CHAPTER II LITERATURE REVIEW
2.8 Fundamentals and Application of Micellar-Enhanced Ultrafiltration
Micellar-Enhanced Ultrafiltration Membrane (MEUF) is a technology that employs surfactant micelles to solubilize inorganic and organic pollutants from the effluent stream. It is a membrane based separation technique mainly investigated for wastewater treatment. This method allows dissolved matter, such as organic molecules or ions, to be rejected by an ultrafiltration membrane due to molecular weight enlargement using surfactants. The membrane used in this process is ultrafiltration (UF) membrane. It is a membranes with pore sizes in the range of 0.1 to 0.001 micron. Typically, UF membranes will remove high molecular-weight substances, colloidal materials, soluble pollutant and organic and inorganic polymeric molecules.
In MEUF, the surfactant is added to the aqueous stream containing contaminants or solute (e.g. metal ion, organic materials, low molecular weight solute) above its critical micelle concentration (CMC) (Landaburru-Aguire et al., 2009). When the surfactant concentration exceeding the CMC value, the surfactant monomers will assemble (Chung et al., 2009, Huang et al., 2012b) and aggregate to form large amphiphilic transparent micelles (Luo et al., 2010). Above the critical micelle concentration (CMC), surfactant monomers spontaneously aggregate into micelles. The micelles are having a hydrodynamic diameter significantly larger than the pore diameter of ultrafiltration membrane (Misra et al., 2009; Chung et al., 2009; Huang et al., 2009). The contaminants or solute will entrap in micelles if they tend to strongly attracted by micelle surface and will solubilize in the micelle interior (Zaghbani et al., 2008). Micelles containing solubilized contaminants with a larger diameter than membrane pore size will be rejected by the membrane during ultrafiltration process leaving only water,
25 unsolubilized contaminants and surfactant monomers in permeate stream (Misra et al., 2009; Zaghbani et al., 2008). Selection of surfactant is significant to ensure the efficiency of MEUF process. Based on the literature study, the MEUF of wastewater commonly can be classified into four categories; (i) MEUF using a cationic surfactant, (ii) MEUF using an anionic surfactant, (iii) MEUF using a nonionic surfactant, and (iv) MEUF using a mixed surfactant.
The micelle size is in the same order of magnitude as the pore sizes of ultrafiltration membranes. By selection of an appropriate membrane for the ultrafiltration process, the micelles can be rejected by the membrane whereby the surfactant monomers pass through. This fundamental concept of MEUF was already studied before for anionic surfactants and for a nonionic surfactant (Melo et al., 2017; Grzegorzek and Majewska-Nowak, 2018). The main advantage of MEUF over conventional ultrafiltration is that it can even rejected a low concentrations molecules, which is usually too small to be rejected by ultrafiltration membranes. The pollutant molecules can bind to the micelles because of ionic or hydrophobic interactions and subsequently separated together with them in the ultrafiltration step (Figure 2.7).
Figure 2.7 Schematic representation of MEUF
This process utilizes the high efficiency of reverse osmosis (RO) and high permeates flux of ultrafiltration membrane (UF) (Baek et al., 2003). The main principle of this process is to increase the size of pollutant molecules by forming a complex with surfactant. Cationic or anionic surfactants are used for the removal of inorganic pollutants. In this system, the surfactant forms micelles at critical
26 micelle concentration (cmc). The aggregation number ranges from 50 to 100. (Bade and Lee, 2011). Micelle (cationic or anionic) has high electrical potential on its surface where anionic or cationic pollutants can be bounded depending upon the charge characteristic of the pollutants. When the solution containing micelle is passed to the membrane ultrafiltration, micelle retains on the membrane surface.
Unbound ions and surfactant monomers pass through the ultrafiltration membrane to the permeate side.
In general, the MEUF performance is explained by the flux profile and
%rejection. Flux is defined as the flow rate of a solution goes through the membrane (permeate solution) per effective area of the membrane. While, rejection is the amount of particles/substances that have been removed from the feedwater. The performance of MEUF is not only based on simple relations but also a very complex process that depends on a miscellaneous parameters. Solute rejection efficiency and permeate flux depend on several parameter, such as the characteristics of added solutes, membrane type, surfactant type, and various operating conditions. (Bade and Lee, 2011, Schwarze et al., 2015). A schematic overview is given in Figure 2.8.
Many studies have been carried out to investigate the performance of MEUF and how it is influenced by this different parameters. Commonly, there are no universal experimental conditions that can be applied to MEUF experiments. In fact, experimental parameters have to be selected based on the individual system.
27 Figure 2.8 Experimental parameters that influence the performance of MEUF
Micellar enhanced ultrafiltration (MEUF) has been used for the removal of various organic and/or inorganic pollutant from aqueous phase (Baek et al., 2003).
It is particularly effective for removal of single components such as Cd2+, Mn2+, Zn2+, Cu2+, Cr3+, Pd2+, Al3+, and many other. It is also effective for simultaneous removal of Ni2+ and Co2+, and Ni2+ and Zn2+. The application of MEUF for dye removal has also been conducted before, Table 2.4 presents the previous study of MEUF for dye removal.
MEUF
Membrane Selection
Material MWCO Pore Size
Surfactant Selection
Type CMC
Aggregation structure & Size Single or Mixed System
Operating Condition
Operating Mode TMP
pH Temperature Concentration
Solutes
Ions
Organic Molecule Salt
Single or Mixed System
28 Table 2.4. Application of MEUF for Dye Removal
Membrane Surfactant Dye Compound
Result Reference Polyethersulfone CPC 2x and
4x CMC
Remazol Blue, Black, Yellow
COD Rejection:
70%
Dye Rejection 96%
(Aryanti et al., 2017)
PVDF (Polyvinylidene
fluoride)
SDS (2,5 kg/m3)
OMW (Olive mill wastewater)
Dye rejection 74%
(El-Abbassi et al., 2011) Hollow
membrane
SDS 8,27 mM
Methylene blue (MB)
Dye rejection 99,2%
(Zeng et al., 2011) Polysulfone SDS
8 mM
Methylene blue (MB)
Dye rejection 96%
(Huang et al., 2012) Cellulose
membrane
CTAB 2 mM
Eriochrome Blue Black r
Dye rejection 99%
(Zaghbani et al., 2009) Cellulose
Membrane 10 kDa
SDS 10- 100mM
Saffarin T Rejection 99% (Zaghbani et al., 2008) Polimeric
membrane
CPC 1 gr/L
RO5 and RO16
Reactive Black 599,7%
rejected,Reactive Orange 1699,6%
rejected
(Ahmad et al., 2006)
Cellulose membrane
SDS 4 mM
Methylene blue (MB)
SDS rejection
>97%
(Zaghbani et al., 2008) Organic
Polyamide
CPC (10 kg/m3)
Eosin Dye rejection 70.45% (Purkait et al., 2004)
29