High-efficiency Treatment of Eutrophic Surface Water by Flocculation-microbubble Air Flotation

Aiming at algae blooms and phosphorus pollution in eutrophic surface water, a microbubble flotation device on basis of enhanced flocculation was developed for algae and phosphorus removal for emergency pollution control. The size and spatial distribution of microbubbles in the air flotation device were measured using a high-speed camera. The type, substance content and dosage of the coagulant were optimized to realize the efficient removal of algae and total phosphorus and reduction of turbidity. The results show that the developed air flotation device can generate stable microbubbles at the pressure of 0.32 MPa. The size of microbubbles increased gradually with the flow in ascending and horizontal directions, yet the mean diameter was within the optimal range of air bubbles for removal of algae (21.6-34.4 μm). When polyaluminum chloride (PAC) (alumina content: 29%, dosage: 40 mg·L^-1) was used as the coagulant, the removal efficiencies of algae, turbidity, total phosphorus, chlorophyll a, and COD in the eutrophic surface water reached 93.2±1.7%, 85.3±0.7%, 79.4±2.0%, 78.5±1.5% and 58.9±13.5%, respectively, after a flocculation time of 11.8 min, demonstrating the simultaneous effective removal of algae and phosphorus by the developed microbubble flotation device.