An antifouling polyether sulphone (PES) microfiltration membrane was developed by physical blending of TiO2 nanoparticle for membrane bioreactor (MBR) treating tannery wastewater. Incorporation of anti-fouling materials into the polymer by physical blending and composite PES membranes were synthesized using TiO2 nanoparticle and the membranes were made by Non-Induced Phase Inversion Method (NIPS). The membrane morphology was studied using scanning electron microscopy (SEM) and the stability of the membranes was measured by calculating the tensile strength. From the results of contact angle measurements, the hydrophilicity of the membranes was found to increase with the PES/ 4% TiO2. From the fouling rate analysis, TiO2 nanoparticle incorporated membrane PES/ TiO2 has a higher antibiofouling effect. The antimicrobial properties of TiO2 guaranteed an anti-bio-fouling effect thus by preventing the microbial growth in the membrane. The percentage of COD removal was found to be 89% and the complete removal of suspended solids has been observed.
Research Article
Performance studies of Fine-tuned Poly Ether Sulphone Composite Membranes using Azadirachta indica for Antifouling Properties in Industrial wastewater treatment
https://doi.org/10.21203/rs.3.rs-5286631/v1
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Polymeric membranes
Tannery wastewater
antifouling membranes
Industries generates wastewater which contains pollutants of different types including copper (Cu), sulfides, phenolic compounds chromium (Cr), petroleum hydrocarbons, volatile organic compounds (VOCs), chlorinated compounds, biocides, lignin, tannins, ammonium nitrogen, mercury (Hg) etc. [1][2]. Like any other water-intensive industries, Tannery sector also plays a vital role in discharging enormous amount of wastewater. Also, Tannery industry plays an significant role in employment generation for many countries like India, China, Vietnam, Italy, Bangladesh, Brazil, etc., as, there are about 2500–3000 tanneries are present and most of them (nearly 80%) are carrying chrome tanning process [3]. This industry is contributing to the economic growth and the major women employment sector, about 4 million women involved in this business.
In tanning process, three major process is important such as preparation of hides/skins, tanning, and finishing. However, about 85% of wastewater is discharged during the processing of skins and hides. The wastewater generated from the tannery has high color values, (a basic dark brown colored waste) and these effluents are rich in COD, BOD, TDS, chromium, sulphides and a high pH [4]. In India, about 28–40m3of wastewater is generated during processing of one tonne of raw hides/skins.
There are certain methods followed traditionally for the wastewater treatments which includes physico-chemical and biological treatment. Currently there are many advanced techniques followed which includes membrane filtration, ion-exchange, electrolysis, adsorption, etc. Integrating membrane filtration with activated sludge process, so called membrane bioreactors (MBRs) is the best option as it has a capability to contain high MLSS, low sludge production and low space consumption [5].
Membrane fouling is the main problem with MBRs, and it depends on various influencing factors such as membrane surface, porosity, pore size and hydrophilicity. Membrane foulants in MBRs can be grouped into three main categories. They are bio foulants, organic foulants and inorganic foulants based on their biological and chemical characteristics. Fouling can be significantly observed by the two parameters like permeate flux and transmembrane pressure (TMP), which determines identification and extent of fouling [6]. The increase in irreversible fraction of membrane arises from the number of filtration cycles increases. Chemical cleaning is important for the production rate increase as well as for the improvement of its permeability [7]. As these membrane biofouling causes increased transmembrane pressure, decreased permeate production, and a shorter lifetime of membrane modules [8]. Various antifouling solutions have been developed to address the issues posed by biofouling. Physical interference of biofilm carriers using the backwash, application of chemical wash, or sonication [9], blending/chemical modification of membranes (e.g. coating with nanoparticles and modifying membranes with organic functional groups) [10], and biocidal control are few examples of adoption of antifouling strategies [11][12][13]. TiO2 nanoparticles possess an excellent photocatalytic activity. TiO2 NPs also has chemical stability, hydrophilicity, thermal, mechanical and permeability, and. Due to these positive properties, TiO2 was considered to be an ideal additive for synthesizing membranes. Many studies have proved that TiO2 based membranes have better properties than the other NPs [14].
