**4. Chitosan**

Chitosan is a biopolymer coagulant which is non-toxic, biodegradable, renewable and environmental friendly [47]. Chitosan is a type of marine polymer which has widely used in practical fields such as wastewater management, pharmacology, biochemistry and biomedical. Chitosan is a cellulose-like polyelectrolyte biopolymer which derived from de-acetylation of chitin, as shown in **Figure 8**. Chitin

**Figure 8.** *Derivation of chitosan from chitin [47].*

*Performance of Chitosan as Natural Coagulant in Oil Palm Mill Effluent Treatment DOI: http://dx.doi.org/10.5772/intechopen.94330*

can easily found in marine nature, and it is occurring in the insects, yeast, fungi and exoskeletons of crustaceans [45]. Chitosan contains a high amount of amino functions that provide novel binding properties for heavy metals in wastewater [48]. Chitosan can coagulate effectively at pH less than 4.5 as strong acidic condition exaggerates POME to form unstable flocs [49]. The mechanisms involved in the coagulation can divide into two main categories which are charge neutralization or electrostatic interaction and sweep coagulation/co-precipitation [50]. The chitosan coagulation process is charge neutralization while synthetic coagulant such as ferric chloride (FeCl3) is sweep coagulation as shown in **Figure 9** [51]. The flocs formed by charge neutralization are smaller than the flocs formed through sweep coagulation [52]. The smaller sized flocs could bring fouling risk to the membrane if membrane technologies are used.
