How can chitosan be used for water purification?
Chitosan is approved both for drinking water purification and for industrial waste water treatment, and it is also used for filtering water in swimming pools. Chitosan-based filters can remove many contaminants from polluted water. This includes particulate and colloidal matter from turbid waters, colorants, but also oil and grease which can bind to chitosan due to the hydrophobic character of its N-acetylglucosamine units. Depending on the pH, chitosan filters can also trap anionic (i.e. negatively charged) contaminants, such as humic acids that often stain drinking water originating from peat bogs e.g. in Norway, or proteins e.g. in the waste water of breweries which can bind to the glucosamine units in chitosan which are positively charged at slightly acidic pH values. On the other hand, at neutral pH values, the free electron pair of the glucosamine units' free amino groups can complex heavy metals from industrial waste waters. Chitosan is also approved for clarifying fruit juices, e.g. by filtering out negatively charged, pectin-rich plant cell wall fragments.