Microbial changes in sludge after ultrasonic treatment: microbial viability, microbial community, and functional bacteria

Large amount of sludge is produced in wastewater treatment plants and requires proper handling. Ultrasonic treatment of sludge has multiple functions. This study examined in details the change of microbial community in ultrasound treated sludge. Results revealed that ultrasound effectively cracked the sludge and reduced the microbial viability. In the untreated sludge, the proportion of living cells approximated 97.3 %, and after ultrasonic treatment, the value decreased to 50.7 %. In addition, sonication effectively lysed sludge and reduced its particle size from 90.1 to 35.8 μm. Ultrasonic treatment altered the distribution of microbial genera in sludge and increased the relative proportion of Terrimonas . Following the functional predictions of PICRUSt2 and FAPROTAX, ultrasonic treatment improved N and P removal capacities of the sludge. Functional bacteria analysis revealed that ultrasonic treatment affected the communities of denitrifying, nitrifying, and phosphate-accumulating microbes; it decreased the diversity of nitrifying bacteria while increasing the diversity of denitrifying and phosphate-accumulating bacteria. Notably, this is the first study to focus exclusively on microbial changes in sludge caused by ultrasonic treatment, including predictions of microbial functions and genes. It may lay a foundation for subsequent practical applications.