Turbidity fluctuation as a measure of floe size in a coagulation pilot study

摘要

A nephlometric turbidimeter was coupled with a data acquisition unit for online measurement of turbidity fluctuation, called the Nephelometric turbidimeter monitoring system (NTMS). According to Poison-distribution theory, the turbidity Standard Deviation (SD) calculated from the data collected by an NTMS follows the computed value obtained from the "turbidity fluctuation technique". Hence, using SiO_2 solution as test waters (10 NTU-1000 NTU), the experimental results reveal that it exists a good correlation between the turbidity SD and the square root of particle numbers (N~(1/2)). Furthermore, the NTMS was applied in the operation of a 500 ml/min coagulation pilot plant. The pilot plant was operated with a range of coagulation pH values, coagulant doses and velocity gradients (G). Floe sizes were determined from digital images. The result shows that the standard deviation of the turbidity measurement (turbidity SD) was correlated with floe size under the various operating conditions. Therefore, turbidity SD can be utilized to determine the appropriate operation conditions including the coagulation pH, dose and velocity gradient. This newly developed technology may be used in water treatment plants in the near future.