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

This study developed an alum coagulation diagram for turbidity and Total Or ganic 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 pre sent 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 remova l regions mostly overlapped. The difference was in the restabilization regi on. The restabilization region was wider for turbidity removal than for TOC removal. This study also evaluated flee structures using fractal dimension s. For this purpose, three different methods [automatic image analysis (AIA ) and small angle laser light scattering (SALLS)] were used to calculate fr actal dimensions of flocs formed under different coagulation mechanisms. Th ere was no difference detected between fractal dimensions of the flocs by t he AIA method. The SALLS method was, however, able to detect the difference between the flocs. Flocs formed under sweep-flee coagulation were larger a nd more compact than those formed under charge neutralization. (C) 2001 Els evier Science B.V. All rights reserved.