**3. Results**

The major findings illustrated and analyzed in this section are concluded in the following two sections.

#### **3.1. Flux**

Pure water flux and solution flux (both single and mixture salt solutions) at various pressure magnitudes are highlighted and discussed in this section. The flux observed to be reduced after modification but with less than 30% compared to the unmodified membrane flux.

**Figure 1.** Pure water flux of unmodified and modified membranes

As illustrated in Figure 1, pure water flux for both unmodified and modified membranes was obtained at different applied pressures ranging from 2 to 10 bar. Membrane permeability was defined as the slope of pure water flux versus pressure. Apparently, the pure water flux of the membrane decreased after modification by about 30%. Accordingly, the permeability had shown some 24% decreasing after modification. Both flux and permeability decreasing is evidently confirming pore size decreasing following the modification process. Membrane permeation decreasing and increasing with membranes modified by UV grafting can be found in the literature. The increase in permeation of modified membranes was observed by Puro et al. [23] when modifying commercial polyethersulfone membranes (NTR7450 Nitto Denko) following the immersion method. The study also demonstrated pore size increasing in some of the modified membranes. In contrast, UV-initiated grafting of membrane pore walls may reduce pore size according to Yu et al. [24]. In their work, they stated that for membranes with small pores, most of the polyacrylic acid may be grafted on the membrane surface, not on the pore walls. Abu Seman et al. [7] observed both mechanisms depending on the degree of grafting, which was related to UV irradiation time and monomer concentration.

flushed with ultrapure water before and after use. Solutions of MgSO4, NaCl, Na2SO4, and KCl at four various concentrations each (1000, 2000, 3000, and 4000 ppm) were used as the feed for unmodified and modified membranes to measure their rejection and determine the best performing membranes in terms of rejection. The concentrations of the feed and permeate were measured depending on solution conductivity measurements using a commercial conductiv‐

The major findings illustrated and analyzed in this section are concluded in the following two

Pure water flux and solution flux (both single and mixture salt solutions) at various pressure magnitudes are highlighted and discussed in this section. The flux observed to be reduced after modification but with less than 30% compared to the unmodified membrane flux.

As illustrated in Figure 1, pure water flux for both unmodified and modified membranes was obtained at different applied pressures ranging from 2 to 10 bar. Membrane permeability was defined as the slope of pure water flux versus pressure. Apparently, the pure water flux of the

ity meter supplied by Martini instruments (Romania).

**Figure 1.** Pure water flux of unmodified and modified membranes

**3. Results**

26 Desalination Updates

sections.

**3.1. Flux**

**Figure 2.** MgSO4 solution flux for unmodified membrane at various concentrations

Figures 2 and 3 showed the effect of MgSO4 concentration increasing on unmodified and modified membranes flux. For unmodified membrane the flux decreased with concentration. However, the decreasing for unmodified and modified membranes was 11% and 17%, respectively (flux decreasing from 1 g/L to 4 g/L). The same observations noticed for Na2SO4 solution (Figures 4 and 5) but with different percentage (30% and 7% for unmodified and modified membranes, respectively).

For NaCl (Figures 6 and 7), the observations were different, as the flux at 2 and 4 bar pressure for both unmodified and modified membranes decreased with concentration but increased at higher pressure magnitude with concentration.

**Figure 3.** MgSO4 solution flux for modified membrane at various concentrations

**Figure 4.** Na2SO4 solution flux for unmodified membrane at various concentrations

Modified Nanofiltration Membranes Performance Improvement for Desalination Applications http://dx.doi.org/10.5772/60212 29

**Figure 5.** Na2SO4 solution flux for modified membrane at various concentrations

**Figure 3.** MgSO4 solution flux for modified membrane at various concentrations

28 Desalination Updates

**Figure 4.** Na2SO4 solution flux for unmodified membrane at various concentrations

**Figure 6.** NaCl solution flux for unmodified membrane at various concentrations

**Figure 7.** NaCl solution flux for modified membrane at various concentrations

**Figure 8.** KCl solution flux for unmodified membrane at various concentrations

The same observations noticed for KCl solution (Figures 8 and 9) but with different percentage (55% and 1% for unmodified and modified membranes, respectively). It is worth mentioning that increasing concentrations have much more influence on unmodified membrane than the modified one for all solutions.

