The effect of supporting matrix on sludge granulation under low hydraulic shear force: Performance, microbial...

Granular sludge usually takes extracellular polymers (EPS) as matrices for colonizing microorganisms and maintaining structural stability. However, the low strength of EPS threatens the disintegration of granules, especially under low hydraulic shear force. To accelerate the formation and enhance the stability of granules, micro-sized melamine (ME) sponges (RA) and polyurethane (PU) sponges (RB) were screened out as matrix substitutes for developing aerobic granular biofilm (AGB) in this study. The superficial gas velocity was 0.8 cm s^-1. Both reactors achieved over 95% ammonium nitrogen removal efficiency within 10 days. During stabilization period, the chemical oxygen demand, total nitrogen and total phosphorus removal efficiencies were 90.5%, 70% and 95% in RA and 87.8%, 83% and 88% in RB, respectively. Confocal laser scanning microscopy (CLSM) detection revealed that β-polysaccharide was more concentrated in the outer layer in PU-AGB but uniformly dispersed in ME-AGB. The denitrifying phosphorus accumulating organisms (Flavobacterium) was dominant in RA, while the denitrifying glycogen accumulating organisms (Candidatus_Competibacter) was dominant in RB. Fluorescence in situ hybridization (FISH) analysis indicated that the microbial distribution in ME-AGB was relatively uniform, while there was a significant migration of functional microorganisms in PU-AGB. The super-hydrophilicity of ME and the high hydrophobicity of PU may be the main reasons for these differences. Overall, this study indicated that ME sponge is a more suitable material for supporting AGB than PU sponge.