oils, surface properties of the suspended matter, degree of bubble dispersion, type of
chemicals added, temperature, and pH should also be considered when designing a
flotation system for effective oily wastewater treatment (Bennett and Peters 1988;
Edzwald et al. 1992).
Dissolved air flotation have shown its outstanding efficiency in oily wastewater
treatment with the oil removal performance of up to 95% (Rattanapan et al. 2011; da
Rocha e Silva et al. 2015). Several patents on the dissolved air flotation systems for
oily wastewater treatment have been filed since the last decade. The improvement
trends of the dissolved air flotation systems are towards three main areas, namely
(a) the reduction of the treated fluid aeration time, (b) the improvement of the
uniformity of the released gas stage distribution, and (c) the integration of the
dissolved air flotation with other purification processes (Eskin et al. 2015). Several
patents have claimed to have reduced the aeration time through the introduction of
pressure vessels with enhanced efficiencies (BKT Co. Ltd and I SAN Co. Ltd 2008;
Akim et al. 2010). To improve the uniformity of the released gas stage distribution,
some improvement designs such as flotation cells with diamond or cone-shaped
guides, ring aerator and propeller blade have been implemented to evenly distribute
the saturated fluid (Patrick 2008; Friedman et al. 2006; K-pack Korea Co. Ltd 2008).
In addition, the combination of the dissolved air flotation process with thin layer
sedimentation, ozonation, and filtration has also been introduced to enhance the
efficiency of the oily wastewater treatment (Woodley and Foong 2002; Crowell
2008).
Induced Air Flotation
Induced air flotation is another flotation mode for the oily wastewater separation in
which the bubbles are mechanically formed using a high-speed mechanical impeller
and an air injection system. The induced air bubbles normally exhibit the diameters
in the range of 1000 μm (Moosai and Dawe 2003). This flotation technique has low
retention time and can be as low as 4 min which allows small footprint (Moosai and
Dawe 2003). Besides, some researchers also suggested that the use of larger bubble
size also allows more compact flotation systems (Jameson 1999; Yan and Jameson
2004). In addition, induced air flotation can achieve the airflow rates of 100% in the
wastewater stream, whereas the amount of air supplied is typically about 5.6% for
dissolved air flotation. However, in practice, the high shear rate in the conventional
mechanical flotation cells tends to result in the breakage of fragile flocs and the
redispersion of particles before flotation can occur (Jameson 1999; Zabel 1992).
Besides, the large bubble size could also lead to poor bubble-particle collision
efficiency, and consequently results in the low separation performance (Li and
Tsuge 2006). Hence, this flotation mode is not as favorable as dissolved air flotation
in the oily wastewater applications.
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M. H. D. Othman et al.
chemicals added, temperature, and pH should also be considered when designing a
flotation system for effective oily wastewater treatment (Bennett and Peters 1988;
Edzwald et al. 1992).
Dissolved air flotation have shown its outstanding efficiency in oily wastewater
treatment with the oil removal performance of up to 95% (Rattanapan et al. 2011; da
Rocha e Silva et al. 2015). Several patents on the dissolved air flotation systems for
oily wastewater treatment have been filed since the last decade. The improvement
trends of the dissolved air flotation systems are towards three main areas, namely
(a) the reduction of the treated fluid aeration time, (b) the improvement of the
uniformity of the released gas stage distribution, and (c) the integration of the
dissolved air flotation with other purification processes (Eskin et al. 2015). Several
patents have claimed to have reduced the aeration time through the introduction of
pressure vessels with enhanced efficiencies (BKT Co. Ltd and I SAN Co. Ltd 2008;
Akim et al. 2010). To improve the uniformity of the released gas stage distribution,
some improvement designs such as flotation cells with diamond or cone-shaped
guides, ring aerator and propeller blade have been implemented to evenly distribute
the saturated fluid (Patrick 2008; Friedman et al. 2006; K-pack Korea Co. Ltd 2008).
In addition, the combination of the dissolved air flotation process with thin layer
sedimentation, ozonation, and filtration has also been introduced to enhance the
efficiency of the oily wastewater treatment (Woodley and Foong 2002; Crowell
2008).
Induced Air Flotation
Induced air flotation is another flotation mode for the oily wastewater separation in
which the bubbles are mechanically formed using a high-speed mechanical impeller
and an air injection system. The induced air bubbles normally exhibit the diameters
in the range of 1000 μm (Moosai and Dawe 2003). This flotation technique has low
retention time and can be as low as 4 min which allows small footprint (Moosai and
Dawe 2003). Besides, some researchers also suggested that the use of larger bubble
size also allows more compact flotation systems (Jameson 1999; Yan and Jameson
2004). In addition, induced air flotation can achieve the airflow rates of 100% in the
wastewater stream, whereas the amount of air supplied is typically about 5.6% for
dissolved air flotation. However, in practice, the high shear rate in the conventional
mechanical flotation cells tends to result in the breakage of fragile flocs and the
redispersion of particles before flotation can occur (Jameson 1999; Zabel 1992).
Besides, the large bubble size could also lead to poor bubble-particle collision
efficiency, and consequently results in the low separation performance (Li and
Tsuge 2006). Hence, this flotation mode is not as favorable as dissolved air flotation
in the oily wastewater applications.
360
M. H. D. Othman et al.