Circular-by-design biofiltration media from recycled polymers for decentralised wastewater treatment

Decentralised wastewater treatment is critical for global sanitation, yet its performance depends strongly on the biofiltration media used. Recycled polymers are emerging as circular alternatives to mineral and virgin carriers, linking wastewater treatment with plastic waste valorisation. This review synthesises evidence from fixed-film and moving-bed systems. Recycled-polymer media achieved COD removals of 78–88%, total‑nitrogen removals of 64–77% and total‑phosphorus removals of up to 87%, demonstrating performance comparable to conventional media when carrier geometry, hydraulics and operating conditions are appropriately matched to the treatment objective. Across the literature, reactor configuration and loading conditions were found to exert a stronger influence on performance than polymer type alone. The review identifies quantitative design criteria for carrier selection, including target wettability, specific surface area, and void fraction, and integrates these into an engineering decision framework within a media-selection decision tree. Techno-economic, life-cycle and regulatory considerations are evaluated alongside treatment performance. Evidence on microplastic release and additive leaching further indicates that durability and environmental safety must be incorporated into material selection and qualification procedures. The findings suggest that recycled polymer carriers are technically viable for decentralised wastewater treatment, but their wider implementation will require long-term field validation, harmonised testing protocols, and robust safety assessment frameworks.