Extracellular Polysaccharide Properties Of Microbial Aggregates And Their Effects On Microbial Aggregate Performance

Microbial aggregates are important treatment units in wastewater bioreactors,and different forms of microbial aggregates have different structural forms and sludge characteristics.Extracellular polymer（EPS）has an important influence on the morphology and surface characteristics of microbial aggregates,which in turn affects sludge characteristics and treatment efficiency.The main substances of EPS are proteins and polysaccharides.At present,researchers have studied protein in depth,but there are relatively few studies on polysaccharides.Therefore,it is of great theoretical value and practical significance to deeply study the characteristics of extracellular polysaccharides in EPS and their influence on the performance of microbial aggregates.In this paper,three typical types of microbial aggregates,Anammox granular sludge,activated sludge and biofilm,were investigated as objects to investigate the performance of different microbial aggregates and the physical and chemical characteristics of extracellular polysaccharides.The effect of body properties,and enzymatic hydrolysis of different types of extracellular polysaccharides,analysis of the impact of different types of polysaccharides on the performance of microbial mud aggregates,in-depth study of the effects of extracellular polysaccharides on the performance of microbial aggregates,for wastewater biological treatment Engineering regulation provides a theoretical basis.The paper draws the following main conclusions:（1）Anammox granular sludge is iron red ellipsoidal particles with a particle size distribution of 1.0-4.5mm,an average particle size of 2.71mm,a biomass of 27.80 g/L,excellent sedimentation performance,and strong aggregation ability.The biofilm adheres to the carrier with a thickness of about 0.5 cm and a biomass of 6800 mg/L.It has strong adhesion and good aggregation ability.The activated sludge is light yellow flocculent,the average particle size is 153.2μm,the biomass is 4300 mg/L,and the settling performance is good.The hydrophobicity of Anammox granular sludge,biofilm,and activated sludge weakens in sequence,and the surface charge of the sludge increases in sequence.According to XDLVO theoretical analysis,the interface adsorption free energy of Anammox granular sludge,biofilm and activated sludge increases sequentially.The XDLVO curve shows that there is no obvious potential energy barrier for Anammox granular sludge,and the sludge is more conducive to aggregation.There is a certain potential energy barrier between activated sludge and biofilm,but the potential energy barrier of biofilm is smaller than that of activated sludge.（2）The total amount of Anammox granular sludge,activated sludge and biofilm EPS is 625.15 mg/g VSS,250.99 mg/g VSS,240.49 mg/g VSS,and the polysaccharide content is 78.20 mg/g VSS,43.14 mg/g VSS,43.76 mg/g VSS,respectively.Anammox granular sludge produced more EPS and polysaccharides than activated sludge and biofilm.The extracellular protein andα-polysaccharide of the three kinds of sludge aggregates are distributed in the core of the aggregate and are less in the edge.The spatial distribution of the two is similar,and theβ-polysaccharide is evenly distributed throughout the aggregate.Observing the microscopic morphology of the extracellular polysaccharides of aggregates,it was found that the extracellular polysaccharides of Anammox granular sludge exhibited gel properties,and the structure of the extracellular polysaccharides of activated sludge had good water holding capacity.The N-containing compounds in Anammox granular sludge extracellular polysaccharides,biofilm extracellular polysaccharides,and activated sludge extracellular polysaccharides increase in sequence,and the O-containing compounds decrease in sequence.Functional group analysis found that the content of alkane organics,uronic acid and sulfate in the extracellular polysaccharide of Anammox granular sludge was higher than that of activated sludge and biofilm.Alkane organics are conducive to the expression of the hydrophobicity of aggregates,and can promote the aggregation of aggregates.Uronic acid and sulfate radicals are conducive to the formation of gels and bridging effects,and contribute to the structural stability of aggregates.（3）After the Anammox granular sludge was hydrolyzed withα-amylase,the sludge was slightly swollen,and the particle strength decreased by 1.33%.After theβ-amylase hydrolysis,the sludge was slightly disintegrated,and the particle strength decreased by 10.67%,indicating thatβ-polysaccharides were The structural stability of the sludge has an important influence,andβ-polysaccharide plays a skeleton role in the sludge aggregates.The enzymatic hydrolyzed sludge found that the sludge hydrolyzed byα-amylase had a hydrophilic layer,and the aggregation ability decreased by 34.62%.Afterβ-amylase hydrolysis,the biological density of the sludge outer layer became smaller and the aggregation ability decreased by 5.83%.After enzymatic hydrolysis,the surface hydrophobicity index and flocculation capacity of the sludge were significantly reduced,and the Zeta potential had no significant effect.From the surface thermodynamic analysis,it can be seen that the enzymatic hydrolysis increases the interface adsorption free energyΔG＿adh on the sludge surface,the gravitational effect on the sludge surface is weakened,and the repulsive effect is enhanced.The XDLVO curve shows that the enzymatic hydrolysis increases the potential energy barrier of the sludge,and the potential energy barrier curve ofα-polysaccharide hydrolysis is higher than that ofβ-polysaccharide hydrolysis.After enzymatic hydrolysis,the content of protein in EPS did not change significantly,and the content of polysaccharide decreased significantly.After the hydrolysis ofα-polysaccharides,the content of alkane functional groups decreased,and the strong hydrophobicity promoted the mutual adsorption between microbial aggregates,indicating thatα-polysaccharides had an adsorption effect.After the hydrolysis ofα-polysaccharide,the decrease of hydroxyl content was significantly greater than that ofβ-polysaccharide.The hydroxyl group can bridge with divalent cations such as Ca²⁺and Mg²⁺to form a bridging effect,indicating thatα-polysaccharide has a bridging effect in microbial aggregates.