Impact of ultrasonication on sludge characteristics: Aerobic granular sludge versus waste activated sludge

The aerobic granular sludge (AGS) process is a promising wastewater treatment technology that is considered as an alternative to the conventional activated sludge (CAS) process. Due to poor hydrolysis, sludge produced by AGS processes has low digestibility resulting in a decrease in energy recovery. Therefore, pretreatment methods such as ultrasonication, can be used to accelerate hydrolysis, and improve solubilization and anaerobic digestibility. The purpose of this study was to determine the effect of ultrasonication pretreatment on AGS in comparison to waste activated sludge (WAS). Two different intensities (50 W and 100 W) were applied to AGS and WAS and the release of organic compounds, phosphorus, ammonium, and heavy metals to the supernatant were observed. Volatile fatty acids and proteins were the most abundant organic compounds released from AGS and WAS samples, respectively. Phosphorus release in AGS (5.68 f 1.14 %) was lower than WAS (10.48 f 0.23 %) at 100 W ultrasonication intensity. Similarly, the release of ammonium in AGS (10.30 f 0.03 %) was less than WAS (14.05 f 0.01 %). The release of heavy metals showed a similar trend for both sludge samples, increasing with higher ultrasonication intensity. This correlation has been confirmed by Pearson's correlation coefficient analysis. Ultrasonication pretreatment improved the sludge disintegration more in AGS than WAS which can lead to enhancement of AGS digestibility.