**4.2 Performance of chitosan paired with other method in POME treatment**

This study was done by combining ultrasound (US) cavitation, chitosan and ferric chloride (FeCl3) in different ways to determine the best combination and order of treatment. Every treatment method is conducted by following the result of optimum condition obtained from previous studies. The result is shown in **Figure 11**.

From the graph in **Figure 11**, the COD removal for the combination of ultrasound (US) cavitation, followed by ferric chloride coagulation treatment, is the highest, at

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

56.26%. Besides, the color removal for this combination is the highest among other combinations, at 92.41%.

Furthermore, among all these combinations where chitosan is present, the COD removal percentage is less substantially, ranging from 35.1% to 40.12%, which can be observe at the combination of US- FeCl3 (ultrasound and ferric chloride) that shows the COD removal at 56.26%. However, when chitosan added after it, the COD removal percentage drops to 38.61%, due to chitosan being a natural coagulant that is biodegradable [47]. Chitosan is not very useful in coagulating the organic pollutant (COD), which dissolved in the POME [53]. Therefore, chitosan will become the pollutant, contributing to COD and causing the COD removal percentage to decrease. Even though ferric chloride performs better when paired with other polishing methods, the dosage usage of chitosan in POME treatment is lesser and hence more superior in terms of cost-effectiveness and environmentally friendly method for palm oil mills in dealing with wastewaters.
