Effect Of Copper Ions And Tetracycline On The Formation Process Of Aerobic Granular Sludge

Heavy metals or antibiotics can affect the biological treatment of sewage,and they are often detected in the livestock and poultry wastewater at the same time.There is still a lack of systematic research on the influence of the coexistence of the two on the biological treatment system.Aerobic granular sludge(AGS)technology has been tried to treat all kinds of wastewater,which has the characteristics of good effluent quality,good sludge settling performance and strong impulsion load resistance.The formation of granular sludge is the premise of good treatment effect of aerobic granular sludge technology.In this study,sequential batch reactor(SBR)treatment of high ammonia nitrogen wastewater as the research object,by addi ng 4 mg/L copper ions and 0.5mg/L tetracycline(TC)to R1 influent water,at the same time,adding copper ions(R2)and tetracycline(R3)alone and blank(R4)group as the control,the effects of heavy metals and antibiotics on sludge characteristics,pollutant removal efficiency,extracellular polymeric substance(EPS)characteristics and microbial community structure in the process of flocculated sludge granulation were studied.The purpose is to provide a reference for exploring the influence of copper ions and TC on biological treatment system,and also provide technical support for the formation of AGS.Compared with the presence of copper ions and TC alone,the coexistence of the two can promote the formation of AGS,and could improve the biomass and sludge settling performance in the reactor,but would reduce the sludge nitrification activity.The average particle size of R1,R2,R3 and R4 at mature stage was 408.65,384.66,380.53 and 211.32 μm,respectively.Mixed liquid suspended solid(MLSS)stabilized at 6884.15,7887.69,5833.51 and 4865.47 mg/L,sludge volume index(SVI)value stabilized at 42.91,34.11,54.89 and 75.49 m L/g,and the average nitrification activity of sludge during AGS culture was 80.58,102.22,97.68 and 123.38 mg/g·h,respectively.In the process of AGS cultivation,the SBR reactor had a good effect on the treatment of pollutants during the stable period.The addition of copper ion s and TC had little effect on the removal of ammonia nitrogen and COD,and the removal rates of both were basically stable at about 99% and 80%.The removal rate of TC increased gradually with the prolongation of culture time,and the average removal rate of TC in R1 reactor with the addition of copper ions was 8.33%higher than that in R3 reactor.With the extension of aeration time in a single cycle,the concentration of TC in the water decreased gradually,LB-EPS and TB-EPS participated in the adsorption process of TC,and TC gradually transferred from LB-EPS to TB-EPS.With the formation of granular sludge,the protein(PN)and polysaccharide(PS)contents of sludge EPS increased gradually,and the presence of copper ions and TC promoted the secretion of more EPS by microorganisms,and the main component of EPS was PN,which was mainly concentrated in TB-EPS.Compared with blank,the content of PN in TB-EPS in R1,R2 and R3 reactors was increased by 15.12,8.77 and 3.5 mg/g,respectively,and the content of PS was increased by 18.76,3.89 and 11.03 mg/g,respectively.The influence of copper ions and TC on the characteristic of EPS was different because of the different location of TB-EPS and LB-EPS.Copper ions and TC increased the fluorescence intensity of aromatic proteins and soluble microbial by-product IV fluorescence substances in TB-EPS,and made the characteristic peak of soluble microbial by-product a blue shift.The effect on LB-EPS was more complex.The addition of exogenous substances decreased the fluorescence intensity of tyrosine,increased the fluorescence intensity of tryptophan and soluble microbial by-products in the reactor with copper ions and TC alone,and decreased the fluorescence intensity in the reactor with the coexistence of copper ions and TC.Fluorescence intensity of humic acids increased in the reactor with copper ions,but decreased in the reactor with TC alone.Copper ions and TC affected population structure and potential metabolic function in microorganism.Copper ions decreased species richness and increased species diversity,while TC increased species richness and diversity,and the coexistence of the two decreased species richness and diversity.The addition of copper ions and TC made the relative abundance of some microorganisms decrease or even disappear,but new drug-resistant bacteria appeared.The dominant bacteria genera in R3 and R4 were Thauera,Flavobacterium,Lactococcus and Paracoccus.The dominant strains in R1 and R2 reactors were Thauera,Flavobacterium,Pseudoxanthomonasa and Micropruin.Among the metabolic pathways of microbial biodegradation of organic matter,Amino Acid Metabolism,Carbohydrate Metabolism and Energy Metabolism had the highest relative abundance.The relative abundance of Amino Acid Metabolism increased in the reactor where copper ions and TC exist alone,while the relative abundance of Amino Acid Metabolism decreased in the reactor where copper ions and TC coexist.The relative abundance of Energy Metabolism increased when TC alone exist,while decreased when copper ions alone exist.At the same time,the addition of TC had a strong inhibitory effect on nitrifying enzyme and denitrifying enzyme in the reactor,while the mixed addition of copper ions and TC promoted the production of nitrifying enzyme and denitrifying enzyme in the nitrification process.