Effects of pH and dosage on pollutant removal and floc structure during coagulation

This study developed an alum coagulation diagram for turbidity and Total Organic Carbon (TOC) removal using raw water instead of synthetic water. The study results indicate that the sweep flee area for raw water shifts into a more acidic region than that for synthetic water due to organic matter present in raw water. Since organic matter has a much higher surface area and negative charge than turbidity causing matter, it dominates coagulation and moves the sweep flee area into the acidic region. Turbidity and TOC removal regions mostly overlapped. The difference was in the restabilization region. The restabilization region was wider for turbidity removal than for TOC removal. This study also evaluated flee structures using fractal dimensions. For this purpose, three different methods [automatic image analysis (AIA) and small angle laser light scattering (SALLS)] were used to calculate fractal dimensions of flocs formed under different coagulation mechanisms. There was no difference detected between fractal dimensions of the flocs by the AIA method. The SALLS method was, however, able to detect the difference between the flocs. Flocs formed under sweep-flee coagulation were larger and more compact than those formed under charge neutralization. (C) 2001 Elsevier Science B.V. All rights reserved.