air into pressurized wastewater, and then releasing the pressure. Oil is usually
removed from wastewater mainly by using the dissolved air flotation (DAF) technique for bubble generation. The other flotation techniques are namely dispersed or
induced air and electrolytic flotation, which are less frequently used [30]. Brief
information on each technique is provided below.
Dispersed (Induced) Air Flotation (IAF)
This method is widely used for oil-water separation (oily sewage). In this technique,
air bubbles are formed by mechanically dispersing air injected under rotating
impellers or sparged by diffuser. The technology makes use of the centrifugal
force developed [31, 32].
Vacuum Flotation
In this system, air is first dispersed into the wastewater to achieve saturation
conditions. Partial vacuum is then applied to the wastewater. This results in the
generation of small air bubbles that attach themselves to the solid particles and make
them rise. Typically, a cylindrical tank maintained under vacuum and continuously
fed with wastewater is used for this purpose [29].
Dissolved Air Flotation (DAF)
DAF is very common method used for removal of suspended solids, oils, and other
contaminants by introducing small air bubbles into the wastewater containing the
suspended solids/free oil to be floated [33]. The fine air bubbles attach themselves to
the chemically conditioned particles and, as they rise to the surface, the solids float to
the surface with them, where they are mechanically skimmed and removed from the
tank. The air is dissolved under pressure of 3–6 bar. The air is introduced into a
recycle stream of treated wastewater after being passed through a DAF unit. This
supersaturated mixture of air and wastewater flows to a large flotation tank in which
the pressure release and generation of numerous small air bubbles occur. Mechanical
skimming or suction withdrawal is used to remove the thickened solids/oil particles
attached to the air bubbles. Chemicals such as polymers, aluminum sulfate, or ferric
chloride can be used to enhance flocculation and, therefore, the adhesion of bubbles
[11]. Flotation units can be provided for recycling to prevent the incoming solids to
be subjected to the shearing action of the pressurizing pump. By using this technique, free FOG, BOD/COD, SS, nitrogen, and phosphorus levels are reduced.
8 Vegetable Oil Refining Wastes
341
removed from wastewater mainly by using the dissolved air flotation (DAF) technique for bubble generation. The other flotation techniques are namely dispersed or
induced air and electrolytic flotation, which are less frequently used [30]. Brief
information on each technique is provided below.
Dispersed (Induced) Air Flotation (IAF)
This method is widely used for oil-water separation (oily sewage). In this technique,
air bubbles are formed by mechanically dispersing air injected under rotating
impellers or sparged by diffuser. The technology makes use of the centrifugal
force developed [31, 32].
Vacuum Flotation
In this system, air is first dispersed into the wastewater to achieve saturation
conditions. Partial vacuum is then applied to the wastewater. This results in the
generation of small air bubbles that attach themselves to the solid particles and make
them rise. Typically, a cylindrical tank maintained under vacuum and continuously
fed with wastewater is used for this purpose [29].
Dissolved Air Flotation (DAF)
DAF is very common method used for removal of suspended solids, oils, and other
contaminants by introducing small air bubbles into the wastewater containing the
suspended solids/free oil to be floated [33]. The fine air bubbles attach themselves to
the chemically conditioned particles and, as they rise to the surface, the solids float to
the surface with them, where they are mechanically skimmed and removed from the
tank. The air is dissolved under pressure of 3–6 bar. The air is introduced into a
recycle stream of treated wastewater after being passed through a DAF unit. This
supersaturated mixture of air and wastewater flows to a large flotation tank in which
the pressure release and generation of numerous small air bubbles occur. Mechanical
skimming or suction withdrawal is used to remove the thickened solids/oil particles
attached to the air bubbles. Chemicals such as polymers, aluminum sulfate, or ferric
chloride can be used to enhance flocculation and, therefore, the adhesion of bubbles
[11]. Flotation units can be provided for recycling to prevent the incoming solids to
be subjected to the shearing action of the pressurizing pump. By using this technique, free FOG, BOD/COD, SS, nitrogen, and phosphorus levels are reduced.
8 Vegetable Oil Refining Wastes
341