A^2/O工艺中好氧污泥絮体的分形结构与理化特征分析

Fractal Structure and Physicochemical Characteristics Analysis of Aerobic Sludge Floc in A^2/O Process

采用图像法和沉降柱法分别研究了A2/O工艺中好氧污泥絮体的形貌、粒度分布、低维分形维数和沉降速率、有效密度、空隙率以及质量分形维数,并尝试探讨了上述相关性质与这些污泥宏观操作性质(沉降、压缩、脱水和稳定性)相关的各种理化指标以及胞外高分子物质(EPS)的含量之间的变化关系.结果表明,污泥絮体呈现不规则的形貌,表面具有空隙.其有效密度一般随着其粒径的增加而降低,而空隙率和沉降速率却呈现与有效密度相反的变化趋势,这些均表明了污泥絮体的分形结构的存在.2次所采集的污泥絮体的中位直径分别为248.81、332.86μm,有效密度的平均值分别为0.0040、0.0072g·cm-3,自由沉降速率的平均值分别为2.67、4.79mm·s-1,空隙率的平均值分别为0.94、0.89,一维分形维数分别为1.03、1.19,二维分形维数分别为1.64、1.84,采用基于Logan经验公式的有效密度-最大直径的双对数关系确定的质量分形维数分别为1.74、2.29.尽管第2次所采集的污泥絮体较为密实,但其表面粗糙程度却比第1次的低.此外,研究中发现絮凝能力较高或负电荷较高的A2/O好氧污泥絮体具有高的SVI和ZSV值;分形维数较低的污泥具有高的剪切敏感性和低絮体强度,相应的污泥稳定性低;EPS总量高的污泥脱水性能差,EPS中蛋白质含量高的污泥其表面电荷也较高.

Image analysis method, free settling test were performed to determine the morphology, particle size distribution, free setting velocity, effective density, porosity and fractal dimensions in different topological spaces of aerobic sludge flocs in A2/O process. Then the physicochemical indices, corresponding to the sludge properties such as： settleability, compressibility, dewaterability and stability, were measured. Besides these, the extra-cellular polymeric substances （EPS） were extracted from sludge and classified as different components. The results showed that the sludge floc with irregular morphology was high porous. The effective densities of these sludge flocs generally increased with the increase of their size, but the porosities within the flocs and their free settling velocities decreased accordingly. The median diameters of the sludge flocs at two different sampling times were 248.81 μm, 332.86 μm, respectively. Their corresponding average effective densities were 0.004 0, 0.007 2 g·cm^-3, and average free settling velocities were 2.67 mm·s^-1, 4.79 mm·s^-1, and giving the average porosities of 0.94, 0.89. The dimensional analysis methods, based on power law correlations between floc perimeter, projected area and maximum length, were used to determine the one- and two-dimensional fractal dimensions （D1 and D2 ） of sludge flocs, giving D1 = 1.03 or 1.19, D2 = 1.64 or 1.84. The mass fractal dimensions （Dr） of these sludge flocs were determined by the bi-logarithm relations of effective density （based on Logan empirical equation）-maximum diameter which equaled to 1.74 or 2.29. The above results demonstrated that the second sample of sludge flocs was larger and more compact, but smoother than the first sample. Moreover, the results also showed that the sludge flocs in A^2/O process with high flocculating ability or high negative surface charge had high values of sludge volume index （SVI） and zone setting velocity （ZSV）, and low values of fractal dimensions in 2-D or 3-D spaces of sludge flocs correlated to high shear sensitivity and low floc strength, indicating low sludge stability. The high quantity of extra-cellular substances（EPS） in the sludge was related to poor dewaterability. As same as the conclusion of literature, the protein component in EPS could improve the negative surface charge of sludge flocs.