**5. Application of CA membranes**

#### **5.1 Mirofiltration**

In a combination with solvents, CA and polyethyleneimine (PEI), which were cross-linked by polyisocyanate, were combined to prepare a modified MF membrane via phase inversion approach. PEI may provide linkage sites for affinity-separated ligands in the membranes or serve as ligands for metal chelation, endotoxin elimination, or ion exchange [46]. The impacts of phase inversion time, induced by water vapor mixed with PEI and cross-linking agent concentrations, were examined in the function of membrane performance. The prepared blend membranes with 0.15 50 wt.% PEI/CA ratio and 0.5 wt.% cross-linking agent/PEI were used to adsorb Cu2+ and bovine serum albumin (BSA) separately. The produced membrane has a maximum Cu2+ ion adsorption capacity of 7.42 mg/g dry membrane. The maximum BSA adsorption capacities are of 86.6 and 43.8 mg/g dry membranes for the membranes with and without the chelating Cu2+ ion, respectively.

Commercial CA-MF membranes were modified to exhibit antibacterial capabilities by being impregnated with thymol mixed in very critical solvents. Batch impregnation was used, and the thymol loading was watched as a result of treatment pressure and time. *Staphylococcus aureus* and *Pseudomonas aeruginosa* were used to test the obtained materials' antibiofilm capacities, while *S. aureus* and *Escherichia coli* were used to test the blockage of membranes in contact with bacteria. The finding's results showed a quick impregnation process that could achieve high thymol loads in just 0.5 h at 15 MPa and 20 MPa. A concentration of 20%Thymol exhibited high antibiofilm effects against the tested strains without changing the membrane performance. The research revealed that the specified polymer could benefit from these potent antibacterial characteristics. These great antibacterial characteristics could be sustainably added to the commercial polymer structure of membranes. The results revealed also that the modification of the commercial cellulose acetate microfiltration membranes with polymeric structure might be successfully accomplished in a quick (30 min) and safe environmental procedure. Therefore, modified membranes with great antibacterial properties may find use in the biomedical sector and venting.

#### **5.2 Ultrafiltration**

Ultrafiltration (UF) membrane was prepared by Ounifi et al. [53] by using the Manjikian process by phase inversion with progressively rising polymer concentrations (cellulose acetate at 15, 16.5, 18, and 21 wt.%). At increased polymer concentrations, the membranes showed improved ability to retain pathogenic and epidemiological Uro Pathogenic Escherichia coli (UPEC). The membranes with the highest polymer concentration were able to hold back an entire discharge of 8 U-log bacteria.

By using a blending method, new fouling-resistant UF membranes were prepared for cadmium (Cd) remediation by fusing the adaptability of CA with the intricate characteristics of poly(acrylic acid) (PAA). Since CA/PAA membranes performed better than pure CA membranes in UF experiments, it was clear that the mixture had many advantages. Overall, PAA is a useful additive for creating CA membranes with enhanced antifouling exploitable qualities for the UF treatment of heavy metalpolluted water bodies.

The synthesis, evaluation, and use of polyurethane (PU) with cellulose acetate blend membranes are all part of this research [89]. Numerous characterization methods, including contact angle measurement, ATR-FTIR, water content, and SEM, have been used to investigate the characteristics of PU-CA blend membranes. It was determined that common functional groups were used as raw materials (polyurethane and cellulose acetate) in the PU-CA mixed membrane. It was demonstrated by contact angle measurements and water content values that cellulose acetate's addition decreased the hydrophilicity of the modified membranes, due to the fact that pure polyurethane membrane has higher hydrophilicity than pure cellulose acetate. Aqueous potassium dichromate solution used for ultrafiltration as one of the promising separation techniques was used to test the suitability of the modified membranes. The PU-CA1 membrane was experienced varied chromium ion concentrations for many pH and pressure levels. At pH 3 and 0.4 MPa, process economy was attained for all chromium ion concentrations. The PU-CA1 membrane offers a novel option for the treatment of effluents in the textile sector due to its specific properties.

