The coagulant dosage of an existing water plant is mainly determined based on the experience of water treatment process and influent/effluent water quality indexes that have time hysteresis effects. To solve this problem, the effect of coagulant dosage on a number of parameters used to evaluate the efficiency of flocculation in a setup was determined by using the micro-vortex flocculation technology in conjunction with the investigation of the relation between the equivalent diameter and the fractal dimension. By means of the machine vision system and computerized analysis, the effects of floc quantity, floc equivalent diameter and fractal dimension can be assessed. The correlations of these parameters with turbidity and ζ potential of the settling water, taken as measures for effluent quality, were explored. The study results show that the optimal flocculation effect with a turbidity removal rate of 97.9% is achieved at the poly-aluminum chloride dosage of 20 mg/L. Meanwhile, a power exponential relation between the floc equivalent diameter and the fractal dimension was established with a correlation coefficient R2 of 0.826; relations among the effluent turbidity and the floc quantity, equivalent diameter, fractal dimension were established with a correlation coefficient R2 of 0.982, 0.851, and 0.875, respectively; equations between the ζ potential and the floc quantity, equivalent diameter, fractal dimension were also established where the correlation coefficient R2 were 0.868, 0.879, and 0.942, respectively. These results may provide excellent reference data for water plants to feed back the coagulant by floc performance parameters, which could relieve the hysteresis effect efficiently.
Keywords: Micro-vortex flocculation; equivalent diameter; floc performance parameter; fractal dimension; machine vision.