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Industrial sludge is characterized by high moisture content, complex composition, and significant organic toxicity. This research aimed to improve the performance of Chlorococcum humicola in removing hydroquinone-domesticated sludge toxicity through the addition of indole-3-acetic acid (IAA). The maximum cell density and dry weight of C. humicola were attained when the IAA concentration was 5.0 × 10−6 mol/L, at 6.79 × 107 cells/mL and 2.60 g/L, respectively. The toxicity of the sludge degradation rate reached its peak level of 59.70% on the 20th day. The toxicity reduction was consistent with the decrease of RNA degradation-related proteins such as A5FN12, which can be hydrolyzed and absorbed by C. humicola via active transport. In the presence of IAA, C. humicola increased its energy production processes, such as glycolysis and oxidative phosphorylation, to facilitate active transport. Moreover, the efficiency of signal transduction was improved, leading to enhanced cellular metabolism. The suppression of biosynthesis of glutathione and arginine at the molecular level may contribute to this observed trend. Overall, this study provides new insights into the mechanism by which IAA promotes the degradation of sludge toxicity by C. humicola , offering a novel method and theoretical basis for the safe and resource-based utilization of industrial sludge. [Display omitted] • IAA can promote the growth of C. humicola. • Sludge toxicity correlates with RNA degradation proteins. • C. humicola enhanced ATP production processes with the addition of IAA. • Signaling pathway enhanced and the biosynthesis of glutathione and arginine declined. Minimal research exists on biological detoxifying treatment of industrial residual sludge. This research reveals the mechanism on the removal of sludge toxicity by algae with exogenous IAA. [ABSTRACT FROM AUTHOR]

[Display omitted] • Liquid fraction (Add L) from crushed granules initialed microalgae aggregation. • 0.5–2 mm stable granules formed with harvesting > 90% in 30 min by Add L addition. • Add L addition shortened the start-up of microalgae granulation from 150 d to 1–2 d. • Enhanced tightly bound extracellular polymers (EPS) favor aggregate integrity. • Aromatic proteins in EPS play a crucial role in granulation of microalgae. Biomass harvesting is the bottleneck for microalgae-based technologies in practical application for simultaneous wastewater remediation and resource recovery. Biogranulation has been proven to possess high potentials for cost-effective microalgae cultivation and harvesting, while the long start-up duration (about several months) is challenging its application in real wastewater treatment. This study examined the contribution of intact and crushed microalgae granules, and the solid and liquid (Add L) fractions from crushed microalgae granules to the rapid granulation of single-cell microalgae (Ankistrodesmus falcatus var. acicularis) suspension. In addition to > 90% organics and 70–80% total N removal, microalgae aggregates were obtained with excellent settleability when Add L was used as additives, achieving harvesting efficiency of 90.75 ± 1.23% during the 24-h aggregation tests in comparison to 17.74 ± 0.29% by the control. The continuous increase of polysaccharides in soluble extracellular polymeric substances (EPS) might be responsible for cells capture and adhesion at the early stage of aggregation, while the enhanced secretion of bound EPS (mainly tightly bound EPS (TB-EPS)) from 41.86 ± 5.08 to 264.05 ± 6.41 mg/g-volatile suspended solids (VSS) favored the formation of stable microalgae aggregates with better integrity. The fluorescence intensity of aromatic proteins in loosely bound EPS (LB-EPS) and TB-EPS was dramatically strengthened in response to the Add L addition, most probably due to its crucial role in microalgae granulation and stable structure. Results from this study may propose a novel approach for rapid and high-efficiency harvesting of microalgae via biogranulation, which can promote the practical application of microalgae-based wastewater treatment systems. [ABSTRACT FROM AUTHOR]