Investigation into cross-contamination during cleaning efficiency testing in PET recycling

The cleaning efficiency of a PET recycling process is typically investigated by artificial contamination of post-consumer PET flakes within a so-called challenge test. Challenging of pilot plants or industrial scale lines is done be introducing a certain amount of contaminated flakes while running the process with non-contaminated flakes of different colour. After decontamination the contaminated flakes are separated from the non-contaminated flakes and only the contaminated flakes were analysed due to their residual contamination level. The European Food Safety Authority (EFSA), however, raised the question about cross-contamination, which might reduce the overall cleaning efficiency of the recycling process. Cross-contamination is defined as the transfer of surrogate contaminants from the initially contaminated to the initially not contaminated material during a challenge test. Data for the phenomenon of cross contamination are not available in the scientific literature. Aim of the study was to close this gap by providing experimental data for cross-contamination by use of several challenge tests. As a result cross contamination was found only at ratios of 1:1 between contaminated and non-contaminated PET flakes. At higher ratios which were typically applied in challenge tests on pilot plant or industrial scale line cross contamination do not play a significant role. In addition, the results show that cross-contamination is negligible for volatile compounds. (C) 2016 Elsevier B.V. All rights reserved.