自养菌和异养菌胞外聚合物对活性污泥絮凝特性的影响

为探讨自养菌和异养菌胞外聚合物(Extracellular polymeric substances,EPS)的差异及其对活性污泥表面及絮凝特性的影响,研究了有机负荷为0、0.30和0.74 kg·kg-1·d-1时,污泥松散附着胞外聚合物(loosely bound EPS,LB-EPS)和紧密粘附胞外聚合物(tightly bound EPS,TBEPS)的组分含量、形态、表面特性以及絮凝性能的差异,并就LB-EPS与TB-EPS对污泥絮凝特性影响的作用机理进行了探讨.结果表明,有机负荷越高,多糖含量越高,EPS总量及蛋白质含量越低.由三维荧光光谱测定结果可知,类富里酸物质为异养菌而非自养菌的代谢产物,且有机负荷越高,TB-EPS中的类富里酸荧光峰强度越大.自养和异养污泥的絮凝机理不同,自养活性污泥通过自养菌菌体自身生物絮凝作用形成密实的污泥絮体,LB-EPS与TB-EPS对其絮体形态、表面及絮凝特性影响较小;异养活性污泥絮体形态在TB-EPS提取后发生明显改变,TB-EPS在异养活性污泥絮体聚集时发挥着主要作用.包裹着LB-EPS的污泥表面负电荷多且疏水性差,不利于异养污泥生物絮凝.有机负荷越高,污泥表面Zeta电位负电性越强,相对疏水性(relative hydrophobity,RH)越小,污泥稳定性越差.

Influence of extracellular polymeric substances of autotrophic and heterotrophic bacterium on flocculating characteristics of activated sludge

To elucidate the difference of extracellular polymeric substances (EPS) between the autotrophic and heterotrophic bacterium and their influence on flocculating characteristics, the composition, content, morphology, surface and flocculating characteristics of loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) were studied under the organic loading rates of 0, 0.30 and 0.74 kg·kg^-1·d^-1. The mechanism of influence of LB-EPS and TB-EPS on the characteristics of activated sludge flocculation was also discussed. It was clear that the higher organic loading rate and polysaccharide content were, the lower amount of EPS and protein. The results of three-dimensional excitation emission matrix fluorescence spectroscopy revealed that the fulvic-like acid in EPS was the cell metabolic product of heterotrophic bacterium, rather than autotrophic bacterium; the higher organic loading rate was, the higher the fluorophore intensity of fulvic-like acid in TB-EPS. The flocculation mechanism of autotrophic and heterotrophic bacterium was different. The autotrophic-based activated sludge could form the dense flocs due to the bio-flocculation of autotrophic bacteria. Their floc morphology, surface and flocculating characteristics were not significantly affected by LB-EPS and TB-EPS. While the surface characteristics of heterotrophic-based activated sludge were changed obviously after the extraction of TB-EPS, which played an important role during their flocculation process. The sludge with LB-EPS, which had more negative charge and lower hydrophobicity, was unfavorable for the bioflocculation of heterotrophic-based activated sludge. With the organic loading rate increasing, the higher zeta potential electronegativity on sludge surface, the smaller relative hydrophobity (RH) and the worse sludge stability could be observed.