| Heavy metals and antibiotics are often detected in many kinds of wastewater,such as livestock and poultry breeding wastewater,and their co-existence will affect the biological system of sewage.Aerobic granular sludge(AGS)has been used for various sewage treatment because of its good settling performance,high pollutant removal effect,and better impact load resistance.Previous studies paid more attention to the decontamination effects of heavy metals or antibiotics on AGS,while there were few reports on the long-term coexistence of the two.Moreover,studies on the mechanism of antibiotic removal by AGS were still limited.It is of great significance to study the removal characteristics of AGS and the dynamic changes of microbial community under the condition of long-term coexistence of heavy metals and antibiotics,so as to comprehensively understand the treatment characteristics of AGS wastewater containing heavy metals and antibiotics.In this study,four sequential batch reactors(SBRs)with the same structure were used to treat artificially simulated wastewater containing high concentrations of ammonia nitrogen,copper ions and tetracycline(TC).In the wastewater,4 mg/L copper ions and TC(0.5 and 2.0mg/L,respectively)were added in R1 simultaneously,and 4 mg/L copper ions were added separately in R2.0.5 and 2.0mg/L TC were added separately in R3,and no copper ions and TC were added as control group in R4.In the presence of copper ions and TC,the effects of AGS sludge characteristics,pollutant removal,the extracellular polymers(EPS)content and composition changes,and microbial community structure were studied.The effects of copper ions on TC removal effect and pathway were analyzed,and the binding ability and reaction sequence of EPS and exogenous substances(copper ions and TC)cultured under different influent water conditions were analyzed.The results provided a reference for the influence of copper ion and TC co-existence on AGS biological treatment system.Compared with the control group,the presence of copper ion and TC could increase the sludge particle size,improve the sludge settling performance and change the sludge concentration.The mean particle sizes of R1,R2,R3 and R4 during the stable period were 279.30,447.70,365.30 and 204.40 μm,respectively.The Mixed liquid suspended solid values were stable at 5410.50、6852.32、4795.50 and 6020 mg/L,respectively,and sludge volume index were stable at 35.21、26.94、40.20 and 45.01 m L/g.AGS had a good effect on the removal of pollutants.The addition of copper ion and TC has little effect on the removal of ammonia nitrogen and COD,and the removal rates of the two were basically stable at 98% and 80%-85%.But it will affect the nitrification activity of sludge.Copper ion alone and co-existing with TC can inhibit the nitrification activity of sludge,low concentration of TC(0.5mg/L)can stimulate the nitrification activity of sludge,high concentration of TC(2.0 mg/L)can reduce the nitrification activity of R1 and R3 by 57.04% and54.99%,respectively,in the short term,and then gradually recover.AGS could effectively remove TC,and the presence of copper ions will change the removal path of TC.Under long-term operation conditions,AGS removed more than 90% of TC,and with the extension of operation time,the biodegradation rates of R1 and R3 increased from 15.69% and 25.19% to 18.39% and39.58%.After adding copper ions,TC was still mainly adsorbed and removed,but the adsorption process changed from cell biological adsorption to EPS adsorption.The results of qualitative and quantitative analysis showed that the presence of copper ion and TC could change the content,composition and functional group content of the extracellular polymer.When TC concentration increased from 0.5mg/L to 2.0mg/L,sludge PN and PS in R1 and R3 reactors increased respectively.Acidic hydroxyl(-OH),amino-N-H,-COOH,amide and major functional groups of carbohydrates were all involved in the copper ion /TC binding process.Compared with R4 in the control group,the content of free amino group in R1-EPS in the presence of copper ion and TC increased,and the addition of both stimulated EPS to secrete more PN to bind with them,thus reducing the toxic effect of both on sludge microorganisms.The increase of TC concentration can stimulate microorganisms to secrete more oxygen-containing functional groups to reduce their toxic effects on sludge microorganisms.The presence of copper ion and TC would change the binding order of EPS and exogenous substances,and would cause the static quenching of EPS components.The binding ability of the AGS-EPS component cultured with TC(copper ion)was enhanced to reduce its toxic effect.When TC concentration was 2mg/L,the nitrification capacity of R2-EPS and R3-EPS decreased by 44.35% and 1.51%,respectively.In the process of reaction between AGS-EPS cultured with copper ion and TC,humus had a preference over protein,and the protein component of EPS was preferred to humus and its combination when the two were cultured separately.Copper ion and TC could affect microbial population structure and potential metabolic function.The relative abundance of Flavobacterium,which was thought to have potential TC removal function,was high.The increased abundance of the strain further improved the biological removal effect of TC,which was consistent with the removal pathway of TC.With the increased of TC concentration,Paracoccus and Thauera became the dominant flora in the reactor(R3).Carbohydrate Metabolism,Amino Acid Metabolism and Energy Metabolism were the highest metabolic pathways in microbial carbohydrate metabolism.The presence of copper ion will inhibit nitrate reductase related to denitrification,while the presence of low concentration TC will stimulate the formation of more nitrate reductase. |
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