Impact of fiber-based super-bridging agents on contaminant removal via settling and screening: microplastics, textile fibers, and turbidity

The water treatment industry relies heavily on coagulation and flocculation processes. This technology requires large amounts of chemicals and large settling tanks for floc separation. The flocs formed during conventional treatment are small (< 100 µm), which limit their removal by gravitational separation. To improve floc separation, fiber-based super-bridging agents have been added to the coagulation/flocculation process. When fibers were used in combination with a coagulant and flocculant, the flocs formed were 10 – 100 times larger, and settling was remarkably improved. The tested super-bridging agents also led to a 50% reduction in demand for both the coagulant and flocculant. The use of super-bridging agents is an effective technique for reducing turbidity and improving the removal of emerging contaminants in both synthetic and natural surface water. Formation of very large flocs with fibers also allowed the replacement of settling by screening without any effect on removal of monitored contaminants. Fibrous treatment removed up to 78% of turbidity when using a 5000 µm screen mesh size, compared to only 45% with conventional treatment (coagulant and flocculant, no fibers). Super-bridging agents also drastically improved microplastic removal. The fibrous treatment removed 80% of 15 µm polyethylene beads, compared to only 20% with the conventional treatment. Such low removal indicates potential concerns regarding the effective removal of smaller microplastics in existing water treatment plants.