The Efficiency of Different Digestion and Separation Methods for Extracting Microplastics in Typical Organic Solid Waste

Plastics are common raw materials of products originating from human activities. Their physical nature may include disintegrated small granules or fragments with particle size less than 5 mm—microplastics (MPs) which are considered as emerging contaminant in the environment. Previous research has demonstrated that organic solid waste (OSW) was contaminated by microplastics. Subsequent to biological treatment, OSW products such as compost and biogas residues would be mixed the soil as fertilizers or conditioners; while, the MPs in these OSW would also enter the soil at the same time, imparting potential ecological risks. Thus, it is important to detect the MPs in biologically treated OSW products. However, it was unknown whether some of the digestion and separation methods could be used to effectively extract MPs in these typical OSW, limiting the research on MP abundance in these OSW and restricting the comparability of relevant studies. Therefore, the present study compared the effects of seven digestion protocols on the MPs and organic matter, and the most suitable protocol containing 30% (v/v) H2O2 was determined. Furthermore, the recovery rates of spiked MPs were used to evaluate three separation methods. The results showed that the two-stage density separation of NaCl solution (ρ = 1.19 g·cm−3) and NaBr solution (ρ = 1.53 g·cm−3) was optimal, and the recovery rate of spiked MPs by two-stage density separation was higher than 86%. Based on these results, the scheme of “30% (v/v) H2O2 pretreatment and two-stage density separation” was constructed for MPs extraction from biologically treated products of OSW, which could be applied to the related studies.