**Figure 9.** KCl solution flux for modified membrane at various concentrations

It is worth mentioning that flux may decline with time and concentration increasing, as osmotic pressure increased leading to reducing net driving pressure. Such observation is potentially associated with a dead-end filtration system, while for cross-flow system, flux decline may be lesser or may occur with longer time running.

#### **3.2. Rejection**

**Figure 7.** NaCl solution flux for modified membrane at various concentrations

30 Desalination Updates

**Figure 8.** KCl solution flux for unmodified membrane at various concentrations

Rejection rates at various pressure magnitudes and for different concentrations are highlighted and discussed in this section. In addition, rejection of both modified and unmodified NF membranes for solutions consisting of a mixture of salts is also included. The rejection rates witnessed an increase after membrane modification took place with about 11–30% for mag‐ nesium sulfate and sodium sulfate, and 50–60% for sodium chloride and potassium chloride.

Figures 10 and 11 illustrate membrane rejection for both MgSO4 and Na2SO4 at various concentrations, respectively. MgSO4 and Na2SO4 rejection of modified and unmodified membranes decreased with concentration increase. The rejection observed for modified

**Figure 10.** Membrane rejection (unmodified and modified) for MgSO4 at various concentrations

**Figure 11.** Membrane rejection (unmodified and modified) for Na2SO4 at various concentrations

membrane was higher than that observed for unmodified membrane at all concentrations for both MgSO4 and Na2SO4. However, concentration increasing found to have more influence on unmodified membrane than the modified one. For the modified membrane, MgSO4 rejection decreased by 12% from 1g/L to 4 g/L while rejection decreased for unmodified membrane with nearly 20%. For Na2SO4, rejection was reasonably decreased for unmodified membrane from 98% to 85% (difference is 13%) while for the modified membrane, the rejection decreased from 100% to 92% (difference is 8% only). This attributes to the fact that pore geometry and size have reasonably changed leading to better rejection as well as lowering concentration increas‐ ing effect on the membrane at this concentration range (1–4 g/L) [6, 25].

Modified Nanofiltration Membranes Performance Improvement for Desalination Applications http://dx.doi.org/10.5772/60212 33

**Figure 12.** Membrane rejection (unmodified and modified) for NaCl at various concentrations

**Figure 13.** Membrane rejection (unmodified and modified) for KCl at various concentrations

membrane was higher than that observed for unmodified membrane at all concentrations for both MgSO4 and Na2SO4. However, concentration increasing found to have more influence on unmodified membrane than the modified one. For the modified membrane, MgSO4 rejection decreased by 12% from 1g/L to 4 g/L while rejection decreased for unmodified membrane with nearly 20%. For Na2SO4, rejection was reasonably decreased for unmodified membrane from 98% to 85% (difference is 13%) while for the modified membrane, the rejection decreased from 100% to 92% (difference is 8% only). This attributes to the fact that pore geometry and size have reasonably changed leading to better rejection as well as lowering concentration increas‐

ing effect on the membrane at this concentration range (1–4 g/L) [6, 25].

