4.2 Article

Surface Chemical Groups of Flocs Are Key Factors for the Growth of Flocs in Sweep Coagulation: A Case Study of Surface Occupation by Humic Acid

Journal

ACS ES&T ENGINEERING
Volume 2, Issue 12, Pages 2301-2310

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acsestengg.2c00229

Keywords

alum floc; floc breakage; floc regrowth; humic acid; adsorption

Funding

  1. Key Research and Development Plan of the Ministry of Science and Technology
  2. [2019YFC1906501]
  3. [2019YFD1100104]

Ask authors/readers for more resources

This study investigated the effects of humic acid on the formation, breakage, and regrowth of alum flocs in the coagulation process. The results showed that humic acid can affect floc growth, and the extent of this effect depends on the dosage. Similar effects were also observed for natural organic matter in real surface water. Based on these findings, a mechanism for floc growth, breakage, and regrowth was proposed.
Coagulation is one of the most common processes in water treatment. Charge neutralization and sweep flocculation are recognized as the primary coagulation mechanisms. However, in-depth understanding on floc growth, breakage, and regrowth is still unclear. In this study, the formation, breakage, and regrowth of alum flocs with humic acid (HA) added either before coagulant addition or during the floc breakage stage were investigated. The floc size continuously decreased with the increase in floc breakage events, and eventually, to a stable value. The floc growth was not affected by the addition of HA before coagulant addition. However, it was prevented as HA was added during the breakage stage, and the prevention extent increased with HA dose. Similar results were also found for natural organic matter (NOM) from real surface water. These results suggested that HA/NOM can cover the active site on the floc surface, and the coverage differed for fresh flocs (newly precipitated) and old flocs (after breakage), which, respectively, represent the case in conventional coagulation and sludge recirculation. Based on these findings, the illustration of floc growth, breakage, and regrowth processes was put forward. We concluded that the charge neutralization and sweep flocculation mechanisms only explained the possibility of flocs approaching each other; whether flocs can connect to each other depends on the activated functional groups on the floc surface. The results in this study revealed the underlying mechanism of collision effectiveness in coagulation, complementing the existing understanding of the coagulation process.

Authors

I am an author on this paper
Click your name to claim this paper and add it to your profile.

Reviews

Primary Rating

4.2
Not enough ratings

Secondary Ratings

Novelty
-
Significance
-
Scientific rigor
-
Rate this paper

Recommended

No Data Available
No Data Available