Fiber-based super-bridging agents improve flotation and settling during water treatment

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1016/j.jwpe.2024.105499. This is version 1 of this Preprint.

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Authors

Badr Raissouni, Mohamed Lotfi Benkara, Mathieu Lapointe 

Abstract

Increasing demand for water poses a major challenge to the water treatment industry. To maintain their floc removal efficiency, water treatment plants are expected to require larger separation units and use more chemicals, namely, coagulants and flocculants. Conventional physicochemical treatments produce flocs that are limited in size, which limits floc removal efficiency via gravitation-based processes such as settling and flotation. Introducing fiber-based super-bridging agents has improved the floc size, which is 10–100 times larger than conventional flocs. Such improvements could lead to important gains in floc separation and ultimately increase the capacity of water treatment plants. This study analyzed the behavior and interaction of fibers under various coagulation/flocculation conditions to improve flotation and settling. Residual turbidity < 1.5 NTU was systematically achieved when the fibers were combined with conventional physicochemical treatments (alum and polyacrylamide). The results also showed that fiber-based super-bridging agents can allow a ~50 % reduction in coagulant. Three types of renewable fibers originating from the residues were selected for jar tests: softwood cellulose, brown fibers extracted from recycled cardboard boxes, and hemp fibers. The floc settling rate increased considerably when fibers were previously incorporated into the floc structure during aggregation, thus acting as a super-bridging agent. The benefits of fibers on floc settling velocity were particularly pronounced during suboptimal coagulation, as the injection of fibers compensated for poor coagulation conditions. Air bubbles during air flotation were also better incorporated into the larger and more porous floc structure obtained via the fibers, which drastically improved floc removal during flotation. Ultimately, such fiber-based super-bridging agents can be introduced in existing water treatment plants for wastewater and drinking water applications to increase plant capacity, reduce the demand for coagulants/flocculants, and improve contaminant removal.

DOI

https://doi.org/10.31223/X59Q4Z

Subjects

Chemical Engineering, Civil and Environmental Engineering, Engineering

Keywords

Floc separation, Coagulation and flocculation, water quality, Super-bridging agents, Settling, Flotation, Water Pollution, Coagulation and Flocculation, water quality, Super-bridging agents, Settling, Flotation, Water Pollution

Dates

Published: 2024-03-07 16:09

Last Updated: 2024-03-08 00:09

License

CC-BY Attribution-NonCommercial 4.0 International

Additional Metadata

Conflict of interest statement:
M. Lapointe applied for a patent on using fiber-based materials in water treatment. The authors declare no conflicts of interest.