Raw water clarification by flotation with microbubbles and nanobubbles generated with a multiphase pump.

Area of Science:

• Environmental Engineering
• Fluid Dynamics
• Water Treatment Technologies

Background:

• Conventional water clarification methods face challenges with efficiency, especially at high hydraulic loads.
• Microbubble (MB) and Nanobubble (NB) generation typically requires specialized equipment.
• Optimizing bubble size and concentration is crucial for effective flotation.

Purpose of the Study:

• To investigate the generation of microbubbles (MBs) and nanobubbles (NBs) using a centrifugal multiphase pump for raw water clarification.
• To compare the efficiency of flotation using pump-generated bubbles (F-MP) against traditional lamellar settling.
• To assess the performance of F-MP under high hydraulic loads in a real-world water treatment plant (WTP).

Main Methods:

• Air was injected into a centrifugal multiphase pump to produce MBs and NBs.
• Gas dispersion parameters (bubble Sauter diameter, air holdup, bubble surface area flux, NB concentration) were measured under optimal pump pressure (4 bar).
• A comparative study was conducted between F-MP and lamellar settling at a WTP in Brazil.

Main Results:

• Optimal conditions yielded a bubble Sauter diameter of 75 μm, air holdup of 1.2%, bubble surface area flux of 34 s⁻¹, and NB concentration of 1 × 10⁸ NBs mL⁻¹ (220 nm).
• F-MP demonstrated higher separation efficiency than lamellar settling at high hydraulic loads (9-15 m h⁻¹).
• F-MP achieved a final turbidity of 2 NTU from a feed of 10-25 NTU, surpassing the WTP's target of 5 NTU, without polymer addition.

Conclusions:

• Centrifugal multiphase pumps can effectively generate MBs and NBs for water flotation.
• F-MP offers a superior alternative to lamellar settling for raw water clarification, particularly under high hydraulic loads.
• The use of pump-generated bubbles opens new avenues for research and application in advanced flotation technologies.