Backwash Water Recovery
Leopold® Clari-DAF® System
Normal Clarification Cycle
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 20 to 60 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. One—stage flocculation is used to cause the particles to collide and form floc particles.
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 20 to 60 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 periodically removed.