Extracellular Polymeric Substances(EPS) And Surface Characteristics Of Anammox Granular Sludge

Anammox process has the advantages of no need for carbon sources,low energy consumption,and low sludge production.However,due to the slow growth and environmental sensitivity of anammox bacteria,the application of the anammox process was limited.The anammox granular sludge has attracted attentions from researchers because of its advantages of retaining a large amount of biomass,good settling performance and strong resistance to shock.Because the characteristics of extracellular polymeric substances?EPS?greatly affect the aggregation of granular sludge,it is of great theoretical and practical significance to study the characteristics of EPS in depth.In this paper,the anammox granular sludge with different morphology,different particle size and different salinity were investigated.The EPS composition and functional group characteristics,zeta potential and hydrophobicity,protein and monosaccharide composition,and the effect of salinity on the surface free energy of anammox granular sludge were analyzed.The purpose of the paper was to provide a theoretical basis and practical reference for the rapid granulation of anammox granular sludge and its efficient treatment of nitrogenous wastewater.The paper has obtained the following main conclusions:?1?Characteristics of anammox sludge and microbial communityThe particle size distribution of anammox granular sludge in EGSB reactor was generally normal distribution.With the increase of particle size of granular sludge,the"iron red"characteristics of anammox bacteria became more and more obvious.Candidatus jettennia was main genus of anammox granular sludge.As the particle size of granular sludge increased from 0.5-1.4 mm to>2.8 mm,the abundance of Candidatus jettennia increased from 33.06%to 60.33%.The salinity conditions were not conducive to granulation of anammox granular sludge.The increase of salinity led to the emergence of more salt-tolerant unclassified_fBrocadiaceae in the reactor,thereby maintaining the nitrogen removal capacity of the reactor.?2?EPS characteristics and composition of different forms of anammox sludgeThe PN/PS of EPS in anammox granular sludge,anammox flocculent sludge and activated sludge were 7.66,4.62 and 3.93,respectively.The higher content of?-sheet and C-?C/H?in the anammox granular sludge EPS promoted the accumulation of granular sludge.The flocculation efficiencies of EPS in anammox granular sludge,anammox flocculent sludge and activated sludge were 62.76%,35.57%and 17.27%,respectively,and the zeta potential was-23.5mV,-26.9 mV and-38.7 mV,the relative hydrophobicity were 53.42%,42.04%,and 36.76%.The EPS flocculation ability of the three sludges were consistent with the trend of the Zeta potential.430,392 and 24 proteins were obtained from EPS samples of anammox granular sludge,anammox flocculent sludge and activated sludge,respectively.The protein in anammox sludge EPS was mainly produced by cell decay and cell lysis.The anammox granular sludge has a greater number of ionic binding active proteins,the heterocyclic mixture binding active protein,organic ring mixture binding active protein,and cofactor binding active protein compared with anammox flocculent sludge.Both anammox granular sludge and activated sludge EPS contain 8 monosaccharides such as fucose,arabinose,galactose,glucose,xylose,fructose,galacturonic acid and glucuronic acid.The anammox granular sludge EPS contains a large amount of mannose,which is not detected in the activated sludge.?3?EPS and Surface Characteristics of anammox granular sludge with different particle sizesWith the increase of granular sludge size from 0.5-1.4 mm to>2.8 mm,the PS content was between?10.69±0.11?-?12.28±0.15?mg/g VSS,and the PN content was increased from 56.88±0.86 mg/g VSS to 98.59±2.10 mg/g VSS,and PN/PS increased from 5.32 to 9.05.The change in EPS composition was beneficial to the aggregation of granular sludge.As the particle size increase,the change of relative content of the protein secondary structure in EPS was favorable for the hydrophobicity of the granular sludge,thereby promoted the aggregation of the granular sludge.With the increase of granular sludge size,the change of hydrophobicity and Zeta potential of the sludge surface were beneficial to the accumulation of sludge.EPS enhanced the hydrophobicity and reduced the negative electric repulsive force of anammox granular sludge.The PN in the EPS play a important role in this process.The content of Na,K,Ca and Mg in EPS were positively correlated with the particle size of anammox granular sludge.The metal element in the EPS exists not only in ionic state but also in a form combined chemically with organic substance.The presence of extracellular metal ions reduced the surface repulsive force of the EPS,thereby promoted the aggregation of the granular sludge.?4?Analysis of EPS and surface free energy of anammox granular sludge with different salinitiesThe salinity promoted the production of polysaccharide,inhibited the production of protein in EPS,and thus changed the composition of EPS.The high salt condition inhibited the production of the?-sheet structure,which in turn affected the aggregation of the granular sludge.Under salinity conditions,the molecular weight distribution range of EPS was wider than that under salt-free conditions.With the increase of salinity,the Mw of anammox granular sludge EPS increased from 1.865×10⁴ Da to6.064×10⁴ Da,and Mw/Mn increased from 1.667 to 5.160.With the increase of salinity,the zeta potential decreased and the hydrophobicity increased on the surface of anammox granular sludge.Under the conditions of 0g/L,15g/L and 30g/L salinity,the aggregation ability of anammox granular sludge were20.4%,13.8%and 6.7%,respectively.The salinity conditions changed the relative proportion of?G_BL^LW and?G_BL^AB.Under salinity conditions,the?G_BL^AB play an important role in the granulation of anammox granular sludge.Under salinity conditions,the changes of W_A and W_R would increase the repulsive force of sludge accumulation,which was not conducive to the granulation of anammox granular sludge.