Effects Of Different Conductive Nanomaterials On Anaerobic Digestion Performance And Reduction Of Antibiotic Resistance Genes In Sludge

Anaerobic digestion is one of the important means for sewage sludge treatment in sewage treatment plants.In addition to a large amount of organic matter,the sludge also contains antibiotics and resistance genes that can not be ignored.If the sludge is directly discharged without effective treatment,it will pose a certain risk to environmental safety,horizontal gene transfer is an important reason for the increased risk of antibiotic resistance genes transmission in sludge.The results showed that anaerobic digestion technology can reduce the abundance of antibiotic resistance genes in sludge to some extent.Adding additives has become a widely used method to improve the anaerobic digestion performance of sludge.Nanomaterials are one of the most important additives to enhance the anaerobic digestion performance.This paper combined with real-time quantity PCR(RT-qPCR)and 16s rRNA amplification sequencing such as molecular biology methods through a 36-day fermentation experiment,exploring the effects of four conductive nanomaterials(nano-carbon powder,nano-Al₂O₃,nano-Zn O,nano-Cu O)on sludge anaerobic digestion performance,diversity and abundance of microbial community and abudance of the mobile gene elements.(1)How did the four conductive nanomaterials affect the anaerobic digestion performance was discussed(The dosage of the four conductive nanomaterials is 50.0 mg g^-1TS).The results showed that the biogas production increased by 16.9%and 23.4%with the addition of nano carbon powder and nano-Al₂O₃,respectively,but the biogas production decreased by 90.2%and 17.3%with the addition of nano-Zn O and nano-Cu O,respectively.The removal efficiency of sludge total solids was improved by 38.73%and 27.11%with the addition of nano carbon powder and nano-Al₂O₃,respectively,but the removal rate of total solids(TS)was reduced by 70.67%and 43.70%with the addition of nano-Zn O and nano-Cu O.(2)Kinetic analysis indicated four conductive nanomaterials could shorten the lag phase of anaerobic digestion sludge with an average rate of 51.75%.(3)The results of 16S rRNA amplicon sequencing showed that the Euryarchaeota was the most abundant phylum among all the phylum in each group of reactors,and Methanosaeta was the main archaea.Methanosaeta was enriched in nano carbon powder and nano-Al₂O₃ reactor,and Firmicutes was the main phylum of the bacterial community in the five groups of reactors.The addition of nano carbon powder and nano-Al₂O₃ had a positive effect on the diversity and richness of the archaeal community.However,the addition of nano-Zn O and nano-Cu O had a significant negative effect on the diversity and richness of the microbial community,among which the presence of nano-Zn O had the greatest negative effect on the community richness and diversity of archaea.(4)Redundancy analysis(RDA)showed that there was a strong correlation between Methanosaeta and biogas production,Clostridium?sensu?stricto?12,Leptolinea,Syntrophomonas and Longilinea showed obviously relationship with p H and biogas production,and the genera belong to Firmicutes and Chloroflexi could conduce to methanogenesis process.(5)RT-qPCR was used to characterize the change in the abundance of mobile gene elements of antibiotic resistance genes in the anaerobic digestion system.The results showed that the addition of four conductive nanomaterials enriched the relative abundance of Int I-1?tnp A-01?tnp A-02?tnp A-04?tnp A-05?tnp A-07 during anaerobic digestion.However,the reduction rate of IS613 relative abundance in the nano-Cu O reactor increased by 9.19%,indicating that the addition of nano-Cu O may reduce the possibility of gene horizontal transfer in the anaerobic digestion reactor,and nano-Cu O may have the potential to improve the reduction efficiency of antibiotic resistance genes during anaerobic digestion.