Characterizing polyaluminum chloride (PACl) coagulation floc using an on-line continuous turbidity monitoring system

This investigation applies an ordinary Nephelometric turbidimeter with a data acquisition unit in an on-line continuous turbidity monitoring system, called the Nephelometric turbidimeter monitoring system (NTMS). The floc diameter is measured by monitoring the turbidity oscillation amplitude with an NTMS, and digital image analysis is performed to elucidate the characteristics of the coagulation floc, including floc diameter, fractal dimension, strength factor and floc strength (σ, N/m2). The results of the Jar test reveal that under different mixing velocity gradients (G), the floc diameter is proportional to the standard deviation (SD) of the measured turbidity value. The close relationship between the strength factor, calculated from the SD value and the estimated theoretical floc strength (σ, N/m2) was also obtained. The fractal dimension increased with G and its value was between 1.29 and 1.38. Therefore, this on-line continuous turbidity monitoring system may be used in the future to obtain the SD of the measured turbidity values to predict the structural properties of the formed coagulation floc.