Efficacy Of AMBBR Process In Treating Sulfadiazine Wastewater And Microbial Mechanism

Due to the widespread use of antibiotics in medicine and animal husbandry,antibiotics are constantly flowing into the environment,and because of their hard-to-degrade characteristics,they show"pseudo-persistence".However,the traditional activated sludge method is difficult to remove antibiotics from the environment.In this study,based on the new magnetic filler developed in the laboratory,Alternately Move Bed Biofilm Reactor（AMBBR）was established to treat different concentrations of sulfadiazine wastewater.We investigated the structure,function and metabolic properties of the microbial community in response to sulfadiazine.The following results were obtained.（1）When the sulfadiazine concentration was at the microgram level,the reactor had good denitrification and decarbonization performance,with COD_crremoval rate of 93.06%,ammonia nitrogen removal rate of 95.15%,and sulfadiazine removal rate stabilized at about 95%.The higher the concentration of antibiotics,the more the denitrification and decarbonization performance of the reactor was inhibited,and the removal rates of COD_cr,ammonia nitrogen and sulfadiazine decreased to 80.14%,73.61%and 78.15%,respectively,but the amount of antibiotics removed per unit biofilm amount increased significantly,and the biofilm degradation capacity was enhanced significantly.Low concentrations of sulfadiazine induced microorganisms to secrete more extracellular polymers,EPS（PN）in large amounts on the cell surface to counteract their biotoxicity,while high concentrations of sulfadiazine inhibited the secretion of EPS by microorganisms.（2）High-throughput sequencing showed that the presence of sulfadiazine firstly reduced the abundance and diversity of the bacterial community,and selected microorganisms to enrich some specific groups of bacteria.At the phylum level,the dominant phyla before and after the reaction were Proteobacteria,Bacteroidota and Firmicutes;at the genus level,Trichococcus replaced Acinetobacter as the dominant genus in the biofilm,together with norank＿f＿＿Bacteroidetes＿vadin HA17 together,adapting to the environment where sulfadiazine is present and promoting the recovery of reactor nitrification performance by secreting extracellular substances to enhance biofilm resistance to sulfadiazine.Both redundancy analysis and structural equation modeling indicated that the presence of sulfadiazine enhanced the tolerance of Trichococcus,Nitrosomonas and other flora to participate in the biodegradation of sulfadiazine and become potentially resistant flora.（3）A strain,No.Y23,was isolated from the biofilm that could effectively degrade sulfadiazine and was able to reach 81.36%degradation rate of sulfadiazine at 72 h.After morphological observation,16S r RNA gene sequencing and phylogenetic tree kinship analysis,Y23 showed 99%homology with Bacillus cereus strain K1M45,which was identified as Bacillus cereus and the best incubation time for the degradation bacteria was determined to be 35 h.（4）Microbial functions and metabolic pathways were changed by sulfadiazine.Biofilms were involved in the removal of contaminants through a variety of pathways including active transport,oxidative phosphorylation,glycolysis,and pyruvate metabolism by 3561 enzymes including oxidoreductases,transferases,ligases,and hydrolases.The functions of genes with increased abundance were mainly related to carbon metabolism,nitrogen metabolism and adaptation to antibiotic environmental stresses.The presence of sulfadiazine promotes the enrichment of the corresponding resistance genes in the reactor and enhances biofilm resistance.The absolute abundance of sul1,a sulfonamide resistance gene,was higher than that of sul2,with an absolute abundance of 6.34×10⁹copies/g VSS,and microorganisms carrying the sul1 gene were more likely to survive.