# Bio-Sourced and Biodegradable Membranes
## 3 Biodegradable Antifouling Membrane Properties
### Biodegradable Membranes for Oil Fouling  
Oil fouling is one of the major challenges involved in oil/water separation owing to the low surface energy of oil droplets. In this regard, several bio-inspired materials have been employed to fabricate different filters with self-cleaning and antifouling properties [131]. Chitosan (CS) is among the bio-based polymers, containing hydroxyl and amino groups and showing hydrophilic behavior in air and oleophobic properties in water. In addition to those characteristics, its biocompatibility, non-toxicity, and low cost allow chitosan to be an excellent alternative to treat oily wastewater with a separation efficiency of more than 99% [132, 133, 134, 135, 136]. Chitosan can also be used as an adsorbent for removing dyes, macromolecules, and heavy metals from a system with a high permeate flux recovery rate [137, 138]. [PERSON] et al. [113] used the chitosan-coated mesh to remove the oil from the hypersaline environments and solution at various pH levels. Their research on fabricating a bio-inspired filter with stable wettability in complex environments was inspired by shrimp shells. Shrimp shells are both hydrophilic and oleophilic in the air (contact angles of about 41\({}^{\circ}\) and 24.7\({}^{\circ}\) for water and oil, respectively). However, the shells exhibit a superoleophobic property once placed in seawater (oil contact angle > 150\({}^{\circ}\)). CS is the deacetylation form of chitin, which is the major component of shrimp shells. Despite chitin, CS can be dissolved in an acid solution and form filtration films. The spin coating technique was used to fabricate the CS film, and the result showed that the water contact angle of the film in the air and the oil contact angle in the water was about 7\({}^{\circ}\) and 155\({}^{\circ}\), respectively. [PERSON] et al. [116] also used chitosan (CS) and caffe acid (CAF) as the biodegradable coating agents on cotton fibres to prepare a superwettable filter for oil/water separation. The hydrophilicity (contact angle of almost 0\({}^{\circ}\)) and underwater superoleophobicity (oil contact angle \(\geq\) 160\({}^{\circ}\)) of those polymers result in high permeate flux (up to 50,050 L h\({}^{-1}\) m\({}^{-2}\) bar\({}^{-1}\)) and separation efficiency (>99.9%) under low applied pressure (0.1 bar). Despite its inability to form a film, chitin can be used as an additive to the polymer solution or as a coating agent to modify the surface properties of membranes. In the research conducted by [PERSON] et al. [139], chitin nanocrystals were coated on electrospun cellulose acetate (CA) to improve its antifouling properties. The nanofibrous CA has hydrophobic surfaces with a water contact angle of about 132\({}^{\circ}\). However, the results showed that the cellulose acetate/chitin membrane turned superhydrophilic characteristics (water contact angle of almost 0\({}^{\circ}\)). The modified membranes were found to be less prone to biofouling, especially toward the solutions which contain bovine serum albumin (BSA) and humic acid (HA), such that no flux decay was observed over a complete filtration cycle. In recent decades, chitosan-based composite membranes have gained increasing attention. The antifouling properties of chitosan have been found to be useful in developing membrane separation processes for water purification and wastewater treatment [138, 140, 141, 142, 143, 144, 145, 146].