[Extracellular Polymeric Substances of ANAMMOX Granular Sludge and Its Effects on Sludge Surface Characteristics]

The anaerobic ammonium oxidation(ANAMMOX) granular sludge in the EGSB reactor was divided into three groups according to particle size, which were R1 (0.5-1.4 mm), R2 (1.4-2.8 mm), and R3 (>2.8 mm). Extracellular polymeric substances (EPS) of different sizes from ANAMMOX granular sludge were extracted, and the EPS characteristics and their influence on the surface characteristics of ANAMMOX aggregates were analyzed. With the increased particle size of ANAMMOX granular sludge, the PS content was between (10.69±0.11)-(12.28±0.15) mg·g^-1, while the PN content increased from (56.88±0.86) mg·g^-1 to (98.59±2.10) mg·g^-1, and PN/PS increased from 5.32 to 9.05. The EPS functional groups and the content of three-dimensional fluorescent components of different size ANAMMOX granular sludge were different. As the granular sludge size increased, the value of α-helix/(β-sheet + random coil) gradually decreased from 0.60 to 0.43, which is beneficial to the hydrophobicity expression of the sludge. Due to the increased particle size of the granular sludge, the hydrophobicity of the sludge surface increased from 54.2% to 63.1%, and the Zeta potential increased from -41.2 mV to -31.5 mV. The increased hydrophobicity and surface charge are beneficial to the formation of sludge aggregates. EPS can enhance ANAMMOX sludge hydrophobicity and increase Zeta potential. The presence of PN in EPS is essential to this process.