PH—Postharvest Technology: Kinetics of Gravity Settling of Cassava Starch in its Aqueous Suspension

Cassava starch owing to its low cost, easy extractability, high viscosity, bland taste, neutral flavour and easy degradation finds extensive use in food, feed and industrial sector. Settling is a prime unit operation in cassava processing where the extracted starch is separated from its aqueous suspension under gravity. Settling characteristics of cassava starch in different columns with varying concentrations were analysed and a mathematical model was derived for describing the hindered settling velocity of starch particle in suspension. Starch particles obeyed discrete or flocculent settling at low concentrations (⩽6%) and hindered or compression settling was more predominant at higher concentrations (⩾10%). Free falling velocity of cassava starch particle as calculated by Stokeʹs equation was found to be 1·69×10−4m s−1 and as the concentration of the suspension increased, the settling velocity decreased. The effect was reversed when the height of suspension was increased. The diameter of settling column did not have any influence on the settling velocity. A mathematical model for the hindered settling velocity was developed as a function of free falling velocity, fluid volumetric concentration and ratio of height of suspension to diameter of settling column.