Extracellular polymeric substances as paper coating biomaterials derived from anaerobic granular sludge

Recovering extracellular polymeric substances (EPS) from waste granular sludge offers a cost-effective and sustainable approach for transforming wastewater resources into industrially valuable products. Yet, the application potential of these EPS in real-world scenarios, particularly in paper manufacturing, remains underexplored. Here we show the feasibility of EPS-based biomaterials, derived from anaerobic granular sludges, as novel coating agents in paper production. We systematically characterised the rheological properties of various EPS-based suspensions. When applied as surface sizing agents, these EPS-based biomaterials formed a distinct, ultra-thin layer on paper, as evidenced by scanning electron microscopy. A comprehensive evaluation of water and oil penetration, along with barrier properties, revealed that EPS-enhanced coatings markedly diminished water absorption while significantly bolstering oil and grease resistance. Optimal performance was observed in EPS variants with elevated protein and hydrophobic contents, correlating with their superior rheological characteristics. The enhanced water-barrier and grease resistance of EPS-coated paper can be attributed to its non-porous, fine surface structure and the functional groups in EPS, particularly the high protein content and hydrophobic humic-like substances. This research marks the first demonstration of utilizing EPS from anaerobic granular sludge as paper-coating biomaterials, bridging a critical knowledge gap in the sustainable use of biopolymers in industrial applications.