Polyethersulfone (PES) is considered as popular polymers in the field of wastewater treatment, which is used for the fabrication of microfiltration membranes in MBRs. Membrane forming property has made the PES as a superior candidate. As a membrane material, PES properties can be controlled by having changes in the composition of casting solution. Without addition of any pore formers, the hydrophobicity of PES membranes will make them for susceptible to fouling by the adsorbing the foulants, which leads to a low membrane flux and poor antifouling property [15]. Therefore, its hydrophobic nature of the bare membranes materials loses its application in membrane field.
In the present study, physical modification of membrane material strategy has been used to reduce the bio-fouling and improve the efficiency of tannery wastewater treatment system. The addition of nanoparticles is expected to increase in hydrophilicity due to increasing in mean pore size, as a result of porous nature of TiO2 nanoparticles.
Potassium dichromate, Ferroin indicator, COD acid, Mercuric sulfate, Ferrous ammonium sulfate, Ferric Chloride, Calcium Chloride, Phosphate Buffer, Magnesium sulfate, Alkali Iodide, Manganese Sulfate, Conc. H2SO4, Starch indicator, Chitosan (with purity > 90% and viscosity 200.00 cps) were purchased from SIGMA-ALDRICH. Acetic acid, Sodium hydroxide, Titanium (IV) butoxide, Dimethyl Sulfoxide (DMSO), Ethanol, Acetone, E.coli, Bacillus subtilis, Mueller hinton agar, Polyethersulfone (PES), Polyvinylpyrrolidone (PVP), N-methyl-2-pyrrolidone (NMP) were purchased from SRL. The tannery wastewater was collected from tannery common effluent treatment plant (CETP), in Tamil Nadu. The sample was collected in 50-liter plastic containers, which was transported and stored in the laboratory.
2.1 Wastewater characterization
The characterization of the wastewater was determined based on the standard methods for the examination of water and wastewater (APHA, 2004). Chemical Oxygen Demand (COD) and colour values have been considered for the removal of pollutants. The COD removal and colour removal efficiency of the system have been calculated by the following equation,
2.2 Membrane Analysis
The flux (J) is an important parameter for knowing the filtration performance of the membranes and this could be calculated by the following [16] Eq. (5):
$$\:J=Q/A$$
3
Here, J denotes the membrane flux and it its unit is (L/h/m2), Q defines the discharge (L/h) whereas A means surface area of the membrane (m2).
The flux recovery ratio (FRR) is another parameter to check the antifouling properties and this can be determined by following Eq. (5) [17],
$$\:FRR=\frac{{Jw}_{2}}{{Jw}_{1}}\:100\%$$
4
Water absorption and swelling degree are important criterion to calculate its porosity and hydrophilic nature of the material. Measured 2cm x 2cm membranes were cut and immersed into deionized water at room temperature for 10h of time. After 10h, the wet membranes were weighted after clearing the excessive water using wash cloth. Now, the membrane samples had to be dried at 50°C in a hot air oven for 4 h and then the dried membrane was weighed. Water absorption percentage was calculated using Eq. (1),
$$\:W=\frac{Ww-Wd}{Wd}\:\%$$
5
The strength of the membranes cab be obtained by knowing its tensile strength and the percentage elongation. The tensile strength can be calculated by using Universal Testing Machine(UTM) on following equations [18] (3) & (4),
$$\:T=P/A$$
6
$$\:E=\frac{\varDelta\:L}{L}*100\%$$
7
2.3 Material Characterization
Scanning Electron Microscopy of the synthesized titanium dioxide nanoparticles was observed by Tescan Field Emission Scanning Electron microscope (FE-SEM) analysis. FT-IR spectrum was measured in the range between 500 to 4000 cm− 1 using the Perkin Elmer spectrophotometer. The antibacterial activity of synthesized TiO2 nanoparticles were studied by the disk diffusion method for both gram-positive and gram-negative bacteria. The TGA of synthesized membranes were analyzed by the TA Instruments, Waters Austria. Crystalline properties of the membranes were examined by an X-ray diffractometer (Rigaku) with monochromatic Cu Ka radiation (l = 0.154 nm). Uniaxial tensile testing was used to study the mechanical strength of the membrane.
