Effects Of Exogenous AHLs And Activated Sludge On The Repai(?)Process Of Disintegrated Aerobic Granular Sludge

Aerobic granular sludge(AGS)technology has developed rapidly in recent years.It has a dense structure,excellent sedimentation capacity and water treatment capacity It has gradually become a research hotspot in the field of biological treatment of domestic sewage and industrial wastewater,and has a wide range of applications.However,aerobic granular sludge has the problems of low stability of structure system and disintegration of later granules in the process of long-term operation or storage,which limits the wide application of aerobic granular sludge.Therefore,effective remediation of disintegrated aerobic granular sludge and sustainable operation of aerobic granular sludge process are the key ways for its large,scale application.In this paper,two methods of repairing decomposed aerobic granular sludge,namely,adding different concentration of AHLs signal molecules and adding activated sludge,were proposed.The evolution of morphology,extracellular polymer,physicochemical properties,microbial community structure and reactor performance of aerobic granular sludge during the process of repairing were systematically investigated,and the repairing mechanism of aerobic granular sludge was explored.The main research contents and results are as follows:The main conclusionsare as follows:(1)Adding exogenous AHLs of low concentration(50 nmol/L)and high concentration(500 nmol/L),the granular density and hydrophobicity of aerobic granular sludge increased obviously.At the same time,the exopolymer secretion of granular sludge increased significantly,especially the tightly bound proteins.The effect of medium and low concentration AHLs on the remediation of granular sludge was the most obvious.The particle density and hydrophobicity increased from 13.5±1.28 gVSS/L,31.06±1.08%to 49.99±2.37 gVSS/L and 79.30±1.78%respectively.The addition of exogenous AHLs will affect microorganisms at the gene level,mainly in the changes of microbial community structure and the abundance of microbial quorum sensing function.When a high concentration of AHLs(500 nmol/L)was added to the R2 reactor,the abundance of quorum induction quenching bacteria in the microbial community increased,resulting in the decrease of the concentration of endogenous AHLs in aerobic granular sludge.At the same time,exogenous AHLs affect the expression of some functional genes.The concentration of exogenous AHLs(50 nmol/L)has a significant effect on the activity of sludge,which promotes the re-granulation of disintegrated granular sludge debris.(2)The hydrophobicity,density,integrity and settling performance of the granular sludge were greatly improved by adding activated sludge.The hydrophobicity of the experimental group increased from 42±2.57%to 67.09±1.36%at the beginning of the experiment.At the same time,the granulation rate of the activated sludge itself was accelerated,and the granulation rate of the granular sludge could reach about 90%in about 18 days.Activated sludge adheres to the decomposed aerobic granular sludge to form new aerobic granular sludge,which prolongs the service life of the aged granules.In terms of quorum sensing,activated sludge can compensate for the lack and deficiency of some signal molecules in the decomposed aerobic granular sludge,and produce more AHLs in the process of attachment and growth to repair the disintegrated granular sludge;furthermore,activated sludge is added at the beginning of the long-term storage aerobic granular sludge activation process,which can achieve better water treatment efficiency in the early stage of start-up.As a result,the removal rates of COD and NH4-N in the effluent of the reactor are about 85%and 90%respectively,which can greatly shorten the start-up time of the reactor.