Dissolved Air Flotation (DAF) System
The ALAR Dissolved Air Flotation [DAF] is a water clarification system that is excellent for high volumes of wastewater containing low percent solids. The ALAR DAF uses dissolved or inspirited air to concentrate and float fine solids, fats, oil and grease. The streamlined design uses minimal space while providing ample residence time.
The bridge of the DAF is equipped with a wiper blade that sweeps the surface sludge at a controlled rate. The concentrated float is moved into a sludge discharge trough and transferred to a sludge settling tank. The tank size should be capable of holding up to 10% of the original volume of incoming wastewater. (Example: 50,000gal incoming = 5,000 gal sludge tank).
Chemical separation is often necessary as a pretreatment (prior to the DAF) using a coagulant and flocculent polymer. These polymers break apart the emulsified solids from the water and allows them to concentrate into a buoyant material.
Flocculation or coagulation of solids is typically accomplished through the addition of cationic and/or anionic polymers; resulting in easier solid floatation and less dissolved air usage. In many cases, the use of polymers promotes stronger floc formation, lower float volumes, and lower float moisture content. If using a DAF sludge dewatering filter, such as an ALAR Auto-Vac, additional polymer dosage is not necessary for filtration.
The polymer-enhanced sludge will increase the filtration rates, and produce high quality effluent and drier solids.
DAF Rule of Thumb:
Screening: Although occasionally overlooked by designers, proper screening of large solids (e.g., product solids, trash) from an industrial wastewater reduces the solids loading on a DAF, can improve chemical conditioning downstream, and reduces maintenance requirements due to clogged valves, pumps, and piping.
Equalization: Proper equalization of an industrial effluent can provide a more constant and homogeneous flow to the DAF unit. This can improve the effectiveness of the chemical program used for coagulation and flocculation prior to the DAF unit. In addition, equalization reduces hydraulic surging which can be detrimental to system performance. In some cases, equalization tanks can be sized to allow operation of the DAF unit during specific time periods (e.g., a single plant shift), thus reducing operator labor costs.
Chemical Addition: Most chemical addition systems utilize either flocculation (floc) tubes or flash/floc tanks to introduce chemicals into the process flow. These systems must be designed to provide the proper amount of time and mixing energy for the chemical program employed. In addition, precise pH control will typically improve the performance of most chemical programs.
Float Handling: The pH adjustment chemicals, coagulants, and polymers used in a chemical program will impact the available methods of disposal and/or utilization of the float generated by a DAF system. The moisture content and volume of material recovered by a system will vary and must be considered when sizing transfer pumps, storage tanks, and dewatering systems (such as an ALAR Auto-Vac® or Micro-Klean®).
The ALAR Engineering Department designs each system to meet the customer's build-to specifications. ALAR begins with stock layouts, and customizes the auxiliary equipment according to the customer's specifications.
These stock layouts are available in PDF format. Contact ALAR for more information.