**Figure 11.** Membrane rejection (unmodified and modified) for Na2SO4 at various concentrations

**Figure 10.** Membrane rejection (unmodified and modified) for MgSO4 at various concentrations

32 Desalination Updates

Figures 12 and 13 illustrate membranes rejection for both NaCl and KCl at various concentra‐ tions, respectively (concentration range: 1–4 g/L). Two main observations worth concluding: firstly, the significance increase of both NaCl and KCl rejection at all concentrations for modified membrane over unmodified ones (for NaCl, modified membrane had rejection increasing from 39% to 72% in average while for KCl rejection increased from 59% to 75%); secondly, concentration increase had lower influence on both NaCl and KCl rejection for the modified membrane over the unmodified membrane (rejection decreased with concentration for NaCl and KCl by 26% and 44 % for unmodified and 25% and 22% for modified membrane). Although NF membranes are more vulnerable to chloride ions than sulfate ions, modified membrane seemed to have more consistent performance and less concentration increasing influence in terms of rejection than unmodified membrane. Generally, salt rejection values may suffer some decline with time as applied dissolved solids concentrations increase.

### **4. Conclusions**

A commercial NF membrane was modified via UV-grafted surface modification method to obtain better salt rejection and reasonable flux while desalting brackish water. The study provides valuable information about flux and rejection changes and the relationship with pressure changing before and after modification. Experimental works included in the study investigate modified and unmodified NF membranes performance while filtering synthesized single salt solution at various concentrations (ranged from 1000 ppm to 4000 ppm) and various pressure magnitudes (pressure ranged from 2 to 10 bars). Following the modification, the rejection rates showed an increase with about 11–30% for magnesium sulfate and sodium sulfate, and 50–60% for sodium chloride and potassium chloride. It is worth mentioning that concentration increase was found to have lower effect on membrane rejection after modifica‐ tion.

### **Author details**

#### A. A. Abuhabib1,2

Address all correspondence to: azz200@hotmail.com

1 Environmental Engineering Department, Engineering Faculty, Islamic University of Gaza, Gaza, Palestine

2 Development planning Department, University College of Applied Sciences (UCAS), Gaza, Palestine

### **References**

[1] N. Hilal, H. Al-Zoubi, N.A. Darwish, A.W. Mohammad, M. Abu Arabi, A compre‐ hensive review of nanofiltration membranes: Treatment, pretreatment, modelling, and atomic force microscopy, Desalination, 170 (2004) 281-308.

[2] A. Mohammad, Y. Teow, W. Ang, Y. Chung, D. Oatley-Radcliffe, N. Hilal, Nanofil‐ tration membranes review: Recent advances and future prospects, Desalination, (2014).

for NaCl and KCl by 26% and 44 % for unmodified and 25% and 22% for modified membrane). Although NF membranes are more vulnerable to chloride ions than sulfate ions, modified membrane seemed to have more consistent performance and less concentration increasing influence in terms of rejection than unmodified membrane. Generally, salt rejection values may suffer some decline with time as applied dissolved solids concentrations increase.

A commercial NF membrane was modified via UV-grafted surface modification method to obtain better salt rejection and reasonable flux while desalting brackish water. The study provides valuable information about flux and rejection changes and the relationship with pressure changing before and after modification. Experimental works included in the study investigate modified and unmodified NF membranes performance while filtering synthesized single salt solution at various concentrations (ranged from 1000 ppm to 4000 ppm) and various pressure magnitudes (pressure ranged from 2 to 10 bars). Following the modification, the rejection rates showed an increase with about 11–30% for magnesium sulfate and sodium sulfate, and 50–60% for sodium chloride and potassium chloride. It is worth mentioning that concentration increase was found to have lower effect on membrane rejection after modifica‐

1 Environmental Engineering Department, Engineering Faculty, Islamic University of Gaza,

2 Development planning Department, University College of Applied Sciences (UCAS),

[1] N. Hilal, H. Al-Zoubi, N.A. Darwish, A.W. Mohammad, M. Abu Arabi, A compre‐ hensive review of nanofiltration membranes: Treatment, pretreatment, modelling,

and atomic force microscopy, Desalination, 170 (2004) 281-308.

**4. Conclusions**

34 Desalination Updates

tion.

**Author details**

A. A. Abuhabib1,2

Gaza, Palestine

Gaza, Palestine

**References**

Address all correspondence to: azz200@hotmail.com

