How the Natural Organic Matter to Coagulant Ratio Impacts on Floc Structural Properties

Abstract

Periods of elevated natural organic matter (NOM) loadings at water treatment works (WTW) can lead to operational problems as a result of deterioration in floc structural quality. This study used a range of diagnostic tools to evaluate floc structure with increasing organic fraction in the floc. It was observed that when the organic fraction in the floc went significantly over a mass ratio of 1 mg of DOC to 1 mg of Fe (coagulant), the floc size, settling velocity, fractal dimension, and strength were seen to decrease even when the NOM removed during coagulation remained high. A model was proposed to explain these changes that was dependent upon the adsorption of NOM on primary particle surfaces. The operational significance of these results suggests that for the coagulant under investigation the correct coagulant dose must be applied to give good floc structure.

Characterization of kaolin flocs formed by polyacrylamide as flocculation aids

“…An increased value of strength factor indicates that flocs are better able to withstand shear force and thus should be considered stronger than those with a lower factor. Meanwhile, an increase in the recovery factor shows that flocs have better regrowth ability after high shear (Jarvis et al, 2005c).…”

Exploring How Organic Matter Controls Structural Transformations in Natural Aquatic Nanocolloidal Dispersions

“…Many complementary investigative techniques have been deployed including sedimentation (17), rheology (18b, 19a), electrokinetics (18b, 19a), imaging (16,25,26,27,28), and various forms of light scattering (20), particularly photon correlation spectroscopy (13,15,29). One unintentional consequence of the use of optical techniques (and indeed sedimentation and some atomic force microscopy) is that the length scales (ie, particle sizes) probed are typically hundreds to thousands of nm.…”

Evaluation of enhanced coagulation coupled with magnetic ion exchange (MIEX) in natural organic matter and sulfamethoxazole removals: The role of Al-based coagulant characteristic

“…Boller and Blaser [39] declared that the small particles generally have lower solid/liquid separation efficiencies than the larger ones. It has also been claimed by Jarvis et al [40] that smaller sizes of organic matter flocs would pose a challenge to the sedimentation process and this could explained the inferior SMX removal ability of Al 13 . The higher of the Al 13 dosage, the smaller aggregates obtained in the steady stage.…”