Dynamic extraction of microplastics from simulated and natural freshwaters using a rotating coiled column

At present, microplastic pollution in aquatic environments is raising increasing concerns on its risks for the human health. The efficiency of existing water treatment technologies, which are based on different physical principles, is still insufficient for the removal of microplastics from aqueous media, and hence, novel methods are needed. Thus far, liquid-liquid extraction has not been used in water treatment processes; however, it has great potential for removing microplastics from water. This study was aimed at the development of a novel method based on dynamic liquid-liquid extraction in a rotating coiled column for the removal of microplastics from aqueous samples. It was demonstrated that liquid-liquid extraction in a rotating coiled column (inner capacity 25 of mL) using castor oil as the stationary phase offered more than 96% recovery rate of the five most abundant microplastics (μPE, μPP, μPS, μPVC, and μPET) of different sizes (<63, 63-100, and 100-250 μm) from simulated freshwater (sample volume of 20 mL). An average recovery rate of 100% was observed for the mixture of these five microplastics from a spiked natural river water sample. Notably, the recovery rate was not dependent on the size and type of microplastics under study. It was also found that in a column with a tubing bore of 1.6 mm, the flow rate of the aqueous suspension of microplastics (mobile phase) could be increased up to 5 mL min^-1 without decreasing the extraction efficiency. The scale-up of the extraction process was also possible.