[Effect of natural organic matter on coagulation efficiency and characterization of the flocs formed]

Coagulation is an efficient way to remove the natural organic matter in water. Our works primarily focused on the effect of natural organic matter on coagulation and the properties of the flocs formed. PACl25 was used as the coagulant in this research to simulate the process of coagulation, and typical substance of NOM, humic acid and citric acid were used to prepare the model water. The impact of NOM on the size, fractal dimension, Zeta potential of the flocs and residual aluminum in solution was explored. The experiment results showed that as the concentration of humic acid and citric acid increased in the experimental range, the size and growth velocity of flocs, Zeta potential and fractal dimension showed a tendency of decrease (when the concentration of humic acid increased from 0 mg x L(-1) to 10 mg x L(-1), citric acid increased from 0 micromol x L(-1) to 7 micromol x L(-1), the size of flocs before breakage was decreased by 34.2% and 53.1%, respectively, the Zeta potential decreased from about 10 mV to approximately -10 mV and -2.5 mV, the growth velocity of the flocs was decreased by 42.6% and 77.5%, and the fractal dimension declined by 0.08 and 0.094), which showed the occupying of the floc surface by NOM resulted in the decrease of its activity and compactivity. However, the residual aluminum was not affected by the decrease of coagulation efficiency.