Dissolved Air Flotation

The DAF unit acts to remove the suspended solids (TSS) from the wastewater source. The DAF pump recirculates DAF effluent and flash mixes it with ambient air (aspirated on the suction side of the DAF pump). The air dissolves into the effluent under the pressure of the pump.

The air-water solution is then passed through a saturation tank to allow additional time for the air to dissolve and to remove any coalesced air bubbles. The solution is then expanded across diaphragm control valves leading into WSI’s proprietary diffusers inside the body of the DAF. By reducing the pressure of the solution rapidly (expanding), the dissolved air is forced out of solution in the form of micro-bubbles (90% of the bubbles formed are less than 10 µm in diameter).

The small bubbles collect under the biomass floc and float it to the surface, forming a thickened sludge blanket on the surface of the DAF that is raked directly into a sludge holding tank. The DAF provides greater thickening of the sludge as well as a reduced footprint from a conventional clarifier. Settled sludge is periodically pumped to the sludge holding tank via progressive cavity pump.

WSI DAF Designs

Stainless Steel Design

WSI DAF Systems, will be constructed from 3/16” stainless steel plate. The body is constructed with three independent cone bottom collection hoppers with pneumatically operated valve connection point. All process chambers of WSI DAF units are fabricated into the system. This includes: Two DAF floatation zones, scum collection hoppers with rail system, and effluent weir chamber.

Electrical & Controls

The system is provided with a main control panel that houses the Variable Frequency Drives (VFDs), motor starters, relays, Programmable Logic Controller (PLC) and Human Machine Interface (HMI). The VFDs are configured for the torque share operation mode. The panel enclosure is NEMA 4X with a side mount air conditioning unit to protect the control components in a wet, washdown environment. The HMI provides the press operational information in a graphical format to the operator and allows the adjustment of set points and parameters. The panel is provided with physical Hand-Off-Auto switches for all motors, enabling the system to be operated in an automatic mode as well as manually and overriding the logic controller.

When in automatic mode, the logic controller will flow pace the polymer injection rate to meet the operators desired dosage per feedback from the sludge magnetic flow meter.

Nikuni DAF Pumps

The Nikuni DAF pump is a high flow micro-bubble generator made from 316 stainless steel. The Nikuni pump is a highly precise pumping mechanism that generates microbubbles by utilizing two hydro-dynamic principles: negative pressure sucking both air and water simultaneously from each port; air effectively mixed into water; which properly produces pressurized nitrogen-enriched discharge.

Manuals

Saturation Tank

The saturation tank is constructed from 304L Schedule 10 pipe and is designed and fabricated in such a way that coarse bubbles from the air enriching process are collected and discharge into the DAF effluent chamber. This prevents coarse bubbles from disrupting the sludge blanket that is formed in the floatation zone.

Micro Bubble Distribution

The Micro bubbles generated from the Nikuni pump system are dispersed into the DAF by three to six precisely located white water injectors. These injectors are constructed out of 1.5” schedule 10 304 stainless steel pipe. These pipes run the width of the DAF and have a proprietary grooved design opening for proper distribution and enhanced flocculation. Each injector has a diaphragm valve that will allow the operator to dial in the precise distribution of white water.

Surface Skimmer System

The skimmer system is comprised of two parallel lengths of ultraviolet stabilized glass reinforced Nylon 6/6 chain with stainless steel paddles and buna rubber wiper assemblies. The skimmer system is powered by a helical worm gear motor that is VFD controlled. This allows the operator to have precise control over the speed at which the paddle skims across the top layer of the DAF. This is important as to not disrupt the gentle nature of the sludge blanket that is formed in the floatation zone of the DAF. The paddle is the width of the DAF body and gently pushes the skimmed sludge up a stainless steel beach and into a collection hopper. The ends of the stainless steel paddles are supported by UHMW blocks which ride on internal rails. This allows the paddles to interface the sludge blanket at a consistent elevation along the length of the DAF and gently collect the thickened sludge, pushing it into the sludge hopper.