Environmental Engineering Reference
In-Depth Information
They outlined membrane characteristics governing factors. Trans membrane pressure drop (TmP) is outlined in major detail.
The delineated features are effects of TmP on flow rate and rejection. They described in detail the physics behind the effects of
TmP on flux rate. The effects of the TmP on the permeate flux at different solute concentrations can be observed by keeping
the operating temperature and pH constant. The permeate flux at the steady state increases, with the applied pressure at all
concentrations. An increase in flux was noted with an increase in the operating pressure. Since nanofiltration is basically a
pressure-driven filtration process, flux is supposed to increase with pressure. The phenomenon can be mathematically explained.
Hong et al. [4] delineated the chemical and physical aspects of natural organic matter (nOm) fouling of nanofiltration mem-
branes. The role of chemical and physical interactions in nOm fouling of nanofiltration membranes is systematically investi-
gated. Results of fouling experiments with three basic acids demonstrate that membrane fouling increases with increasing
electrolyte (naCl) concentration, decreasing solution pH, and addition of divalent cations (Ca
2+
). At fixed solution ionic
strength, the presence of calcium ions, at concentrations typical of those found in natural waters, has a marked effect on mem-
brane fouling. Divalent cations interact specifically with carboxyl functional groups and thus substantially reduce charge and
the electrostatic repulsion between humic macromolecules.
In recent years, membrane filtration has emerged as a viable treatment alternative to comply with existing and pending water
quality regulations. Of particular interest is the use of nanofiltration as a treatment alternative for the removal of nOm, a pre-
cursor of disinfection by-products, in anticipation of more stringent regulations. nanofiltration technology also offers a versatile
approach to meeting multiple water quality objectives, such as the control of organic, inorganic, and microbial contaminants.
Successful application of nanofiltration technology, however, requires efficient control of membrane fouling. fouling, often
associated with the accumulation of substances on the membrane surface or within the membrane pore structure, worsens mem-
brane performance and ultimately shortens membrane life.
Hilal et al. [5] reviewed research work on using Afm toward improvement in nanofiltration membrane properties for desa-
lination pretreatment.
Seawater is characterized by having a high degree of hardness, varying turbidity and bacterial contacts, and high total dissolved
solids (TDS). These properties give rise to major problems such as scaling, fouling, high energy requirements, and the requirement
of high-quality construction materials. To solve seawater desalination problems and to minimize their effect on productivity and
water cost of conventional plants, a new approach using nanofiltration as pretreatment to both RO and thermal processes has been
shown to enhance the production of desalted water and reduce the cost, yet it is an environmentally friendly process.
The following areas were covered:
a. Development of high-performance nanofiltration membranes
b. Development of accurate and practical characterization methods
c. Development of a good predictive modeling technique
The use of Afm in membrane studies was also outlined in detail.
Hilal et al. [6] attempted a comprehensive review of nanofiltration membranes and dealt with its treatment, pretreatment,
modeling, and Afm. This review addresses the application of Afm in studying the morphology of membrane surfaces as part
of nanofiltration membrane characterization.
A comprehensive review of nanofiltration in water treatments is presented including a review of the applications of nanofiltration
in treating water as well as in the pretreatment process for desalination; the mechanism as well as minimization of nanofiltra-
tion membrane fouling problems; and the theories for modeling and transport of salt and charged and noncharged organic
compounds in nanofiltration membranes.
Ashaghi et al. [7] dealt with nanofiltration in detail in their research review on ceramic ultrafiltration and nanofiltration
membranes for oilfield-produced water treatment. Produced water is any fossil water that is brought to the surface along with
crude oil or natural gas. By far, produced water is the largest by-product or waste stream by volume associated with oil and
gas production. The volume of produced water is dependent upon the state of maturation of the field. There is an urgent need
for new technologies for produced water treatment due to increased focus on water conservation and environmental regula-
tion. Ceramic ultrafiltration and nanofiltration membranes represent a relatively new class of materials available for the
treatment of produced water. According to their research, the issues needing to be addressed are the prevention of membrane
fouling during operation and the provision of an expedient, cost-effective, and nonhazardous means of cleaning fouled mem-
branes. The researchers embarked on the present study because there are not enough existing studies related to the treatment
of oilfield-produced water using ceramic membranes. Ceramic membrane systems under nanofiltration and ultrafiltration
conditions have proven to be economically attractive for the treatment of produced waters with elevated concentrations of
oils and low to medium diameters of the particles.
no research review is complete unless the mechanisms of membrane science or nanofiltration are not taken into account.
