# Bio-Sourced and Biodegradable Membranes
## 3 Biodegradable Antifouling Membrane Properties  
Fouling is a serious drawback of polymeric membranes used in membrane-based separation processes. This phenomenon occurs as a result of particle-membrane and particle-particle attachments on the membrane surface or within the pores, which is mostly due to the hydrophobicity of the membranes [111]. This phenomenon can be observed at the membrane surface as well as in the membrane pores as a result of sieving and adsorption. In the sieving mechanism, particles larger than the membrane pores agglomerate and partially/completely block the pores (intermediate/complete blockage). A further accumulation of particles on the membrane surface would lead to the formation of cake layer. In addition, small particles enter the pores and are adsorbed (intermolecular interaction) to the pore wall, causing an internal blockage (standard blockage) [112]. Figure 9 shows the schematic of membrane fouling mechanisms.  
Several methods have been employed to prevent fouling formation (feed pre-treatment or membrane modification) or clean the membrane surface (chemical/biological cleaning, electrochemical, advanced oxidation, ultrasonic cleaning, forward/backflushing, pulsing mode, vibration, air sparging, and electrical field). Many of these methods suffer from limitations such as reduced membrane lifetime due to frequent cleaning, higher operating costs and energy consumption due to system downtime and interruption of filtering, and secondary pollutants as a result of the use of chemical/biological agents for surface cleaning [112; 113]. The foulant-membrane interaction and fouling behavior are mainly controlled by the chemistry/surface properties of membranes. Therefore, there is a great demand for membranes with antifouling properties to reduce the cleaning costs and  
\begin{table}
\begin{tabular}{c c c c} \hline
**No.** & **Membrane Material** & **Synthesis Method** & **Main Applications** \\ \hline
5 & Cyclodextrin & Enzymatic conversion of starch & Water treatment \\ \hline
6 & Alginate & Processing of biomaterials (algae) & Dyes and heavy metals removal \\ \hline
7 & Silk fibroin & Processing of biomaterials (insects cocoons) & Heavy metals removal \\ \hline
8 & Collagen & Processing of biomaterials (animal & Water separation, pervaporation \\  & & connecting tissues) & \\ \hline
9 & Polyhydroxybutyrate & Glucose and starch conversion & Biomedical application, dye \\  & & by microorganisms & removal, microfiltration \\ \hline  & & **Synthesized from bio-sourced chemicals** & \\ \hline
1 & Polylactic acid & Polycondensation or ring-opening & Water separation, tissue \\  & & polymerization of lactic acid, produced by & regeneration \\  & & aerobic fermentation of glucose or starch. & \\ \hline  & & Polycondensation of succinidic acid and & \\
2 & Polybutylene succinate & 1,4-butanediol. Succinic acid is produced by & \\  & & biomass fermentation. 1,4-butanediol is & \\  & & produced by succinidic acid hydrogenation & \\ \hline  & & **Petrochemical** & \\ \hline
1 & Poly-\(\epsilon\)-caprolactone & Ring-opening polymerization of & Biomedical applications \\  & & \(\epsilon\)-caprolactone & \\ \hline
2 & Polypropylene fumarate & Polycondensation of fumarate with & \\  & & propylene glycol & Biomedical applications \\ \hline
3 & Poly-ethylene glycol & Polygondensation of ethylene glycol or & \\  & & ring-opening polymerization of & \\  & & ethylene oxide & \\ \hline
4 & Poly-vinyl alcohol & Hydrolysis of polyvinyl acetate & Wound dressing \\ \hline
5 & Polyurethane and & Polycondensation of diisocyanates with diols & \\  & & polyurethane urea & and diamines & Biomedical application, agriculture \\ \hline \end{tabular}
\end{table}
Table 1: Cont.  
prevent membrane damage. Natural antifoulant materials have shown promising results and proved to be an environmentally friendly solution to membrane fouling [114; 115; 116; 117]. Figure 10 shows the antifouling properties of various types of membranes.