# Microbial Biopolymers: From Production to Environmental Applications--A Review
## 6 Applications of Microbial Biopolymers
### Microbial Biopolymers as Coagulants and Flocculants  
Coagulation and flocculation are two interrelated methods commonly known as the most economical processes used in water treatment for solid-particle removal. Despite their interconnection, coagulation and flocculation are entirely different phenomena. Coagulation is an electrostatic phenomenon that occurs through the charge neutralization of suspended particles and colloids. It is induced by adding coagulants that destabilize the particles, leading to their collision and aggregation. This, in turn, initiates the formation of flocs, which precipitate from the suspension due to the influence of gravity. Flocculation takes place to further enhance the downstream processes by creating larger and heavier flocs, thereby enhancing the effective removal of impurities. While coagulation occurs in a short time frame of less than 10 s, flocculation is a long physical process lasting about 20-45 min [274,308]. A large variety of coagulants and flocculants have been used for wastewater treatment. Commonly used inorganic coagulants, such as aluminum sulfate, aluminum chloride ferrous sulfate, etc. [309, 310, 311], have caused environmental and ecological concerns due to their generation of additional sludge volume [312,313]. Hence, microbial biopolymers emerged as a viable solution [312,314]. Among the variety classes of biopolymers, polysaccharides have garnered significant attention from the scientific community, mainly due to their functional groups present on the surface, contributing to the effective adsorption of different contaminants in the flocculation process [315, 316, 317]. As described in the recent literature, chitosan, cellulose, alginate, pullulan, xanthan gum, and their derivatives are bio-based flocculants. Those polysaccharides have shown their ability as relevant agents in the elimination of turbidity, total dissolved solids (TDS), chemical oxygen demand (COD), metal cations, inorganic anions, dyes, pesticides, minerals, microorganisms, and numerous other pollutants found in various types of wastewaters [318]. Other biofloculants based on dextran [319, 320, 321], pectin [322,323], and lignin [324], as well as their grafted derivatives, have also been reported for color-reducing, turbidity, COD, or heavy metal ions. Table 6 provides an overview of recently reported biopolymers and their derivatives as coagulants and flocculants investigated for water treatment. With the emergence of nanocomposite-based biopolymers, reports regarding the utilization of biopolymers in their unmodified form are notably limited. This can be attributed to the very developed surface area of nanoparticles, characterized by a notable abundance of active sites and functional groups, which positively enhance water treatment [325,326]. However, despite the multiple gains in using nanofloculants, real concerns remain about the potential environmental impacts regarding the introduction of these particles into the ecosystem. Uncertainty surrounding whether nanoparticles will induce toxic effects within the natural environment persists [318]. Recent reports highlight that direct flocculation, operating independently from coagulation, is emerging as a notably cost-effective alterna