Study On Ultrasonic Coupled Bioleaching Pretreatment For Enhancing Municipal Sludge Dewatering And Simultaneously Mitigating Antibiotic Resistant Genes

Sludge dewatering is a key step for decreasing sludge volume and reducing the operating costs of municipal wastewater treatment plants.At present,the bioleaching based on Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans has been proved to be an effective way to improve the sludge dewaterability.However,it needs to be strengthened and improved because of some disadvantages,such as low sludge dewatering efficiency and long reaction time.In this study,the effect of the combined ultrasonic and bioleaching treatment on the dewatering performance of sludge have been discussed.The mechanism of the combination treatment was revealed according to the change of sludge characteristics and extracellular polymeric substances(EPS).Furthermore,there are a large number of antibiotics resistance genes(ARGs)in municipal sludge.The accumulation of ARGs limits the resource utilizationof sludge,so it is necessary to study the synergetic effect of ultrasonic coupled bioleaching on t he removal of ARGs.In this study,tetracycline gene(tet)and sulfonamide gene(sul),which are widely present in sludge,were used to reveal the effect of the combined ultrasonic and bioleaching on the relative and absolute abundance of ARGs.The change of sludge microbial community was analyzed by high-throughput sequencing.And potential hosts of tet and sul were analyzed by Spearman correlation test.Finally,the conditioned sludge was filtered under high pressure by the ultrahigh pressure filtration system to explore the engineering application prospects of this combined ultrasonic and bioleaching trearment.The toxicity of heavy metal,phytotoxicity of the dewater sludge cake and the economic cost of the combined trearment were analyzed,evaluating the agricultural potential of the dewater sludge cake.The results show that compared with the individual bioleaching treatment,the combined ultrasonic and bioleaching treatment can significantly improve the sludge dewaterability and shorten the reaction time by 12.5%.The optimal conditions of this combined treatment were ultrasonic density of 0.08 W/m L,ultrasonic time of 8 s,bioleaching time of 42 h,Fe2+ concentration of 2.4 g/L and S0 concentration of 2 g/L.Under these conditions,the specific resistance of filtration(SRF)decreased by 84.95%.The analysis results of sludge characteristics and EPS show that EPS would fall off from the surface of sludge caused by ultrasonic treatment.Due to the loss of the protection of EPS,the native bacterial cells in the sludge are faster and more directly acidified andoxidized in the process of bioleaching,resulting degradation or releases of proteins and polysaccharides.Therefore,more bound water of sludge release after the combined of ultrasonic and bioleaching treatment,thereby greatly improving the sludge dewaterability.The effects of the combined ultrasonic and bioleaching treatment on sludge ARGs were studied.The results show that the diversity and biomass of bacterial in sludge decreased significantly after the combined treatment.Absolute abundance of various gene subtypes of sul and tet decreased by 1.56?1.58 and 0.34?1.23 log units,respectively.The relative abundance of the sul decreased while the tet increased.The results of Spearman correlation test show that the main potential hosts carrying the sul of sul gene were Proteobacteria,while the main potential hosts carrying the tet were Proteobacteria and Firmicutes.The results of ultrahigh pressure filtration experiment show that sludge deep dewatering was achieved by ultrasonic-bioleaching-lime conditioning combined with ultrahigh pressure filtration system.After ultrasonic-bioleaching-lime conditioning,the water removal of sludge was 87.01%,which was 12.33% higher than that of sludge treated by bioleaching-lime conditioning.Likewise,the moisture content of the dewater sludge cake reduced to 49.94%,which was 16.1% lower than that of sludge treated by bioleaching-lime conditioning.The results of toxicity evaluation show that the sludge cake has favorable value of agriculture.The concentration of heavy metal was much less than the agricultural standard,and the germination index of cabbage was higher than 80%.Furthermore,economic analysis shows that the total cost of the combined treatment was 50.08% and 8.73% decreased in PAM pretreatment and Fenton pretreatment,respectively.In summary,the results show that the ultrasonic coupled bioleaching process can effectively improve the sludge dewaterability and synergically reduce the ARGs.This treatment has certain potential application value.