| The combination of aerobic granular sludge and membrane bioreactor technology has a good performance in improving effluent quality,reducing floor space,and reducing membrane pollution.In this research,a stable continuous flow aerobic granular sludge-membrane bioreactor was studied,and the influence of dissolved oxygen changes on the stability of aerobic granular sludge was discussed using proteomics technology.This research uses artificial simulated wastewater and the test period is 90 days.It is divided into five stages according to the gradient of dissolved oxygen.The dissolved oxygen concentration is first reduced and then increased,and the corresponding detection and analysis are carried out.During the whole experiment,the dissolved oxygen in the reactor and the transmembrane pressure difference of the membrane module were recorded continuously,the sludge changes were observed with an optical microscope,the water quality index was measured every day,and the extracellular polymer concentration of the sludge was measured every 5-8 days.The sludge particle size change was observed by using laser particle size analyzer,the succession of microbial communities was analyzed by using high-throughput sequencing technology,and the protein function change in extracellular polymers was analyzed using proteomics technology,thereby analyzing the change in the stability of aerobic granular sludge.The aerobic granular sludge-membrane bioreactor has a high pollutant removal efficiency during the 90-day experimental period.The average removal rate of COD is 94.08%.The denitrification capacity of the reactor is also relatively good and the average removal rate of total nitrogen was 90.8%.The removal effect of the reactor was relatively stable throughout the experiment.The particle size of granular sludge changes with the change of dissolved oxygen concentration.When the dissolved oxygen is maintained at 1.5 mg/L,the granular sludge is about 700 μm,while the dissolved oxygen drops to 0-0.5 mg/L,the minimum particle size is324 μm.The content of polysaccharide and protein in the extracellular polymer of granular sludge also changed with the change of dissolved oxygen concentration,and the change of protein content showed a certain pattern.For the TB-EPS in the aeration zone,the average value of TB-PN in the first and second stages is 98.45 mg/g MLSS,the average value of TB-PN in the third stage is reduced to 68.21 mg/g MLSS,and for the fourth and fifth stages,it increases to138.46 mg/g MLSS.High-throughput sequencing results showed that changes in dissolved oxygen led to the succession of the microbial community.Thiothrix had the highest content,and the increase in Saprospiraceae content led to a decrease in the protein content in EPS.The decrease of protein content loosens the structure of granular sludge and further promotes the disintegration of granular sludge.The changes in the nitrifying and denitrifying bacteria such as Sphaerotilus also explain the results of the changes in the protein content of the extracellular polymer.The proteomics results showed that at very low DO values(0-0.5 mg/L),the protein function of protein tag produced by Enterobacter hormaechei was significantly enriched,which degrades the structural proteins in the granular sludge.This is an important reason for the destruction of the AGS structure.In addition,the results of proteomics analysis also showed that the number of proteins involved in extracellular structure and nuclear structure function was zero,which means that the PN in TB-EPS was mainly involved in the functional role rather than participating in a structural composition.In summary,this topic sets up a dissolved oxygen concentration gradient in the membrane bioreactor to observe the whole process of granular sludge from stable existence to cracking to rapid formation of stable particles again,and reveals the important factors that affect the stability of granular sludge. |
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