Synergistic flocculation performance and underlying mechanisms of a novel bioflocculant flocan with coagulant iron salt

Flocculation is an integral part of wastewater treatment units and various flocculants have been employed to strengthen the flocs formation and produce clean water. Natural polysaccharides have been employed as eco-friendly bioflocculants for the treatment of turbid water. In the study, flocan is a named exopolysaccharide (EPS) isolated from a coastal mudflat with a high yield of 8.3 g/L. Flocan consisted of glucose, mannose , galactose , and glucuronic acid in a molar ratio of 2:3:1:1, along with pyruvate modifications. As the bioflocculant agent, flocan exhibited more than 85 % removal efficiency in kaolin suspension in terms of a concentration of 10 mg/L at pH 3. The addition of iron salts with flocan showed high flocculation efficiency in acidic kaolin suspension (99.37 %) and acidic coal wastewater (99.44 %). The carboxyl/hydroxyl groups and branched structure of flocan provided ionic interactions and promoted higher bridging between bioflocculants and negatively charged particles. Coagulants FeCl 3 enhanced the flocculating activity via neutralizing and stabilizing the residual negative charge of functional groups. Treatment with EDTA decreased the ionic interactions and reversed the flocculation significantly. Compared with the current bioflocculants, the superior production, low dosage, and excellent flocculating activity implied that flocan showed great potential in acidic wastewater treatment industrially. The coagulants/bioflocculants combination appears to be a promising and sustainable technology for wastewater flocculation. • A novel bioflocculant flocan with a high yield of 8.3 g/L was developed. • Flocan has comparable efficiency in acidic turbid/coal wastewater treatment . • A coagulant/bioflocculant combination method was used for wastewater treatment. • The maximum flocculation efficiency was 99.44 % mediated by the bridging mechanism.