Ultrasonic coupled bioleaching pretreatment for enhancing sewage sludge dewatering: Simultaneously mitigating antibiotic resistant genes and changing microbial communities

Abstract In this study, ultrasonic as a pretreatment coupled with bioleaching was used to enhance sludge dewaterability. Changes in microbial diversity and antibiotic resistant genes (ARGs) were studied during the combined treatment process. The results show that under optimal conditions, combined ultrasonic and bioleaching treatment led to decreases in the specific resistance of filtration and bioleaching time by 7.59% and 12.5%, respectively, compared with single bioleaching process. Using high pressure filtration system, the water content of sludge cake treated by the combined treatment was decreased to 58.04%, which was 10.04% lower than bioleaching sludge. After combined treatment, the microbial diversity and the total number of bacteria in the sludge decreased significantly, which caused the decreases in the absolute abundance of sulfonamide and tetracycline ARGs by 1.56–1.58 and 0.34–1.23 log units, respectively. However, the decrease in the total bacterial biomass was greater than the decrease in the number of potential hosts carrying the tetracycline ARG, resulting in an increase in the relative abundance of tetracycline gene. Furthermore, this study proposed a mechanism of the dewatering and ARGs, involving the combined ultrasonic and bioleaching treatment: Firstly, ultrasonic cavitation causes extracellular polymeric substances (EPS) to fall off the surface of sludge; Secondly, this faster and directly makes bacteria cells affected by bio-acidification and bio-oxidation. In this case, the cells could be more easily destroyed by the combined ultrasonic and bioleaching treatment, compared with individual bioleaching treatment; As a result, stronger dewaterability and more removal rates of ARGs were achieved under the combined treatment. The economic analyses showed that the combined ultrasonic and bioleaching treatment is a more practical and economical technique for achieving deep dewatering of sludge.