Persulfate-assisted anaerobic digestion systems: advances in microbial electron transport chain reconstruction and...

Persulfate-based advanced oxidation processes (PS-AOPs) coupled with anaerobic digestion (AD) present a novel strategy for efficient energy recovery and resource utilization of organic solid waste. In this integrated system, reactive oxygen species (ROS) play a critical role, yet the mechanism by which ROS from PS-AOPs pretreatment affects AD remains unclear. This review systematically assesses the roles of PS-AOPs in AD systems. ROS are produced through thermal, iron-based and carbonaceous activation. These ROS disrupt hydrophilic functional groups of lignocellulose and extracellular polymeric substances. Such reactions cause physical disintegration and chemical modification at the solid-liquid interface, thereby enhancing substrate bioavailability and solid-liquid separation. ROS-induced oxidative stress enriches stress-tolerant microbes, which generate small-molecule acids and facilitate methanogenesis. Small organics from ROS decomposition also stimulate anaerobic fermentative bacteria. Meanwhile, accumulated SO₄^2- facilitates the proliferation of sulfate-reducing bacteria (SRB), reshaping metabolic functions. ROS oxidation yields small organic molecules. These compounds serve as electron donors and substrates. These organic molecules impose selective pressure to modulate system redox potential and enrich DIET-related microbes. Meanwhile, SRBs mediate sulfur cycling to lower hydrogen partial pressure and promote SCFAs conversion to HAc. The interaction accelerates interspecies electron transfer and methanogenesis. Additionally, ROS degrade emerging contaminants through ring-opening, deamination and hydroxylation reactions. Furthermore, functional degrading bacteria are enriched to construct a synergistic chemical-biological purification system. Finally, this review summarizes major existing challenges, such as microbial damage from excessive oxidation, imbalanced electron competition and toxic byproduct formation. The findings provide valuable references for practical application of PS-AOPs-assisted AD.