Basically, there are 3 different dissolved air flotation systems combining various clarification technologies. Depending on the type of feed waste streams, selection can vary in order to suit the processes. The list below will provide and discuss in details about the type of flotation systems in use in wastewater treatment plants.
Total Aeration of Raw Wastewater
In Direct Aeration, the incoming waste feed is pressurized and aerated. Thus, this system is only suitable to be used for application involving materials that can withstand the shearing force in the closed system and still remain stable. Control and optimization of this type of DAF system involve increasing amount of dissolved air by playing around with the pressure or by adjusting the flow rate of the incoming stream. For a new operator handling the plant, this might pose a challenge but once the operating parameters have been established, running the system would be a routine task. Sometimes it is also necessary to lower down the feed flow rate in order to prevent overload situations.
Partial Aeration of Raw Waste
Partial Aeration or at times referred to as “effluent recycle system” can be used especially for those materials that produce a fragile floc characteristics during separation that would otherwise easily disintegrate caused by the intense mixing happening in the pressurized vessel. In recycle systems, gas is dissolved and the stream is mixed with the feed inlet at a point just right before pressure is released. Combining both streams before entering the flotation area will allow more contact between the gas and solids and thus leads to better efficiency. Compared to the total aeration, partial recycle system would actually require larger space buildup because of the combined feed and generally operate on a much lower capacity.
Aeration of Recycle
This system is sometimes identified and called the dispersed air flotation unit and it is widely used in oily wastewater application especially in the major oil refinery industries. Clarification involves dispersing the air into a vessel mechanically entrained as fine bubbles into the solution containing both water and the oil particulate. Apart from treating wastewater, the dispersed flotation system can also be applied and used in water flooding for crude oil recovery but instead of using air for dispersion, the role is taken over by using natural gas.
Find out more about the operating principle of the Dissolved Air Flotation (DAF) System.