Titanium dioxide (TiO2) nanoparticles is a well-known photocatalyst for its anti-microbial property. TiO2 NPs have been synthesized using the green synthesis approach, based on the study carried out by the researchers previously [14]. The Azadirachta indica leaves i.e., leaves from Eucalyptus tree, were collected from CSIR -CLRI campus. Approximately about 30 g of fresh Azadirachta indica leaves were washed thoroughly using tap water initially and cut into small pieces. All the remaining dirt present in them, was removed by washing the leaves thoroughly using the distilled water. The cleaned leaves were then boiled in water bath containing 200 mL of distilled water for the duration of 50 minutes. After boiling, this extract was filtered using Whatman filter paper to remove the particulates and suspended matters. The obtained extract was then stored at lower temperature say, 3°C for further use. 10 mL of extracts of Azadirachta indica leaves as shown in the figure, was then added with 5 mM of aqueous titanium dioxide for nanoparticles synthesis. The obtained titanium dioxide NPs were purified by using centrifuge process for 40 min using the distilled water. The obtained product was then dispersed in the deionized water as shown in the figure. Finally, heat treatment about 60–65°C has been given for 2 h and then the obtained product was stored for further use (Fig. 1).
3.1 Scanning Electron Microscopy (SEM) Analysis
3.2 X- Ray Diffraction Analysis
XRD analysis are used extensively for the examination of materials. The XRD analysis was performed by the using the model Rigaku, Japan. The XRD pattern of TiO2 nanoparticles obtained using the solvothermal method is shown in Fig. 4. From the result, it is observed that the diffraction peaks are in align to tetragonal anatase TiO2 phase. Hence the obtained results were in good agreement with JCPDS card number 21-1272. Peaks absorbed at 25°, 38°, 48°, 55°, 62° and 75⁰ along with miller indices values (1 0 1), (1 1 2), (2 0 0), (2 1 1), (2 1 3) and (2 1 5) respectively. All the diffraction peaks can be indexed to the tetragonal anatase TiO2 phase. The XRD peak broadening in the graph, clearly indicates the small nanoparticles size [15]. (2009)). The so-obtained lattice parameters of the TiO2 nanoparticles were found to be respectively a = b = 0.3785 nm and c = 0.9513 nm. The average crystallite size of the obtained material was measured by Debye-Schereer’s equation.
3.3 FTIR spectra
FTIR spectra of TiO2 nanoparticle is given in the Fig. 5. The FTIR spectrum of the titanium dioxide nanoparticles by green synthesis, has showed the peaks around 1640 cm− 1, 733 cm− 1 and wide areas between 3500–2000 cm− 1 and 500–800 cm− 1. The peak obtained at the 733 may corresponds to the stretching vibration of Ti–O–Ti of titanium dioxide nanoparticles. The small absorption peak obtained at 1640 cm− 1 and wide area between 500–800 cm− 1 peaking at 733 cm− 1 shows the presence of TiO2 nanoparticle and the similar findings corresponding peaks have been observed by Thakur [14].
