Dissolved Air Flotation (D.A.F)
A Dissolved Air Flotation Separator System (DAF System) is designed to break out oil from water through a chemical and physical process that is similar to a clarifier that is found in most wastewater plants. While the DAF systems vary widely throughout railroad environment wastewater treatment systems, the provided illustration shows common components of these DAF. The DAF may be proceeded by an oil water separator (OWS) or an equalization basin, or both. The DAF System (illustration 1) is typically made up of the following:
DAF System Illustration
The wastewater first flows into a chemical contact chamber (1) through the influent pipe where the waste is then introduced to a flocculant (2) that allows the waste to break free from the water. The wastewater is then pulled from the chemical contact tank and pumped, by the process pumps (3) into the air injection tank (4) where air from the air system is forced into the water. A coagulant is added as it enters the flotation chamber (5) for separation. The coagulant acts as a large net to bind all the pin floc and the micro air bubbles together so they can be collected by the surface and bottom skimming equipment (6) and placed into a sludge tank (7). The treated water then leaves the system through the effluent pipe.
The Proprietary Advantages of a Watermen Dissolved Air Flotation Units
The Watermen surge tank recirculation system is designed for 10-60-minute mixing or retention time for coagulant to react, reducing chemical dosage. Surge tank recirculation system also allows for pH adjustment, if necessary. Rectangular units with in-line mixing tubes do not allow enough time for full coagulant reaction and pH cannot be adjusted.
The Watermen DAF units have 2-3 times more volume of water in the separator tank than in a rectangular unit. This provides not only the lifting of the solids to the top surface with air, but enough height to utilize the hydraulic head pressure of 6 to 12 feet to separate the cleared water to the bottom of the separator unit. This reduces the amount of carryover of pin floc which raises TSS totals and fouls filters. The DAF unit also acts as a safeguard against slug flows of oily water.
In a rectangular unit there is not much depth for solids separation, so flocculant aid chemicals are used at double the rate used in Watermen DAF units to “over-flocculate” the solids to prevent carryover. The Watermen DAF units can be run in total recycle, meaning all the flow is pressurized and can be recirculated between the separator tank and surge tank for as long as necessary to add a higher chemical dosage, readjust pH, and reduce C.O.D, B.O.D., or TSS. Watermen DAF units can be run in full recycle to clean the unit itself. No other DAF system on the market has that advantage. Other units are only internally recycled and, if water is not up to standards, a recycle line to the head of the WWTP must be piped.
Watermen DAF’s have a self-cleaning feature so that when new effluent is brought in the discharge stays perfectly clean. Other DAF units usually produce poor quality water the first 5-10 minutes of discharge which has caused quality violations. Watermen DAF units can be packaged up to 200-gpm flow in a skid mounted unit, 22 feet by 11 feet with the chemical tanks, chemical pumps, circulation pumps, surge tank, air tank, recycle system, and electrical system included. The only requirements are the influent and effluent lines and electrical supply. Units can easily move from site to site. The footprint of other DAF units require that all of the components listed above be installed separately taking up to several months to construct. The Watermen DAF unit can be erected within 6 hours. In order to seal against the elements, the final process for Watermen DAF units is to be coated with Carboline epoxy paint.