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

Abstract

Increasing demand for water poses a major challenge to the water treatment industry. Consequently, water treatment plants are expected to require larger separation units and use more chemicals. Physicochemical treatments produce flocs that are limited in size, which limits floc removal efficiency during gravitational separation. 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. The results also showed that fibers can allow a ~ 50 % reduction in coagulant. The benefits of fibers on floc size 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 with fibers, which drastically improved floc removal during flotation. The best turbidity removal after flotation was obtained when combining 2 mg of cationic polyacrylamide and 200 mg of softwood fibers/L. Fiber-based super-bridging agents can be introduced in existing water treatment plants to increase plant capacity, reduce the demand for coagulants/flocculants, and improve contaminant removal.