Quantifying microplastics and their retention in greywater treatment systems of different scales

This study investigated microplastic (MP) concentrations (>10 µm) in greywater from three sources: two single households (2–5 residents), a residential building (~100 residents), and an urban district (~1,000 residents). Additionally, evaluated the MP retention capacity of five decentralized greywater treatment systems: two on-site package plants (type A and B), a vertical flow (VF) green wall with four filter material (hemp, biochar, pumice, composted fiber soil), a horizontal flow (HF) green wall (biochar and LECA), and a hybrid treatment wetland (HTW) using Filtralite®. MPs were quantified using TED-GC/MS and Py-GC/MS. Influent MP concentrations ranged from 0.3 to 2280 µg/L, with the highest levels in single households and the lowest (≤5 µg/L) in the influents from urban district. Common polymers included polyamide (PA), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET). Polyethylene (PE) was absent in all samples. HTW and HF green wall achieved >99% MP retention. VF green wall with biochar, pumice, and composted fiber soil retained >97%, while type A reached >91%. Mineral wool of system B and hemp from VF green wall had low MP retention. Further research should address standardized sampling and analytical methods, long-term stability, including environmental impact assessment for treated greywater reuse.