CHAPTER IV RESULT AND DISCUSSION
4.7 Model of Fouling Mechanism
75
76 mechanism model with the experimental data. Based on the fitted model, the MEUF of remazol red RB and Blue TQ showing a similar results.
Table 4.7 Mathematical model parameter of UF and MEUF blocking phenomena on indigo sol dye removal
Remazol Dye
CMC
Complete Blocking (n=2)
Intermediate Blocking (n=1)
Standard Blocking (n=3/2)
Cake Formation (n=0)
R2 Kc R2 Ki R2 Ks R2 Kfc
Red RB
0 (UF) 0.9232 -0.0038 0.9235 0.0001 0.9523 0.0001 0.9214 3.10-7 0.5 0.8783 -0.0027 0.8872 0.0001 0.8878 0.0002 0.9124 1.10-6 1 0.8872 -0.0037 0.8551 0.0004 0.8682 0.0004 0.8699 1.10-5 1.5 0.8764 -0.0036 0.871 0.0003 0.8719 0.0003 0.8293 4.10-6 2 0.9009 -0.0113 0.8137 0.0035 0.8879 0.0022 0.6898 0.0007
Blue TQ
0 (UF) 0.8691 -0.002 0.8695 9.10-5 0.8965 9.10-5 0.8631 3.10-7 0.5 0.9096 -0.0057 0.9177 0.0003 0.918 0.0003 0.9252 3.10-6 1 0.8762 -0.0039 0.8494 0.0004 0.8565 0.0004 0.776 2.10-5 1.5 0.9138 -0.0035 0.8997 0.0003 0.9119 0.0003 0.8956 6.10-6 2 0.9746 -0.0032 0.9478 0.0002 0.9479 0.0002 0.9418 4.10-6
The UF process without addition of saponin fitted to the fouling mechanism of standard blocking, with the R2 of 0.9523 and 0.8965 for remazol red and blue respectively. The molecular size of remazol red and blue was way smaller than the membrane MWCO. This fact supporting the phenomena of dye molecule to easily goes through the membrane pore. Some of the dye molecule may entrapped inside the membrane pore instead of escaping it. This was resulting to the blocking of membrane pore which shows a standard blocking mechanism in this study. Figure 4.15 shows the illustration of membrane fouling mechanism. The previous study of MEUF for synthesis of galacto-oligosaccharides also proposed the fact that a solid molecule with molecular weight less than the membrane MWCO supposed to caused standard blocking. The blocking process also follows with a weak ability of membrane rejection (Cordove et al., 2016), which correspond with this study.
77 The micellar-enhanced ultrafiltration of all remazol dye with saponin concentration above it CMC shows a fitting to complete blocking mechanism, with range of R2 from 0.8762 to 0.9746. Complete blocking is the blocking mechanism resulting a reduction of open pores without deposition of foulant particles on the membrane surface. This blocking occurs when the foulant particle size is similar or bigger than the membrane pore size (Grzegorzek and Majewska-Nowak, 2018;
Sarkar et al., 2009). As explained before, that addition of saponin above the CMC will generates a molecular grow because of the micelle formation. The dye molecule will gro in sized and expected to be bigger than the membrane MWCO.
Resulting to a complete blocking of membrane pore. However, this molecule was supposed to not develop a cake layer and there might be only a "flowing cake" layer and a very small (or nil) "stagnant cake" layer on the membrane surface (Field et al., 1995). The big molecule of dye only blocked the pore membrane due to the pressure caused by the feed flow and not generates a cake layer.
Instead, the formation cake was taken a places when the saponin was added below the CMC. Indicated by the fitted data to the cake formation fouling mechanism (R2 of 0,9252). In this condition, the solution consist of free saponin molecule, free dye molecule and a little amount of uncompleted surfactant micelle.
The free saponin molecule is an amphiphilic substance with both of hydrophobic and hydrophilic part. While the PES membrane use in this study was tend to be hydrophobic. Because of this characteristic, some of the dye was attached to the saponin structure and the saponin structure can be attach in the membrane surface.
On the membrane surface, the concentration of solute (saponin and dye) was increased inducing a concentration polarization (Cordove et al., 2016). Hence, when the solution filtered by PES membrane the molecule will deposit on the membrane surface, causing fouling over the time of filtration, and induce membrane pore blocking. The illustration of blocking condition based on the micelle formation is presented in Figure 4.16. Considering the blocking mechanism, the MEUF of dye wastewater using saponin as the surfactant should be conducted with saponin concentration above its CMC.
78
(a) (b)
(c) (d)
Figure 4.16 Illustration of membrane blocking based on the formation of surfactant micelle, (a) without saponin, (b) below CMC, (c) at CMC,
(d) above CMC
The determination of fouling mechanism also confirmed by the FTIR and SEM analysis. Figure 4.17 shows the FTIR spectra of clean membrane and fouled membrane. Generaly, the spectra of both fouled membrane shows a similar spectra with the clean membrane. However, the fouled membrane without addition of saponin shows a peak of C-N and O=S=O at 1010.69 and 918.12 respectively. The peaks was reflecting the specific fungtional group of remazol blue as the foulant. A weak peak at 3402.43 cm-1 also can be assumed to be the small amount of –OH group from the remazol blue. The molecular structure of remazol blue can be seen in Figure 4.12(A). As for fouled membrane with addition of saponin, a similar peaks of C-N and O=S=O also showed at 1041.56 cm-1 and 910.4 cm-1 respectively. Look
79 after the no saponin fouled membrane, the peaks reflects the structure of remazol blue dye. Another peak of –OH and –CH stretch vibration at 3302.13 and 2939.52 respectively. Those peak shows the functional group of saponin molecule. As expected from the modeling calculation, either in present of saponin or not, the remazol dye remained as a foulant on the membrane surface. The addition of saponin in the ultrafiltration feed also showed an addition of saponin foulant. The saponin foulant was identified as the saponin monomer as the micelle functional group was not identified.
