Enhanced methane production from anaerobic digestion of waste activated sludge by combining ultrasound with potassium permanganate pretreatment

The influence of ultrasound (US) and potassium permanganate (KMnO4) co-pretreatment on anaerobic digestion of waste activated sludge (WAS) was investigated in this survey. Results showed that KMnO4 (0.3 g/g TSS) cooperated with US (1 W/mL, 15 min) pretreatment significantly increased the cumulative methane yield to 174.44 ± 3.65 mL/g VS compared to the control group (108.72 ± 2.56 mL/g VS), solo US (125.39 ± 2.56 mL/g VS), and solo KMnO4 pretreatment group (160.83 ± 1.61 mL/g VS). Mechanistic investigation revealed that US combined with KMnO4 pretreatment effectively disrupted the structure of extracellular polymeric substances and cell walls by generating reactive radicals, accelerating the release of organics and hydrolytic enzymes as well as improving the biodegradability of soluble organics. Modeling analysis illustrated that the biochemical methane potential and hydrolysis rate of WAS were enhanced under US + KMnO4 pretreatment. Microbial community distribution indicated that the co-pretreatment of US and KMnO4 elevated the total relative abundance of functional microorganisms associated with anaerobic digestion (22.01 %) compared to the control (10.69 %), US alone (12.24 %) and KMnO4 alone (16.20 %).