emulsions particularly with oily wastewater as well as for oilfield produced water
treatment, besides being effectively and efficiently used in the treatment of wastewaters from various industries such as agri-food, textile, pharmaceutical, and petrochemical industries [15]. These processes offer various advantages such as high
selectivity, easy separation, high oil removal efficiency, easy maintenance, economic and fast operation, and stationary parts with compact modular construction
[15, 61, 62].
Membrane systems or membrane bioreactors (MBR) are used in some variations
on conventional activated sludge whereby a number of membrane modules, or
cartridges, are placed within the body of the reactor vessel. After biological treatment, effluent is pumped under static head pressure to the membrane unit in which
the solids and liquids are separated, the clean wastewater is discharged, and the
concentrated mixed liquor is pumped back to the bioreactor. The MBR can be
operated in either aerobic or anaerobic mode [11].
MBRs are typically used to obtain high-quality effluents free from contaminants
that can be reused and recycled in the process itself or in other applications [63]. In
another study, Masoudnia et al. [64] used MF consisting of polyvinylidene fluoride
membrane for separation of oil-water emulsions. A number of studies have been
conducted to treat oily wastewaters by employing various types of inorganic and
organic membranes [65–67]. Despite their low cost and various advantages, most
organic membranes cannot tolerate harsh conditions, for example, high temperature
and pressure, and fly ash that limit the membrane regeneration [68]. In contrast,
inorganic membranes such as ceramic membranes can work efficiently under high
temperatures and pressures due to their excellent thermal and mechanical durability
as well as their chemical resistivity. Therefore, they can be used under extreme
process condition for regeneration [69].
An MBR is very efficient in biomass separation, allowing the biomass concentration within the upstream reactor to be up to ten times greater than the concentration normally attainable in a conventional suspended growth system. Secondary
sedimentation is not required in MBR process and MLSS levels achieved can vary
from 12 to 17,000 mg/L. However, MBR system has very high operational cost
especially the energy cost of pumping. This cost may be minimized by applying
gravity feed of the wastewater. Another drawback of these systems which is the most
common one is fouling. The main forms of fouling are identified as the deposition of
solids as a cake layer, pore plugging/clogging by colloidal particles, adsorption of
soluble compounds, and biofouling. In order to control this problem, aeration and
backwashing have been tried, but these cause an additional production of wastewater. DAF can be used to scour and clean the membrane surfaces to prevent biofouling
[11]. Fouling in MBR systems can potentially be controlled by coupling coagulation
and flocculation to the process [70].
The space requirement for MBR is very low compared to conventional activated
sludge. This system is ideal for higher-strength, acidic, and lower-volume wastewaters. It is more useful in situations where a long solids retention time is required to
reach the necessary biological degradation of the pollutants. Likewise, wastewater
containing not readily degradable compounds, e.g., phenols, pesticides, herbicides,
8 Vegetable Oil Refining Wastes
351
treatment, besides being effectively and efficiently used in the treatment of wastewaters from various industries such as agri-food, textile, pharmaceutical, and petrochemical industries [15]. These processes offer various advantages such as high
selectivity, easy separation, high oil removal efficiency, easy maintenance, economic and fast operation, and stationary parts with compact modular construction
[15, 61, 62].
Membrane systems or membrane bioreactors (MBR) are used in some variations
on conventional activated sludge whereby a number of membrane modules, or
cartridges, are placed within the body of the reactor vessel. After biological treatment, effluent is pumped under static head pressure to the membrane unit in which
the solids and liquids are separated, the clean wastewater is discharged, and the
concentrated mixed liquor is pumped back to the bioreactor. The MBR can be
operated in either aerobic or anaerobic mode [11].
MBRs are typically used to obtain high-quality effluents free from contaminants
that can be reused and recycled in the process itself or in other applications [63]. In
another study, Masoudnia et al. [64] used MF consisting of polyvinylidene fluoride
membrane for separation of oil-water emulsions. A number of studies have been
conducted to treat oily wastewaters by employing various types of inorganic and
organic membranes [65–67]. Despite their low cost and various advantages, most
organic membranes cannot tolerate harsh conditions, for example, high temperature
and pressure, and fly ash that limit the membrane regeneration [68]. In contrast,
inorganic membranes such as ceramic membranes can work efficiently under high
temperatures and pressures due to their excellent thermal and mechanical durability
as well as their chemical resistivity. Therefore, they can be used under extreme
process condition for regeneration [69].
An MBR is very efficient in biomass separation, allowing the biomass concentration within the upstream reactor to be up to ten times greater than the concentration normally attainable in a conventional suspended growth system. Secondary
sedimentation is not required in MBR process and MLSS levels achieved can vary
from 12 to 17,000 mg/L. However, MBR system has very high operational cost
especially the energy cost of pumping. This cost may be minimized by applying
gravity feed of the wastewater. Another drawback of these systems which is the most
common one is fouling. The main forms of fouling are identified as the deposition of
solids as a cake layer, pore plugging/clogging by colloidal particles, adsorption of
soluble compounds, and biofouling. In order to control this problem, aeration and
backwashing have been tried, but these cause an additional production of wastewater. DAF can be used to scour and clean the membrane surfaces to prevent biofouling
[11]. Fouling in MBR systems can potentially be controlled by coupling coagulation
and flocculation to the process [70].
The space requirement for MBR is very low compared to conventional activated
sludge. This system is ideal for higher-strength, acidic, and lower-volume wastewaters. It is more useful in situations where a long solids retention time is required to
reach the necessary biological degradation of the pollutants. Likewise, wastewater
containing not readily degradable compounds, e.g., phenols, pesticides, herbicides,
8 Vegetable Oil Refining Wastes
351