Modeling and Optimization of the Coagulation–Flocculation Process in Turbidity Removal from Aqueous Solutions Using Rice Starch

Natural coagulants have received much attention for turbidity removal, thanks to their environmental friendliness. The present study investigates potential application of rice starch for removal of turbidity from aqueous solutions. It considers the effects of four main factors, namely settling time (40-140 min), pH (2-8), slow stirring speed (20-60 rpm), and rice starch dosage (0-200 mg/L), each at five levels, by means of central composite design. Results show that a quadratic model can adequately describe turbidity removal in case of non-autoclaved rice starch with statistics of R2= 0.95, R2adj.= 0.91, R2pred.= 0.77, AP = 23.75, and CV = 4.77. It has also been found that the performance of non-autoclaved rice starch is superior to the autoclaved variety, in terms of removal efficiency and floc size. In the optimal point, predicted by the model, a removal efficiency equal to 98.4% can be attained, using non-autoclaved rice starch, which is higher than that of the autoclaved rice starch (71.29%). The significant effective parameters have proven to be settling time along with pH. Overall, rice starch can be considered a promising high potential coagulant for removal of turbidity from water or wastewater.