Cellulose Acetate Membrane Preparation for Wastewater Treatment

*Ibtissem Ounifi, Fatma Khaled, Malak Kahloul, Hanen Ajari and Amor Hafiane*

## **Abstract**

For a long time, humans have used cellulose, as a natural, renewable, and transformative polymer, for scientific development to create new technologies. Cellulose is the most abundant biopolymer on Earth, accounting for more than 50% of terrestrial biomass. For this reason, the treated cellulose (cellulose acetate (CA)) was used in the membrane preparation for water desalination. However, membrane preparation has recently attracted big attention of several research groups. In this case, cellulose acetate (CA), as an inexpensive hydrophilic biopolymer, was chosen as a polymer for preparing the membranes via the inversion phase, since it offers an efficient purification benefit with low energy consumption and less cost. The purpose of this chapter is to describe the various types of membrane preparation based on cellulose acetate, with pathogens, bacteria, and heavy metal (cadmium), and the applications of these membranes in the treatment of contaminated water, to ensure a clean water supply for both human and industrial uses.

**Keywords:** cellulose acetate, membrane preparation, water desalination, hydrophilic, wastewater treatment

### **1. Introduction**

In the last decades, the population, industrial, agriculture, and urbanization growth has continually increased and by adding climate change and policymaking problems, the fresh and accessible water has been reduced in the world. As a result of global problems, the demand for pure water increased more and more [1, 2]. As well as the problem of heavy metal contamination of water supplies, which is producing major environmental and health implications, there is a growing need for water desalination technology [3–5].

Recently, membrane separation technology has been attracting considerable attention due to its potential applications over conventional approaches such as thermal desalination. Membrane process becomes widely used in water desalination, wastewater treatment, pharmaceutical filtration, and even in energy generation due

to their different properties such as being environmentally friendliness, simple operation, high efficiency, low operating cost, low energy use, and scalability [5–7].

Generally, the basic function of the membrane is to separate different mixtures by concentrating small molecules and allowing others to pass. This specific function as well as the other advantages makes membrane technology the principally used application in many separation membrane processes such as water, wastewater treatment, and adsorption, which gives it an important part in the water challenge (**Figure 1**) [8, 9].

Membrane separation is based on an efficient and scalable methodology by using some or without no harmful chemicals by-product formation. Membrane fabrication from synthetic polymers becomes very much used in various separation membrane applications. Generally, several polymers are used such as polysulfone (PSF), polypropylene (PP), polyethylene (PE), polyethersulfone (PES), polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), chitosan (CS), and cellulose acetate (CA) [10–13]. Nowadays, CA polymers attract a big interest in membrane fabrication due to their biodegradable polymer propriety, hydrophilicity nature, and large disposability, since cellulose is an organic compound widely existing on the earth [14, 15]. Generally, cellulose can be found in plants, wood, algae, tunicates, and even in bacteria, and its annual extracted production can attain around 7 × 1010 tons per year, which highly encourages the use of cellulose [16]. As result, many researchers focused on membrane fabrication with the derivatives of cellulose such as cellulose acetate CA [14, 15].

The CA membrane's performance was improved by its high chemical and mechanical stability, high hydrophilicity with desalination pilot, high transport properties, low protein adsorption, excellent water affinity, and excellent film-forming property [17]. Due to their desirable properties and environmental aspects, CA-based membranes have been used in several separation membrane applications, such as gas separation [18], reverse osmosis (RO) [19], nanofiltration (NF) [20], ultrafiltration

**Figure 1.** *CA-based membrane applications.*

#### *Cellulose Acetate Membrane Preparation for Wastewater Treatment DOI: http://dx.doi.org/10.5772/intechopen.109416*

(UF) [21], microfiltration [22] (MF), pervaporation [23], and ion exchange [24], and it has been widely used to electrospun fibers for it simple processing [25].

More than separation membrane technology, CA has the potential to be used securely in industrial and biomedical applications such as wound dressing [26] because of its low toxicity and biodegradability [27].

The wide use of CA membranes can be attributed to the fact of the importance of CA in the manufacturing of biodegradable membranes, besides the possibility of improving membrane performance through the addition of additives [28], particularly nanomaterials. Therefore, to improve the CA membrane's performance, the membrane solution can be mixed with the right organic or inorganic additives in the phase inversion technique [29]. To modify CA membranes, some researchers changed the solvent in the membrane casting solution. Various solvents were tentatively used to prepare CA casting solution, including N-methyl pyrrolidone (NMP), N, N-dimethyl acetamide (DMAc), and a composed solvent of N, N-dimethylformamide (DMF), acetone, or 2-propanol [30–32].

This chapter aims to present the cellulose properties and its derivatives and to study the use of CA polymer in the preparation of polymeric separation membranes applied in different applications. First, a presentation of CA properties will be carried out. Then, different CA membrane configurations will be described. Thus, the performance of the fabricated CA membrane in those applications will be studied and discussed, by taking the CA as the used polymer on the one hand and as an additive on other hand.

### **2. Cellulose acetate properties**

Cellulose acetate is an important cellulose derivative due to its properties, which are used in different applications. It is extracted from natural and renewable resources. Further, CA is a natural polymer that is characterized by flexibility, biodegradability, non-poisonous, and eco-friendly [33]. Due to its important and unique benefits of biodegradability and nontoxic behavior [27], CA has been used frequently in membrane manufacturing, especially in the treatment of water and wastewater technologies. Several polymers have been used in the membrane synthesis, but the CA membranes are the most preferred according to their durability, low cost, and especially required hydrophilic and biodegradability properties [34, 35].

Also, by dint of their chemical and thermal stability (**Figure 2**), good water retention capacity, and great resistance to methanol permeation, the CA membranes are used in many other applications such as gas separation for CO2 capture or nitrogen generation [36] and fuel separation for fossil fuel and natural gas drainage [37].

**Figure 2.** *Chemical structure of cellulose acetate.*

Several molecular weights of CA were used in membranes synthesis, which are usually attained at 30,000 g mol−1 [38], 37,000 g mol−1 [39], 50,000 g mol−1 [40], and 60,000 g mol−1 [41], between 39 and 40% of this weight is acetyl.

One of the main properties of CA is the possibility of dissolution in green solvents with the ability to use in the phase inversion technique for membrane fabrication [42, 43]. Totally, bio-based NF membranes were fabricated using CA as a base membrane and several glycerol derivatives (monoacetin, diacetin, triacetin, and glycerolformal) as green solvents 2-methyl tetrahydrofuran as a co-solvent to reach rejection in the NF range [44]. The greatest membranes resulted from diacetin solvent by permeability in the range of 5.5–12.8 L m−2 h−1 bar−1 and *>*90% Rose Bengal rejection.
