Biopolymer recovery from waste activated sludge toward self-healing mortar crack

Activated sludge (AS) offers great potential for resource recovery considering its high organic and nutrient content. However, low recovery efficiency and high costs are directing the focus toward the high-valuable resource recovery. This study extracted 71.5 ± 5.9 mg/g VSS of alginate-like exopolysaccharides from AS (ALE/AS) and applied it to mortar as a novel biopolymer agent for crack self-healing. With a mortar crack of 120 μm, addition of 0.5 wt% ALE/AS yielded a high crack closure ratio of 86.5 % within 28 days. In comparison to commercial healing agents, marginal flexural strength reduction with ALE/AS addition (17.9 % vs 30.2–50.5 %) was demonstrated. The abundance of COO− group in GG blocks of ALE/AS resulted in a higher cross-link capacity with Ca2+, while the reduction of hydrophilic residues (e.g., COO− and OH) after complexation engendered a lower swelling capacity, which facilitated self-healing and flexural strength maintenance. Molecular dynamics (MD) revealed that lower Ca2+ diffusivity, arising from the stronger electrostatic interactions between the COO− groups and Ca2+, resulted in a high Ca2+ concentration around the cracks, leading to CaCO3 deposition and healed cracks. The outcomes of this study provided light on ALE-based mortar crack healing and presented a possibility for multi-level AS resource recovery. [Display omitted] •Activated sludge (AS)-extracted ALE is a promising engineering resource.•ALE/AS was shown to be a novel crack-healing agent with an 86.5 % crack closure ratio.•ALE/AS modified mortar demonstrated a minor flexural strength reduction (