MATHEMATICAL MODELING OF CLARIFLOCCULATOR

Abstract

The combined unit of flocculator and clarifier is known as clariflocculator. For better understanding of clariflocculator we must know about flocculation and settling characteristics of flocs. Flocculation refers to the agglomeration of particles in a solution. Most commonly, flocculation is used to describe the removal of sediment from a fluid. Some literatures are available to describe the flocculation modeling. The mathematical representation of flocculation, i.e. the process whereby destabilized suspended combine together to form floes. Flocculation depends on many parameters like pH, mixing, temperature, ionic strength, coagulant doses but short range forces like electrostatic repulsion, Van der Waals or hydrodynamic forces play a very important role in flocculation. Rate of aggregation of floes is a function of collision efficiency and collision frequency. According to literature there are many approaches to describe flocculation like rectilinear approach, curvilinear approach, size based and class based approach and population balance approach. In this report data extracted from literature has been used for mathematical modeling of clariflocculator. It is observed that size of flocs is normally distributed during flocculation. So the distribution has a particular mean size and standard deviation. It is observed that mean particle size follows a definite trend with time at different velocity gradients. A mathematical relation has been developed to define the relation of mean particle size and time using fractal approach and Euclidian approach. A relation for growth of floes has also been developed to predict the fate of growth of floes with time. To correlate the settling efficiency mean particle size and settling velocity has been calculated using the expressions available in literature. Based on the calculations it is observed that expression for growth of floes can be used to develop a mathematical modeling of clariflocculator where type II settling process can be modeled as type I settling process. Keywords Flocculation, settling efficiency, particle size distribution, Design of clariflocculator