DAF (Dissolved Air Flotation) Clarification
Leopold® Clari-DAF® System
Leopold® Clari-DAF® dissolved air flotation systems create millions of microbubbles to float solid particles to the surface of the water where they are removed as floating sludge, usually by mechanical skimming.
Normal Clarification Cycle
Chemical coagulants are introduced to improve flocculation efficiency.
The water is stirred to distribute the chemical coagulant among the solid particles to create particle collisions and cause the particles to flocculate.
Air under pressure is dissolved into water according to Henry’s Law of Dissolution. Reducing the pressure back to atmospheric via a special device creates millions of "microbubbles" approximately 30 to 100 microns in diameter. The microbubbles attach to floc in the water and float it to the surface for removal.
The process starts with the addition of chemicals and rapidly mixing the raw water with coagulants. Good coagulation is one of the most important factors affecting flotation. Two-stage tapered flocculation is used to cause the particles to collide and form flow particles using low tip speed to prevent floc from being sheared.
A saturator is used to take a fraction of the throughput and recycle it back to a pressure vessel. A compressor provides air to the tank and mixes with the water to collect in the tank reservoir as saturated air.
The aerated water is delivered to a distribution header that spans the width of the DAF cell. The header has a series of specially designed nozzles. The pressure drop through the nozzle produces a cloud of microbubbles approximately 30 to 100 microns in diameter.
The tiny bubbles rise through the coagulated water, capturing floc as they ascend to the surface. The tiny bubbles rise under laminar flow at a rate following a modified Stokes equation.
A blanket of sludge forms on the surface of the flotation cell. The blanket is supported from beneath by tiny air bubbles and is removed from the surface of the water by mechanical or hydraulic means.