Alginate-like extracellular polymers recovery from industrial activated sludge: characteristics and application potential

Alginate-like extracellular polymers (ALEs) recovery from excess sludge produced in wastewater treatment plants (WWTPs) has drawn considerable attention as they offer a sustainable strategy for achieving a circular economy. However, the prospect of ALEs recovery from activated sludge of industrial WWTPs remains to be elucidated. In this study, the yields, physicochemical properties and potential applications of ALEs from industrial excess sludge were investigated. The results showed that ALEs' yields were ranged from 140 to 267 mg/g·VSS, and the alginate equivalents of the extracted ALE were 29 %–48 %. Ca²⁺-ALE hydrogels were immediately formed by cross-linking ALEs with CaCl₂, suggesting their high ionic gel-forming property. Fourier Transform Infrared (FTIR) and Raman spectral analyses showed that ALE possessed abundant functional groups related to protein and polysaccharide, and the similarities of functional groups between ALEs and commercial alginate were 40 %–61 %. Elemental analysis using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) revealed that the extracted ALEs possessed relatively low concentrations of heavy metals, which ensured its potential application. Based on the film-forming property, amphiphilicity and hydrophobicity, the extracted ALEs could be applied as a water-proof surface coating. Additionally, the ALEs hydrogel beads showed great absorption capacities for Cd²⁺ and Cu²⁺, being 132.31 ± 0.40 mg/g and 71.85 ± 0.40 mg/g, respectively, which were comparable to those of commercial alginate-based gel beads. This study expands our understanding of the ALEs biomaterials recovery and applications from industrial excess sludge.