Impact of fiber properties on floc formation and turbidity removal

Abstract

The water treatment industry is interested in sustainable approaches to minimize chemical demand in the coagulation and flocculation process. In conventional physicochemical treatment, lower water temperatures act to slow down particle collisions, chemical reactions, floc formation, and floc settling rates. This study explored the use of fiber-based super-bridging agents to compensate for the effect of temperature on the coagulation-flocculation process. The efficacy of recycled cellulose fibers was evaluated at the lab scale (250 mL) at various temperatures, demonstrating high turbidity removal with both settling and screening as floc separation methods. For the fiber-based treatment, turbidity differences at temperatures near 5 °C, 10 °C, and 20 °C were minimal indicating that this technology is more effective than the conventional approach (coagulant and flocculant) which showed significant variations between temperatures. Furthermore, regardless of the fiber source and properties, different cellulose fibers were efficient in turbidity removal acting as a super-bridging agent. Additional experiments were conducted to understand how fiber length and diameter distributions influenced the performance of the fiber-based treatment. Fibers of length > 2000 µm and diameter < 100 µm were more efficient in reducing turbidity and translated to lower chemical demand (i.e., 20 % reduction in alum demand for a target water quality of 20 NTU) in the coagulation and flocculation process. This sustainable fiber-based water treatment approach has the potential to lower the operational cost of water treatment plants operating at different water temperatures as a function of the season and geographical location, though techno-economic analysis is required to validate this hypothesis.