Study On The Effect Of Influent Nitrogen And Phosphorus Content And Carbon Source Types On The Characteristics Of Sbr Activated Sludge

C,N,and P are important elements that make up cells and play an important role in the synthesis and metabolism of microorganisms.The activated sludge process takes activated sludge flocs as the main body to remove pollutants in wastewater while microorganisms grow and multiply.However,when the nutrient ratio of the influent is imbalanced or the type of carbon source in the influent is changed,it may lead to changes in the treatment performance of the reactor,the aggregation capacity and the settling performance of activated sludge flocs.The performance of sludge is often affected by its surface hydrophobicity and zeta potential,while the abundant charged,polar and non-polar functional groups on Extracellular Polymeric Substances（EPS）directly affect the surface properties of the sludge.Exopolysaccharides（PS）is the main hydrophilic component in EPS.Its content,hydrophilicity and hydrophobicity,and functional group composition will directly affect the properties of EPS.Therefore,studying its influence mechanism on sludge performance from the perspective of EPS and PS has important theoretical value and practical significance.In this paper,activated sludge under the conditions of limited influent nitrogen and phosphorus content and different hydrophilic carbon sources is the research object,and the reactor processing performance,sludge settling performance,aggregation capacity,particle size and morphology,microorganisms community diversity;combined with sludge zeta potential and hydrophobicity,analysis based on XDLVO theory,EPS content,relative hydrophobicity and functional group composition,as well as PS morphology,zeta potential,functional group composition.The influencing factors of sludge settling performance and aggregation capacity were analyzed,and the reasons for the decline of sludge settling performance and aggregation capacity were discussed.The research results of the thesis can provide a theoretical basis for a deep understanding of the sludge performance changes of activated sludge under different influent media,and provide technical support for ensuring the normal operation of the reactor.The paper got the following main conclusions:（1）The influence of influent nitrogen content on the performance of activated sludgeThe removal rates of COD,NH₄⁺-N and TN in the reactor remained stable,maintaining above 85%,99%and 70%respectively.The TP removal rate was stable in the control stage and the nitrogen restriction stage,but the phosphorus removal effect of the reactor deteriorated to less than 30%in the nitrogen deficiency stage.In the nitrogen deficiency stage,the sludge biomass dropped below 3000 mg/L,and the SVI increased from 30 m L/g to about 60 m L/g.As the nitrogen content of the influent water decreases,the degree of sludge aggregation decreases,the particle size increases,but the floc structure becomes loose.The zeta potential of the sludge increases during the nitrogen limitation stage,but decreases during the nitrogen deficiency stage,and the hydrophobicity decreases as the nitrogen content of the influent water decreases.The analysis based on the XDLVO theory shows that the accumulation of microorganisms in the sludge during the nitrogen limitation and nitrogen deficiency stage is hindered by the energy barrier,which is not conducive to the accumulation.In the nitrogen restriction stage,the content of EPS and its components increase,and the nitrogen deficiency stage decreases,and the content of EPS and its components decreases,while the hydrophobicity of PN/PS,EPS and its components all show decrease.Correlation analysis shows that the reduction of the hydrophobicity of the EPS components leads to a decrease in the hydrophobicity of the sludge,which in turn leads to a decrease in the degree of aggregation.Combining FTIR and XPS,it is found that the decrease of EPS hydrophobic functional group and the change of protein secondary structure in nitrogen limitation stage are the reasons for the decrease of sludge aggregation.In the nitrogen deficiency stage,the content of hydrophobic functional groups and intermolecular hydrogen bonds of PS decreases,and the content of hydrophilic components increases,resulting in a further decrease in the degree of sludge aggregation and an increase in SVI.（2）The influence of phosphorus content in influent on the performance of activated sludgeThe removal rates of COD and TP in the reactor were stabilized above 90%and70-80%respectively.In the phosphorus deficiency stage,the concentration of NH₄⁺-N and TN in the effluent rose rapidly,and the removal rate decreased to about 60%and20%.With the decrease of the phosphorus content in the influent,the sludge biomass is maintained at about 4000 mg/L.Although the SVI is unchanged,the sludge aggregation degree gradually decreases.The sludge particle size decreases during the phosphorus deficiency stage and the sludge initially disintegrates.As the phosphorus content of the influent water decreases,the hydrophobicity and zeta potential of the sludge decrease significantly.The analysis based on XDLVO theory shows that the decrease of sludge hydrophobicity is the main reason for the decrease of sludge aggregation capacity.As the phosphorus content of the influent water decreases,the PN content and its hydrophobicity remain basically unchanged,while the PS content and its hydrophobicity gradually increases.Correlation analysis shows that the PS content and its hydrophobicity change is the main reason for the decrease of sludge hydrophobicity,and has nothing to do with PN.Combined with the XDLVO theoretical analysis,FTIR and XPS results,it is found that with the decrease of the phosphorus content in the influent,the protein-related amide I and II regions and the protein secondary structure in the EPS have not changed significantly,while the increase of the PS content,the increase in the content of hydrophilic functional groups,the decrease in the content of hydrophobic functional groups and intermolecular hydrogen bonds,leads to a decrease in the hydrophobicity of the sludge,resulting in a decrease in the sludge aggregation capacity.（3）The influence of hydrophilic carbon source on the performance of activated sludgeDuring the operation of the reactor,the removal rates of COD,NH₄⁺-N,TN and TP were maintained at approximately 90%,99%,70-80%and 70-80%,respectively.The concentration of TN in the effluent of the aspartic acid stage increased slightly,but the removal rate was basically maintained at more than 70%.As the hydrophilicity of the influent carbon source increases,the sludge biomass is maintained at 3000-4000 mg/L.Although the SVI remains unchanged,the degree of aggregation gradually decreases,the particle size gradually increases,and the structure becomes loose.As the hydrophilicity of the influent carbon source increases,the hydrophobicity and zeta potential of the sludge gradually decrease.The content of EPS and its components increases,while PN/PS gradually decreases.Correlation analysis shows that the degree of sludge aggregation is significantly related to its hydrophobicity,zeta potential.The hydrophobicity of sludge is significantly related to the content and properties of EPS and its components,and the zeta potential is significantly related to PN/PS.Combining the content of EPS and PS,hydrophilicity and hydrophobicity and functional group changes,it is found that with the increase of the hydrophilicity of the influent carbon source,the decrease of PN/PS,the increase of the hydrophilicity and electronegative functional group content of EPS and PS affect the sludge.Hydrophobicity and zeta potential,thereby reducing the degree of sludge aggregation.In summary,the limitation of nitrogen and phosphorus content and the enhancement of the hydrophilicity of carbon sources in influent water will lead to a decrease in the degree of sludge aggregation.The former two are mainly caused by the decrease in sludge hydrophobicity,while the latter is affected by the sludge hydrophobicity and zeta potential.The changes in EPS functional groups and protein secondary structure in the nitrogen limitation stage are not conducive to the expression of its hydrophobicity and reduce the hydrophobicity of the sludge.During the nitrogen deficiency stage,the increase in the content of the hydrophilic functional groups of PS and the decrease in the content of hydrophobic functional groups and intermolecular hydrogen bonds caused the hydrophobicity of the sludge to further decrease.In the phosphorus restriction of influent water,due to the increase of PS content,the decrease of hydrophobic functional group content and the increase of hydrophilic functional group content,the hydrophobicity of sludge gradually decreases.The enhancement of the hydrophilicity of the influent carbon source leads to an increase in the content of the hydrophilic and electronegative functional groups of the EPS and PS,thereby reducing the hydrophobicity and zeta potential of the sludge,which affects the aggregation ability of the sludge.