Indole-3-acetic acid mediated removal of sludge toxicity by microalgae: Focus on the role of extracellular polymeric substances

The use of indole-3-acid (IAA) as an additive aided in achieving the objectives of reducing sludge extract toxicity, increasing Tetradesmus obliquus biomass yield, and enhancing extracellular polysaccharide production. Proteomics analysis can unveil the microalgae's response mechanism to sludge toxicity stress. With 10-6 M IAA addition, microalgae biomass reached 3.426 ± 0.067 g/L. Sludge extract demonstrated 78.3 ± 3.2% total organic carbon removal and 72.2 ± 2.1% toxicity removal. Extracellular polysaccharides and proteins witnessed 2.08 and 1.76-fold increments, respectively. Proteomic analysis indicated that Tetradesmus obliquus directed carbon sources towards glycogen accumulation and amino acid synthesis, regulating pathways associated with carbon metabolism (glycolysis, TCA cycle, and amino acid metabolism) to adapt to the stressful environment. These findings lay the groundwork for future waste sludge treatment and offer novel insights into microalgae cultivation and extracellular polysaccharide enrichment in sludge.