Biological flocculants used for turbidity elimination during coagulation in water treatment

Research was investigated about bioflocculants (BFs) used for turbidity removal from kaolin clay solution and raw water based on jar tests. The results show that the elimination efficiency to turbidity from kaolin clay solution by BFs is 84%, over 5-19 mg/L, which is lower than 93% for Al₂(SO₄)₃ and 94% for Fe₂(SO₄)₃. From the variation of Zeta potential and pH, it was demonstrated that coagulation with BFs was governed by bridging flocculation. It was also observed that the addition of a small amount of inorganic salts (Fe or Al) could substantially enhance the coagulation efficiency. It appeared likely that the combined applications of inorganic salts and BFs resulted in an enhancement of charge neutralization and bridging flocculation. The case study shows that the combination of Fe and BFs can effectively eliminate turbidity from raw water at low dosage and neutral pH (by 94.6%). For biodegradable nature of produced sludge and reducing the health risk related to aluminum accumulation, BFs are considered to be a new type of environmental-friendly flocculants.