Figure 4.17. FTIR Spectra of clean PES membrane and fouled membrane.
The SEM analysis was also conduct to confirm the membrane fouling mechanism. The SEM figure of clean and fouled membrane was showed in Figure 4.18. The figure shows that the used membrane was fouled compared to the clean membrane. The thick layer of cake fouling was identified from the surface of membrane use to filter the feed with saponin concentration under CMC. This result was correspondence to the modeling calculation which claims that the process with saponin addition under CMC concentration shows cake formation fouling mechanism. While the other fouled membrane shows a thiner fouling. However, different type of fouling was found from the SEM analysis. The fouled membrane
80 without addition of saponin shows an organic fouling, a similar appearance of organic fouling was found from the previous research by Hu et al. (2013). It is expected, as the dye wastewater model was made using remazol dye, which is an organic dye. On the other hand, by the addition of saponin in the feed, a colloidal fouling was shown. Colloidal fouling refers to a fuling of membrane surface caused by the colloids or particles depositing on the membrane materials (Khayet, 2016).
The common colloidal fouling formed by organic macromolecules in the feed solution, such as polysaccharides (Tang et al., 2011). Saponin is one of a polysaccharides surfactant, therefore the colloidal deposition of saponin in the membrane surface is possible. According to the modelling calculation, the addition of saponin above the CMC will change the fouling mechanism from cake formation to the complete blocking. The SEM analysis shows a compatible results, where, the membrane use to filter wastewater with addition of saponin above the CMC shows less fouling.
(a) (b)
(c) (d)
Figure 4.18 SEM figure of (a) clean membrane, and fouled membrane (b) without saponin, (c) with saponin under CMC, (d) with saponin above saponin
81
CHAPTER V
CONCLUSION AND SUGESTION
5.1 CONCLUSIONS
In this study, the extraction of saponin from the pericarps of Sapindus rarak was extracted under various extraction condition. Maceration extraction (ME) and ultrasound-asissted extraction (UAE) methods was used and compared. The investigation of surfactant characteristics for the saponin extracts has conducted by FTIR, measurement of CMC, HLB number analysis, and the surfactant ability to solubilize dye. The MEUF system performance to remove dye pollutant was also investigated using saponin as the natural surfactant. The research results were,
1.) The saponin extraction giving highest saponin yield was conducted under the temperature of 30oC, at ratio of 10 mL/gr, running for 40 minutes using UAE methods. The highest saponin yield obtained was 27.87125 mg of saponin/100 mg dry-grounded Sapindus rarak feed. Compared to the ME, the results of UAE showing a better performance of faster extraction time, lower temperature, and less solvent requirement.
2.) The FTIR analysis shows that both of pure saponin and saponin extract has a similar functional group and the structure depicts the structure of monodesmosidic oleanane triterpenoid saponins. The CMC of pure saponin and extracts saponin were 0.07% w/w of saponin content and 7% w/w of extract saponin / 0.2% w/w of saponin content, respectivey. Increase of saponin concentration above CMC helps to stabilize the foam. The HLB number of 18.7 and 16.8 were found for pure saponin and extract saponin respectively.
3.) From the dye solubilization study it is known that addition of more saponin in dye solution increased the solubilized dye. The solubilization power (SP) of extract rarak is similar with the pure saponin for both remazol dye. The ΔG of Sapindus rarak saponin and pure commercialized saponin for remazol red and blue showing a negative value, suggests that, the process was feasible and spontaneous.
82 4.) The MEUF performance analysis presented that the highest flux profile was achieved without any addition of saponin, but the %rejection of dye was very low. In the other hand, the addition of surfactant decrease the flux value until a certain point, but increasing the %rejection of dye molecule. Highest % rejection of dye of 97.02% and 99.42% for remazol red and blue respectively, at the saponin concentration of 2 times CMC. A very low Lm was found for the solution with saponin below CMC, in both of remazol dye. At the CMC, the micelle loading increased significantly. However, further addition of saponin leads to decrease the Lm into 0.0352 mM/mM and 0.0428 mM/mM for remazol red and blue respectively. The fouling mechanism of UF process was standard blocking, UF process with addition of saponin below CMC shows a cake formation blocking, and the addition of saponin above CMC shows complete blocking mechanism.
5.2 SUGESTIONS
This research is expected to contribute for further research related to the application natural-based saponin for MEUF system and can be applied to achieve an efficient methods to treat dye wastewater. Further investigation is definitely needed to obtain more comprehensive study, such as its application for more variative pollutant. The investigation for different kind of pollutant with various characteristic (ionic, hydrophobic, etc.) will help to understand the solubilization nature of saponin as well. To accomplish more thorough knowledge of MEUF using natural-based surfactant, further study using such as the combination of saponin with ionic surfactant, and a study using real wastewater from textile industry will also help. Another plant source of saponin also suggested to be studied more in the future such as, Jatropha curcas L., Acacia collinsii.
83
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