[Influence of Activated Sludge Surface Properties on Flocculating Settling and Effluent Suspend Solid]

In this paper, the influence of the surface properties of the activated sludge on flocculating settling and ESS was studied in seven different sewage treatment plants in Beijing, such as the sludge volume index (SVI), the protein/carbohydrate (P/C) ratio in extracellular polymeric substance, Zeta potential, two-dimensional fractal dimension(D_2f). The relationships between the surface properties of the activated sludge and flocculation ability (FA) or effluent suspend solid(ESS) were also analyzed. The results showed that no obvious correlation was obtained between SVI and FA or ESS, but obvious negative correlation between the FA and ESS (R²=0.787) was observed. When the P/C increased from 1.28 to 25.34, the FA could increase from 0.19 to 0.73 correspondingly, but the ESS decreased from 14.89 mg·L^-1 to 6.08 mg·L^-1. This was because the amino acids in protein with positive charge could neutralize the negative charge on the surface of floc, the increase of protein ratio in EPS could decrease the absolute value of Zeta potential, which made a contribution to form more stable floc structure, and improved the ability of flocculation. Moreover, the Zeta potential had a positive correlation with FA but a negative correlation with ESS. The absolute value of Zeta potential decreased by 1 mV, FA increased by 0.059 and ESS decreased by 0.934 mg·L^-1 correspondingly. In addition, there was an obvious index correlation (R²=0.935, P<0.01) between D_2f and FA; While D_2f increased from 1.10 to 1.45, FA could increase by 4.3 times and ESS decreased linearly (R²=0.868).