3.1 Treatment of oily wastewater .1 Experimental
3.1.2 Results and discussion
3.1.2.1 Performance in synthetic oily wastewater treatment
The elaborated novel tubular ceramic membrane was applied for the treatment of synthetic oily wastewater emulsions. Applied pressure, feed oil concentration and cross flow rates are the important variables that affect the treatment process in terms of permeate flux and rejection.
Hence, the effect of these parameters was investigated as a function of time.
3.1.2.1.1 Effect of applied pressure
Figure 3.3(a) shows the permeate flux profiles with time for various applied pressures (69, 138, 207, 278 and 345 kPa) at a cross flow rate of 1.11 × 10-6 m3/s with feed concentration of 100 ppm.
It can be seen from the figure that the permeate flux declines sharply at the initial period and becomes gradual thereafter in the microfiltration run. The reasons for the flux reductions are owing to concentration polarization on the surface of membrane and blocking of pore in the porous ceramic structure. In addition, it is noticed that the permeate flux increases with increasing applied pressures due to the higher driving forces acted on the membrane. However, the permeate flux profile on increasing applied pressure does not follow the linear trend (see Figure 3.3(a) (insert)). This is due to concentration polarization and adsorptive of oil on the surface that creates further resistances to transport liquid through the membrane (Chakrabarty et al. 2008). The rate of flux decline is higher at higher applied pressure due to the immediate formation of oil layer on the surface of the membrane, which makes membrane fouling faster while increasing the applied pressure. Figure 3.3(b) presents the rejection of oil with time for various applied pressures. It is noticed that the oil rejection declines with an increase in applied pressure. This occurs due to the fact that oil droplets can deform more at higher shear and the changed shape may enable their permeation at higher pressure. Moreover, the percentage of oil rejection slightly increases with duration of microfiltration. This is possibly due to the reduction
of membrane pore sizes, which happens by the adsorption of oil droplets on the surface of the membrane. The fabricated membrane exhibits excellent rejection performance according to the results depicted in Figure 3.3(b). The membrane shows the highest rejection of 99.98% at a lower applied pressure of 69 kPa with permeate flux of 3.16 × 10-5 m3/m2s.
Figure 3.3: Influence of applied pressure on (a) permeate flux and (b) oil rejection
10 20 30 40 50 60
90 92 94 96 98 100
Oil rejection (%)
Time (min)
69 kPa 138 kPa 207 kPa 278 kPa 345 kPa (b)
0 500 1000 1500 2000 2500 3000 3500 0.000028
0.000042 0.000056 0.000070 0.000084 0.000098 0.000112 0.000126
0 50 100 150 200 250 300 350
0.00000 0.00001 0.00002 0.00003 0.00004 0.00005
Permeate flux(m3/m2s)
Applied pressure (kPa)
69 kPa 138 kPa 207 kPa 278 kPa 345 kPa
Permeate flux (m3 /m2 s)
Time (s) (a)
3.1.2.1.2 Effect of feed concentration
Figure 3.4(a) illustrates the permeate flux plots with time for various feed concentrations (50, 75, 100, 150 and 200 ppm) at applied pressure of 207 kPa with the cross flow rate of 1.11 × 10-6 m3/s. Figure 3.4(a) clearly demonstrates that an increase in the oil concentration results larger flux decline. The coalesced oil sticks over the membrane, which creates fouling resulting a declined premeate flux at higher feed concentration (see Figure 3.4(a) (insert)). Similar kind of trends is also reported in the literature (Monash and Pugazhenthi 2011). From Figure 3.4(b), it is apparent that the rejection enhances with an increase in feed concentration due to the enhancement of oil droplet size and density of droplet at higher concentrations. At higher concentrations, the coalescence of the oil droplets forms a larger droplet that offers a greater rejection. The highest percentage of oil rejection (99.64%) is obtained for the feed concentration of 200 ppm with permeate flux of 1.74 × 10-5 m3/m2s.
3.1.2.1.3 Effect of cross flow rate
Figure 3.5(a) represents permeate flux plots with respect to time for different cross flow rates (5.55 × 10-7, 1.11 × 10-6 and 1.66 × 10-6 m3/s) at applied pressure of 207 kPa with feed concentration of 100 ppm. It is noticed that the permeate flux of the membrane enhances with increasing the cross flow rate (see Figure 3.5(a) (insert)). It can be explained that an increment of the cross flow rate reduces the concentration polarization. Additionally, increasing the cross flow rate offers enhancement in the shear stress on the membrane surface, which diminishes the thickness of the adhered oil layer on the surface of the membrane. Figure 3.5(a) signifies that an increase in the cross flow rate decreases the rate of flux decline. This is due to the fact that the increasing cross flow rate restricts the cake layer occurrence on the surface of the membrane.
Figure 3.5(b) points out that the percentage of oil rejection reduces slightly with increasing cross flow rate. This is due to the reduction of oil layer thickness on the surface of the membrane at a
higher cross flow rate, as we discussed previously. At a lower cross flow rate, the formation of the cake layer is more, which acts as an additional barrier on the surface of the membrane resulting improved oil rejection. The higher cross flow rates depreciates the formation of cake layer, consequently the oil rejection decreases. For that reason, the percentage of oil rejection declines with rising cross flow rates. The highest percentage of oil rejection (99.86%) is obtained for lower cross flow rate of 5.55 × 10-7 m3/s with permeate flux of 2.24 × 10-5 m=/m2s.
Figure 3.4: Effect of feed concentration on (a) permeate flux and (b) oil rejection
10 20 30 40 50 60
90 92 94 96 98 100
200 ppm 150 ppm 100 ppm 75 ppm 50 ppm
Oil rejection (%)
Time (min) (b)
0 500 1000 1500 2000 2500 3000 3500 0.00002
0.00004 0.00006 0.00008 0.00010 0.00012 0.00014 0.00016
50 75 100 125 150 175 200
0.00000 0.00002 0.00004 0.00006 0.00008
Permeate flux(m3/m2s)
Oil concentration (ppm)
50 ppm 75 ppm 100 ppm 150 ppm 200 ppm
Permeate flux (m3 /m2 s)
Time (s) (a)
Figure 3.5: Effect of cross flow rate on (a) permeate flux and (b) oil rejection