Most of the countries around the world have their own environmental standards.
The standard of effluents discharge can be defined as the concentration limits of the
specific contaminant that is permissible to be directly discharged into the water
stream. With this standard, enforcement control is much easier to be conducted and
early prevention of water pollution can be achieved. The permissible oil and grease
discharge concentration varies in different countries. For instance, in Unites States of
America, the maximum limits of oil and grease discharge are 42 mg/L day and
29 mg/L month (Fakhru’l-Razi et al. 2009), whereby the Malaysian Department of
Environment sets the maximum limit of oil and grease discharge at 1 mg/L for
standard A (the effluent discharger at the upstream of water supply intake) and
10 mg/L for standard B (the effluent discharged at the downstream of water supply
intake) (Environmental Quality Act and Regulations Handbook 2009). The standard
limits may also vary based on the types of industry. For example, Indonesia has set
its discharge standards based on the type of industry, in which the limits are 5 mg/L,
25 mg/L, and 30 mg/L for leather tanning and textiles, oil refining and urea fertilizer,
and palm oil industries, respectively. On the other hand, Singapore has set the
standard limits based on water use in which the limits vary from 5 to 30 mg/L
(Tong et al. 1999).
11.2 Conventional Oily Wastewater Treatment Methods
11.2.1 Flotation Treatment
Flotation treatment is a process of removing the suspended oil particles from the
wastewater by bringing the oil particles to the surface of the aqueous medium. The
froth layer containing the oil particles forms on the surface of the aqueous medium
which will then be skimmed and separated from the aqueous medium. The use of
flotation in oily wastewater treatment have been attracting much attention owing to
the high separation efficiency, availability of the flotation equipment with large
processing capacity, and low sludge generation (Rubio et al. 2002; Yu et al.
2017). In addition, the flotation treatment also requires low capital investment and
operational costs (Li et al. 2007).
Dissolved Air Flotation
Dissolved air flotation is the most commonly used flotation technique for the
industrial oily wastewater treatment (Yu et al. 2017; Zouboulis and Avranas
2000). In this technique, the tiny air bubbles are injected into the wastewater
containing oil particles in which the air bubbles attach to the oil droplets. The
adhesion of air bubbles increases the buoyancy of the oil particles, and consequently
leads to the rapid movement of the oil particles to the surface of the aqueous
wastewater. Dissolved air flotation is effective in removing oil droplets with the
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M. H. D. Othman et al.
The standard of effluents discharge can be defined as the concentration limits of the
specific contaminant that is permissible to be directly discharged into the water
stream. With this standard, enforcement control is much easier to be conducted and
early prevention of water pollution can be achieved. The permissible oil and grease
discharge concentration varies in different countries. For instance, in Unites States of
America, the maximum limits of oil and grease discharge are 42 mg/L day and
29 mg/L month (Fakhru’l-Razi et al. 2009), whereby the Malaysian Department of
Environment sets the maximum limit of oil and grease discharge at 1 mg/L for
standard A (the effluent discharger at the upstream of water supply intake) and
10 mg/L for standard B (the effluent discharged at the downstream of water supply
intake) (Environmental Quality Act and Regulations Handbook 2009). The standard
limits may also vary based on the types of industry. For example, Indonesia has set
its discharge standards based on the type of industry, in which the limits are 5 mg/L,
25 mg/L, and 30 mg/L for leather tanning and textiles, oil refining and urea fertilizer,
and palm oil industries, respectively. On the other hand, Singapore has set the
standard limits based on water use in which the limits vary from 5 to 30 mg/L
(Tong et al. 1999).
11.2 Conventional Oily Wastewater Treatment Methods
11.2.1 Flotation Treatment
Flotation treatment is a process of removing the suspended oil particles from the
wastewater by bringing the oil particles to the surface of the aqueous medium. The
froth layer containing the oil particles forms on the surface of the aqueous medium
which will then be skimmed and separated from the aqueous medium. The use of
flotation in oily wastewater treatment have been attracting much attention owing to
the high separation efficiency, availability of the flotation equipment with large
processing capacity, and low sludge generation (Rubio et al. 2002; Yu et al.
2017). In addition, the flotation treatment also requires low capital investment and
operational costs (Li et al. 2007).
Dissolved Air Flotation
Dissolved air flotation is the most commonly used flotation technique for the
industrial oily wastewater treatment (Yu et al. 2017; Zouboulis and Avranas
2000). In this technique, the tiny air bubbles are injected into the wastewater
containing oil particles in which the air bubbles attach to the oil droplets. The
adhesion of air bubbles increases the buoyancy of the oil particles, and consequently
leads to the rapid movement of the oil particles to the surface of the aqueous
wastewater. Dissolved air flotation is effective in removing oil droplets with the
358
M. H. D. Othman et al.