Calcium contents above 0.8 wt% have been reported to negatively influence the melt behavior of recovered PA 6.6 . So, the potential accumulation of Ca 2+ in PA precipitate has to be prevented when designing a PA recycling process with CEW. Therefore, the Ca 2+ content of the recovered PA was measured for two samples. Values of 0.0037 and 0.0002 wt% were obtained in the recovered samples of the experiments with CEW C and CEW E after 3 h, at 75 • C ultrasonic energy supply with a CEW:PA mass ratio of 8.5 (S5) †. For reference, the Ca 2+ content of virgin PA 6 filaments was measured to be 0.004 wt% (S4) †. Thus, we conclude that our experimental method removes any remaining calcium -introduced from the CEW solvent -sufficiently from the precipitated PA 6 regardless of the applied CEW composition. The amount of water and time of washing are certainly parameters that can be further optimized, drastically lowering the water demand of the process, but they are outside of the scope of this study.