3.4 Antibacterial test for the nanoparticles
The E.coli and the Bacillus subtilis strains were used for the antibacterial tests as gram negative and gram positive bacteria. Nutrient agar was used as a growth medium to measure the antibacterial activity of TiO2 nanoparticles. Mueller- Hinton agar, as a growth medium was used to measure the antibacterial activity of TiO₂ nanoparticles. The disk diffusion method was used here which uses by placing a paper disk. It was saturated using antimicrobial agents by bacteria seeded on the agar medium surface. Here the paper discs (Whatmann No.1 filter paper) were saturated by the synthesized TiO2 nanoparticles. Agar well diffusion method was carried out for the nanoparticles were the wells created by the well borer. The plates were left 14 hrs for incubation. And the presence and absence of the zone of inhibition around the disks were measured. The synthesized membranes were punched into circular pieces and placed on the agar medium, and these plates were subjected to incubation for 14 hrs of time. The absence of zone of inhibition and presence of the zone of inhibition around the disks were measured. TiO2 nanoparticles are well-known for the antimicrobial activity. The synthesized TiO2 NPs activity was done by disk diffusion method. From the study, it is learnt that the inhibition zone of 2mm were formed against both gram negative and gram-positive bacteria. The formation of rings proves that the synthesized TiO₂ NPs embedded in the PES membrane al has antibacterial activity. It was also noted from the plates that 3mg/ml of TiO₂ NPs shows more antibacterial activity against both the gram positive and gram-negative bacteria. From Fig. 6, it shows that 3mg/ml of TiO₂ NPs, it is observed that more antibacterial activity against both gram positive and gram-negative bacteria have taken place in 3mg/ml of TiO₂ NPs.
3.5 Synthesis of modified pes membranes
PES Membranes and the composites membranes have been casted using the non-induced phase inversion method (NIPS). Initially, the PES membranes were made without the use of pore former, PVP. During the synthesize of the PES membrane alone, 14 wt% PES powder was dissolved in the solvent NMP at 65°C under constant vigorous stirring for 24h. For the synthesis of the modified composite membranes, the synthesized nanoparticle was mixed with the different ratio of PES and NMP at different concentrations. The synthesized nanoparticles in the concentration of 1%, 2%, 3% and 4% have been used. This has been carried out by dissolving the polymer in the NMP and different concentration of the nanoparticles at 60°C under constant vigorous stirring for 2 hrs and then the solutions were cooled to the room temperature. The resultant polymer blend solution was de-aerated for few hours to eliminate the air bubbles present in the solution. The solution was then used for the casting of flat sheets with the help of flat sheet casting machine. The compositions for casting solutions are listed in Table.1.
3.6 FTIR of synthesized membranes
FTIR result in Fig. 7 shows that, comparison of different composition of synthesized membrane. The spectrum of these five different synthesized membranes is characterized by the appearance of a peak around 1745 cm − 1 (associated with the C = O group of dimers of carboxylic acids).
3.7 Contact angle
The hydrophilicity of the membranes was measured using sessile drop method. The prepared membrane of sample size of 200 mm x 200 mm was washed with distilled water and removed the excess water droplets to remove the moisture present in it. The contact angle was measured by placing the membrane and allowed the sessile drop distilled water on the dry membrane surface (Table 2.). The modified membranes have the good pores which shows the better hydrophilic behavior of the membrane. The hydrophilic membrane surfaces strongly attach to the water groups when compared to the hydrophobic membranes [19].
3.8 Uniaxial tensile test
In this study, tensile strength and elongation at break were determined. The synthesized membranes with different metal oxide loading are given for tensile strength testing. With increase in metal oxides, the interaction between TiO2 improves the stability of the membrane [20]. With increasing loading rate, the tensile strength increased from 2.44 MPa to 3.05 MPa (Fig. 8) (Table 3).
