Micro-response Mechanism Of Aerobic Granular Sludge With Different Particle Sizes Under Representative Medicine Stress

Compared with the traditional activated sludge process,aerobic granular sludge(AGS)has the advantages of dense microstructure,good settling performance,high biomass retention rate and rich microbial population.Therefore,AGS has good pollutant removal efficiency and toxicity tolerance,and has received extensive attention in the field of wastewater treatment.However,the unclear formation mechanism of AGS and the difficulty of maintaining the stability of the system under long-term operating conditions have always restricted the promotion and application of AGS technology.Particle size is one of the most significant characteristics of AGS growth,and it is an important link between the macro structure and micro properties of AGS.In the process of microbial growth and reproduction,different stress conditions can cause microbes to perform different stressful behaviors,and further change the microbial population function within the AGS and the appearance and structure of the AGS.In this paper,two different types of drugs,tetracycline and dexamethasone,are added to the feed water to acclimate and cultivate AGS.Taking the mature AGS with different particle sizes as the research object,the changes of the physicochemical characteristics of mature AGS are observed and microbial populations under the stress conditions of different drugs are analyzed.Extracellular polymeric substances(EPS)and microbial quorum sensing are two key factors in AGS,therefore,the regulatory factors of AGS particle size are explored and the stability maintenance mechanism of AGS are further studied,which will help select the aerobic granular sludge with suitable particle size in different wastewater environment,and provide theoretical basis and practical reference for maintaining the stable operation of AGS system in actual wastewater treatment.The results are as follows:(1)The total EPS of AGS cultured under no drug stress is higher in AGS of 0.6-1 mm and 3-4 mm.The protein content of TB-EPS,which is an important part of EPS,accounts for 60% of the total EPS content.The AGS with a particle size of 0.6-1 mm has the highest hydrophobic PN content and the highest PN/PS value,which is favorable to the continued increase of AGS.The SMP in the AGS with large particle size contains more humic acid and fulvic acid,which can enhance the adsorption capacity of AGS and reduce the damage of toxic substances to AGS,which is beneficial to the removal of pollutants in the environment.C4-HSL,C6-HSL and C8-HSL promote the formation and stabilization of AGS with large particle size,respectively,and can affect the distribution of AGS particle size.(2)Tetracycline stress conditions can accelerate the formation of AGS.AGS with a particle size of 3-4 mm has the highest PN content and the most stable particle structure,and its PN/PS can reach 9.93.Tetracycline stress can stimulate the secretion of C6-HSL in AGS,and C8-HSL can regulate the particle size of AGS under tetracycline stress.The relative abundance of signal molecule producing strains Zoogloea,Arcobacter and Acidovorax increase with the increase of AGS particle size,which may be the main secreting strains of C8-HSL.Tetracycline affects the regulation of signal molecules on PN and PS in the hydrophilic and hydrophobic EPS.TPIA-PN,TPIA-PS,TPIN-PN,and HPI-PS have a good response ability to the stimulation of tetracycline.At the same time,the particle size has a strong correlation with TPIA-PS.It is speculated that the presence of TPIA-PS in the reactor will help increase the particle size of AGS.There are 860 proteins involved in the regulation of antibiotic biosynthesis pathway in AGS under tetracycline stress,which reflects that tetracycline drugs have produced persistent selective pressure on microorganisms in AGS and strengthened the resistance of AGS to tetracycline.The proteins related to stress function are significantly enriched in 3-4 mm and larger than 4 mm AGS.The proteins related to detoxification function are only significantly enriched in 3-4 mm AGS,which indicated that3-4 mm AGS have stronger resistance and degradation ability to tetracycline.(3)The particle size of AGS cultured under dexamethasone stress was smaller and changed dynamically in the range of 0.2-2 mm.The ATP concentration of active microorganisms in AGS was low,and the biological threat index was higher.Dexamethasone inhibited the energy metabolism of microorganisms in AGS,stimulating the secretion of PS in AGS,and affected the distribution of PS in AGS.The proportion of proline and tryptophan-like proteins in the EPS of the AGS with a particle size of 0.6-0.8 mm is higher than that of the other groups of AGS,and the resistance to adverse environments is stronger.In this reactor,3OC8-HSL and C8-HSL jointly participate in the regulation of particle size,and dexamethasone strengthens the function of 3OC8-HSL in particle size regulation.Lampropedia can abundantly exist in AGS cultured under the stress of tetracycline and dexamethasone,and can effectively resist the stress of drugs.Dexamethasone stimulates the activity of ABC transporter and quorum sensing-related proteins in AGS,strengthening the communication of microorganisms in the system,regulating the stress mechanism of dexamethasone,and alleviates the harm caused by dexamethasone to AGS.