Study On The Effect Of Polystyrene(PS)inhibition On The Performance Of Aerobic Granular Sludge And Microbial Community

The aerobic granular sludge（AGS）reactor has a dense structure and high concentration of extracellular polymeric substances（EPS）,so it has strong resistance to toxicity and impact load,and has a very broad application prospect.In recent years,as a hot issue of environmental pollutants,microplastics have been increasingly studied on their impact on reactors.But at present,there are very few studies on the treatment performance of AGS reactors under the inhibition of microplastics,especially from the perspectives of sludge activity,sludge aggregation performance and microorganisms.In this paper,the change of the specific denitrification rate that characterized the activity of sludge under the acute inhibition of PS was studied in this paper;And the change characteristics of the activity of four enzymes related to denitrification were discussed;Through the detection of reactive oxygen species and lactate dehydrogenase,the stress response of sludge under acute inhibition of PS was observed.In addition,by measuring the zeta potential,surface hydrophobicity and aggregation properties of the AGS surface,the changes in the surface properties of the sludge under acute inhibition were observed;and the XDLVO curve was used to further explained the aggregation under the inhibition conditions.Finally,the high-throughput sequencing segment was used to analyze the changes in AGS microbial community structure at the genus level under acute inhibition and long-term stress of the actual microplastic concentration in the sewage plant,and further clarified the effect of microplastics on AGS through the analysis of functional proteins.The research provided theoretical support for the subsequent AGS reactor operation to deal with the impact load research of microplastics.Through research,the main conclusions of this article are as follows:（1）The AGS reactor in this experiment achieved granulation within 60 days.SS and VSS were 7.08g/L and 6.29g/L,respectively;the ratio of VSS/SS increased from 0.72 at the time of inoculation to 0.90;the value of SVI decreased from 102.34m L/g32.78m L/g,SV₃₀/SV₅>0.90;The average particle size increased from 88.00μm at the time of inoculation to 612.43μm,and the sludge>200μm reached 92.90%;For the sludge’s EPS content,protein increased while polysaccharides decreased slightly.The contents were 135.10mg protein/gvss and 23.39mg polysaccharide/gvss,respectively.The ratio of protein/polysaccharide increased from 1.53 to 5.78;The removal rate of COD and NH₄⁺-N were close to 100%,and the removal rate of TN and TP has also stabilized at about 75%.The reactor basically reached a stable state..The surface of mature granular sludge was relatively regular and smooth,the structure was compact,and the whole was spherical;β-polysaccharides were mainly distributed on the outer surface of the sludge,and they were entangled with each other to form a network structure,which acted as a skeleton.The internal protein andα-polysaccharide were embedded in it,forming a dense EPS together.（2）Acute inhibition of polystyrene（PS）had an inhibitory effect on AGS activity:AGS activity was characterized by the determination of the specific denitrification rate of AGS,compared to 0mg/L,the specific ammonia oxidation rate（SAOR）,the specific nitrate nitrogen oxidation rate（SNOR）,the specific nitrate reduction rate（SNIRR）rate and the specific nitrate reduction（SNRR）rate of 50mg/L,100mg/L and 200mg/L all had different degrees of decline;in addition,The activity of enzymes related to denitrification had also declined;Under the acute inhibition of PS,the content of reactive oxygen species（ROS）and lactate dehydrogenase（LDH）in AGS increased,indicating that the cells suffered a certain degree of oxidative damage and the cell membrane was damaged;PS microspheres were densely adsorbed on the cell surface,and the cell membrane appeared damaged,at the same time the cell membrane appeared softened,and the folds increased.CLMS images showed that the content of dead bacteria increased under the acute inhibition of PS;The content of protein and polysaccharides in EPS decreased,and the network structure formed byβ-polysaccharides was constantly shrinking.（3）Under the acute inhibition of PS,the zeta potential,hydrophobicity and aggregation rate of AGS decreased,which means that the surface charge of AGS increased and the adhesion between cells decreased;Thermodynamic calculations showed that the main component of free energy of interface adsorption（）was Lewis acid-base interaction energy（）,and the fluctuation of was mainly due to the change of,while and appeard increasing trend,the rise of the two was not conducive to the aggregation and stability of particles;Based on the XDLVO theoretical analysis,the van der Waals action energy（W_A）changed little under the acute inhibition of PS;With the increase of PS concentration,the electrostatic repulsion energy（W_R）showed an upward trend;The Lewis acid-base energy consumption(W_AB)of 0mg/L was similar with 50mg/L,100mg/L and 200mg/L were also relatively close;The total interaction energy(W_TOT)showed that a potential barrier appeared at the cell spacing of 5nm.As the PS concentration increased,the potential barrier also gradually increased,the more difficult it was for cells to gather.（4）Under the long-term stress of PS,the water quality treatment capacity of the AGS reactor decreased.The cell membrane was damaged and the mechanical properties were changed.Under the acute inhibition of PS,when the concentration was 50mg/L,the abundance of AGS microbial community was reduced.PS concentrations of100mg/L and 200mg/L could increase the abundance of microbial community;The addition of PS reduced the diversity of AGS microbial community.In long-term stress,1mg/L and 5mg/L PS simultaneously reduced the abundance and diversity of microorganisms.Under the acute inhibition of PS,the OUT of the four experimental groups were equivalent;Under the long-term stress of PS,the number of OUT of 1mg/L and 5mg/L decreased significantly,and the number of OUT shared by the two was the largest,indicated that the microorganisms of the two experimental groups was highly similar.At the genus level,under the acute inhibition of PS,Candidatus＿Competibacter and Thiothrix had the highest abundance.In long-term stress,Flavobacterium replaced Candidatus＿Competibacter as the dominant species.The analysis of functional proteins showed that under the acute inhibition of PS,the related functions of protein,cell membrane and cytoskeleton synthesis were promoted,while the functional proteins of cell movement and inorganic ion transport function were weakened.Under the long-term stress of PS,protein synthesis and cell movement functions were promoted,but the functional proteins of cell membrane and cytoskeleton synthesis and organic matter transport were inhibited.