**4.1 Performance of chitosan in POME treatment**

The optimum condition for coagulation treatment with chitosan as a coagulant is about 100 ppm (mg/L) of POME at pH 4.5. The removal percentage for the COD, the color and the TSS is 15.39%, 85.79 and 97%, respectively. The results are shown in **Figure 10**. The graph in **Figure 10** showed that any further increase in dosage does not increase the color and the TSS removal significantly. However, a further increase in dosage causes the COD to increase. The negative result of the COD

**Figure 9.** *Chitosan charge neutralization and FeCl3 sweep coagulation.*

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**Figure 10.** *Effect of chitosan dosage in pollutant removal (COD, color and TSS).*

removal observed with the addition of chitosan, which is a natural biopolymer coagulant (an impurity) that causes the COD to increase when the dosage exceeds its saturation point. In essence, the low COD removal was due to natural properties of POME as chitosan is not effective in removing dissolved solid [53]. Typical raw POME has a total solid of 40,000 mg/L, while 34,000 mg/L of it is dissolved solid [2]. Furthermore, TSS removal is very effective at low chitosan dosage [45]. However, chitosan is effective in removing suspended solids that contributes to the COD but not total dissolved solids (TDS).
