pH值对活性污泥胞外聚合物分子结构和表面特征影响研究

为明确胞外聚合物（extracellular polymeric substances,EPS）对污水污泥性质的影响机制,通过改变pH值,考察了市政废水和饮料废水2种活性污泥胞外聚合物组分变化,采用红外光谱对比分析了pH值对EPS分子结构的影响,并通过胶体滴定测定其表面电荷,最终结合活性污泥提取EPS前后扫描电子显微镜观察,从宏观上佐证了表面特性和分子结构分析.结果表明,强酸条件下（pH 3）,可提取EPS比中性条件下时下降50%,其中多糖下降约30%,蛋白质下降约65%～70%;在强碱条件下（pH 11）,可提取EPS比pH 7时升高20%～30%,其中多糖升高约15%,蛋白质升高20%～50%.红外光谱分析表明,羟基在强酸强碱条件下均发生了变化,羧酸、多聚糖、酚类和蛋白质肽键在强酸条件下（pH 3）消失;胶体滴定结果表明,2种污泥提取EPS表面负电荷随pH上升而下降;扫描电镜分析表明,相对于碱性条件下,酸性条件使活性污泥中微生物细胞更易于破碎.pH值可改变活性污泥EPS组分、浓度以及其中基团组成,从而改变EPS表面特性,最终导致污泥状态改变.

Effects of pH on the Surface Characteristics and Molecular Structure of Extracellular Polymeric Substances from Activated Sludge

To understand the mechanisms of extracellular polymeric substances (EPS) influencing sludge characteristics, change in constituents of extractable EPS from municipal wastewater and beverage wastewater sludge at varied pH was investigated. Fourier transform infrared (FTIR) spectrophotometry was used to analyze the effect of pH on the functional groups in EPS. Surface charge was measured by colloid titration. Finally, surface charge measurements and molecular structure analysis were evidenced by Scanning Electron Microscopy (SEM) observation of the sludge samples before and after EPS extraction at different pH. The results show that at strong acid condition (pH3), the extractable EPS are lower than those at neutral condition by about 50% including 30% decreasing in polysaccharides and 65%~70% in protein. At strong alkali condition (pH11), the extractable EPS are higher than those at neutral condition by 20%~30% including about 15% increasing in polysaccharides and 20%~50% in protein. Hydroxyl changes both at alkali and acid condition. Carboxyl acid, polysaccharides, phenolic groups, and amino groups in protein disappear at acid condition (pH3). Negative surface charge of EPS from both of the sludges increases with pH. Observation of sludge by SEM indicates that compared with alkali condition, acid condition is more effective in making the bacterial cell broken. The results suggest that pH changes the constituents, concentration and functional groups in EPS, consequently the surface charge of EPS. As a result, sludge characteristics are changed.