeting these sustainability criteria. The group’s MetaPure technology recovers materials like PET bottles and polyolefin packages, and enables the recyclate obtained to be used in equivalent applications. In their work to achieve continuous system optimisation, the development team at Krones have been proactively examining the washing module’s water consumption.

“In the recycling process, the plastics are ground into flakes in wet mills and then washed,” Product Manager Astrid Kadlubski explained. “This produces wastewater containing various dissolved substances, depending on the input material concerned.”

In addition to common soiling, the wastewater might contain organic residues of the packages’ content, or cleaning agents from the washing process and printing ink particles removed from bottles and labels.

“In many recycling lines, the water is recirculated and treated in a bypass,” Kadlubski said. “With the result that the process water’s dirt load keeps on rising and ultimately impairs the end product’s quality.” To counter this, Krones has developed an intelligent solution for the complete treatment of the washing and mill water. The solution entails several advantages for recycling-line operation: “Firstly, this reduces both fresh water consumption and wastewater incidence. Secondly, the recycling process is kept at a consistently high level of quality,” Kadlubski explained. “And last but not least, such treatment makes sure that the wastewater discharged into the municipal system complies with the relevant specifications. Needless to say, this also applies for the ultrastringent regulations in Germany.”

Image caption: Krones’ MetaPure technology recovers materials in a way that enables the recyclate obtained to be used in equivalent applications.