|
MEMBRANE |
PES (wt %) |
PVP (wt %) |
TiO2 (wt %) |
NMP (wt %) |
|---|---|---|---|---|
|
SAMPLE a (S1) |
16 |
4 |
- |
80 |
|
SAMPLE b (S2) |
16 |
4 |
1 |
79 |
|
SAMPLE c (S3) |
16 |
4 |
2 |
78 |
|
SAMPLE d (S4) |
16 |
4 |
3 |
77 |
|
SAMPLE e (S5) |
16 |
4 |
4 |
76 |
Table.2 Contact angle measurements of the composite membranes
|
Sample |
Contact angle (degree) |
|
A |
72 |
|
B |
55 |
|
C |
54 |
|
D |
55 |
|
E |
56 |
Table 3. Mechanical strength of the synthesized membrane
|
Sample |
A |
B |
D |
E |
|
Tensile strength (MPa) |
2.44 |
2.61 |
2.94 |
3.05 |
|
Elongation (%) |
3.55 |
3.01 |
3.87 |
3.65 |
3.9 Thermogravimetric analysis
The thermogravimetric analysis PES and PES/ TiO2 composite membranes are interpreted in Fig. 9. It was observed that the increased in decomposition temperature had increased the amount of TiO2. From the results, it is observed that the TiO2 nanoparticles were distributed uniformly in the surface of the membrane. This reveals the compatibility between PES and TiO2 nanoparticles. Due to the addition of TiO2, additional heat absorbed by the TiO2 which leads to delay in the decomposition temperature of PES/TiO2.
3.10 Flux measurements
Flux measurements explains the extent of porosity and hydrophilicity of the membranes [21][22]. Pure water flux of PES/TiO2 nanoparticle blend membranes with different percentages of TiO2 were measured using vacuum membrane distillation process. Flux (J) of bare PES membrane is 183 LMH. The Flux (J) of PES/ TiO2 membrane was found to be 208 LMH. The TiO2 blend membrane increases the flux due to enhancement of membrane hydrophilicity and porosity. Clearly it is noted that the addition of TiO2 in membrane caused increased flux than the bare PES membranes. The lab scale of 15 L working volume membrane bioreactor was operated for 24 hrs. The membrane flux after an hour of operation was measured as 165 LMH for bare membrane whereas the PES/TiO2 membrane was still 202 LMH. The flux after 24 hrs. were taken for checking the flux. The flow of bare PES membrane was 0.1944 LPH and the area was 0.00138m2. Flux (J) of PES membrane is 138.8 LM. Whereas the flow of PES/TiO2 membrane was 0.27 LPH and the area was same as mentioned above. Flux (J) of PES/ TiO2 membrane is 196 LMH. The results of the flux measurements indicate that the bare PES membrane’s flux reduced from 183 LMH to 138.8 LMH which indicates the membrane was fouled easily and in the membranes with the addition of TiO2 the flux reduced from 208 LMH to 196 LMH which indicates that the membrane fouling is lower in the membranes made with the addition of TiO2 than the bare PES membranes (Fig. 10).
3.11 Performance of fine-tuned in TSS and COD removal
The performance of the fine-tuned membrane has been calculated by observing the colour and COD removal in tannery wastewater and it was monitored throughout the experiments. The initial COD was about 5500mg/L and the TSS was found to be 7800 mg/L. During the filtration experiments, the samples were collected for TSS and organic removal. The COD and TSS removal were found to be 89% and 100% by fine-tuned membranes, whereas the commercial pristine membranes showed 78% removal of COD. The presence of TiO2 nanoparticles has the benefits of clearing filamentous bacteria which blocks the pores as it has anti-microbial effect and also as a photocatalyst it helps in the decomposition of organic chemicals.
From the study, it is observed that the incorporation of nanoparticles helps in overcoming the fouling issues. The mechanical strength, hydrophilicity, morphology and structural properties have been evaluated for both the prepared nanoparticles and membranes. From the flux measurement results, it was observed that nanoparticles have huge impact on the decrease in flux decline, which will save the membranes from biofouling issues. Also, the removal of COD was found to be 89% after the filtration. This study will pave the way for membrane bioreactor field for industrial wastewater treatment.
Author Contribution
U.S. - Methodology, manuscript preparation and reviewS.J. - AnalysisV.S. - Review
Acknowledgement
The authors thankfully acknowledge the financial support provided by CLRI (STS-32) for carrying out this research work.
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No competing interests reported.