Temperature-driven trade-offs in peracetic acid-enhanced anaerobic fermentation of waste activated sludge for volatile fatty acids production: Decoupling hydrolysis efficiency and microbial acidification

Recovering volatile fatty acids (VFAs) from waste activated sludge (WAS) is crucial for carbon recycling yet limited by low hydrolysis and rapid VFAs consumption. This study investigated the regulatory role of temperature (25, 35, 55 °C) in peracetic acid (PAA)-enhanced anaerobic fermentation of WAS. At 55 °C, sludge particle size was minimized, hydrolysis efficiency (56.61%) and soluble organic release peaked, reactive oxygen species (ROS) signals were strongest, and XDLVO indicated the weakest inter-particle attraction. Net VFA yield at 55 °C(3358 mg COD/L) was comparable to that at 35 °C (3243 mg COD/L), while acidification efficiency (38.13%) was lower than that at 25 °C (45.20%). 16S rRNA sequencing revealed that thermophilic hydrolytic-acidogenic bacteria were enriched at 55 °C, but the overall abundance of hydrolytic-acidogenic bacteria decreased, community diversity declined, and acid-consuming bacteria were enriched, reducing hydrolysate conversion to VFAs and consuming some VFAs. In contrast, 35 °C enriched efficient acidogens (e.g., Paraclostridium and Macellibacteroides) while suppressing acid-consuming populations, achieving efficient hydrolysis–acidogenesis coupling. Thus, the key role of temperature in PAA treatment is to optimize the microbial community for coupling hydrolysis products with acidogenesis, rather than simply enhancing hydrolysis, supporting WAS resource recovery and carbon-neutral wastewater treatment.