Yiwen Liu

Medium-chain fatty acids (MCFAs) offer a sustainable route for valorizing waste-activated sludge (WAS) into higher-value products, yet their bioproduction is constrained by the rigid extracellular polymeric substance (EPS) barrier and inefficient chain elongation (CE). Here, we develop a synergistic pretreatment strategy employing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([Emim][OTf], a representative ionic liquid) and sodium percarbonate (SPC) to sequentially enhance sludge solubilization and targeted MCFA production. The maximum MCFA yield reaches 5910 mg COD/L in the combined group, 1.3-, 1.1-, and 0.7-fold higher than the control (2537 mg COD/L), [Emim][OTf] alone (2888 mg COD/L), and SPC alone (3409 mg COD/L) groups, respectively. Mechanistically, SPC acted as the primary oxidant to disrupt EPS and cell membranes, while [Emim][OTf] synergistically amplified this effect, as evidenced by enhanced protein solubilization and the progressive mineralization of organic nitrogen to ammonium. The combined pretreatment enriched acidogens (e.g., Proteiniclasticum, 96.8-fold increase), CE-associated Bacillota and Petrimonas (1.1- and 24-fold increases), and MCFA release-associated thioesterase-encoding genes (e.g., fluoroacetyl-CoA thioesterase, 0.5-fold increase). These findings demonstrate that [Emim][OTf] not only activates SPC-mediated sludge disintegration but also facilitates CE, as evidenced by a 1.7-fold increase in MCFA selectivity in model substrate tests, offering a dual-functional strategy for the efficient recovery of MCFA from WAS.

Organic carbon valorization via anaerobic sludge fermentation is intrinsically constrained by biopolymer recalcitrance and methanogenic diversion. We introduced 1,3-Dichloro-5,5-dimethylhydantoin (DCDMH) pretreatment leveraging controlled oxidative disruption and microbial metabolic regulation to boost short-chain fatty acid (SCFA) production. At optimal dosage (0.025 g/g TSS), SCFA yield increased by 192.1%, driven by enhanced substrate liberation and biochemical conversion. Molecular docking and 2D-COS FTIR analyses collectively indicate that the N-Cl moiety of DCDMH preferentially oxidized hydrophobic proteins within extracellular polymeric substances, while the derived HClO could penetrate cells to damage intracellular components. This dual action disrupted structural integrity, accelerating macromolecular substrate release and conversion, and enriching stress-tolerant hydrolytic/acidogenic bacteria. Sustained HClO release established oxidative stress wherein reactive oxygen species (ROS) functioned as metabolic signals beyond mere damage indicators. Moderate intracellular ROS stress stimulated substrate acidogenesis while suppressing methanogenic carbon sinks, and enhanced the gene abundances associated with antioxidant defenses and acidogenic pathways. Crucially, this work reveals for the first time the hormetic effect of DCDMH-derived HClO on acidogenic metabolism, providing a new insight into the application of chlorine-containing disinfectants in related fields.