emulsions are broken and dispersed oils are removed. Typical treatment technology
is chemical treatment. In some applications, tertiary treatment is also used to remove
finely dispersed and soluble oil fractions. Ultrafiltration, biological treatment, or
carbon adsorption may be used as a tertiary treatment method.
Physicochemical (skimming of oil, air flotation, flocculation, coagulation) treatment to remove colloidal pollutants followed by biological treatment to degrade
dissolved organics is the most commonly used technique applied to vegetable oil
refining wastewater effluent [18].
Primary treatment used in the vegetable oil sector generally includes grease traps,
skimmers or oil-water separators for separation of floating solids, flow and load
equalization, and sedimentation for suspended solids reduction using clarifiers
[11]. The purpose of primary treatment is to remove free-floating oil and grease
and suspended solids. This will also reduce the BOD and COD concentration. High
correlation in terms of correlation coefficient (R
2 ) has been determined between
COD with O&G on a large scale by Saatci et al. [19] as 0.92 and by Aslan [20] as
0.90 for sunflower oil refining wastewaters and 0.81 for corn oil refining wastewaters
indicating that a decrease in O&G may highly reduce the COD values. This can be
achieved either by gravity settling or by dissolved air flotation (DAF).
Further, secondary treatment is applied and either chemical or biological processes are used. In general, the wastewater is well suited to biological treatment.
Biological treatment, typically anaerobic followed by aerobic treatment (activated
sludge, trickling filters, and rotating biological contactors) for reduction of soluble
organic matter (BOD), biological nutrient removal for reduction in nitrogen and
phosphorus, chlorination of effluent when disinfection is required, dewatering and
disposal of residuals, and, in some instances, composting or land application of
wastewater treatment residuals of acceptable quality may be possible [11].
The basic process of chemical treatment is coagulation [21, 22]. The efficiency of
treatment depends on the ratio of free oil to emulsified oil. The free oil can be easily
removed from wastewater by physical processes using coagulating agents, e.g., alum
and ferric chloride for phase separation [23]. Additional engineering controls may be
required to contain and neutralize nuisance odors [24, 25].
3.3.1 Unit Operations in Wastewater Treatment of Vegetable Oil
Refining
The wastewater to be treated should also be analyzed for total oil and grease,
including determination of the free, emulsified, and dissolved oil fractions. Although
oil-water separators are designed to remove free oil, they also remove solids.
Therefore, the solids content of the wastewater is important in overall system design.
Analyses should include TSS, volatile suspended solids (VSS), and settleable solids.
These analyses will help determine the amount and frequency of settled materials
that will need to be removed from the bottom of the oil-water separator and the
advisability of providing grit removal upstream of the oil-water separator.
8 Vegetable Oil Refining Wastes
339
is chemical treatment. In some applications, tertiary treatment is also used to remove
finely dispersed and soluble oil fractions. Ultrafiltration, biological treatment, or
carbon adsorption may be used as a tertiary treatment method.
Physicochemical (skimming of oil, air flotation, flocculation, coagulation) treatment to remove colloidal pollutants followed by biological treatment to degrade
dissolved organics is the most commonly used technique applied to vegetable oil
refining wastewater effluent [18].
Primary treatment used in the vegetable oil sector generally includes grease traps,
skimmers or oil-water separators for separation of floating solids, flow and load
equalization, and sedimentation for suspended solids reduction using clarifiers
[11]. The purpose of primary treatment is to remove free-floating oil and grease
and suspended solids. This will also reduce the BOD and COD concentration. High
correlation in terms of correlation coefficient (R
2 ) has been determined between
COD with O&G on a large scale by Saatci et al. [19] as 0.92 and by Aslan [20] as
0.90 for sunflower oil refining wastewaters and 0.81 for corn oil refining wastewaters
indicating that a decrease in O&G may highly reduce the COD values. This can be
achieved either by gravity settling or by dissolved air flotation (DAF).
Further, secondary treatment is applied and either chemical or biological processes are used. In general, the wastewater is well suited to biological treatment.
Biological treatment, typically anaerobic followed by aerobic treatment (activated
sludge, trickling filters, and rotating biological contactors) for reduction of soluble
organic matter (BOD), biological nutrient removal for reduction in nitrogen and
phosphorus, chlorination of effluent when disinfection is required, dewatering and
disposal of residuals, and, in some instances, composting or land application of
wastewater treatment residuals of acceptable quality may be possible [11].
The basic process of chemical treatment is coagulation [21, 22]. The efficiency of
treatment depends on the ratio of free oil to emulsified oil. The free oil can be easily
removed from wastewater by physical processes using coagulating agents, e.g., alum
and ferric chloride for phase separation [23]. Additional engineering controls may be
required to contain and neutralize nuisance odors [24, 25].
3.3.1 Unit Operations in Wastewater Treatment of Vegetable Oil
Refining
The wastewater to be treated should also be analyzed for total oil and grease,
including determination of the free, emulsified, and dissolved oil fractions. Although
oil-water separators are designed to remove free oil, they also remove solids.
Therefore, the solids content of the wastewater is important in overall system design.
Analyses should include TSS, volatile suspended solids (VSS), and settleable solids.
These analyses will help determine the amount and frequency of settled materials
that will need to be removed from the bottom of the oil-water separator and the
advisability of providing grit removal upstream of the oil-water separator.
8 Vegetable Oil Refining Wastes
339