Adhesion and binding properties of extracellular polymeric substances (EPS) extracted from activated sludge

Extracellular polymeric substances (EPS) harvested from biological sludge can be utilized as high-value biomaterials. This study investigated the adhesion and binding properties of activated sludge EPS on hydrophilic and hydrophobic surfaces under varying pH and total solids (TS) levels. At a 2.5% TS content, lower pH was able to enhance adhesion performance on both surface types, yielding capacities of 1000-2500 mg/m² and 500-1500 mg/m² for hydrophilic and hydrophobic surfaces, respectively. Increased TS further promoted surface adhesion, however saturation occurred at approximately 2500 mg/m² on hydrophilic surfaces at 5.3% TS, whereas adhesion continued to increase on hydrophobic surfaces. Adsorption isotherm model simulations suggested that EPS-surface interactions were governed by distinct adsorption mechanisms. The distribution of functional groups and the structural arrangement of EPS aggregates, modulated by pH and TS, appeared to regulate these interfacial interactions. Additionally, EPS exhibited strong microbead binding capacities ranging from 2.0-6.0 mg beads per mg EPS, facilitating effective attachment of microbeads to both surface morphologies. These findings proved the potential of EPS as versatile, sustainable, bio-based adhesives and binders with broad applicability.