#### **5.3 Nanofiltration**

CA-NF membranes were prepared by using the phase inversion method [54]. The concentration of cellulose acetate was varied from 22 to 25 wt.% to investigate its effect on the characteristics of the membrane. The membrane's characterization revealed that the increase of CA concentration makes it more hydrophilic and decreases the membrane's porosity, consequently reduction in water permeability across the membrane, while it increases salt retention. Knowing that the size exclusion mechanism predominates the transport mechanism through the membrane, the ions rejection was sequenced in the following order: R(Na2SO4) > R(CaCl2) > R(NaCl) as determined by the hydration energy and hydrated radii of the ions. CA NF membranes have been successfully used for cadmium elimination. The rejection rate of removed cadmium reached up to 98%. In terms of steric hindrance and hydration energy, the results revealed that the Cd2+ coupled with divalent anions is more rejected than that coupled with monovalent anions. Additionally, the retention reduces from 10−4 to 10−2 mol L−1 when the salt concentration rises. Thus, the obtained results showed the feasibility of using developed CA-NF membranes in removing cadmium from contaminated water.

In order to increase the rejection of Pb2+ions and the permeation flux, vinyl triethoxysilane-graphene oxide/gum arabic was added as filler to modify the CA-based membranes [39]. By using NF membranes, the rejection of Pb2+ions was studied by investigating the effect of contact time, pH, permeation flux, and pressure. It was demonstrated that at pH 9, the rejection reached its optimal with 97.6%, whereas a low pH of 1–6 was not required for salt rejection. The permeation flux was 8.6 l m−2 h−1, which is caused by concentration and pressure variations. The special characteristics of the nanomaterial-based membrane and their connection to the current treatment methods offer great prospects to revolutionize water and wastewater treatment as well as to further our knowledge of membrane performance. NF-CA may present a significant factor in the commercial manufacturing of membranes.

### **5.4 Reverse osmosis**

Diainabo et al. aimed to evaluate the pertinence of CA, PSF, and silica (SiO2) for the treatment of wastewater. For this purpose, PSF-blended CA hybrid filtration membranes (CA/PSF) also PSF-blended and SiO2-embedded CA hybrid adsorption membranes (CA/PSF-SiO2) were prepared and characterized for Cu2+, Fe2+, and Zn2+ ions elimination from contaminated aqueous solutions. Phase inversion method was used to prepare the membranes by using CA, PSF, and SiO2 granules that were dissolved in N, N dimethyl formamide (DMF). Different pore sizes were detected at the rough surfaces and cross sections of the membranes, which were studied by using SEM. The obtained membranes' porosity and pore sizes ranged from 26.8 ± 0.3 to 81.1 ± 0.3 μm and from 1.26 to 1.38%, respectively, based on the differentiation. The membranes' contact angles varied from 49 to 76 degrees on their glass side and from 56 to 77 degrees on their air side [90].

More than 90% of the initial metal ions present in the polluted solution, which was concentrated at 40 mg L−1, were taken up by the hybrid filtration polymer membranes. CA/PSF-SiO2 membranes were used in adsorption tests. These substances were found to have a higher capacity for adsorption than many other well-known adsorbents in the literature, which reach 70 mg g−1 for CA/PSF 85/15-SiO2 for Cu2+.


#### **Table 2.**

*Some of the application of CA membrane.*

Finally, it was discovered that the removal of Cu2+, Fe2+, and Zn2+ could be improved by coupling adsorption with ultrafiltration in the tangential mode. This allowed for a removal efficiency of 95% for Cu2+ at a low metal concentration of 60 mg L−1, and at a high metal concentration of 900 mg L−1, it showed a great removal efficiency of around 98% [90].

In order to remove metal ions from AMD, the performance of a combined filtration and adsorption process was studied. The prepared membranes showed the ability to extract metal ions from polluted solutions at low concentrations of 40 and 60 mg L−1, whereas at a high concentration of 900 mg L−1, the filtration was ineffective. The selected adsorbents demonstrated a better adsorption capacity than those from other adsorbents used in the literature. The maximum adsorption efficiency with the CA/PSF 85/15-SiO2 membrane reached between 35 and 70 mg g−1 of Cu2+, Fe2+, and Zn2+ ions, while the adsorbent had the lowest capacity adsorption with CA/PSA-SiO2 membrane reached from 20 to 61 mg g−1 toward the same metal ions. By combining the effects of the filtration and adsorption membranes, a great metal uptake was obtained at both low and high concentrations. Consequently, this strategy presents a reliable method to remove the metal from aqueous solutions, and it has potential use in industrial wastewater treatment (**Table 2**) [100].
