Magnetic bio preconcentration (MBP) for chemical-free cost-effective and low carbon sewage organics recovery

A magnetic bio-preconcentration (MBP) process combining magnetic seeds (MS) and magnetic field (MF) was proposed to address sewage organic matter (OM) capture-separation trade-off issues for resource recovery, optimally recovering 82.4% of chemical oxygen demand (COD) in raw sewage with mineralization of 12.3%. Separability improved markedly with 10-min settled Sludge Volume (SV₁₀) decreasing to 46% and the effective concentration factor (η) increasing to 10.5, due to MBP-driven restructuring of extracellular polymeric substances (EPS). Soluble EPS (S-EPS) and tightly bound EPS (TB-EPS) increased to 69.00 and 186.17 mg/L, respectively, while loosely bound EPS (LB-EPS) remained below 20% of total EPS. In MBP, protein (PN) was enriched in S-EPS (25.89 mg/L) and humic acids (HA) migrated from LB-EPS (13.05 mg/L) to S-EPS (32.25 mg/L), consistent with strengthened PN-/HA detected in 3D excitation-emission matrix fluorescence spectroscopy. Time-of-flight secondary ion mass spectrometry demonstrated enrichment of hydrophilic PN and polysaccharide (PS) in S-EPS, increasing hydrogen-bonding interaction sites for OM capturing. Quinone-like HA were recognized major promotor via redox mediation, while aniline-/phenol-like structures were identified to promote MS-EPS coupling and retention of aromatic/hydrophobic OM by aromatic interactions. Principally, MBP supported LB-EPS as an exchange layer and TB-EPS enriched in structural PN and PS, reinforcing stable cellular flocculation and microenvironment. With an energy consumption of 0.023 kWh/m³ and a carbon emission of 0.022 kg CO₂eq/m³ at operational cost of ∼0.004 USD/m³, MBP offered a low-carbon alternative for sewage preconcentration towards sustainability.