HomeMy WebLinkAbout1.34 DAF description.pdfDissolved Air Filtration (DAF) Unit
The Double -DAFTM Solids Thickener is designed to recover solids from plant wastewater
prior to discharge to a sewer system. Influent water is pumped into the coagulation
chamber of the DAF tank. Coagulants are then mixed using high speed mixers to create
pin floc (granular type of sludge particle). Flow is then directed up and through a port
into the flocculation chamber. Here polymer is thoroughly mixed using low speed mixers
to enhance flock formation. Flow out of the stilling chamber is directed upward over the
downstream baffle wall allowing the more dense solids to settle to the bottom and the
floatable solids to rise. Micro - AireTM aerated recycle enters via VanAire supplied
breakout valves immediately downstream from the baffle. The flow path created by the
baffle leaves the floc /solids in a bubble -rich zone near the surface so the floatable solids
need only travel about a foot to the surface. This minimizes the amount of buoyancy lost
due to the re- absorption of bubbles into the wastewater.
As the wastewater stream continues on the flow path through the DAF Thickener, it
flows through the part of the DAF Thickener unique to the Double -DAFTM system. A
cross -flow plate -pack, which is located mid -DAF Thickener, provides a damping effect
on the water in the DAF Thickener, and provides a surface for the coalescing of bubbles
and microscopic particles. As the bubbles and particles build up on the underside of the
plates, the particles agglomerate into larger particles, eventually floating to the surface.
Our cross -flow design does not affect the normal flow patterns in the DAF Thickener; so
hydraulic loading rates are not affected. A second hit of Micro - AireTM aeration is
administered just below the plate pack for enhanced recovery /removal of water
contaminates and late forming floc. The second recycle air hit imitates and has the
effectiveness of the second DAF Thickener is a series system.
Floated solids are then skimmed from the surface of the DAF Thickener using a variable
speed concurrent skimming system for maximum float density. A limit switch stops the
flights on the beach plate for an adjustable period of time to allow free water to drain
from the float. A pitched false floor concentrates settled solids near four blow down
valves where they can be removed via manually or automatically controlled "blow down"
valves(s). There are also blow down valves located in each chamber and near the effluent
end for removal of settled solids from this area. Floated solids are held in the float
hopper, which is located near the effluent end of the DAF Thickener. A bridle pipe is
provided to mount a level sensor to start and stop a customer supplied float pump, and to
stop the skimming flight system on a float hopper high level.
An adjustable rectangular weir located between the float hopper and the clear well
controls the level of DAF Thickener. The weird is adjusted to maintain DAF water at the
front edge of the beach during low flow. Water passing over the weir exits the clarifier
through the DAF effluent pipe.