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

Anaerobic digestion of waste activated sludge (WAS) has always been restricted by the low rate of sludge hy-drolysis, 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 disin-tegration 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 pre-treatment 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 biode-gradability 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 %.

Automated summary

This study explored a novel ultrasonic-enhanced percarbonate oxidation technique to improve anaerobic digestion of waste activated sludge. The results showed that ultrasonic waves enhanced the oxidation reaction and reduced the required oxidant dosage, leading to a 46.8% increase in cumulative methane yield after optimal pretreatment. Kinetic analysis demonstrated that ultrasonic-enhanced percarbonate oxidation improved both the hydrolysis rate and biochemical methane potential. Mechanistic exploration revealed that ultrasonic-enhanced percarbonate oxidation promoted the solubilization, hydrolysis, and acidification of substrates during pretreatment, providing abundant reaction intermediates for subsequent methanation. Additionally, it improved the biodegradability of soluble substrates and altered the physical characteristics of the sludge, creating favorable conditions for anaerobic biotransformation.