Flocculation Performance and Mechanisms of Conventional and Modified Cassava Peel Starch in Chemical Oxygen Demand Reduction for Municipal Wastewater Treatment

Abstract

In this study, modified cationic cassava peel starch grafted with 3-chloro-2-hydroxpropyl trimethyl ammonium chloride (ME.St-g-CatCHP) flocculant was developed by etherification with 0.95 degrees of substitution (DS). The flocculation performance of ME.St-g-CatCHP was compared with a conventional starch (ME.St) flocculant in removing chemical oxygen demand (COD). The results showed that dosage, pH and settling time significantly affected the flocculation performance (p-value < 0.05). The ME.St-g-CatCHP demonstrated a better flocculation performance to achieve 88.63% removal efficiency with optimum conditions obtained at pH 7, dosage 360 mg/L, 29 mins settling time, 278 rpm within 1 min of rapid mixing and 31 rpm within 53 mins of slow mixing. Response Surface Methodology was applied to optimize ME.St-g-CatCHP quadratic model showed that R2 = 0.98 and adjusted R2 = 0.83. Charge neutralization played a dominant role in the flocculation process by ME.St-g-CatCHP due to strong positive polyelectrolyte across the whole pH range between pH 2 and 11. While bridging mechanisms could be the main contributor to the flocculation process by ME.St during the slow adsorption process. The findings supported that modified ME.St-g-CatCHP increased the COD removal efficiency from 74% to 88% removal efficiency compared to ME.St, and shortened the settling period from 107 to 29 mins.