C. Nanofiltration:
Nano filtration is mainly utilized for removal of selective dissolved organichydrocarbon pollutants and hardness at moderate pressure: 3–20 bar. Some features
like design and operation, as well as physical dimensions of membrane elements of
nanofiltration are almost same as reverse osmosis. Hence, nanofiltration membranes
can be accommodated in reverse osmosis modules. But main difference between
these two filtrations is that salt and metal abandonment is higher with higher
operating pressures. The particle size of the retentate ranges from 0.001 to
0.01 μm and the hydraulic permeability is 1.5 to 30 L/m
2 hr-bar in nanofiltration.
This membrane may be composite or porous asymmetric. Commercial nanofiltration
membranes possess a fixed charge that causes ions to be separated based on size,
electrical effects and ion interactions. However, it can replace reverse osmosis in
wastewater treatment due to its less energy requirement and higher flux.
Nanofiltration membranes usually exhibit greater efficiency in rejecting hydrophilic
compounds than the hydrophobic ones. Around 90–95% pollutant rejection can be
achieved by this process (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017).
D. Reverse Osmosis:
Reverse osmosis uses a semipermeable membrane where dissolved solids, ions,
pyrogens, nitrate, etc., are removed from wastewater and the retained particle size
varies from 0.0001 to 0.001 μm. Reverse osmosis is operated when the pressure
difference is higher than the osmotic pressure (5–120 bar). It is a most commonly
used process for desalting of oily wastewater. The reverse osmosis membrane is
nonporous, asymmetric or composite and has a hydraulic permeability of
0.05–1.5 L/m
2 hr-bar. After reverse osmosis, the water may be reused in the
petroleum industry. The reverse osmosis membranes require pre-treatment by
microfiltration or ultrafiltration, because they have very fine pores which are easily
plugged by suspended solids. The concentration of oil and grease in the reverse
osmosis feed water is recommended to be less than 0.1 mg/L. The salt rejection
capacity using this technology may be as high as 99%. It is successfully used
worldwide for wastewater treatment but requires high-energy consumption in
terms of pressure (International Petroleum Industry Environmental Conservation
Association 2010; Shahryar 2017).
Membrane Bio-reactor
Membrane bio-reactor is a membrane-based biological treatment where a membrane
process (microfiltration) combines with a suspended growth process (activated
sludge) to improve secondary clarification in activated sludge system. The
microfiltration membrane is placed in a membrane tank (steel) at a low vacuum to
draw water through the membrane as well as pump out the filtered water while the
solids are retained in the bio-reactor. The air is compressed and inserted into the
8 Treatment of Petroleum Hydrocarbon Pollutants in Water
265
Nano filtration is mainly utilized for removal of selective dissolved organichydrocarbon pollutants and hardness at moderate pressure: 3–20 bar. Some features
like design and operation, as well as physical dimensions of membrane elements of
nanofiltration are almost same as reverse osmosis. Hence, nanofiltration membranes
can be accommodated in reverse osmosis modules. But main difference between
these two filtrations is that salt and metal abandonment is higher with higher
operating pressures. The particle size of the retentate ranges from 0.001 to
0.01 μm and the hydraulic permeability is 1.5 to 30 L/m
2 hr-bar in nanofiltration.
This membrane may be composite or porous asymmetric. Commercial nanofiltration
membranes possess a fixed charge that causes ions to be separated based on size,
electrical effects and ion interactions. However, it can replace reverse osmosis in
wastewater treatment due to its less energy requirement and higher flux.
Nanofiltration membranes usually exhibit greater efficiency in rejecting hydrophilic
compounds than the hydrophobic ones. Around 90–95% pollutant rejection can be
achieved by this process (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017).
D. Reverse Osmosis:
Reverse osmosis uses a semipermeable membrane where dissolved solids, ions,
pyrogens, nitrate, etc., are removed from wastewater and the retained particle size
varies from 0.0001 to 0.001 μm. Reverse osmosis is operated when the pressure
difference is higher than the osmotic pressure (5–120 bar). It is a most commonly
used process for desalting of oily wastewater. The reverse osmosis membrane is
nonporous, asymmetric or composite and has a hydraulic permeability of
0.05–1.5 L/m
2 hr-bar. After reverse osmosis, the water may be reused in the
petroleum industry. The reverse osmosis membranes require pre-treatment by
microfiltration or ultrafiltration, because they have very fine pores which are easily
plugged by suspended solids. The concentration of oil and grease in the reverse
osmosis feed water is recommended to be less than 0.1 mg/L. The salt rejection
capacity using this technology may be as high as 99%. It is successfully used
worldwide for wastewater treatment but requires high-energy consumption in
terms of pressure (International Petroleum Industry Environmental Conservation
Association 2010; Shahryar 2017).
Membrane Bio-reactor
Membrane bio-reactor is a membrane-based biological treatment where a membrane
process (microfiltration) combines with a suspended growth process (activated
sludge) to improve secondary clarification in activated sludge system. The
microfiltration membrane is placed in a membrane tank (steel) at a low vacuum to
draw water through the membrane as well as pump out the filtered water while the
solids are retained in the bio-reactor. The air is compressed and inserted into the
8 Treatment of Petroleum Hydrocarbon Pollutants in Water
265