Chitosan is a multifunctional polysaccharide widely distributed in nature (the second largest biopolymer after cellulose), produced by the alkaline N-deacetylation of chitin. There are many studies showing that chitosan has the ability of biosorption to remove pollutants in wastewater. They can be used as coagulants/flocculants for contaminated wastewater, for heavy metal or metalloid adsorption, for dye removal from industrial wastewater such as textile wastewater, and for removal of other organic pollutants such as organochlorine pesticides , organic oxidation or fat and oil impurities.
Natural chitosan is insoluble in water or organic solvents, but at acidic pH (below pH 5), when free amino groups are protonated, chitosan becomes a soluble cationic polymer with high charge density. These characteristics determine that chitosan can adsorb pollutants in waste in acidic environment.
1) Flocculants and coagulants for industrial wastewater treatment.
In most polluted wastewater, most of the polluting colloids are negatively charged, and chitosan, as a cationic polymer, can effectively remove and neutralize negative ion pollutants. The positively charged polymer formed by chitosan in an acidic environment has the characteristics of long molecular chains and can combine with anionic pollutants faster. Greater floating and settling velocities can be formed in a short time.
Based on the high affinity of chitosan to different pollutants, there are many studies showing that these properties of chitosan can be used to remove dyes in solution or textile wastewater, organic matter in pulp (such as lignin and chlorinated compounds) and prove that papermaking Heavy metals and phenolic compounds in mill wastewater, cardboard mill wastewater and inorganic suspensions in kaolinite suspensions.
2) Chitosan is used as a metal ion adsorbent for industrial wastewater treatment.
Numerous studies have shown that chitosan can be used as a heavy metal adsorbent in commercial and industrial wastewater treatment. Chitosan forms protonated (–OH 2 + , –NH 3 +) functional groups in an acidic environment, and these functional groups produce complexation, electrostatic attraction, microprecipitation, and ion exchange with heavy metal ions to complete the adsorption of heavy metal ions.
Chitosan has made progress in large-scale commercial applications as an efficient cationic flocculant and adsorbent, but its application range is limited due to the low solubility of chitosan in water and the need to work in an acidic environment.