# Microbial Biopolymers: From Production to Environmental Applications--A Review
## 6 Applications of Microbial Biopolymers
### Microbial Biopolymers as Filters in Membrane Processes  
The capacity of microbial biopolymers to develop biofilms, set up selective barriers, and improve filtration effectiveness is the idea underlying their application as filters in membrane processes. Impaction, electrostatic contact, diffusion, and interception are prominent processes involved in biopolymer filtering [241; 349]. Filtration is a method used for the separation of solid particles and large molecules from liquid suspensions through a porous barrier such as a membrane. Membranes possess selective permeability, controlling the passage of mass through their porous surfaces through interactions with the materials to be separated. The efficiency of this technique is directly linked to the size of the membrane's pores and the characteristics of the material used [350]. A wide variety of membranes with different conformations and structures are available. Membrane filtration techniques such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) are distinguished by their varying pore sizes, ranging from 5000 nm in MF to 0.2 nm in RO [351]. As with all membrane filtration processes, the main downside that limits their large-scale applications is membrane fouling, which occurs due to contaminants that adhere to the membrane's surface or get trapped within its pores over time, forming a layer that hinders the flow of desired components through the membrane. This phenomenon reduces filtration efficiency as well as the membranes' lifespan and increases energy consumption [352; 353]. Recently, biopolymer nanocomposite membranes have gained popularity as a promising solution for mitigating membrane fouling. They have shown improved antifouling properties by minimizing the adhesion of flocculants and improving water permeability, thereby enhancing filtration process efficiency [354; 355]. This, in turn, has played a pivotal role in fueling the fast growth of membrane filtration technologies and has boosted the number of publications focused on the utilization of membranes for separating oil-water emulsions [356]. The use of natural fillers such as nitrocellulose or chitosan nanoparticles within biopolymer membranes has significantly enhanced membrane stability and reduced the dosage of chemicals and the volume of sludge. Therefore, biopolymers stand out as an environmentally friendly, efficient, and sustainable alternative to conventional membrane filtration techniques [350; 357] Among the different biopolymers, hydrophilic biopolymers, such as bacterial cellulose, chitosan, alginate, and hyaluronic acid, are preferred for membrane processes due to their durability and ability to withstand corrosive substances that may be present in the wastewater. As highlighted by [PERSON] et al. [87], a bacterial-cellulose matrix can be used to separate almost all oil during the filtration of oily effluents and can be washed and reused up to 20 times without losing its filtration efficiency. Surface modification can further enhance retaining specific contaminants like heavy metals and dyes, thus improving the membrane's permeability and selectivity [358]. For example, [PERSON] et al. [359] demonstrated that a modified chitosan-cellulose acetate-TiO\({}_{2}\)-based membrane can be used for the demulsification of oil-water emulsion, reaching up to 99% in separation efficiency. As highlighted by [PERSON] and [PERSON] [360], recent advancements in microbial polymer thin-film nanocomposite membranes, incorporating nanof fillers like carbon-based materials, metals, and metal oxides, have garnered considerable attention in the field of water purification due to their notable characteristics, including hydrophilicity, thermal stability, selectivity, permeability, and thermal resistance.