Ultrasonic radiation enhances percarbonate oxidation for improving anaerobic digestion of waste activated sludge

[Display omitted] •US-enhanced SPC oxidation effectively improves anaerobic WAS digestion.•Methane yield is enhanced by 46.8 % under the optimal condition.•US-enhanced SPC boosts biodegradability and increases specific surface area of WAS.•US-enhanced SPC improves key bioprocesses during pretreatment and digestion phases.•US-enhanced SPC pretreatment enriches functional microorganisms by 73.7 %. Anaerobic digestion of waste activated sludge (WAS) has always been restricted by the low rate of sludge hydrolysis, due to the complex substrates structured by cell walls, intracellular constituents and extracellular polymeric substances (EPS), leading to a long retention time and a low methane output. This study reported a novel ultrasonic (US)-enhanced percarbonate oxidation to improve anaerobic WAS digestion. Results showed that US enhanced sodium percarbonate (SPC) oxidation and reduced the SPC dosage required for WAS disintegration as compared to sole SPC groups, with the cumulative methane yield being enhanced by 46.8 % after the optimal pretreatment, i.e., US + 0.15 g SPC/g TSS. Kinetic analysis demonstrated that US-enhanced SPC pretreatment boosted both the hydrolysis rate and biochemical methane potential of anaerobic WAS digestion, simultaneously. Mechanistic explorations revealed that US-enhanced SPC significantly promoted substrates solubilization, hydrolysis and acidification during the pretreatment stage, providing huge amounts of reaction intermediates directly available for subsequent methanation. Meanwhile, US-enhanced SPC improved biodegradability of soluble substrates, reduced particle size and increased specific surface area of WAS, which created preferable conditions for anaerobic biotransformation. Further analysis suggested that US-enhanced SPC boosted the metabolic activity associated with key bioprocesses in digestion system, in accord with enhanced methane production. Likewise, microbial community analysis illustrated the functional microbes (e.g., Romboutsia sp.) participating in key bioprocesses were enriched by US-enhanced SPC pretreatment, with their total abundances increasing from 13.3 % to 23.1 %.